The (mostly) correct way to measure specific power

"GhostZ" (GhostZ)
08/26/2013 at 13:20 • Filed to: fuel, displacement, dick measuring, Honda fanboys, specific power, GhostZ

"An RB26 can get 380HP per liter if tuned!" "Nascar engines take four times the displacement to get the same power as F1 engines!" "All big, fat american V8s are inefficient" "There's no replacement for displacement!" Please stop. Let me explain why you are wrong.

A recent comment (not a bad one! A good comment!) made me think about how we cro-magnons beat and wail about our favorite engines and why its the best. I'm guilty of it too, often using the 4v DOHC 160HP 2-liter Nissan S20 engine, from 1969, as an amazing example of ahead-of-its-time tech. But I'm wrong too.

Left: The average Honda or Mazda enthusiast during a HP/liter argument. Large bone club and posse of barbarians not pictured.

Engine efficiency has nothing to do with RPM, Displacement, or boost. It has to do with all of them. So if you compare two engines, you have to compare all of that. I'm going to show you how to make an accurate, apples-to-apples comparison between engines. This only works if the use the same fuel, however, and you only care about peak power. (if you can find numbers for low throttle driving, you can compare by fuel economy)

The only accurate specific power measurement is an amount of air taken in an amount of time, providing a proportional HP level. If you need more air to make the same peak HP in over the same amount of time with the same fuel, then you are losing efficiency somewhere. That is why air flow (l/s, CFM, whatever you measure it by) is how most racing parts (such as heads, exhaust, intake, etc.) are measured.

So here's how you can accurately measure specific power, to end internet debates once and for all:

1. Start with the displacement. This is the amount of area swept by the cylinder per cycle. If it is a 2 stroke or a rotary, you double it, because for the same as a 4-stroke cycle, a 2-stroke can run twice.

2. Multiply by the number of atmospheres that the engine takes in. This is boost, measured in Bar. Since N/A engines are in 1 bar already (14.5 psi at sea level) any additional boost is added onto it. So an engine at 15 psi runs at 1 bar boost, or 2 bars of air pressure. So multiply the displacement by 2 if that is the case.

3. Multiply that by the peak RPM that the engine is getting this air. We know how much air per cycle is flowing, now we want to know how much per minute. A more accurate way (instead of doubling displacement) to measure rotaries or two-strokes is to double their RPM (as it should be called cycles per minute), but either way works.

4. Divide the resulting number by the HP produced at that RPM.

The lower the number, the less liters (or ci if you use that) air is needed per minute for each unit of HP produced over that minute.

For our basis of comparison, let's use the Ford 5.0 Coyote:

5.0l liters, 1 atmosphere of pressure, 412HP @ 6500 RPM
5 x 1 x 6500 = 32500 / 412 = 78.8 liters per minute per HP.

So let's run some examples:

Nissan RB26DETT: 2.6liters x (1+.7 bar) x 6800 = 30056 / 276 hp = 128 per minute per HP

WOAH WOAH WOAH. What the hell happened? Is the RB26 really that much less efficient than this big, heavy, American V8?

No. It's because the published numbers, as many people know, about the RB26DETT are false. It produced about 330 HP, not 276, at 10 psi, and was designed to produce 450HP at 15psi with the stock, restrictive exhaust and intake system modified. So let's do that again:

2.6 x 1.7 x 6800 = 30056 / 330 = 91 per HP
2.6 x 2 x 6800 = 35360 / 450 = 78 per HP

So as you can see, the race-trim RB26DETT, 20 years ago, was about as efficient as the new Ford 5.0. This shows that while our power production isn't any better (both are DOHC 4v) our reliability is way up and our costs way down compared to the race engine.

What about some of those theoretical, 1000HP builds? Well, let's go with the JUN GT-R, which I believe had 1000HP at about 2 bar of boost and 9000rpm. (they would rev to 10,000, but the peak power came on earlier)

2.6 x 3 x 9000 = 70200 / 1000 = 70.2

That's a pretty damn efficient engine for the power output, but what about the new Alpha Omega GT-R from AMS? 1700 HP is a lot...

3.8 x 3.8 (40psi) x 8000 / 1700 = 115520 / 1700 = 67.95

Despite being almost 15 years newer, with what they have to work with, the record-breaking Alpha Omega only manages 3 HP per liter of air per minute better than the JUN R32. This makes sense, since there is virtually no new technology that one utilizes over the other. Small marginal improvements across the board, but nothing big.

Best of all, this counts for fuel economy as well, if you calculate the HP, airflow, and RPM at varying throttle levels. You could find out which engine gets the best fuel economy by measuring how HP is necessary to move the car as fast as you need, and then try to make that HP with the least possible airflow. The reason hybrids are able to get so good fuel economy is that the loss of engine efficiency is made up for in gains with electric motors.

Here are some more numbers I worked out, for your enjoyment. See if you can find the lowest HP/liter/minute engine out there:

NOTE: High numbers means either a really inefficient exhaust/intake (so the engine is starved for air) or lots of friction and resistance. Low numbers mean the opposite. Engines that use E85, Nitromethane, and Biofuel are proportionally lower, and (depending on energy-per-volume and air/fuel ratio, are going to show up as amazing)

Nissan S20: 2 x 1 x 8000 = 16000 / 160 = 100 per HP
1930s Deusenberg Model J: 6.8 x 1 x 3500 (est.) = 23800 / 265 = 90 per HP
1930s Deusenberg Model SSJ: 6.8 x 2.5 x 3500 (est.) = 47600 / 400 = 119 per HP
Nissan L28: 2.8 x 1 x 5600 / 150 = 15680 / 150 = 104 per HP
Nissan L28ET: 2.8 x 1.5 x 5600 = 130.6 per HP
Ford Flathead V8: 3.9 x 1 x 2000 = 7800 / 110 = 70.9
413 Wedge: 6.8 x 1 x 4800 = 32640 / 390 = 83.7 per HP (it was probably higher, SAE Net VS Gross)
2008 GT-R: 3.8 x 1.7bar x 6400rpm = 41344 / 485 = 85 per HP
2013 GT-R: 3.8 x 2bar x 6400rpm = 48640 / 550 = 88.4 per HP (sacrificing efficiency for more power!)

2013 Subaru BRZ: 2 x 1 x 7000 = 14000 / 200 = 70 per HP (!!)
1960's Mustang 315 Racecar: 4.7 x 1 x 6000rpm = 28200 / 315 = 89 per HP
Porsche 917 Can Am engine: 5.4 x 3.7(!!!) x 7800 = 155844 / 1580 = 98 per HP
Honda S2000: 2 x 1 x 9800 = 19600 / 247 = 79 per HP
EK Type R: 1.6 x 1 x 8200 = 13120 / 185 = 70 per HP
Top fuel Dragracer: 8.2 x 4.5 x 8400 = 309960 / 8000 = 38 per HP (Nitromethane, baby!)
Ferrari 458 V8: 4.5 x 1 x 9000 = 40500 / 562 = 72.64 per HP
McLaren F1: 6.1 x 1 x 7400 = 45140 / 618 = 73 per HP
Bugatti Veyron: 8 x 2.1 x 6000 / 1001 = 100800 / 1001 = 100.7 per HP
Bugatti Veyron SS: 8 x 2.25 x 6400 = 115200 / 1200 = 96 per HP
Hennessey Venom GT: 7 x 2.3 x 6600 = 106260 / 1244 = 85.4 per HP
Koenigsegg Agera (gas): 5 x 1.3 x 7500 = 51750 / 960 = 55 per HP
Koenigsegg Agera R (biofuel): 5 x 1.4 x 7500 / 1140 = 47 per HP
1950's Offenhauser 4-cylinder: 4.1 x 1 x 6600 = 2760/ 420 = 64.4 per HP
1963+ Indycar Offenhauser: 2.65 x 4 x 9000 = 95400 / 770 = 123.8 per HP
1961 Ferrari F1 engine: 1.5 x 1 x 9500 = 14250 / 190 = 75 per HP
1967 Ferrari 312/67 F1: 3 x 1 x 10000 = 30000 / 390 = 77 per HP
1970 Lotus 72 (Cosworth DFV): 3 x 1 x 11000 = 33000 / 520 = 63 per HP
1984 Toleman TG184 (Senna): 1.45 x 3 (est.) x 12000 = 52200 / 750 = 70 per HP
1984 Toleman TG184 (Senna) no restrictor: 1.45 x 5 x 12000 = 90000 / 1300 = 67 per HP
1988 MP4/4 (Senna w/Honda engine): 1.5 x 3.5 x 12000 = 63000 / 850 = 74 per HP
1990 MP4/5 (Senna): 3.5 x 1 x 13000 = 45500 / 650 = 70 per HP
2002 BMW P82 (F1): 3 x 1 x 19200 = 57600 / 900 = 64 per HP
2006 Toyota F1 Engine: 2.4 x 1 x 19000 = 45600 / 750 = 60 per HP
2007-2013 Renault RS27: 2.4 x 1 x 18000 = 432 / 750 = 57.6 per HP
2014 F1 engine: 1.6 x 2.5 x 15000 = 78750 / 600 = 131 per HP
My Dad's old 413 Wedge: 7.5 x 1 x 8500 = 63750 / 850 = 75 per HP (nitromethane)

Some Rotaries:

13B REW: 1.3 x 2 x 1.7 x 6000 rpm (est.) = 26520 / 300 = 94.7 per HP
13B Renesis: 1.3 x 2 x 1 x 9000 = 23400 / 250 = 93 per HP
2.6 x 2 x 1.7 x 10500 = 92820/ 930 = 99 per HP

Note: F1 numbers a little sketchy, I had to use a variety of sources and the peak RPMs may not off by 1000 either way, so take them with a +/- 3 liters per minute per HP grain of salt. Efficiency has been about the same since the 70s, with fluctuation based mostly on new fuel and reliability requirements.

How come the Flathead V8 is more efficient than a V-TEC engine, but Nissan's Flathead is horribly inefficient? Reciprocating weight and friction. At 2000rpms, the Flathead (also lacking a lot of peripherals) had so much less friction than a OHC engine. A vast majority of engine power (Koenigsegg estimates about 30%) is lost turning camshafts, and that gets increased exponentially if you have more of them. The Flathead only has to turn a single cam. A DOHC design only becomes more efficient when you add valves or increase the RPMs, since the small friction of the added parts on a OHV engine is much less until higher RPMs.

So wait, then why the heck is the Agera R so absurdly more efficient than every other production engine in existence!? The Agera runs on E85, and the Agera R runs on Biofuel. Both have a lot lower energy density, but a better air/fuel ratio. This means they can make more power out of less air, but have to use lots more fuel to do that. Same goes for Nitromethane. The power gains from E85 (~15-20%) are the same as the specific power drop (80% of 70 = gasp, 56!) on the Agera. Nitromethane (30-40%) is also the same drop with a top fuel dragster.

The Agera R, similarly, has so many parts made of carbon fiber, that it weighs considerably less than most engines. The Veyron Engine has a ton of added weight, because it was designed from two V8s, and the doubled parts double the weight. It has 2 more turbos to push as well.

What about my Dad's old 413 wedge (bored to 450-460ci)? While he ran Nitromethane, without boost and with all that heavy weight, he only came in about 13 liters /minute/HP lower than stock. That's how much efficiency is lost to peak at 850HP out of such an old, heavy engine.

And the F1 engines? Oh boy. Here comes the hate. In 2014 engines !!!error: Indecipherable SUB-paragraph formatting!!! and have a 30% tighter fuel usage requirement. The only way to meet those efficiency requirements is to vastly underpower the engine, letting it use very little fuel with less throttle than possible. This makes its peak power efficiency really, really bad. Granted, if you consider the KERS system, it is reduced to 100 liters per minute per HP.

Now we can stop arguing about which engines have the best specific power, and be aware that things like low-throttle fuel economy (vs peak throttle fuel economy), reliability, boost pressure, and peak RPM have more to do with efficiency then straight up displacement.

At the end of the day, yes, there is a "replacement" for displacement. It's call air mass, and the more of it you have, the better. Cylinder displacement, RPM, and Boost all increase it proportionally.

And when you have all three together... well. That's something.

FOR THOSE THAT TL:DR, IN SUMMATION:

So if you want a great engine, make it produce 1 HP for an entire minute with only 70 liters or air if running on gasoline (any octane), 55 liters of air running on E85, and 40 liters of air on Nitromethane. If you're above that, you're losing power somewhere. That power loss may mean better reliability, more fuel economy on the low-end, or less mechanical complexity, which are all great. Or it could mean high friction, too much weight, or a poorly designed engine.

DISCUSSION (64)

Arch Duke Maxyenko, Shit Talk Extraordinaire > GhostZ
08/26/2013 at 12:45

Kinja'd!!!

Demon-Xanth knows how to operate a street. > GhostZ
08/26/2013 at 12:47

The reason why nitromethane is so much "better" on that scale is that it brings a pair of oxygen atoms to the party with it.

GhostZ > Demon-Xanth knows how to operate a street.
08/26/2013 at 12:51

I'd have gone in and tried to normalize for fuel, but that would be too much work for a simple Oppo post.

Atomic Buffalo > GhostZ
08/26/2013 at 12:53

You mention engine mass and fuel consumption a few times in your article, but then retreat to calculating specific power. What's the point of making the most of a unit volume of air if the machinery and fuel required to do so makes the total package less effective? After all, in the context of a single automobile traveling across the earth's surface, air is free and in unlimited supply. You don't have to carry any; in fact you have to move it out of the way.

Specific power is interesting, but isn't producing the needed power from the least fuel with the smallest lightest package the real goal?

davedave1111 > GhostZ
08/26/2013 at 12:55

"low-throttle fuel economy"

I keep trying to find out more about that. There seems to be remarkably little information available.

GhostZ > davedave1111
08/26/2013 at 13:00

I know, right?

I'm convinced that automotive companies have hidden that information, on purpose, because its easier for them to game the bullshit "fuel economy" measurements required by the government.

ddavidn > GhostZ
08/26/2013 at 13:03

So... My 1995 M3 with the S50 and assuming no upgrades:

1. 2,990cc

2. 1 bar

3. 6,000RPM

4. 240HP

= 2.99 * 1 * 6000 = 17940 / 240hp = 74.75

Did I do it right? Thanks for sharing this wealth of information. I am now full of sciences and maths and things.

davedave1111 > GhostZ
08/26/2013 at 13:04

I don't know about the US, but in the EU it's illegal for car companies to give any figures other than the official EU ones. It was well-meant, since otherwise they'd all use their own gamed figures and comparisons would be even harder, but it's not perfect.

It might help if they just increased the number of different cycles they measured; at the moment we get urban, extra-urban, and combined. They could stick with the three headline figures and also give figures for half a dozen variants on each cycle, say, so people could compare a cycle that fits their driving profile more accurately.

Casper > GhostZ
08/26/2013 at 13:07

First, when people argue power per liter, they aren't usually being literal about the air+fuel to power ratios for a bore*stroke calculation as they are about the actual dimensions/weight of the engine. Just getting that out there.

Second, you did a good job showing efficiency drops dramatically as you push beyond standard pressures. Which makes complete sense, it takes more energy to compress and process more air to produce more power. You are trading more of the energy you are creating for more energy creation potential (more work in the turbos, more fuel, more heat, etc). In order to compensate for losses of efficiency due to heat, pressure, etc, you need more everything else.

I generally ignore all the arguments of displacement to power output and focus on engine weight/dimensions to output. That's where tiny v8s, turbo 4s, and tiny crazy v8s like the Hartlys shine.

GhostZ > Atomic Buffalo
08/26/2013 at 13:09

You're talking about the same thing. Gas burns fuel most efficiently in only one ratio, about 15:1. E85 is about 10:1, Methanol is about 5:1 and Nitromethane is like, 1.7:1 but has oxygen in the chemical composition already. Nitrous oxide is similar.

So if you make the same power with less air, you're also using less gas to do it. But the thing is, most of these engines are being calculated at only the peak HP levels.

Manufacturers tend to guard, rather well, how much air flow and HP (remember, fuel usage comes from air flow) you would get at say, 10% throttle, or 20% throttle. Take the Toyota Prius, for example. I'm almost betting that if you took a Prius motor out of the car, and ran it on gas only, it would need 20-30% more fuel to get the same power (even if you set that at say, 20HP) as a much older 4A-GE. Why? Because of two things:

1. The engine has a lot more weight it has to spin, from the A/C to other peripherals.
2. The fuel economy comes from pushing a much more aerodynamic car.
3. When the electric motor kicks in, it reduces the fuel consumption drastically on average.

The goal is to maximize the power output for the least air coming in, at the speed you'll be driving at, while pulling the weight you need to pull. Modern fuel economy requirements take nothing into consideration of overall mechanical efficiency, and instead slap a general measurement to try and guess at real world conditions. That's good for the consumer, but gives little incentive for companies to strive for mechanical performance.

Plus, a super-efficient engine may have reliability problems, or only be efficient in a tiny range, it may be loud or offensive and hard to sell. It is in no way the goal of automotive companies to produce a low fuel consumption engine. They want to sell cars.

GhostZ > davedave1111
08/26/2013 at 13:10

I'd like fuel requirements for the engine as a standalone unit, and then once its in the car. That wouldn't be so hard. That way we know if that hybrid system really does anything, or if its just the low drag coefficient.

GhostZ > Casper
08/26/2013 at 13:13

Exactly!

It's amazing how much loss of power you get by going from a Hydraulic cam to a solid roller. It can be a 10% power loss that can't be regained until you take advantage of that higher redline you can rev to.

davedave1111 > GhostZ
08/26/2013 at 13:16

If you know the Cd, you can calculate the power needed to overcome aerodynamic drag at a given speed. In general, hybrids tend to use the electric bit to help with low speed fuel economy, so it won't have much effect at highway speeds - which is why cars like the Prius aren't particularly efficient on long runs, but do very, very well in stop-start traffic.

davedave1111 > GhostZ
08/26/2013 at 13:21

It is in no way the goal of automotive companies to produce a low fuel consumption engine. They want to sell cars.

There are various parameters that go into car design which can be tuned in various ways, but essentially the whole thing is a series of compromises. A car not only has to be economical, but also carry a reasonable load for its footprint and be safe, for example. That's why we end up with fairly standard shapes, all in a similar range of drag co-efficient for a certain size, all with about the same fuel economy within class, and so-on.

The brackets for things like acceptable fuel economy change over time, but the car companies will generally try and stay within them. That means that even if they do produce a much more economical engine, they'll increase the weight or drag of the car in order to improve something else - performance, safety, load-capacity, or whatever - a bit, rather than leaving the car with outstandingly brilliant economy and compromises in other areas.

Atomic Buffalo > GhostZ
08/26/2013 at 13:28

I'm talking about the size and mass of an engine being important factors in practical engine efficiency. A heavier engine makes the car heavier and more power is required to accelerate it.

Excellent article and discussion, in that factors beyond the combustion chamber are given serious consideration in attempting to explain the overall value in real cars.

LandSpeed-DSM > GhostZ
08/26/2013 at 13:35

Wants to lecture Oppo on efficiency as it relates to power production using airflow: Good

Uses volume instead of mass flow rate: Bad _

I was so excited to read this, as I had just referenced that concept in a reply to a post about specific output in the Peugot 308R discussion.

This is thoroughly flawed.

GooseTheThrottle > GhostZ
08/26/2013 at 13:35

BMW S14 (2.3 x 1 x 6700)/ 195hp= 79 per HP

GhostZ > Atomic Buffalo
08/26/2013 at 13:36

I agree, and camshafts are the next thing to reduce weight and friction in. They can get extremely inefficient to spin at high RPMs (particularly solid ones) enough that at low RPMs, even all of the inefficiencies and weight of a Flathead V8 are outweighed by the really low rolling friction.

Right now I'm thinking about pneumatic valves, camless engines, solid engine lubricant, C/F alloy internal engine parts, etc. that may all be available in the next 20-30 years, which could mean a 200-300% increase in fuel efficiency if cumulatively applied. (camless engines show 30% increase, solid engine lubricant shows a 20-40%, C/F alloy parts could halve the rolling mass) I think we're in the biggest engine tech boom since the 70s brought turbos to play in normal cars.

GooseTheThrottle > GooseTheThrottle
08/26/2013 at 13:40

Mazda Miata 1.8 (1.8 x 1 x 6800)/ 115= 94.6 per HP

GhostZ > LandSpeed-DSM
08/26/2013 at 13:43

If you know the pressure of the volume, you know the mass of the air. 1 liter at 1 bar is the same mass as .5 liters at 2 bar. You can just convert numbers in your head if you want or do an extra calculation. It's all the same, so your complaint doesn't really make sense.

Mass flow rate would be good to know if you wanted to find out where the airflow was being pinched, if you put each part on a flow bench, though.

Volume is actually incredibly important in engine efficiency though. Being able to flow the same air with less volume means smaller port, intake, and valve sizes. That means higher air velocity . Higher velocity means an amplified pulse effect, so (especially on n/a engines) you can drastically improve the volumetric efficiency (by up to 20% easily).

POD > GhostZ
08/26/2013 at 13:49

Firstly, this was excellent! Full of great information, well written, very enjoyable.

Now, I want to make sure I'm doing this right. 2012 Mazdaspeed3 (oh, and we prefer Troglodyte to Barbarians, it's classier).

2300cc

300 horse (with less restrictive intake and exhaust)

15.6 psi boost

peak power at 5500 RPM (red line is higher, but it losses power above 5500)

So 2.3 x 2 x 5500 / 300 = 84 per HP?

Does that seem right?

We use a similar calculation when calculating efficiency of athletes. VO2 max. ml of O2 consumed per kg of body mass per minute. Cross country skiers typically have some of the highest. In the 80-100 mL/(kg·min). Dogs running in the Iditarod Trail Sled Dog Race have VO2 values as high as 240 mL/(kg·min). Average untrained human male is only 35-40 mL/(kg·min). People just aren't that efficient.

Atomic Buffalo > GhostZ
08/26/2013 at 13:51

One thing's for sure — engine cutaways at auto shows have gotten a lot more interesting.

LandSpeed-DSM > GhostZ
08/26/2013 at 13:51

If that were true (which it is not): Provided that at peak rpm the engine remains on the compressor map - why will a 59mm compressor make less power at the same boost compared to say a 67mm or 75mm unit? CHARGE DENSITY

The engine can only ingest a fixed volume. It's how much mass is crammed into that volume that matters. This is a function of pressure and temperature.

Compressor and charge cooler efficiency, latent heat of vaporization for the fuel, combustion chamber and cam design. It all plays a part. If that 1Bar boost is entering the ports at 200*F or 75*F it makes a big damn difference.

Engine Demand Flow which is what you are calculating, in CFM or Liters, is only useful if you account for the density of that Volume. You've also not included Volumetric Efficiency in your demand flow generalization.

That's what I am saying. When I am designing a build for a client, I take their STP demand flow and plot that onto the compressor map for a rough idea. Beyond that though, volume goes out the window and mass is used from then on.

Telling someone a cylinder head or compressor flows XXX cfm is not especially useful if I don't have both the pressure and temperature it was done at.

Which is why pretty much any EMS uses mass for airflow measurements, as below from my own car moving ~69lbs/min @ 37psi boost:

Kinja'd!!!

Your MAF sensor? "Mass Airflow" sensor.

dsigned001 - O.R.C. hunter > GhostZ
08/26/2013 at 13:52

Excellent write up.
Now can you do one for area under the curve? Another overlooked metric, especially where it concerns the rpm the engine stays in under acceleration given the gearing.

GhostZ > POD
08/26/2013 at 13:53

Bingo, spot on. Given how tunable the MS3 is, you can easily see that the engine has higher potential to offer. I know some E85 builds can get to 400 HP pretty easily without an increase in displacement and just a bit more boost. It's about par for the course for a "family" car though.

That's actually really cool about the athlete oxygen consumption. I guess when you get down to it, Muscles are a sort of combustion engine.

PlayerWAN > GhostZ
08/26/2013 at 13:57

Kinja'd!!!

Great article! should be shared on the front page! Also, conspicuously absent are calculations for LSx engines.

GhostZ > dsigned001 - O.R.C. hunter
08/26/2013 at 13:57

It wouldn't be hard if you know the calculus (and the calculus isn't hard to learn) but there are very, very few manufacturer records of power at each RPM, and Dyno sheets are rarely reliable due to the wide variety of conditions, types of dynos, and

So while you could calculate it (just get a data plot, fit a function to it, and run the integral up to the RPM you're at) getting the data for anything other than your own car is difficult. I would take it a step further though, and run those torque numbers (HP be damned) through the transmission and rear end gear, then the wheels, then get the resulting RWTQ @ MPH readings and convert that to RWHP. That gives you the full graph of HP all the way up to your top speed!

What I don't know how to do though, and I wish I did (I'm currently using tuning programs to do it for me) is to calculate air velocities based on cylinder pressures, so you can estimate the pulse effects, thermal efficiency, and pre-detonation features of an engine.

GhostZ > PlayerWAN
08/26/2013 at 14:02

Ah, I didn't think of them. They're pretty good though, from my experience.

1997 LS1 is 5.7 x 1 x 5600 = 31920 / 345 = 92.52

Don't panic, that shows how underrated and how much more performance there is to gain. For example, the LSX 454:

7.44 x 1 x 6200 = 46128 / 620 = 74.4

It's really a high performance engine struggling under restrictive GM guise. It's taps are really only opened up in race cars, high-end corvettes, and crate motors.

Also if you want this on the front page, maybe send me a bump to one of the editors? They usually pay attention to @s on twitter or emails.

dsigned001 - O.R.C. hunter > Casper
08/26/2013 at 14:03

The nice thing about this metric is that it allows for an easy calculation of fuel efficiency as well. E.g. in fsae (as with many other race series) they run air restrictors. Our car (my schools car, I didn't work on it), made great power given the air, but it was very thirsty.
Also a consideration is scalability. It's all well and good to run a 2.0 at a certain efficiency, but if that design isn't scaleable, it becomes difficult to compare it to a larger engine that makes more power. Loading potential is another thing. Even if your Hartley and your pushrod make similar power, you will absolutely not want to put it into your land yacht.

Even though I doubt that I'll ever be an engineer, I love this kind of stuff.

GhostZ > dsigned001 - O.R.C. hunter
08/26/2013 at 14:05

Also, if you really did like the article, maybe give me a bump to one of the editors via email/facebook/twitter and they might promote it?

BREADwagon > GhostZ
08/26/2013 at 14:06

I'm unsure about your description on calculating fuel economy solely based on HP, airflow and RPM. You don't know the AFR, so you cannot calculate TOTAL fuel flow. You may know air flow and power, so you can calculate the total BURNED fuel rate , but you cannot calculate any excess fuel dumped into the combustion chamber (to cool of EGRs or due to poor control systems). A 2.0 liter engine making 100hp at 6000rpm with an AFR of 12:1 has better fuel economy than a 2.0 liter engine making 100hp at 6000rpm with an AFR of 13:1.

Also, an engine wont inherently suffer a VE loss due to being part of a hybrid system. You see a gain in MPG with hybrid systems since MPG is a function not solely dependent on peak VE of an internal combustion engine. We all know real world MPGs are a complex function of car weight, overall drag, gearing, driving style etc etc.

An example are some modern engines that can over-lean out the mixture or deactivate cylinders altogether by holding open the valves at part loads. You'll have a much higher air flow per minute per hp than at peak power numbers, but will be using very little fuel, giving you a very low fuel flow rate. Of course, this isn't at WOT peak power/rpm values, but at normal driving conditions.

I love this stuff.

PlayerWAN > GhostZ
08/26/2013 at 14:09

It'll be interesting to see how much more efficient engines with direct injection are. Take the BRZ FA20 for instance. I'm willing to bet its awesome figures are because of the direct injection system in it.

dsigned001 - O.R.C. hunter > GhostZ
08/26/2013 at 14:14

Lol. That's the thing about physics - you can always do more.
I don't remember how to integrate for an irregular curve, but I think we're fast approaching diminishing returns anyway, as far as comparisons go. A lot of the little superbike engines have great power under the curve, but have such irregular delivery that it's not always a helpful consideration on its own. You also get into issues of application. Comparisons are only helpful for a given (or similar) car.

GhostZ > BREADwagon
08/26/2013 at 14:17

AFR for gasoline is 15:1, ideally, but almost no engines run that. You are right about excess dumped fuel problem. I think if you did this same calculation for low throttle levels, you'd get the ideal fuel consumption if all fuel was burned evenly. Then you just have to figure out how much fuel is lost.

And you're right about VE loss. Gross output isn't necessarily impacted by a hybrid system. But a hybrid system can cause reduced net power, which is important. It only works when its on, basically. I'd like for hybrid manufacturers to post fuel economy numbers for engines removed from the car.

Another concern I didn't address is air/fuel velocity, which has a huge hand on the vacuum effect of an engine and can really improve efficiency. That's the main reason why F1 and Nascar engines are lower than most production engines, and why some N/A engines are better than even very effective turbo versions.

Also, I am not going to touch the thermodynamics of expanding engine parts and intake gases. I'm not ready for that! It's too crazy!

Enginerrrrrrrrr > GhostZ
08/26/2013 at 14:18

This was excellent. I can't promote it enough.

Any knowledge about turbine engines? I assume they are much more efficient, but it would be nice to see a measured amount.

GhostZ > dsigned001 - O.R.C. hunter
08/26/2013 at 14:19

You would break the curve up using points of inflection I think, and integrate it in each part, by fitting a formula to each curve before it changes. That would be easier than integrating a strange curve that you can't normally apply a formula to.

ZeroOrDie - Powered By MZR > GhostZ
08/26/2013 at 14:22

Good read. *cries over DD's #s after calculating*

GhostZ > Enginerrrrrrrrr
08/26/2013 at 14:22

You could do it, but you'd need to know the air intake per minute (no need to calculate displacement, since they are continuous), type of fuel used (airplanes don't use gasoline I think...) and convert the output to HP. Since a lot of jet engines are given for thrust... that might get difficult.

Also, if you really like it, send an email/tweet in Hardibro's direction and see if he'll put it on the front page.

POD > GhostZ
08/26/2013 at 14:24

Sweet thanks! The MZR 2.3 DISI is more efficient then I thought it would be. But my efficiancy expectation when I bought it were rather low.

What I think would also be interesting to see is an "efficiency curve" across the rev range. I'd wonder if the speed3's efficiency improves at say, 3500 RPM. it should be in the 200-250 horse range there. So:

2300*2*3500/250 gives us 64.4 per hp.

The human body is basically a giant engine ran with hundreds of exothermic reactions. O2 is used for combustion, but it can run on surprisingly varied fuel sources.

Next time you go for a work out, feel the temperature of your muscles before and after. It'll give you an idea of the increased enzymatic activity and O2 consumption.

GhostZ > LandSpeed-DSM
08/26/2013 at 14:37

A couple other comments pointed out the lack of temperature in this, which is omitted for a reason, it makes the calculations more complicated and beyond my own scope.

I've been playing with EMS programs in my spare time recently, but I haven't had any formal physics/mechanics/thermodynamics classes (I'm an Econ major) so while I have a general idea how the temperature affects the mass/volume/pressure, I don't know the exact formulas, but it's obvious that for estimation it's a lot easier to calculate volume.

For the sake of comparing two engines, taking the incoming air pressure and putting it as a rate of time is easy to do and a lot more accurate than just comparison displacement/RPM alone. VE's, charge density, intake and exhaust velocity, not much of that can be found by just going to wikipedia, and while most people and do some simple multiplication, very few (including myself) can do fluid thermodynamics.

LandSpeed-DSM > GhostZ
08/26/2013 at 14:44

Which is why people pay me to develop performance solutions for them. Yet I still use HP/Liter or even just Airflow in conversation.

Go figure. Anyways, that was all I wanted to communicate. You are on the right track and approach it more cleverly than most! Apologies if I came off excessively rude, I am not a PR guy for what it's worth.

GhostZ > LandSpeed-DSM
08/26/2013 at 14:47

Excessively rude is nothing compared to valuable feedback .

I've got Engine Analyzer Pro v3.9 running. It's just a trial, since I'm only using it to keep myself from spending tons of money playing with real engines. Do you have an alternative that you know of that might be better?

LandSpeed-DSM > GhostZ
08/26/2013 at 14:53

Honestly that is one of the better programs for the money. Aside from CFD software for manifold design/testing, most everything I do is manual though.

Classroom time has been helpful, but getting my hands dirty and playing with different hardware, fuels and trying different spark/fuel schemes then reviewing data and reading plugs is the only way to really Grok it.

Mattbob > GhostZ
08/26/2013 at 15:00

one word, MATLAB.

GhostZ > LandSpeed-DSM
08/26/2013 at 15:06

Yeah, I don't have those opportunities where I'm at. About 5% of the physics students at my school are applied, the rest are all a wide variety of theoretical fields. Not having the money for a garage/parts means any mechanical mistakes I make are on my wallet, and without years of mechanical experience behind me either, I'm much more content playing with the math on a computer until I can at least afford a parking spot, much less a garage.

I've gotten Engine Analyzer down pretty good though, took me a few hours this last week but I can keep a good engine together and build it well without it blowing up. I've been on the quest for the cheapest way to open up a Ford 5.0 HO. It looks like a decent plenum, AFR 185 heads, and an appropriate cam can pull the power I'd want (350-375) Some custom solid roller cam, intake, exhaust sizes and I can get it to 425, or 499 on E85.

I'd like it if I could find a way to simulate engine reliability, but that definitely comes from having hands-on experience.

GhostZ > Mattbob
08/26/2013 at 15:07

You make me shudder.

That's the word I associate with the depressed math/com sci/physics majors at my school.

Goshen, formerly Darkcode > GhostZ
08/26/2013 at 15:11

This is actually brilliant. Thanks a lot for posting this, you've changed my mindset on specific power.

BREADwagon > GhostZ
08/26/2013 at 15:11

Even though most everyday engines run 14.7:1 (15:1 approx) during part throttle/loads for emissions sake, you can't assume that all part throttle operation is at stoichiometric AFR (14.7:1). You also need to take into account load, and whether or not the motor is in steady state (accelerating due to part load).

I still disagree for a net loss in power with hybrid systems. In fact, since we're talking about flywheel power, then it doesn't matter if the motor is packaged as a hybrid or in a conventional vehicle, VE wont change. What will change is the efficiency of the system converting chemical to kinetic energy. A fuel economy number in MPG for an engine is relatively useless, because MPG ratings are for an automobile as a package.

Mattbob > GhostZ
08/26/2013 at 15:14

Trust me, its is important for engineering, and if you use it a bit, it isn't that intimidating. It is extremely powerful.

LandSpeed-DSM > GhostZ
08/26/2013 at 15:22

Dive in head first, its how I started back in HS. Already had a DD, scraped together what I could and found a fairly clean project in the form of a 4 speed manual 305ci Chevy Monza. Started playing with nitrous, learned a lot.

Sold that for profit and got a Yamaha R6, got to work on installing a GT2560R turbo on it. Sold that, and put the proceeds towards a 5.9L Cummins Ram 2500, played with a few different turbos including a compound setup. Sold that and started to tinker with DSMs.

Next platform will probably be a Foxbody Mustang with a big single and a Lenco trans to do some local radial tire racing.

If you have a DD already sorted, its the best way to learn. This way the project can sit when it has to and you aren't sh*t out of luck when it's time for class/work!

Side note: The weak link in those 302 Fords is the block, some have had a nasty habit of splitting down the middle around the 500whp range!

Kinja'd!!!

McLarry > GhostZ
08/26/2013 at 15:33

Nice writeup. I should think that fuel consumed would need to be considered along with air volume to make a proper efficiency metric, though...That would also make it more relevant to everyone since air is free...so far :P

GhostZ > McLarry
08/26/2013 at 15:37

It depends on how lean the engine is running, and what fuel. If you assume a 15:1 (or 14.7:1) a/f ratio for gas as standard, it still holds. It only becomes an issue when cars start using more fuel than they really need, or that they can combust.

But air is surprisingly not free in an engine. It costs a lot of money to flow air effective, and there are trade-offs for it. While air is free outside of the engine... getting it into the right place can be an expensive, expensive system.

feather-throttle-not-hair > GhostZ
08/26/2013 at 16:10

What a great post! Star for you!

BiTurbo228 - Dr Frankenstein of Spitfires > GhostZ
08/26/2013 at 18:37

I've always taken two views towards engines, and which is better/worse. One follows a similar train to most people's, which is 'which engine makes more power for a given displacement, taking into account whether it's forced induction or NA'.

The other is that it is only the actual power that counts.

So what if your 5.0l V8 only makes 195bhp. If your friend's 2.0l makes 180bhp, it doesn't matter. You're still got 195 and they've got 180.

GhostZ > BiTurbo228 - Dr Frankenstein of Spitfires
08/26/2013 at 18:53

You are completely right about the latter measurement. That is spot-on.

These comparisons are more about where improvement can be made, and how much of the engine's potential is being used. It's a double-edged sword. Yeah, a Honda B16 makes a lot more power more efficiently, but it would be prohibitively expensive to make it keep up in absolute power with a Ford 5.0. That's engine swap logic, basically, in my mind.

Casper > dsigned001 - O.R.C. hunter
08/26/2013 at 19:30

The correct solution to the problem: there should be no land yachts. If the car's too heavy, make it lighter and smaller ;)

Blunion05 drives a pink S2000 (USER WAS BANNED FOR THIS POST) > GhostZ
08/26/2013 at 21:55

I'm too stupid to understand any of this but I'm sure I'll get there some day.

Philbert/Phartnagle > GhostZ
11/02/2013 at 19:06

"There's no replacement for displacement!" Please stop. Let me explain why you are wrong.

Nope, nope, nope!

That statement is not "wrong". It is most frequently used in terms of producing the most power.

A good big engine will always produce more power than a good small engine.

You may have a point about the efficiency of some smaller engines, but you will never be able to prove that fewer cubic inches will produce more power than more cubic inches.

GhostZ > Philbert/Phartnagle
11/02/2013 at 23:04

Did you read the article?

My point is that cubic inches isn't important: air flow is. Cubic inches is one way to estimate air flow, but there are two other major factors. Any decrease in cubic inches can be made up for a proportional increase in RPM or boost. The same can be said of the other two.

Philbert/Phartnagle > GhostZ
11/03/2013 at 00:04

I read part of the article and the statement you claim is "wrong" is not wrong at all.

You cannot just make up for a deficiency in cubic inches with increased RPM's or boost because the larger engine could also benefit equally as well from either or both of those, UNLESS your test limits the larger cubic inch engine to low RPMs and natural aspiration?

Cubic inches are important, because the more cubic inches you have, the more air flow you can get.

Please note that I'm not trying to argue with you here, just disagreeing with part of what you said. I have been a mechanic for well over 30 years now and I have been involved with and worked on car engines that produce over 1400 HP, large diesel generation engines that produce over 4000 HP and many others in between and of lower HP, so I'm not just pulling my thoughts out of thin air.

EDIT: There is only one "substitute" for cubic inches that I know of and seeing your picture of the top fuel car reminded me of it, nitro! How else could you get close to 10,000 HP from a 500 cubic inch engine?

GhostZ > Philbert/Phartnagle
11/03/2013 at 09:49

It isn't wrong to believe that cubic inches are necessary. It is wrong to believe that you can compare engines just on that.

Because I can do this:

I read part of the article and the statement you claim is "wrong" is not wrong at all.

You cannot just make up for a deficiency in RPM with increased cubic inches's or boost because the higher-RPM engine could also benefit equally as well from either or both of those, UNLESS your test limits the higher-RPM engine to small cubic inches and natural aspiration?

RPMs are important, because the more cubic inches you have, the more air flow you can get.

EDIT: There is only one "substitute" for RPMs that I know of and seeing your picture of the top fuel car reminded me of it, nitro! How else could you get close to 10,000 HP from a 500 cubic inch engine?

And by replacing those words, it is all still true . Just because you need cubic inches to make some power, doesn't mean you can't make the same power with less cubic inches.

Let me explain "boost". Boost is the pressure of air that enters the cylinder. Naturally aspirated engines have some form of boost . It's usually lower than 100% though. That's called volumetric efficiency. Higher compression, better head design, tuned intakes or exhausts, these result in higher volumetric efficiencies, and with pulse effects you can make an engine, without a turbo, have over 100% volumetric efficiency. All a turbo does is use some other force to move air, so that the volumetric efficiency is significantly above 100%. 1 bar of boost = 100% added, effectively "doubling" the size of the engine.

The point I'm trying to make (and you made it a bit for me) is that getting 10,000 HP fro ma 500 cubic inch motor is no more impressive than getting 10,000 HP from a 250 cubic inch motor.

Now, getting 10,000 HP from a 500 cubic inch motor, 50psi boost, at 10000 rpm is signifcantly more impressive than getting 10000 HP from a 500 cubic inch motor with 51psi boost and at 10000rpm . That means that you're getting more power from the engine with less air, so the one that requires 50psi to make 10000HP has some inefficiency (reciprocating parts weight, pumping losses, higher friction, worse cooling) that the other motor has an advantage over.

Likewise, a naturally aspirated engine that produces the same power but at a lower elevation (higher "boost" due to increased air pressure) isn't as impressive as one that produces the same power at a higher elevation, because it's doing the same job with less materials.

In fact, if we lived on a planet with twice the gravity, all of our naturally aspirated cars should (theoretically) make twice as much power.

Nitrous oxide actually adds oxygen to the fuel, so it does the same thing a turbocharger does (at least, on a chemical level) and increases the volumetric efficiency. So if you say that nitrous is a substitute for cubic inches, you have to agree that increasing the air pressure, adding a turbocharger or supercharger, or tuning the intakes and exhaust for pulse effects is a substitute as well.

Philbert/Phartnagle > GhostZ
11/03/2013 at 11:37

The more you talk the more you convince me that you really don't know what you are talking about and I don't need an explanation of boost, I know what it is, having operated a generating engine that used one supercharger and two turbochargers.

The "nitro" I mentioned that is used in the top fuel car is NOT nitrous oxide it is nitromethane. You can read about it here- http://en.wikipedia.org/wiki/Top_Fuel

You WILL NOT get the same HP from a 250 cubic inch engine that you can get from a 500 cubic inch engine period. It is impossible to flow the same amount of air/fuel in the smaller engine.

So you are trying to tell me that "gravity" makes air heavier and denser?

What do you think that heavier gravity is going to do to the engine and its parts?

Nitrous oxide or some form of boost is or can be a substitute for cubic inches, but only up to a point, because eventually you will reach that point where the engine can no longer move anymore air.

GhostZ > Philbert/Phartnagle
11/03/2013 at 14:39

We completely agree on theory and technical stuff. That much is true, but we disagree on literally only one point, and you put it well:

You WILL NOT get the same HP from a 250 cubic inch engine that you can get from a 500 cubic inch engine period. It is impossible to flow the same amount of air/fuel in the smaller engine.

And that's where I completely disagree. Moving the same mass of air into a smaller engine will yield the same power. It doesn't matter how it gets there. You could have a 1 cubic inch engine, if it's spinning incredibly fast it will make considerable power. To make horsepower out of a 1 cubic inch motor, you'd have to make it spin 500 times faster than a 500 cubic inch motor, all else staying the same. That's 350,000rpm (assuming the 500ci engine makes peak at 7000). But, theoretically, in some world where valvetrain components could handle those speeds, then it would make the same amount of power. Likewise, a 1 cubic inch motor spinning at 7000rpm with 500 bar boost would make the same power too. That's why a 2-liter honda engine can make the same amount of power as a Ford Small Block, and why the 3.8l V6 in the GT-R can make nearly 2000HP. It's all about forcing air and fuel into the same space, and igniting it. RPM, Displacement, and Boost just describe how the engine does that. Hell, instead of saying "a 500ci engine with no boost is like a 250ci engine with one bar" you could also just say "a one-bar engine at 250ci is as powerful as a no-boost engine at 500ci".

So you are trying to tell me that "gravity" makes air heavier and denser?

Gravity increases air pressure. Higher air pressure does, indeed, make the same volume of air denser and heavier. And that's what matters, not the size of the engine, but the size of the air going into it.

Nitromethane brings 2 oxygen molecules and uses a significantly higher amount of oxygen when it burns. That's why it creates "Effective" boost (or "effective" displacement) boost. Nitrous Oxide is similar to it in that way. Like I said, if you think that Nitromethane and Boost are equated, then you have to agree that Displacement, RPM, and improved volumetric efficiency (along with other methods of getting more power) are substitutable.

Philbert/Phartnagle > GhostZ
11/04/2013 at 11:05

As soon as you build a 250 cubic inch engine that produces close to the 10,000 HP a top fuel engine makes, then I will believe you. Otherwise, nope, nope, nope!

For a smaller cubic inch engine to make the same HP as a larger one (after a certain point where it will exceed the design limitations), it would require that the engine be subjected to unbelieveable pressures and forces which they cannot handle without some type of extreme re-designing or modifications.

I concede that maybe it is possible, but it is highly unlikely that anyone will ever go to the lengths required to absolutely prove it.

P.S. I have the SBF, bring on the Honda. ;)