Power Explained: Horsepower, and why your car does not make what you think it makes.

"CAR_IS_MI" (car-is-mi) 01/31/2014 at 10:02 • Filed to: Power Explainer

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Welcome back to Power Explained; a multi-part series where I explain the tuning process and mechanics involved and how they affect your horsepower numbers. One of the most common questions I get asked in the aftermarket performance world is "I went to XYZ Shop and they said my car made 140hp, but I think it should have made 200hp. What is wrong with their dyno?"

Generally, my response to this is nothing. No I don't mean that I do not respond, but rather, nothing is wrong with the dyno. Now there are sometimes legitimate cases where something is off on the dyno, usually atmospheric readings, but we will get into how various readings can effect your output in a later article.

Usually around this point I ask what modifications your stock EK civic has, to which the response is cold air intake, weld on fart can, and pep boys spark plug wires, or in other words, nothing that actually gives you power.

Now as you !!!error: Indecipherable SUB-paragraph formatting!!! , a dyno is nothing more than a tool, just like a hammer, so when you hit your thumb with a hammer, do you blame the hammer or the user? Exactly, the hammer, then you immediately banish it to the outskirts of the garage for it perilous ways. Unlike the hammer however, when the dyno does not give you the horsepower number you want to see, it is usually because of the car.

!!! UNKNOWN CONTENT TYPE !!!

The key to understanding why your car is nowhere near what you think it should be is understanding how OEM horsepower ratings are calculated. Many time I hear people say things like "My car makes 300 hp from the factory. My intake is good for 10hp, my exhaust for 25 hp, and my tune for 50hp." They then pull out their fingers and toes and 20 minutes later arrive at the conclusion that they should be making 7 million horsepower. I then correct their math, where the sum of those numbers does equal 385.

So my car should be making 385hp then, right?

No. Your factory rating is in Brake Horsepower (BHP). BHP refers to your engines output at the crankshaft, before losses in drivetrain, exhaust, and drive accessories (alternator, power steering pump, etc.). As of 1972 automakers define power output in SAE net output. This indicates the power of your engine at the crankshaft, including losses from exhaust, emissions systems, and drive line accessories. Essentially, your 300 hp engine is 300 hp before any power is lost in the transmission, differential(s), and wheels. Chances are, your 100% stock, 300 hp car is putting anywhere from 240 hp to 260 hp to the wheels.

Great, okay, but my aftermarket parts said they would give me 85 more hp. 260 + 85 = 345 hp right?

Wrong. Most aftermarket manufacturers like to beat around the bush with their advertised numbers. They aren't exactly lying to you, but they aren't always telling you the whole truth either. They did get an extra 10 hp from the same engine as yours, except that engine also already had a full, high flow exhaust, high flow intake manifold, larger throttle body, ported heads, and larger valves. Adding that same intake to your all stock motor might net you 2hp. The same goes for the exhaust and the email tune you got. Your combined intake and exhaust might net you 10 – 15 hp, and if the tune is any good, you might an additional 20 hp from that.

So the 295 hp I put down is actually accurate?

Yes. And to gain more power from your mods, you need to understand how they all work together.

Tune in next week for: Understanding Atmospheric Conditions.

Nibbles > CAR_IS_MI 01/31/2014 at 10:05

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That's why I hate current HP ratings. My Focus is rated at 121 hp. After parasitic losses - primarily through the worst automatic transmission in the world - and elevation losses, I'd be lucky to be putting down 80 hp.

Tom McParland > CAR_IS_MI 01/31/2014 at 10:06

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Great article, I love this technical stuff!

ADabOfOppo; Gone Plaid (Instructables Can Be Confusable) > Nibbles 01/31/2014 at 10:11

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cough buy an SVT cough

Problems solved.

ssidd47 > CAR_IS_MI 01/31/2014 at 10:14

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I think this is one of those times where ignorance is bliss.

But still, thanks for this. Not something I knew before.

Nibbles > ADabOfOppo; Gone Plaid (Instructables Can Be Confusable) 01/31/2014 at 10:14

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Really, nearly anything would solve this problem

The wife is dead set on keeping at least one automatic in the driveway though, and for good reason. We both have knee problems and, when they flare up, it can be kinda hard to clutch. So, once that magical ZF 8HP is placed underneath a Charger or Challenger R/T, I'm pretty sure that's the route we'll go

Mattbob > CAR_IS_MI 01/31/2014 at 10:15

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"banish it to the outskirts of the garage" Nice. Good article!

davesaddiction @ opposite-lock.com > CAR_IS_MI 01/31/2014 at 10:17

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Reading this really make me want to get those test pipes and a tune for my car...

And an exhaust.

And maybe a supercharger.

Why can't real life be as easy as Gran Turismo?!

ADabOfOppo; Gone Plaid (Instructables Can Be Confusable) > Nibbles 01/31/2014 at 10:19

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Vaguely insulting and snarky remark resulting in a poor attempt at humor and sarcasm.

Nibbles > ADabOfOppo; Gone Plaid (Instructables Can Be Confusable) 01/31/2014 at 10:21

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Almost witty retort including references very few people would actually get.

thebigbossyboss > CAR_IS_MI 01/31/2014 at 10:22

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This was informative and interesting. Thanks!

carsandmusic > CAR_IS_MI 01/31/2014 at 10:22

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Thank you for your detailed article! I was about to write an article explaining why German manufacturers don't lie about their horsepower numbers. Modern research resulted in cars with less parasitic losses than older cars (or maybe cars from other manufacturers), thus feeling more powerful than the numbers suggest.

KB Garage > CAR_IS_MI 01/31/2014 at 10:24

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Nah, brah. My intake definitely adds 15hp. I can tell by how hard it pulls. Yo.

Party-vi > CAR_IS_MI 01/31/2014 at 10:28

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" then you immediately banish it to the outskirts of the garage for it perilous ways."

This has happened to a power steering pulley, power steering pump, sledge hammer, leaf springs and countless other evil things in my garage.

KB Garage > KB Garage 01/31/2014 at 10:30

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That is the third time I've been kinja'd in the face in less than ten minutes. Maybe it's just mobile blowing goats today.

Yowen - not necessarily not spaghetti and meatballs > CAR_IS_MI 01/31/2014 at 10:31

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Another point to be made. You also cannot add up the horsepower of your mods. Mods encroach on each others's gains. I like to compare it to speakers, two 100 watt speakers do not make for 200 watt's, it nets you something like 103.

Joe_Limon > CAR_IS_MI 01/31/2014 at 10:38

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I dunno man, my car clearly feels like it adds 10hp whenever I bring it to the car wash.

doodon2whls > CAR_IS_MI 01/31/2014 at 10:45

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In some (admittedly rare) cases, manufacturers have effectively underrated HP/TQ output. For example, besides STP conditions at the air intake (pre airfilter) for dynamometer rating runs, there was no standard for the charge air temperature entering the intake manifold. IOW, to what temperature should the charge air cooler (intercooler) be heatsoaked ? As a result, some manufacturers assumed a worst-case condition for intercooler efficiency and charge air temperature leaving the intercooler. This resulted in lower HP/TQ output (due to increased charge air temps and possibly some minimal boost derate). That means that some customers ran their cars on chassis dynamometers in more optimal conditions and actually put down HP/TQ numbers at the wheels that were near the SAE ('crankshaft') rated HP/TQ.

For example:

(Photo Credit: SportCompactCar)

willkinton247 > CAR_IS_MI 01/31/2014 at 10:46

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Huh. I always thought BHP was the hp measured at the wheels.

Learned something new!

CAR_IS_MI > doodon2whls 01/31/2014 at 11:04

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Yes this is true, some manufacturers will deploy techniques to under rate their HP numbers. This is usually true for the higher end, higher power vehicles (e.g. Honda is not going to try to under rate the civic...). All ratings, however, are still before losses through the transmission / drive line.

CAR_IS_MI > Party-vi 01/31/2014 at 11:10

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Every.

Single.

Time.

CAR_IS_MI > ssidd47 01/31/2014 at 11:19

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I personally don't believe in ignorance. The more you know the more you can accomplish.

CAR_IS_MI > Joe_Limon 01/31/2014 at 11:20

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Maybe that's because your removing 100 lbs of dirt...

Kidding (or am I)

Joe_Limon > CAR_IS_MI 01/31/2014 at 11:22

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That and it feels more grounded to the ground when I put my racing helmet on.

CAR_IS_MI > Nibbles 01/31/2014 at 11:24

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I get it!

CAR_IS_MI > KB Garage 01/31/2014 at 11:25

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FYI your image is still broken.

KB Garage > CAR_IS_MI 01/31/2014 at 11:35

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That's a kinja trap. It waits idly for me to attempt to edit or repost. Then it snaps my neck like a small rodent and laughs as it makes off with the cheese (in this particular case, my images).

CAR_IS_MI > carsandmusic 01/31/2014 at 11:41

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Not necessarily true.

Next weeks article will get a bit more into correction factors and how they effect your output numbers, but for all general purposes, every manufacturer must test their machines in the same general format (at the crank, full accessories, full exhaust and emissions systems in place). What is not controlled is air flow (for cooling purposes and losses due to drive line parts.

When the engine is in the car, it is encased (generally) on 5 of 6 sides , with small openings in a panel or two to allow air to flow through for cooling purposes. A manufacturer could either give the engine more or less air than it will generally receive while inside the car, thus skewing the numbers higher, or lower.

Losses due to drive line are very dependent on the drive line itself. gearing, weight of the rotating parts, etc. etc.

No one manufacturer has a better or worse chance of being right on as these conditions will vary from unit to unit, area to area, and for these reasons, all manufacturer ratings should be taken as generalities.

CAR_IS_MI > Joe_Limon 01/31/2014 at 11:43

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Because your racing helmet is pushing on the roof of the car, therefor exerting downward force on the vehicle...

Joe_Limon > CAR_IS_MI 01/31/2014 at 11:47

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Ooooh, I knew there was a scientific reason for it.

As a side note, the torque curve above is sexy flat.

CAR_IS_MI > Joe_Limon 01/31/2014 at 11:53

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Troll science is the best science.

And thank you, that torque curve belongs to my Jeep.

YSI-what can brown do for you > CAR_IS_MI 01/31/2014 at 12:58

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With my headers I make at least 3000hp. At LEAST!

Velocity- Peuguette Connoisseur > CAR_IS_MI 01/31/2014 at 12:58

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I'm not entirely sure but my intake + ECU retune thing claims to make 20hp with everything else stock, and I've actually seen a lot of proof to back it up.

Casper > CAR_IS_MI 01/31/2014 at 12:58

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This is one of the biggest pet peeves I have talking with other car people. Theoretical HP. For the love of god, if you haven't actually tested the car and tuned it, don't randomly cite HP figures you would like to believe it has. It's like imagining your 1/4 mile times without actually having run it for a slip. There are so many factors that go into the actual result you will almost never get there without actual testing.

CAR_IS_MI > YSI-what can brown do for you 01/31/2014 at 12:59

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You must be running pixie dust in your fuel tank and have the upgraded muffler bearings then.

Casper > CAR_IS_MI 01/31/2014 at 12:59

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He ground up some unicorn bones and added to to the motor oil as well.

For Sweden > CAR_IS_MI 01/31/2014 at 12:59

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Brake horsepower

Power at the crank

EXPLAIN THAT!

Velocity- Peuguette Connoisseur > YSI-what can brown do for you 01/31/2014 at 13:00

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You need more stickers.

CAR_IS_MI > Velocity- Peuguette Connoisseur 01/31/2014 at 13:00

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There are some vehicles in which a basic tune CAN free up some decent numbers. but this is extremely vehicle / engine dependent.

YSI-what can brown do for you > Velocity- Peuguette Connoisseur 01/31/2014 at 13:00

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I have a few on my fridge. . . those should do the trick.

TheLOUDMUSIC- Put it in H! > CAR_IS_MI 01/31/2014 at 13:01

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Now we discuss said reference, right?

If so, I think it kinda fell off after season 3.

YSI-what can brown do for you > CAR_IS_MI 01/31/2014 at 13:01

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I actually welded the exhaust to the driveline. Worked wonders.

Velocity- Peuguette Connoisseur > YSI-what can brown do for you 01/31/2014 at 13:01

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Only if they are JDM

YSI-what can brown do for you > Velocity- Peuguette Connoisseur 01/31/2014 at 13:02

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Damn, they are all American.

Autophile412 - what's the world got in store? > CAR_IS_MI 01/31/2014 at 13:03

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I remember when I tuned my Evo back in the day and did the first pull on the dyno it was so sobering to see 240 as peak hp for a baseline.

To put it in dollar terms I was close to $10k in mods to get 435 whp/ 385 ft lbs torque.

The Evo, if I am not mistaken was rated at 300 hp stock.

deekster_caddy > CAR_IS_MI 01/31/2014 at 13:04

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Wrong. Most aftermarket manufacturers like to beat around the bush with their advertised numbers. They aren't exactly lying to you, but they aren't always telling you the whole truth either. They did get an extra 10 hp from the same engine as yours, except that engine also already had a full, high flow exhaust, high flow intake manifold, larger throttle body, ported heads, and larger valves. Adding that same intake to your all stock motor might net you 2hp. The same goes for the exhaust and the email tune you got. Your combined intake and exhaust might net you 10 – 15 hp, and if the tune is any good, you might an additional 20 hp from that.

This is the most important part of modding that people misunderstand. Think of an engine as a big air pump. Get more air in and out and you can use more fuel too (to make more power). Improving one part along the path does not necessarily improve the entire path. You need to improve the smallest part of the bottleneck before any other improvements will make a difference. What the smallest restriction is varies from car to car, engine design to engine design.

CAR_IS_MI > For Sweden 01/31/2014 at 13:04

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Brake refers to a device which was used to load an engine and hold it at a desired rotational speed

Not an actual brake, usually a fluid type or sometimes electromagnetic used to apply a specific rotational force to the engines output shaft a.k.a "the crank".

For Sweden > CAR_IS_MI 01/31/2014 at 13:06

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MADNESS

CAR_IS_MI > deekster_caddy 01/31/2014 at 13:07

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Yes, but also know that bigger is not always better. There is a semi-fine line where if you go over, you actually end up losing power.

CAR_IS_MI > YSI-what can brown do for you 01/31/2014 at 13:09

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Genius!

Pure genius.

Did you mig weld or tig weld. These things are important...

YSI-what can brown do for you > CAR_IS_MI 01/31/2014 at 13:10

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It was definitely mig welded. I got one from the russians and started the engine up, made the best welds I have ever seen.

CAR_IS_MI > YSI-what can brown do for you 01/31/2014 at 13:12

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I hope it was an updated mig, like a mig-25 or a mig-29...

YSI-what can brown do for you > CAR_IS_MI 01/31/2014 at 13:13

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I want to say it was a 35, cause it was pretty up to date and very very expensive.

deekster_caddy > CAR_IS_MI 01/31/2014 at 13:14

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Yes, of course. Otherwise we would all be making 1000000 horsepowers!!!!!!!

I realize of course that it all has primarily to do with the displacement of the engine, plus other factors like forced induction or NA, use of other power adders, etc.

puddler > CAR_IS_MI 01/31/2014 at 13:35

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i bet the 351 in my furd would dyno in the 60-70 hp range.

Hindered23 > Velocity- Peuguette Connoisseur 01/31/2014 at 13:48

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i believe it. your car has an awesome engine.

Aya, Almost Has A Cosmo With Toyota Engine Owned by a BMW. > CAR_IS_MI 01/31/2014 at 14:12

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Well, don't forget the car also lose power overtime..

Or did it?

carsandmusic > CAR_IS_MI 01/31/2014 at 15:10

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You have more knowledge about this field than I have, so you are obviously right on your comments regarding all the different factors that come into play when measuring engine power outputs. What I wanted to point out is that losses on the drive line differ from car to car, model to model and manufacturer to manufacturer thus making cars feel faster/slower than their hp figures suggest, especially compared to other (competing) cars.

Wacko > CAR_IS_MI 01/31/2014 at 16:36

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you forgot all those go fast stickers that add HP

like this Nissan that should have about 10000 hp now!

crowmolly > davesaddiction @ opposite-lock.com 01/31/2014 at 17:22

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You mean an oil change doesn't give you 10hp?

TwoFortified > CAR_IS_MI 01/31/2014 at 18:56

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Several points.

A) I really like this series. Keep it up!

B) Backlinking to previous articles should be the first thing you do

C) Number your articles (this should be #2)

D) The Gawkersphere always blames the tool, as opposed to the user (see: Guns)

E) Wiser men than me estimate the losses when translating BHP to WHP to be closer to 33%. I believe, by design, this estimate is liberal, because it's seemingly better to have a low estimate than a high one (unless you're just trying to swing dick).

F) Your stock EK's compression is shit, because I know you didn't change your piston rings in the last 15 years. Expect further power losses.

G) (and now to stop being a dick) I wholeheartedly agree with your assessment of HP claims on aftermarket parts. They guestimate the increase as a solid number, when, in reality, you will/should see percentage gains. Maybe those new injectors will bump your power by 10%. On a 180HP car, that's 18HP. On a 500HP car, that's 50HP. This is an oversimplification, but it's closer to reality than saying that a CAI will give you 20 HP all the time on any engine.

Anyway, those are my thoughts. Again, I really enjoy reading these, so please do keep going :)

TwoFortified > YSI-what can brown do for you 01/31/2014 at 19:00

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Yeah, I saw that getting a 3 inch exhaust would give me 50HP, so I had some random guy custom make me a 9 inch exhaust so that I could make 150HP!

I think he just welded together a bunch of Folgers cans, but I can FEEL the difference!

YSI-what can brown do for you > TwoFortified 01/31/2014 at 19:03

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What about your muffler? Did you use a giant coffee canister?

TwoFortified > YSI-what can brown do for you 01/31/2014 at 19:06

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Based on heuristical evidence, the muffler must be bigger than the exhaust.

So naturally, It's a 14 inch muffler. I can fit a basketball in there.

SR20

YSI-what can brown do for you > TwoFortified 01/31/2014 at 19:09

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I tried to use a basketball hoop to draw a design I just ended up going with a soccer goal post as a standard.

TwoFortified > YSI-what can brown do for you 01/31/2014 at 19:16

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Lol. In all seriousness, I actually am considering hooking up a new "catback" (cat. lol), and will likely end up building my own out of roof gutter material because

- It's rectangular, which allows for more ground clearance

- They manufacture bends for it

- It seems like suitable material for an exhaust

- I'm betting I can get gutters with the same volumetric area as a 3 inch.

This idea isn't exactly high on my priority list though.

samssun > Yowen - not necessarily not spaghetti and meatballs 01/31/2014 at 21:25

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Two 100 watt speakers do make for 200 watts (or one speaker getting 200), but your volume/SPL will only increase about 3db for each doubling of power. You need more and more power to make diminishing volume gains, more analogous to needing exponential power to run a faster quarter mile.

If your speaker's sensitivity is 90dB @ 1W, then either doubling the wattage or adding another speaker at the same wattage will get you 93dB. So going from 1 to 128 watts, or over 100x the power, only gets you 21 dB more volume (3db x 7 power doublings). Since it's a log scale, 10dB also equates to 10x the power, so 20dB would be 10^2 or 100x the power. 30dB would be 10^3 or 1000x the power.

XJDano > CAR_IS_MI 01/31/2014 at 23:37

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I do have a question. I have often thought about bringing the metro to a dyno day to see what 254K mile motor puts out, and possibly rebuild a motor and see how much had been sucked out over 16 years & that many miles.

By trying to stay as close to a stock rebuild what #'s would be expected? Remember the window sticker claims 55hp, so there isn't much to lose to begin with.

Also the car is for work and mpg, with little concerns for performance gains that increase HP for getting off the line.

Demon-Xanth knows how to operate a street. > CAR_IS_MI 02/06/2014 at 17:16

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K&N said the FIPK gains me 10HP, so I installed a dozen.

EvilFD > CAR_IS_MI 02/06/2014 at 18:05

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Here's a great video from AMS Performance in Chicago (extremely reputable EVO, GTR, Merc, and Porsche tuner)

I was actually trying to explain some of this to another "car guy" just the other day. I'm always amazed by the misconceptions that alot of gearheads have about what kind of power their vehicle has, or what their modifications are doing.

I was trying to explain how my built EVO can actually fluctuate almost 200whp depending on correction factors (I live in CO, at altitudes of 5k up to 10k) and the type of dyno used. You've explained things pretty well so far. Looking forward to your addition about correction factors and such so I can send it to the aforementioned car buddy. Nice post, should be mandatory reading for car guys and people modifying their cars!

EvilFD > CAR_IS_MI 02/06/2014 at 18:16

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Absolutely. There is a ton to be gained by a simple tune on a few platforms out there. The one that jumps to mind is a CLS63 AMG. A year or two ago, AMS Performance pulled something like 70whp and 110 ft/lbs, plus a 2-3MPG gain out of a bone stock MB CLS63 AMG.

Because? Because boost! A ton of these newer turbo-charged cars can very safetly take a 5psi bump in a basic tune, with no new parts, and become a better car in all categories.

EvilFD > Autophile412 - what's the world got in store? 02/06/2014 at 18:32

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Factory turbo (or small stock-frame turbo) I assume? Is it an VIII or IX? I've had an VIII RS for about 6 years from now. Love it. Although its a big money pit and doesn't even try to lie about being stock anymore!

The USDM VIII was rated at 276hp (Japanese gentlemans agreement numbers).

The USDM IX was rated at 287hp.

KnifeKnut > CAR_IS_MI 02/06/2014 at 18:43

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You forgot one thing. Do a benchmark dyno run before making any mods so that you can actually see what your improvements are. If possible, dyno before and after each mod. Keep reccords. /not a tuner but a student of science

Danger > CAR_IS_MI 02/06/2014 at 19:20

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My Carb'd 85 and 86 Toyota 4x4's were rated at 96hp IIRC. That means in 4wd I was probably putting close to 15 horse...er squirrelpower to each wheel haha.

Danger > Danger 02/06/2014 at 19:21

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V8Demon - Prefers Autos for drag racing. Fite me! > CAR_IS_MI 02/06/2014 at 19:41

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POWAH!

V8Demon - Prefers Autos for drag racing. Fite me! > Nibbles 02/06/2014 at 19:45

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We threw my 2012 Focus SE on my buddy's Dyno for shits & giggles.

They're rated at 160 HP. Made 143 through the 6 speed auto.....

A 2 liter engine that makes more to the tires than a late '70's 5 liter does at the crank.... Progress.

V8Demon - Prefers Autos for drag racing. Fite me! > Casper 02/06/2014 at 19:53

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Someone with half a clue SHOULD be able to give a pretty close guesstimate though. Many people just think they can blow smoke up other people's asses though.

Late 80's Ford 5.0? Heads from an Explorer? GT 40 intake? E-cam?

Yeah, SURE you make 450 hp.....

Nibbles > V8Demon - Prefers Autos for drag racing. Fite me! 02/06/2014 at 20:58

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Unfortunately I have the archaic 4 speed auto and the "California emissions" Duratec 20e. I live at 6000 feet. I doubt my dyno numbers would be triple digits and I really don't care to find out. That would be hella depressing.

Autophile412 - what's the world got in store? > EvilFD 02/06/2014 at 21:45

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It was an VIII with stock turbo.

d16y8 > CAR_IS_MI 02/06/2014 at 22:18

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this is an EG chassis btw (not an EK) ;-p

Casper > V8Demon - Prefers Autos for drag racing. Fite me! 02/07/2014 at 10:08

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Yeah, so long as they were completely honest with themselves, had a good grasp of where the efficiency losses with the specific engine/head/cam setup was, understood the current tune of the fuel/air/exhaust systems, and the like... you can get close. The problem is most people don't have even half the information they need unless they have already been trying to coax power out of an engine and actually tested it in the past (or they do it for a living and see the same configurations day after day).

Hanzr > Joe_Limon 02/07/2014 at 22:34

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Do you put on an HKS sticker on the car every time you wash it? Probably that's why.

Hanzr > YSI-what can brown do for you 02/07/2014 at 22:35

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Oh pfff junior. My Euro taillights alone contribute 4000+hp. Loser

colorfulyawn > CAR_IS_MI 02/12/2014 at 23:54

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There's more to it than that, even.

For example, aftermarket parts are often advertised as adding "10 hp." OK, let's assume that's true. Where in the powerband does that extra 10 hp happen? Your 300-hp engine makes 300 hp at peak, not throughout the entire RPM range (unless it's an electric motor). So yeah, that CAI you just put on may indeed make 10 extra horsepower, but if those 10 ponies are all in a spike at, say, 4,300 RPM, it's entirely possible that you can both add 10 hp and still ultimately have a 300-hp engine.

This only gets more complicated the more parts you add. Your header that adds 12 hp at 6,000 RPM, your cat-back that adds 3 hp at 5,100 rpm, your adjustable FPR that adds 2 hp at 7,000 RPM, the underdrive pulley that adds 17 hp at 3,700 RPM. It's possible to fatten the power curve without adding any peak power at all. In fact, in some cases, you might even lose peak power.

Hell, you can even mod your car, end up with a fatter powerband, less peak power, and still be faster, hence the inevitable butt-dyno and anecdotal data that leads owners to believe they just turned a 300-hp engine into a 350-hp engine.

BJ > CAR_IS_MI 03/25/2014 at 22:27

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Great article.

Please fix the tag! You used the "power explained" tag on your other post, but this one you used "power explaine r ". This'll help others find your articles more easily.

Doug DeMuro > CAR_IS_MI 03/25/2014 at 23:07

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An actual, reasonable, intelligent explanation of dynos and horsepower, ladies and gentlemen!

Team6.1 > CAR_IS_MI 03/25/2014 at 23:57

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Preach! Nothing I hate more than the cold air + tune is going to add "xyz" ridiculous horsepower number. Plus that much more respect to the the guys who have impressive "at the wheels" numbers, and not a magical "i think this is what it SHOULD make" number

fixthefernback > CAR_IS_MI 03/26/2014 at 10:32

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I had an experience where I put my Miata on the dyno expecting somewhere in the 180-200hp range based on virtualdyno and similar setups (it has a turbo, self-tuned megasquirt) and it put down 257hp. I had only street tuned it. The number was confirmed by a second pull, and then confirmed again after turning the boost down by 2psi and putting down around 220hp. What situations can cause the dyno to read too high? No wheel spin was observed, and the straps were tightened for the 2nd & 3rd runs.

This was after several cars had been on the dyno meeting or missing expectations, but the only expectation that was exceeded was my own.

/subtlebrag

CAR_IS_MI > fixthefernback 03/26/2014 at 11:06

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Depending on the manufacturer of dyno, A lot could effect theses numbers. output numbers can be effected by correction factor (SAE vs STD), incorrect air temp / humidity / barometric pressure (some dynos allow the operator to input this). If the dyno requires things like tire size input to calculate hp and that info is entered wrong, this could also throw the graph off. There are many variables that come into play, unfortunately, some manufacturers allow the end user to manipulate all these factors, therefore, you could hypothetically throw a 10hp lawnmower on the dyno and display 500 (or more) hp. On the flip side, there are manufacturers who do not allow you to input ANY of the information, that way these things can not be manipulated, and the number you get is the number you got.

Cebu > CAR_IS_MI 03/26/2014 at 11:30

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Now I actually understand this. Excellent article on something I've wondered about for a while. Also, thanks for finally making me Wikipedia the mathematical definition of a horsepower. MATH.

McLarry > CAR_IS_MI 03/26/2014 at 13:22

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But dude, I've got, like, 20 of these babies on my car, bro! Mad power, bro! Totally smokes Veyrons 'n stuff, bro!

Bigdaddy > KB Garage 03/26/2014 at 16:16

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Kinja trap.

Destructive Tester > CAR_IS_MI 03/26/2014 at 22:56

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Nope, he just visited Yogurt...