Redline - Ask Oppo

"HammerheadFistpunch" (hammerheadfistpunch) 01/14/2015 at 17:31 • Filed to: ask oppo

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No, not that terrible movie, or anything you consume...i mean the cars red line on the tach. I got thinking based on a by a post !!!error: Indecipherable SUB-paragraph formatting!!! and now I have a question about it I never considered until now and I thought I would pick your brains oppo for the answer, or something.

Obviously the redline its there for a reason, there is lots of metal moving very fast in terms of piston speed, valvetrain operation as well as lubrication issues, and other such mechanical limitations and so spending a lot of time there or blasting past it with a bad shift is a bad move....but...and here's the question: Whats the harm in hitting the redline from time to time?

I mean this specifically on vehicles with fuel cuts and hard limits, not on older engines without this safety valve. is there a reason that bouncing of the limiter (fuel cut) is any kind of bad at all?

The redline is the engineering conservative soft line saying that sustained engine operation at these speeds is at the safe limit, anything beyond this is not garenteed and beyond that is the hard, but still conservative, fuel cut limit that wont allow the engine to overrev using the fuel. With these in mind, wouldn't it be safe to assume that the fuel cut represents a max safe working limit and that hitting it isn't detrimental to the safety of the engine? Again, I'm not talking about putting into 2nd and hopping on the freeway for a 4 hour drive, I'm talking 1st [fuel cut] shift, 2nd [fuel cut] shift, etc.

I can't see the harm in this...do you all know something I don't on the subject.

for disclosure I rarely hit the fuel cut on the cruiser because its PAINFUL to get there...but I've done it. I used to do it occasionally with the forester.

Jordan and the Slowrunner, Boomer Intensifies > HammerheadFistpunch 01/14/2015 at 17:33

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On mine, you aren't supposed to due to headgaskets, but I hit it all the time... to keep up with traffic.

For Sweden > HammerheadFistpunch 01/14/2015 at 17:34

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Assuming the car is in good working order and at the proper temperature, hitting redline occasionally should be fine. The engine won't blow up at redline+1; there is a factor of safety.

HammerheadFistpunch > Jordan and the Slowrunner, Boomer Intensifies 01/14/2015 at 17:35

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You aren't supposed to do anything but wait for the day they fail with those mid 90's Toyota HG's.

HammerheadFistpunch > For Sweden 01/14/2015 at 17:36

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redline + 1 is usually the fuel cut, or it is on many cars, is there safety past fuel cut, or is that the line in the sand at which point all bets are off?

Jordan and the Slowrunner, Boomer Intensifies > HammerheadFistpunch 01/14/2015 at 17:36

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Mine are only 15k miles old, I've got a few miles left... hopefully.

TheHondaBro > HammerheadFistpunch 01/14/2015 at 17:36

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I hit it occasionally because VTEC bro.

ADabOfOppo; Gone Plaid (Instructables Can Be Confusable) > HammerheadFistpunch 01/14/2015 at 17:37

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My car (2002 SVT Focus) loves the redline. I actually get better gas mileage when I can drive the shit out of it.

Right now I am averaging like 19-20. During the warmer months I get ~24, and I do my best to hit redline when I get on the on-ramp to work.

For Sweden > HammerheadFistpunch 01/14/2015 at 17:38

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I'd have to imagine there's safety after the fuel cut. If the fuel cut fails, you don't want a bunch of blown engines coming in for warranty work.

Zipppy, Mazdurp builder, Probeski owner and former ricerboy > HammerheadFistpunch 01/14/2015 at 17:39

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I've hit the redline occasionally on the Jetta when going fast, and i had no issues with it tbh. It didn't bounce.

macanamera > HammerheadFistpunch 01/14/2015 at 17:40

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On any modern-ish engine, I can't imagine there is any issue at all.

WhiskeyGolf > HammerheadFistpunch 01/14/2015 at 17:42

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As long as we're asking questions, I have one:

When you say redline, are you talking the absolute tach limit (7k in the photo) or the literal "red line", which in the case of your photo is 5500 RPM?

HammerheadFistpunch > WhiskeyGolf 01/14/2015 at 17:43

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the redline is the redline, the tach limit is some marketers fantasy world.

HammerheadFistpunch > For Sweden 01/14/2015 at 17:44

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or a miss shift.

HammerheadFistpunch > ADabOfOppo; Gone Plaid (Instructables Can Be Confusable) 01/14/2015 at 17:44

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old school cam profiling.

Justin Hughes > HammerheadFistpunch 01/14/2015 at 17:45

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You don't want to hang out there, but a few bangs off the limiter once in a while won't kill it. I've driven autocross courses where I hit the top of 2nd, could've grabbed 3rd, but would've had to instantly downshift back to 2nd again, so I just left it on the limiter instead. This was on a Miata, which can take it just fine.

Manuél Ferrari > HammerheadFistpunch 01/14/2015 at 17:47

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My guess: depends on the quality of the engine. An engine designed well for hard driving can probably take daily WOT shifts at redline with no issue. A poorly designed engine will probably implode if you hit redline daily.

HammerheadFistpunch > Jordan and the Slowrunner, Boomer Intensifies 01/14/2015 at 17:47

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your hg's are only 15k old and you're waiting for them to blow? man, sounds like you should have gone cometic.

HammerheadFistpunch > Zipppy, Mazdurp builder, Probeski owner and former ricerboy 01/14/2015 at 17:47

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i accidentally bounced off the limit in the TDI, but given that the engine is 100% electronically controlled, i suspect it wont let me hurt it at all.

ADabOfOppo; Gone Plaid (Instructables Can Be Confusable) > HammerheadFistpunch 01/14/2015 at 17:51

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Not sure what you mean?

I have a Variable Cam Solenoid, so it does something cam-related. But, yes compared to modern variable-cam engines the SVT Zetec is a dinosaur.

jariten1781 > HammerheadFistpunch 01/14/2015 at 17:52

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You'd get more cycles on the moving parts for the same distance traveled than you would being more conservative if you were doing it all the time. Most likely still won't hurt you since most modern cars die for other reasons than wear on moving engine internals.

NaturallyAspirated > HammerheadFistpunch 01/14/2015 at 17:53

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I've hit redline on my Subaru once or twice - I always feel bad about it, but it doesn't seem to have caused any problems. The Subaru pulls really strong up to redline, then hits the fuel cut HARD, so it makes a lot of noise and the sudden lack of acceleration throws you forward.

My '90 Miata maybe didn't have a rev limiter, or perhaps my RPM gauge was off? I revved that sucker way past redline a few times. Ran strong up until it got rear-ended.

SidewaysOnDirt still misses Bowie > HammerheadFistpunch 01/14/2015 at 17:54

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I don't know. Depends on the car, I guess. My MR2 doesn't seem to mind.

HammerheadFistpunch > ADabOfOppo; Gone Plaid (Instructables Can Be Confusable) 01/14/2015 at 17:58

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I mean it was optimized for high end breathing, old school like.

MultiplaOrgasms > HammerheadFistpunch 01/14/2015 at 18:00

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The Redline is just there to keep the internals from exceeding their limits isn't it? As such the redline and fuel cut off should usually be a bit lower than the engines absolute rev limit. I remember the engines from the good ol' Honda S800 having the redline at 9k or something but being capable of turning at 11k (or more?) without issues. Redlining can be good for some engines. Like the Rover V8 being prone to camshaft issues if you don't give it the beans occaisonally. Stuff like that. You just about answered you own question yourself m8.

camaroboy68ss > HammerheadFistpunch 01/14/2015 at 18:00

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its not great on a motor and occasional use over time will hurt the motor. That's the reason for the rev limiters and such is a safety valve. It's not like in my 68 where if keep my foot in it. I'll suddenly be floating the valves and headed to bending some pushrods or busting a valve:

Jordan and the Slowrunner, Boomer Intensifies > HammerheadFistpunch 01/14/2015 at 18:00

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They've been 15k really, really hard miles. Like 19 y.o. living in an area with a lot of puddles to play with, hard miles. But really, I'm not waiting for them to blow. Everything on it's tight, oil is clean and unburnt, coolant is the same color as it was when it was dropped in, and no fluids are leaking. I just miss my odometer, so I can prove that they only have 15k on them whenever the engine is pulled for an upgrade. For some reason, they still command some money.

HammerheadFistpunch > MultiplaOrgasms 01/14/2015 at 18:03

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I kinda figured I had the answer I wanted to hear, but there is a lot of knowledge on here in oppo waiting to tell me something I didn't know.

ADabOfOppo; Gone Plaid (Instructables Can Be Confusable) > HammerheadFistpunch 01/14/2015 at 18:04

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Perhaps, thought that engine also has a variable-length intake runner system. Longer position for more low-mid torque and a short position for better top end breathing.

Runners are on a pivot, which is connected by a cable to a box in the driver-side fender. Said actuator is programmed to make the switch at around 5k.

Ford tried a bunch of stuff on that motor, even let Cosworth have a go at it.

HammerheadFistpunch > Jordan and the Slowrunner, Boomer Intensifies 01/14/2015 at 18:05

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its my understanding that the new Toyota Hg is a lifetime item no matter how hard you wail on them. The cylinder pressures in those engines is pretty low all around.

Jordan and the Slowrunner, Boomer Intensifies > HammerheadFistpunch 01/14/2015 at 18:07

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Ah, well that's a relief. I feel a whole lot less guilty for abusing it now.

MultiplaOrgasms > HammerheadFistpunch 01/14/2015 at 18:07

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I should point out that while quite educated in the thermodynamic processes of an ICE, my words should not be taken as a reference in a scientific research project, by which I mean that I could be wrong.

crowmolly > HammerheadFistpunch 01/14/2015 at 18:12

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I'd say running it up high into the RPM range every now and then is good for the engine every now and then.

The limiter itself? Probably not that harmful either.

Better question is why? Hero points?

As it was explained to me by a number of old timer stick shift drag racers, you want to maximize torque output both before and after the shift.

Check this out:

In this example I put in torque numbers at a given RPM combined with gear ratios. The calculator figures out the max in/out torque numbers and spits the desired RPM back out.

I am ignoring tire height for now.

If you spin first gear to 6k you get ~3334 lb-ft (305*2.66*4.11)

Your RPM recovery is then at 4015 RPM, ~3211 lb-ft (439*1.78*4.11)

If you decide to spin it to 6.5k (forgot to enter that data point) you would get ~3115 lb-ft (285*2.66*4.11)

Your RPM recovery is around 4349 RPM, ~3255 lb-ft (445*1.78*4.11)

6545 lb-ft applied in the first example

6370 lb-ft applied in the second example

Therefore losing 175 lb-ft.

So aside from making more noise and putting more stress on your rod bolts (unless you're a rotary) I just don't see the point.

imadeaburner > HammerheadFistpunch 01/14/2015 at 18:12

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If its a rev limited that changed engine speed its bad.....those pieces of metal you spoke of are changing between two speeds quickly, and it creates stress having something constantly changing between a high and low speed. Maybe the Connecting rod is weak and that piston won't slow down. Maybe the valve spring has had it.

But if you have a rev limiter that just holds level RPM is not bad, its less wear and tear, less potential for damage there.

crowmolly > For Sweden 01/14/2015 at 18:13

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Uh, not in some of the cars I've been in. Most cars run out of breath before they self destruct but it's possible to downshift your way into BOOM TIME.

HammerheadFistpunch > imadeaburner 01/14/2015 at 18:14

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good point, most fuel cuts i've experienced don't drop more than 500 rpm before hitting it again.

HammerheadFistpunch > crowmolly 01/14/2015 at 18:16

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Oh man, I did so many of those calculations before re-gearing. Why? no reason other than fun really. I will say on the FXT, that the launch was so violent and 1st gear so short that if you weren't paying attention you would hit the fuel cut easy.

crowmolly > HammerheadFistpunch 01/14/2015 at 18:19

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To be honest when I am 1-2 powershifting I'm more worried about exploding trans parts than I am about my torque numbers.

imadeaburner > imadeaburner 01/14/2015 at 18:19

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My car just holds at 7 thousand RPM doesn't bounce or anything like other cars, only time it does bounce is when there is tire spin

imadeaburner > HammerheadFistpunch 01/14/2015 at 18:19

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My car just holds at 7 thousand RPM doesn't bounce or anything like other cars, only time it does bounce is when there is tire spin

HammerheadFistpunch > crowmolly 01/14/2015 at 18:20

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ha! yeah, given my max output is 275 ft-lbs, im not going to blowing up anything anytime soon. Hard launched in the FXT gave me some concern though. I didn't do it that often though, really.

RallyWrench > HammerheadFistpunch 01/14/2015 at 18:26

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The only detriment in hitting fuel cut is that you'll lose power momentarily when it happens, which obviously slows acceleration compared to if you just shift near redline. Of course, there are plenty of engines whose power curve is such that they're not worth spinning that high anyway. Your Cruiser, my Outback, and most diesels are good examples.

HammerheadFistpunch > RallyWrench 01/14/2015 at 18:28

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even the Subaru was pretty much out of puff at 6 grand, the cruiser has given all it has to give at 4500 (redline at 5000, fuel cut at 5200) and the TDI? don't even bother with anything above 3 grand, short shift that mofo

Nibbles > HammerheadFistpunch 01/14/2015 at 20:07

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I've rapped up on the rev limiter before, in a few of my cars. Never in the old Saab - 350,000 miles I was afraid of catastrophic failure. I did hit the limiter in the Dakota though, then proceeded to slam it from 3rd to 4th and broke the tires loose. That was fun.

BrianNutter > HammerheadFistpunch 01/14/2015 at 21:25

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Yellow line is your responsibility to pull the shifter because you've passed peak power for best average power over the next gear spread for best acceleration. In a semi-perfect world...Redline is the manufacturers responsibility as it notates valve float and higher than engineered-in reciprocating mass limits for reduced fatigue life for the bottom end (crank rod pistons).

HammerheadFistpunch > BrianNutter 01/14/2015 at 21:39

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this is a life a quartet mile at a time answer but i like it

BrianNutter > HammerheadFistpunch 01/14/2015 at 21:49

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I make cranks rods and pistons as a living.......all easier than what a valvespring manufacturer has to deal with ;).

Sn210 > HammerheadFistpunch 01/14/2015 at 21:52

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the vtec has not kicked in on my TL yet. I'm scared

HammerheadFistpunch > BrianNutter 01/14/2015 at 21:57

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i was pretty close to getting higher compression pistons recently when i had the head rebuilt, but the cost benefit for me was crazy. you must have liked that write up in car and driver recently about piston tech, i assume. obviously not for informational purposes because it was pretty light but for exposure to what you do.

BrianNutter > HammerheadFistpunch 01/15/2015 at 16:54

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Yep it's a good article and they spoke to some high level guys. Bet they saw some interesting stuff!