[Hawk]

Not worrying about fuel economy is it harmful to your engine to drive it in the top 3rd or top half of its RPM range?

A buddy of mine has a 911 and the car makes real power from 4,000 rpm upwards (I think redline is 7,500rpm) Is it harmful to drive it at 4,500 or 5,000 rpm for extended periods of time?

The normal thing would be to keep it around 2,500 to 3,000 rpm if not driving it hard.

Just wonder if it's bad to have the engine internals spinning faster?

 

[Rejekt]

I don't see how it would be.

Anywhere below the red is considered to be the engines normal operating range, so cruising at 4,500-5,000 rpm while annoying after awhile, shouldn't be an issue....Now sitting at redline all day is a different story.

 

[VDUBfanatic]

As long as the engine is up to operating temperature, and south of the redline, no big deal.

 

[MikkiJayne]

It all depends on the motor I think.

The 16V in my Corrado just loves to spin round to the 7.5K limiter and sings while it's doing it (a bit like the 911 by the sound of it). On the other hand the smallblock 1.6 in my mk2 gets really grumpy at about 4-5K and there's no point pushing it any further cos it doesn't do much.

If the motor is happy at higher rpms then it won't hurt it to use them

 

[Hawk]

How can you tell if your motor is 'happy'?

 

[B3sat16v]

How can you tell if your motor is 'happy'?

If it smiles back at you!

 

[warrenW]

How can you tell if your motor is 'happy'?

it smiles.
duh.

*edit- beat to the punch...ugh!

 

[bootymac]

Is it harmful to drive it at 4,500 or 5,000 rpm for extended periods of time?

That's driving a car the way it's supposed to be driven :thumbup:

 

[Belfi]

Nothing wrong with an Italian tuneup.

 

[ChachiV]

If it smiles back at you!

So the new Mazda 3 is at a constant state of high revs?

 

[LEWXCORE]

So the new Mazda 3 is at a constant state of high revs?

 

[Internal Combustion]

I don't see how it would be.

Anywhere below the red is considered to be the engines normal operating range, so cruising at 4,500-5,000 rpm while annoying after awhile, shouldn't be an issue....Now sitting at redline all day is a different story.

Chances are, you're in a lower gear, so there is more actual torque from the engine to tranny and applied torque to the driveline. You bet your butt it's harder on the car...but quantifying the harm would be difficult.

 

[Burnitwithfire]

Question is, why keep it there? A downshift takes less than a second and you get to keep RPMs lower.

 

[Hawk]

Question is, why keep it there? A downshift takes less than a second and you get to keep RPMs lower.

But the lower RPMs isn't where the power is on most normally aspirated cars. On my buddy's 911 we were doing a twisty section up north and we kept it 4,000rpm or above for about 20 minutes. If we had downshifted to lower revs it would have been a boring ride.

 

[nickthaskater]

Someone needs to make an insert like that out of painted mesh or something (so as to allow airflow while still looking hilariously rad).

 

[LEWXCORE]

But the lower RPMs isn't where the power is on most normally aspirated cars. On my buddy's 911 we were doing a twisty section up north and we kept it 4,000rpm or above for about 20 minutes. If we had downshifted to lower revs it would have been a boring ride.

not to nit-pick, but last I checked.. downshifting put you in a lower gear, raising revs and upshifting puts you in a higher gear, dropping revs.

 

[zzman916]

My car loves being over 4000, but only when its properly warmed up, otherwise i keep it under 3500.
That being said my car cruises on the highway at 4000 while going 80...2.slow gotta love it

 

[compy222]

any sports car should be capable of running in the 3-5k range without any serious issues.

of course, clean oil, regular tune-ups, and clean air filters make a world of difference. not to mention using good quality gas of the right octane.

i've taken my miata on a few longer distance spirited drives in northern mi. running that car on the highway at 3800-4000 rpms, not to mention on the side roads pushing more revs than that. i don't think it has any real detrimental effect. might be a bit more strain on the driveline - again, fluid changes, and regular upkeep can prevent issues.

 

[Traldan]

Shouldn't be any issue if you're doing some 'spirited' driving. No reason to keep the revs there in normal boring operation, though.

 

[1320-20V]

YES.

Since F=Ma and the acceleration rate rises with rpm you components stress level rises rapidly with RPM. Metal components have a fatigue life, and the number of cycles to failure logarithmically decays with the level of the alternating stress. So high RPM is high stress and quick failure.

There is an endurance limit, which is the maximum amount a stress that a metal can take without ever failing. In this definition 10^7 cycles is infinity and the lower asymptote of the logarithm.

In a connecting rod design, the components would be WAY too heavy for a modern gasoline engine to be designed to remain under the endurance limit. They are more than likely designed for a long life, perhaps 2-300K miles of average use. They will certainly not last that long exposed to continuous red-line.

To further reinforce this point, a slow revving diesel has low piston acceleration, and lower exhaust stresses. These rods may be large and slow enough to be close to the endurance limit, and my last "forever".

In contrast a Top fuel dragster uses aluminum rods that DO NOT have and endurance limit. That means that no matter how light the stresses the rods will ALWAYS eventually have a fatigue failure. And since the stresses are incredibly high, the rods are thrown away after one or two runs, a total of only a few hundred cycles.

For example using 10^7 and a 6800 RPM red-line, your engine will last no more than 24.5 hours of continuous red-line.