Question, rev limiters in cars.

norm

norm

norm

Soldato
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If you remove a rev limiter from a car, at what point does the engine fail, what part is most likely to fail first?

PS. How critical is cooling in the running of an engine, if you could maintain a constant temperature around the engine block. What gains in performance are you likely to see? What temperature is optimal?
 
Why would you remove the rev limiter? The peak power is a good bit before the limiter anyway, there's no benefit.

Temperature around the block? That's how aircooled engines work... you'll notice they don't put them in anything anymore.
 
norm said:
If you remove a rev limiter from a car, at what point does the engine fail, what part is most likely to fail first?

PS. How critical is cooling in the running of an engine, if you could maintain a constant temperature around the engine block. What gains in performance are you likely to see? What temperature is optimal?
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The cooling system is the way to mantain the temperature around the engine block. Thats why when it gets too hot thats when the cooling fan kicks in. Otherwise it just runs happily without it.
 
You tend to have valves making contact with pistons before you actually break anything. That's normally because the valve springs can't open and close the valves quick enough to cope with the unexpected high revs. Not to say that won't cause problems, you'll end up with bent valves and a very poorly engine :)
 
I think think temperature wise it varies from car to car, most cars are designed at a cost v performance v reliability staright out the box, I know on mine the stand limit is 6800 and the delimter takes it to 7200 but you need a remap to benefit.

I'm no engine expert but surely running the engine over the specified safe rpm would put excessive strain on the crank and rod bearings.
 
I'd agree that the valves would be the first victim in the event of a limiter removal. Which in turn could lead to damaged pistons, rods, block/bores and cylinder head.

All that would happen way before temp becomes an issue.
 
Cars will generally make more power at a slightly lower temprature than specced by OE although they will be less efficient. Needs to be mapped in though.


As for binning the rev limiter the first thing would be valve bounce (as mentioned above) where the valves cannot operate quickly enough, next in line for failure would be a rod or rod bolts
 
MrMatteh said:
conrods bolts would 'go' first i'd imagine
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My dad, in his younger years wanted his Old Internation 784 tractor to rev higher so it would travel faster inbetween contracting jobs (on the road to Jobs..)

So he opened the Diesel Pump up slightly to allow it to rev higher, the result? 15 years later.

When the tractor recently had the engine rebuilt, there were marks on the inside of the engine where the con rods had been tapping the engine casing :eek:
 
PardonTheWait said:
Why would you remove the rev limiter? The peak power is a good bit before the limiter anyway, there's no benefit.
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If a car makes peak power before the limiter, there is nothing to say that revving higher than peak power would not result in faster acceleration. In fact, it often does.
 
silversurfer said:
Spoon hondas raise the revs to something silly like 12k but then f1 engines do 20k I think

The differences required would be balance in the components. See if you can find something on youtube about it, they might discuss it better
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My guess is that yes, the big enemy is out-of-balance forces. You'd either break a con rod or wreck the big-end bearings.


M
 
Most car engines are built way down to a budget, huge lumps of metal with a "down to a cost" manufacturing process.

It really depends on the car but in most cases on a standard 6.5K RPM rev limit you find on your run of the mill stuff your making peak power at about 5K RPM and the most efficient change point is at around 5.5K to drop you back into peak power for the next gear. Going any higher without engine modification is only useful when your trying to hold onto a single gear on a section of track road where changing up will mean you need to change back down again immediately. Racing at Brands Hatch is often like this with some bikes banging it off the rev limiter down from Druids to Graham Hill as a gear change costs more time than you gain in increased speed.

Once you've had head work to flow more gas, better fuel injection system, full exhaust, increased rate valve springs and light weight valves then you might be able to raise the rev limit and with a re-map get more power. This is on most cars/bikes, there are exceptions in either case.

To get more power you are always looking to flow more air/fuel. This can be done by reducing flow restrictions, increasing compression, increasing capacity or increasing revs.
 
In the S2000 you make power all the way up to the limiter (9250 RPM)

If you do over rev, the most usual damage is to the retainers. These crack, and 5-10-15-20-25-30k miles later, the retainer finally gives up, drops a valve and the engines gone. This is the single most common reason for s2000 engines dying.

Retainers were redesigned for 'AP2' F22C engines, and are significantly less prone to dying through over rev.
 
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