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Curiosity about rev limit

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Old Feb 15, 2008 | 02:22 PM
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Default Curiosity about rev limit

I am a bit of a noob when it comes to tuning and performance enhancement, but I am learning quickly by reading this forum. One thing I have not heard about around here is increasing the rev limit or redline, to say, 7000 RPM like the Z06. Perhaps it requires upgrades to internal engine parts? Maybe it requires better intake and exhaust to handle increased flow? If it could be done without too much trouble, seems like you could get increased area under the curve, thus more usable power. I have heard about this being done on other vehicles, but haven't heard about it here. I did a search for rev limit, and only found people that were afraid they hurt something from hitting the rev limit...
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Old Feb 15, 2008 | 03:13 PM
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push rod V8's usually make their power at low rpm's. Higher rpm's usually don't add much unless the motor is built for it, cam, springs, etc...
IMO, there is really no need for having to rev that high when so much is available down low..
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Old Feb 15, 2008 | 05:48 PM
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Then why the higher limit on the LS7? Why do race V8s rev higher?
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Old Feb 15, 2008 | 05:56 PM
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Horsepower = torque x rpm/5252. So the higher in rpm you make torque, the more horsepower you make, even without increasing the actual torque numbers. That's how F1 cars make such high horsepower from such small cubic inch motors, by reving them to the moon, 19,000 to 20,000 rpm.
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Old Feb 15, 2008 | 06:35 PM
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Cam profile will dictate the RPM band and thus the rev limiter. On a stock engine raising the rev limiter is not a good move because the car starts losing power at the stock limit already, and the springs were not designed to rev higher anyway.
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Old Feb 15, 2008 | 09:56 PM
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The stock srpings are barely good enough for the stock cam. People who get S/C or TT should get better springs because the pressure hitting the back of the valve makes it harder to control even with the stock cam.
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Old Feb 16, 2008 | 10:55 AM
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That's not something you want to mess with. Prevents engine damage. Set where it's at for reason by GM engineering. Go with Vararam and exhaust/headers and tune for extra hp.
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Old Feb 28, 2008 | 07:44 AM
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Thanks for all the replies, guys. Sounds like with the right parts the rev limit could be raised, but there are easier and cheaper ways to get more usable power.
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Old Feb 28, 2008 | 10:01 AM
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I didn't go-with the most radical cam but even my fully built Lingenfelter engine only goes to 6800 RPMs before bumping the rev-limiter (not 7000). IMO anytime you push a stock, cast-piston engine past its design tolerances you're asking for a problem.
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Old Feb 28, 2008 | 01:02 PM
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Originally Posted by Wayne O
I didn't go-with the most radical cam but even my fully built Lingenfelter engine only goes to 6800 RPMs before bumping the rev-limiter (not 7000). IMO anytime you push a stock, cast-piston engine past its design tolerances you're asking for a problem.
Actually it would be very difficult to damage a piston by over reving your engine. The piston material has very little to do with your rev limit.
The factory rev limiter is where it is because the cam/head/manifold configuration does not make much useful power above that RPM (mainly the cam, and it runs out a bit before redline actually).
Increasing the rev limit will first create valve float, so you need stiffer springs. Then you will either experience rod stretch or oiling issues, depending on the motor. With some stronger rods and adequate oiling you could rev the motor well beyond 7K, but it would require a very agressive cam and head porting to make useful power up there.
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Old Feb 28, 2008 | 01:05 PM
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Originally Posted by autox c6
Then why the higher limit on the LS7?
The LS7 is tuned to do so.
Why do race V8s rev higher?
Because they're race engines. Last I looked, there is no pit crew on the interstate.
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Old Feb 28, 2008 | 01:37 PM
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Originally Posted by NORTY
The LS7 is tuned to do so. Because they're race engines. Last I looked, there is no pit crew on the interstate.
Nice answer... But the OP really asked the wrong question... I think a more relevant question to ask would be:
Why do V8 offerings from BMW, Audi and Mercedes Benz rev as high as 8250RPM in fully warrantied, bone stock trim while the Corvette will only to go 6500?

That would be a better question to start a discussion about stroke length, inertial loading, rod stretch, valve float, etc...
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Old Feb 28, 2008 | 02:39 PM
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Reciprocating mass also plays a large part in keeping RPM down. It costs alot of money to make internal moving parts lightweight and strong enough to hold together when spun super fast.
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