: *Whst is the Maximum Safe Rev Limit



austin
05-03-13, 07:19 PM
I have seen several different values being posted around the net for the max safe Rev Limit. Exactly how high can it be raised safely? I have seen a value of 6400rpm being used by several folks running stock "V's" with just a Tune and CAI and achieving very good results (2mph faster 1/4 mile speed). Is 6400rpm safe? Has anyone seen a "V" motor blow at 6400rpm? What did your tuner raise the limit to?

https://www.youtube.com/watch?v=x11oOliu-u8

ptrd
05-03-13, 07:54 PM
A reputable tuner would know, but it's safe to say the rev limiter is there for a reason. What's the purpose of wanting the higher revs if you aren't making more power at that point?

austin
05-03-13, 08:28 PM
A reputable tuner would know, but it's safe to say the rev limiter is there for a reason. What's the purpose of wanting the higher revs if you aren't making more power at that point?

True, but from what I have read and seen from dyno graphs the LSA does make power above the factory Rev Limiter. I guess the real question is drivetrain stability. Can a stock LSA drivetrain (springs, keepers & pushrods), handle 6400rpm shifts without grenading the engine.

I believe the factory Rev Limiter is set to 6200rpm, so I'm only talking about increasing it by 200rpm.

Random84
05-03-13, 09:53 PM
The stock engine makes peak power about 1-200 RPM below factory redline.

Can you raise the rev limiter and get by on OEM internals? You bet.

The question really is, can you run the engine at 6200-6500 for extended periods over the course of several years and - factoring in the natural fatigue life of ANY valve spring - how LONG can you do this before a valve hangs and you smack a piston?

This is a question that few people would want to wager money (or a warranty) on - but even having the springs replaced would come with limitations (ie, replacement schedules every 20K or 50K depending on manufacturer). Remember that the valve spring is also working against the mass of the valve (with that inertia increasing dramatically at higher RPM), as well as the effects of boost in the manifold and cylinder also changing the dynamics of resistance.

For someone who has a low mile street car, and gets one or two launches here and there, it's probably a non-issue over 200RPM (as the factory specs are likely conservative). But you have a heavy valve, boost and longevity to consider; so IMHO it's not something to take as cavalierely as others might. I would only talk to a cylinder head/engine builder familiar with the platform; many tuners are often making nothing more than educated guesses with little skin in the game.

ETA: For reference, the LS9 has titanium rods, hollow stem exhaust valves, titanium intake valves, forged pistons and a host of other differences (ignoring cam lobe profiles) to get another 300 RPM; the Z06 has similarly expensive parts for another 800 RPM (naturally aspirated) over the LSA. Things happen fast at 6500 RPM, and everything has finite fatigue life.

It's easy enough to change springs, but connecting rods, piston pins, etc are another consideration. Valvetrain harmonics and durability is big-money...

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ETA: I've asked this same question before, and the short answer is that there are very few people who know what a safe redline is; and they don't advertise the upgrade on their head/performance packages because you don't want to know how much it costs. :D I would love to hear about other enthusiasts running a 6500 RPM redline for years on the track and how it's held up; but so often the higher redline coincides with other mods, making success or failure hard to judge.

Ross L
05-03-13, 11:42 PM
Guy on another forum speaks of turning his LSA bottom end 7500+ if I'm not mistaken:hide:...still going strong. If you're worried about hurting your car, don't mod it. Although I personally don't think 200 rpms will hurt it, at all. IMO of course.

Mr. LCP
05-04-13, 10:21 AM
Making "more" power with higher revs is irrelevant. What you're doing is making much more power at those higher revs than you would be at much lower revs after you just had to shift (comparably) earlier.

For example, raising shift from 6200 to 6400 might put you at those RPMs from 100-103mph, where even if you aren't making 100% or more of your peak HP, you are making 98-99% of your peak HP. If instead you shifted at 6200/100mph into 4th gear, your RPMs probably drop to 4700 and rise only to 4850 by 103mph, where you are probably making 85-87% of your peak HP. If you figure HP in the 600+ range, for those 3mph, you picked up 75-80hp for those 3mph. Factor in similar increases at each shift. Those increases add up in a race, but the difference is not huge. Ideally, it would be nice to have enough RPM headroom in this engine to go WAY past 6200 (without power falling off dramatically) so that once you get out of 2nd gear, you're in the 95%+ of peak HP range for whole rest of way to maximum speed. That would be much better. Turbo motors are better at this shape of a powerband than supercharged motors. Having very closely spaced gears also helps a lot too.

Alternatively, it's easier, and the car will be faster, if you just make the supercharger spin faster and make even more power at 4700-4850rpm, than it is to extract more power from the 6200-6400rpm range. You can get big increases in power from 4700-4850 easily which will pay dividends all throughout the power band. A little more power from 6200-6400 pales by comparison, and is harder on the engine.

Purevil
05-13-13, 06:05 PM
I'm running mine up to 6700. It pulls hard all the way with just a CAI & 2.55" upper. It was explained to me that with the factory cams low lift, it's easier to get away with the revs on the stock springs. Just my 2cents

the blur
05-14-13, 12:14 AM
I still don't understand why anyone would risk an $8000 motor for a few HP.

Blakester
05-14-13, 12:41 AM
$8000.00. Good luck on that! In my younger day i used to run up an extra 500 rpm. Broke ring lands, bent valves, al kinds of interesting things. I now leave rpm's at factory setting, no more broken parts, still like to drag race though!

DiamondWhtV
05-17-13, 05:54 PM
Max safe rev limit is the point just before the engine craters.

Purevil
05-17-13, 06:05 PM
LMFAO, Diamond!

As for me, if I did t want to push my car, I wouldn't have bought a V. I put 45,000 miles on my C6Z06 with Heads/Cam, CAI, and exhaust reving to 8K pretty much daily. The rev limit is a super safe place to protect dumbasses from blowing their shit up and getting warranty work. Just my 2cents

GMX322V S/C
05-18-13, 12:03 AM
The stock engine makes peak power about 1-200 RPM below factory redline.

Can you raise the rev limiter and get by on OEM internals? You bet.

The question really is, can you run the engine at 6200-6500 for extended periods over the course of several years and - factoring in the natural fatigue life of ANY valve spring - how LONG can you do this before a valve hangs and you smack a piston?

This is a question that few people would want to wager money (or a warranty) on - but even having the springs replaced would come with limitations (ie, replacement schedules every 20K or 50K depending on manufacturer). Remember that the valve spring is also working against the mass of the valve (with that inertia increasing dramatically at higher RPM), as well as the effects of boost in the manifold and cylinder also changing the dynamics of resistance.
The dynamic forces go up as a function of the square of the RPM...

thebigjimsho
05-18-13, 02:32 AM
On the LSA, I'm more concerned with maximizing power to redline. If it was a NA motor, then I'd figure out how to raise the redline...

Random84
05-18-13, 11:07 AM
I put 45,000 miles on my C6Z06 with Heads/Cam, CAI, and exhaust reving to 8K pretty much daily.

I call BS on this without youtube video of you holding it at 8K for a few seconds. Please also mention what, exactly, was done to the heads? I mean, if you're running a full shaft-mounted rocker setup or something then maybe... But OEM LS7 components become unstable at around 76-7800 RPM with the relatively conservative factory cam lobe profiles- meaning valve float, bad spring harmonics and a very real risk of grenading the motor. Solid valves (ie LSA) and forced induction make that drop precipitously in the CTSV, so again I find it hard to believe you're running your otherwise stock LSA to 6800+ without issue for any duration of time.

There is so much wrong with your cavalier attitude (and passing it on as advice) regarding "safe" RPM ranges... it's just mind boggling. I'd really like to see video.

miamictsv
05-18-13, 12:54 PM
My tuner raised the limiter to 6400 rpm but my shift points are at 6200 rpm. He did it so i do not bounce of the rev limiter if i push the car. I am making max 626WHP at 6000 rpm. No issues for the last 2 years. I have not tracked the car yet.

GMX322V S/C
05-18-13, 01:42 PM
My tuner raised the limiter to 6400 rpm but my shift points are at 6200 rpm. He did it so i do not bounce of the rev limiter if i push the car...Same here. With my mods, power keeps building to and through the stock rev limit, so it was raised to 6400--with Patriot Gold .650s added as a precaution.

austin
05-20-13, 07:32 PM
I searched for a LSA Crate motor and in the details section it has 6600rpm as the max recommended rev limit. Everywhere I looked had 6600rpm as the max recommended limit. That is from GM's own LSA spec sheet on every website.

http://www.chevroletperformance.com/...1708&engCat=ls

http://www.jegs.com/p/Chevrolet-Perf...22868/10002/-1

GMX322V S/C
05-20-13, 08:14 PM
I believe it's a typo, since they show the LS9 with the same max RPM. Here is how it is spec'd as a component within a system, i.e., in a whole car whose drivetrain has to carry a 5 year/100,000 mile warranty: http://archives.media.gm.com/us/cadillac/en/product_services/r_cars/r_c_CTS/09CTSVindex.html#specs

This is consistent with every published test and review, as well as how we know the valvetrain is equipped vis-a-vis the LS9.

Purevil
05-22-13, 03:22 PM
I call BS on this without youtube video of you holding it at 8K for a few seconds. Please also mention what, exactly, was done to the heads? I mean, if you're running a full shaft-mounted rocker setup or something then maybe... But OEM LS7 components become unstable at around 76-7800 RPM with the relatively conservative factory cam lobe profiles- meaning valve float, bad spring harmonics and a very real risk of grenading the motor. Solid valves (ie LSA) and forced induction make that drop precipitously in the CTSV, so again I find it hard to believe you're running your otherwise stock LSA to 6800+ without issue for any duration of time.

There is so much wrong with your cavalier attitude (and passing it on as advice) regarding "safe" RPM ranges... it's just mind boggling. I'd really like to see video.


To each his own. I don't have anything to prove, just my 2 cents