JrRifleCoach

See post #11
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I have a stock 04 Z06.
As I'm getting accustomed to the sights and sounds a rev limiter event has prompted this question.
Accelerating hard from 2-3, I hit the rev limiter at the top of 2nd gear.
Quickly shifted to 3rd and for a second or two there was no power.
Almost like it needed to recover from the rev limit event before power would restore.
Yes, I need to be more aware of my shift points and that is certain.
However would bumping up the rev limiter up by 250-500 RPM have any benefit?
Or is it just better to leave well enough alone.

Asking since my experience level with the LSx motors is very limited.

Thanks,

Cosmik de Bris

The rev limiter is there to stop you over revving the engine. Unless you have modded the engine you will receive no benefit from moving the limit up. What about using a shift light and setting it so that you shift at the correct time?

JrRifleCoach

I agree. The question is asked understanding that some of the factory settings can be modified enhancing performance.

Gordy M

Yes, tuning software can modify when the rev limiter is actuated. However, it is more important to understand when the engine is loosing power and peak torque band for the next gear you are shifting to. It has been some time since I played with a Z but as I recall it was somewhere around 6350-6400. Years ago a member named Ranger used to extensively drag his Z and he reported where the sweet spot on his car was for shifting from gear to gear. For autocrossing my C5, first to second shift was right at 5750 rpm. HTH

JrRifleCoach

Seems that this guy needs to stay a tad bit more focused on the HUD from now on.

Just curious, does the rev limiter shut down the fuel or spark?

Thanks Gordy

Supercharged111

Fuel, spark cutout is much more harsh. Top speed limiter in 5th is done by the throttle body. I bumped my limiter for the road course. There are places I'd ping the limiter for a second or 2 but there wasn't enough room to grab a gear. It was fairly easy to occasionally boink the limiter when banging through the first couple gears too, it's still faster to over-rev than to hit that limiter and bring acceleration to a grinding halt.

COSPEED

The bad thing about the rev limiter on DBW cars is it is also a fuel cut, so you can see a very lean condition for a small amount of time with a stock tune.

We do offer remote tuning options that can change the rev limiter to a safe range AND gain more power out of even a stock C5. The best thing about a remote tune is, it is custom tailored to you in your area the way you drive.

Here is the link. Contact us if you have more questions.

tblu92

A stock C5 even a Z06 stops making more HP around 6000 RPM---So it is pointless to run the engine beyond the Max HP band 0f 6000---- because it is making less power up there---Ideally you want to shift where your cam signs off--Stock cam is 6000--If you had a bigger cam yes--shift where your cam signs off---maybe 6200 to 6400 and the car will keep building HP and momentum---But if your cam signs off at 6000 (stock) then you have to regain all the lost HP and TQ you lost by over revving at each shift---Old school rule of thumb is you want it to shift at MAX HP and only drop in RPM's to where the MAX TQ RPM's are-----( typically around 4200 on a stock cam-) otherwise you aren't taking the full advantage of your engine's "power band" Between max TQ and max HP

COSPEED

Just because the engine stops making power doesnt mean you should shift at that RPM. There are alot of things to look at, and I have seen stock Zs make power up to 6200 or so. You dont just shift where the cam "signs off". You are close though.

tblu92

Spitting hairs here--6000--6200---sure depending on mods the HP max level can change
a little----I'm just repeating what I learned at driving school years ago and from my own personal experience in drag racing ( over 1000 passes )-"ideally you want to shift at MAX HP and have the gearing/cam such that the RPM's drop no lower or higher than MAX TQ area "

JrRifleCoach

Pretty much nailed the shift points.
As a matter I'm shifting as the tach is going past the 6K mark.
But even though I'm not hitting the rev limiter at the 2-3 shift,
the engine is still bogging down when hitting 3rd.
It picks back up after a momentary bog but its just at that one spot.
If there were more road I'd be able to report the 3-4 shift.

36K on the car. (Stock) Motor runs just fine otherwise.
Suggestions on places to investigate?

tblu92

Well if your going to get real specific it would require some data logging to see exactly what the AFR and the timing is at that point----Data obtained in 1st and 2nd gear are really not accurate as the engine isn't under a full load--that's why dyno runs are always made in 3rd gear because that's were your engine and trans are at 1:1 gear ratio
See where the RPM's drop down to when you shift into 3rd---Examaple say it drops to 4400----Check your AFR there (with a wideband) and check to see what the "actual timing " is----Also check the actual timing is VS the commanded timing---see if you are getting any knock retard---If so determine if the KR is in fact real (hearing it ping) or false-- If real--you can't add anymore---If false either desensitize your Knock sensors--to get the commanded to equal the actual---If there is NO KR simply are more timing from 4400 to the end of the bog RPM

Supercharged111

Bingo. You don't shift at peak hp, you let the next gear tell you where the shift the previous one. Let's say you see a 2,500 RPM drop when you shift, you want to shift at an RPM that gives the engine the 2,500 RPM with the most hp. This might involve shifting at *gasp* 6,300-6,400. Takes a lot of trial and error to hone in on it (and consistency). I once had a motor that, in N/A form, was said to peak at 7,200 RPM so that's where I shifted. I gained 3 tenths in the 150 meter by shifting at 7,500 RPM and I could repeat those results time and time again.

COSPEED

In a 5/6 spd car and 6 spd auto, the dyno pulls are in 4th gear.

I recently tuned a near stock C5Z and it make power til about 6200 so his shifting with stock tire height and gear ratio is around 6400. With a camshaft all of that will change and we will have to remap it, but you can also short shift to try and hit a torque area and lose speed/forward momentum, when it really isnt that dependent on it on the big end of the track.

Vinny 2001

School of thought is (generally) shift point is 500 RPM past HP peak. In the case of the C5 the cutoff is set to that. The LS1 makes peak HP at 5750 and cut off is 6250. The LS6 makes peak HP at 6000 and cut off is 6500.

Chicago1

Dumb question but maybe you are spinning a bit and causing traction control/active handling to briefly engage thus the power loss? I know on my car even at 668hp the car says F/U if I don't have it in competitive mode and just kills power. I always think I blew something up but remembered I didn't change it just the ecu killing fuel/timing to regain stability/traction.

StatmanRN

Shift light, adjust to come on before rev limiter and allow for response time so you dont hit it because the power cutoff will kill the acceleraton. Mine is set for 5500.

Chicago1

update?

JrRifleCoach

Yes!
After practicing a few launches on the NT05's with TC turned off,
The engine stays with me through all gears.
There is so much tire grip, the 1-2 shift only requires a little throttle feathering to hold traction.