Hitting rev limiter with tune

FoundNemo · 08-13-2021, 09:03 AM

My buddy noticed that in auto mode on his ZL1 A10 (stock rev limiter, untuned TCM, stock fuel cuts, etc) with his headers and tune from the local shop the car will bump the limiter if you floor it on the hwy, which it did not do stock. In gear shifts fine without any issues.

Any thoughts on why that might be since the TCM wasnt tuned, intake is stock, TB is stock, pulley and blower are stock, TCM is untuned, shift points werent changed nor the stock rev limiter or fuel cuts of any sort?

Would raising the rev limiter 100rpms be a safe way to give it breathing room or is that not a good idea on an 18 ZL1 for longevity.

KingLT1 · 08-13-2021, 09:16 AM

When you make more power the goal is to increase the rate of acceleration. When the car accelerates faster then you need to give the TCM more time to make the shift. So Ideally you command a lower shift MPH to make the shift at the same RPM before the power increase. Since the TCM isn't tuned now you have to raise the limiter in order to get a clean shift at the same commanded shift points since most if not all GM transmission controllers primarily shift off of commanded MPH not RPM.

Vigilante375 · 08-13-2021, 09:33 AM

So you are saying that with the car in D and your friend floors the throttle, the engine bounces off the limiter?

But in gear (do you mean manual mode?) It shifts fine?

At what speed is he flooring it? It could be that he is flooring it right where the car would down shift to a speed where there is no room for the car to realize it's going to bounce off the limiter.

Meaning, you go 100% throttle at 55mph but the car shifts to 3rd and 3rd maxes out at 62mph so the car has no time to realize it should have shifted to 4th so it bounce off the limiter for a moment. Just like King said, is making more power and doesn't realize it needs to shift to a lower gear.

Sounds to me like the shop didn't think about tuning the TCM or your friend didn't want it tuned or didn't know.

wnta1ss · 08-13-2021, 10:54 AM

Quote:

Originally Posted by Vigilante375

Sounds to me like the shop didn't think about tuning the TCM or your friend didn't want it tuned or didn't know.

Some big shops are supposedly telling guys that trans tuning is unnecessary for the A10 ZL1 unless you change the camshaft. So this customer probably did not get the whole story on what tuning can do.

JSH · 08-13-2021, 02:37 PM

Quote:

Originally Posted by FoundNemo

My buddy noticed that in auto mode on his ZL1 A10 (stock rev limiter, untuned TCM, stock fuel cuts, etc) with his headers and tune from the local shop the car will bump the limiter if you floor it on the hwy, which it did not do stock. In gear shifts fine without any issues.

Any thoughts on why that might be since the TCM wasnt tuned, intake is stock, TB is stock, pulley and blower are stock, TCM is untuned, shift points werent changed nor the stock rev limiter or fuel cuts of any sort?

Would raising the rev limiter 100rpms be a safe way to give it breathing room or is that not a good idea on an 18 ZL1 for longevity.

Tire spin equals rev limiter hits, particularly in 1-3. If it hits the limiter while not spinning the tire it has other issues.

FoundNemo · 08-13-2021, 02:44 PM

Quote:

Originally Posted by wnta1ss

Some big shops are supposedly telling guys that trans tuning is unnecessary for the A10 ZL1 unless you change the camshaft. So this customer probably did not get the whole story on what tuning can do.

Yea TCM tuning was optional. 80mph WOT will bump the limiter. Is it safe to up the limiter by 100rpms to give it breathing room in the meantime?

wnta1ss · 08-13-2021, 05:16 PM

Quote:

Originally Posted by FoundNemo

Yea TCM tuning was optional. 80mph WOT will bump the limiter. Is it safe to up the limiter by 100rpms to give it breathing room in the meantime?

Always a risk to modify stuff of course. But if the owner is comfortable with it, some do raise the rev limiter to some extent. What are the current settings (several places in the tune that affect this)?

KingLT1 · 08-13-2021, 05:47 PM

Either raise the limiter or tune the TCM. I moved my limiter up to 7k rpm...not going to hurt anything. Ideally it should be 2-300rpm above the shift point. you have to change 4 different areas in the tune to raise the limiter. Extreme, In-gear, oil temp, Startup Modifiers(cold engine)...etc

08-13-2021, 09:03 AM	#1
FoundNemo Drives: 2019 ZL1 Join Date: Oct 2019 Location: GA Posts: 573	Hitting rev limiter with tune My buddy noticed that in auto mode on his ZL1 A10 (stock rev limiter, untuned TCM, stock fuel cuts, etc) with his headers and tune from the local shop the car will bump the limiter if you floor it on the hwy, which it did not do stock. In gear shifts fine without any issues. Any thoughts on why that might be since the TCM wasnt tuned, intake is stock, TB is stock, pulley and blower are stock, TCM is untuned, shift points werent changed nor the stock rev limiter or fuel cuts of any sort? Would raising the rev limiter 100rpms be a safe way to give it breathing room or is that not a good idea on an 18 ZL1 for longevity.

08-13-2021, 09:16 AM	#2
KingLT1 Drives: 2016 1SS NFG A8 Join Date: Aug 2017 Location: 46804 Posts: 7,665	When you make more power the goal is to increase the rate of acceleration. When the car accelerates faster then you need to give the TCM more time to make the shift. So Ideally you command a lower shift MPH to make the shift at the same RPM before the power increase. Since the TCM isn't tuned now you have to raise the limiter in order to get a clean shift at the same commanded shift points since most if not all GM transmission controllers primarily shift off of commanded MPH not RPM. __________________ 2016 NFG SS A8/Whipple 2.9/Fuel System/Flex Fuel

08-13-2021, 05:47 PM	#8
KingLT1 Drives: 2016 1SS NFG A8 Join Date: Aug 2017 Location: 46804 Posts: 7,665	Either raise the limiter or tune the TCM. I moved my limiter up to 7k rpm...not going to hurt anything. Ideally it should be 2-300rpm above the shift point. you have to change 4 different areas in the tune to raise the limiter. Extreme, In-gear, oil temp, Startup Modifiers(cold engine)...etc __________________ 2016 NFG SS A8/Whipple 2.9/Fuel System/Flex Fuel

08-13-2021, 09:33 AM	#3
Vigilante375 Drives: 2018 Camaro ZL1 Join Date: Aug 2018 Location: Georgia Posts: 1,419	So you are saying that with the car in D and your friend floors the throttle, the engine bounces off the limiter? But in gear (do you mean manual mode?) It shifts fine? At what speed is he flooring it? It could be that he is flooring it right where the car would down shift to a speed where there is no room for the car to realize it's going to bounce off the limiter. Meaning, you go 100% throttle at 55mph but the car shifts to 3rd and 3rd maxes out at 62mph so the car has no time to realize it should have shifted to 4th so it bounce off the limiter for a moment. Just like King said, is making more power and doesn't realize it needs to shift to a lower gear. Sounds to me like the shop didn't think about tuning the TCM or your friend didn't want it tuned or didn't know.

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