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Discussion Starter #1
What thing(s) need to be changed in the PCM to give greater or unlimited top speed? There is apparently more than one rpm limiter.

Having done many high-speed runs in an early production '02 Z06 I have discovered several, lets say; "anomalies."

In 2004 21st Century Muscle Cars did a head and cam install. It included a custom tune in the PCM. One of the things they changed was increasing the rev-limit to 6800rpm. From that point on the car tops out at 173-175mph instead of the 179mph it originally did with the factory tune. It doesn’t hit the “hard” rev-limiter; it hits what I will call a “soft” limiter at 6600rpm. 21st Century said they removed all limits in 5th gear, just as it was from the factory, but it is still limited to 173mph now.

Previous to that, it would go faster.
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The first runs in 2002 with unchanged factory tuning in the PCM let the car go over 179mph in 5th gear. The engine/PCM was not a rev-limited in 5th gear according to LS1edit. I didn’t check the tach so I don’t know for sure what rpm it showed, but it must have been somewhat over 6600rpm to attain that speed. Not knowing about the “soft” limiter, I figured hitting the “hard” rev-limiter was imminent, so I shut down the run without knowing what the top speed (within engine rpm limits) could have been.

The car isn’t limited to a certain MPH (not to be confused with RPM) because it has made a high speed run (in 6th gear) on a dyno that was well over 200mph.

There is a big difference between the “soft” and “hard” rpm limiting.

The “hard” limiter shuts down individual fuel injectors and causes the engine to surge and buck. Many people are familiar with this if they have gone a little too fast in first gear.

The “soft” limiter seems to reduce the throttle (no matter how hard your foot is pressing on the gas pedal) to 6600rpm at a steady 173mph while running in 5th gear. There is no cutting of fuel from the injectors, no bucking or surging, just a gentle reduction of acceleration. This car with numerous mods is still accelerating hard up to the point it does this.
 

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The speed limiter is set at 255 mph.
What you are most likely experiecing is torque management.
 

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What you got to do is bring your car to sunny Florida and let Tom tune it the right way.

FRCTOM MT(Master Tuner) :jammin:
 

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IVOZ06 said:
What you got to do is bring your car to sunny Florida and let Tom tune it the right way.

FRCTOM MT(Master Tuner) :jammin:
I got yours bumped up to 640 lbs across the board. :thumb:
Now that your broken in, I'll be at Greg"s 2morrow tuning that other 427. Time to step up your timing and get some more ponies out of that monster.
 

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From that point on the car tops out at 173-175mph instead of the 179mph it originally did with the factory tune
Was the rev limiter raised to allow the 179mph speed in stock form?
 

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Discussion Starter #6 (Edited)
FRC Tom said:
The speed limiter is set at 255 mph.
What you are most likely experiecing is torque management.
That was my first thought also, but it always reduces the throttle at the same 6600rpm/173mph even if you are going downhill with a tailwind. Raising the headlights doesn't make any difference either.

Can the TM setting be adjusted at each 100rpm?

Previous to the head and cam install, 21st Century had changed the T/M settings (not sure how) and that caused the traction control and active handling to not function. I had them put it back to the original factory settings. When I talked to them about this speed problem they said the T/M was still at the factory settings. Has this been a problem with any of your cars?
 

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Discussion Starter #7
RC45 said:
Was the rev limiter raised to allow the 179mph speed in stock form?
No. There was a 9000 limit in 5th gear in the factory tune. The other gears were limited to 6600rpm.
 

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FRISKY said:
No. There was a 9000 limit in 5th gear in the factory tune. The other gears were limited to 6600rpm.
Interesting - I wonder what was stumbling my car when I did my run to redline in 5th. Sure seemed to act like an rpm limiter at 6600 or so.

Did GM ever update this value with subsequent PCM flashes?
 

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Stephanie was having this problem after her H & C install.
I fixed her problem at the Fest with 100 lb increase to the torque man. table.
The traction control table pulls timing at a given rpm.
The only way to disarm it is to set the retard to 0.
Example: at 3600 rpms 25 degrees is pulled at 6400 rpms 31 degrees is pulled.
 

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Discussion Starter #10 (Edited)
FRC Tom said:
Stephanie was having this problem after her H & C install.
I fixed her problem at the Fest with 100 lb increase to the torque man. table.
What type of problem?
FRC Tom said:
The traction control table pulls timing at a given rpm.
The only way to disarm it is to set the retard to 0.
Example: at 3600 rpms 25 degrees is pulled at 6400 rpms 31 degrees is pulled.
Are you saying the Torque Management settings don't have any effect on Traction Control and Active Handling? :-?

I don't know the answers. The only information I have is what 21st Century said they did and the effect it had on the car.
 

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Mainly the active handling. The traction control from my understanding kicks in when the rear tires are spinning faster then the fronts and pulls a bunch of timing.
Active handling slowly controls the car by applying brakes and pulling fuel.
 

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Discussion Starter #12
RC45 said:
Interesting - I wonder what was stumbling my car when I did my run to redline in 5th. Sure seemed to act like an rpm limiter at 6600 or so.

Did GM ever update this value with subsequent PCM flashes?
Folks have posted both 6600 and 9000 in 5th gear in the PCM, but I haven't seen any corresponding dates to be able to show a relationship in the information.
 

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rpm limiters

Frisky,
The Z06 has both a fuel injector rpm limiter and a throttle based rev limiter. In all gears with the exception of fifth the injector rev limiter is in play with the limiter set at 6600 rpm, stock. The limit is set to 9000 or so in 5th gear. The actual control of the rev limiter in 5th is the ETC based number, which for all gears except 5th is 9000 rpm, stock, 5th is set to 6600, stock. So if the ETC rev limiter has not been changed you will still have 6600 rpm in 5th. GM did this to make it softer and safer for the engine, since you can hit 6600 in 5th stock in a Z06, cutting fuel under these conditions is not good. 21CMC will be able to re-program your PCM to raise this limit.
Hope This Helps
Graham.
 

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OK - so I wasn't going nuts when the car stumbled at 6600 in 5th... ;) - it was in fact still pulling.

Now we just need to convince all those yahoos that seem to think a stock C5 Z06 can't reach 180mph+ with Z51 gearing... :p
 

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Rev limiter Yes! Top speed governer...No.

Want an easier way to get faster top end....Change the diameter of the rear tires....? That will effectively change the rear axle....Don't go to far off and if you do change both the front diameter upward and the rearward so the differential is within 2% of stock...


165 with 3.73's or 168 mph w/3.42's(which is what is claimed by GM due to gearing/tire size stock) is fast enough...

If you really want to go faster...change the gearing in 4th,5th and sixth inside the tranny....Cost a few dollars I'm sure yet thats probably the best way to go...

fwiw..I was reading that the MB E55 WAGOn in car and driver magazine gets its @ss up to 150 mph in 24 seconds...(4 seconds faster than a stock 2001 Z06...

If anyone is seriously thinking about top speed capability...I'd say changing out a few of the transmissions gear ratios would be a smart invenstment...

Stay safe and I'm just shooting the breeze....

I only wish I had the wide open safe places to run those kinds of speeds you guys are discussing....

Dam fast anyway you look at it.
 

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Hi Graham, long time no see . . .

Frisky, Graham is quite correct. I started a post (on this forum) on exactly this same topic over 3 years ago. I got some "inside" info along the lines of what Graham just posted, which I could verify with a subsequent update to LS1 Edit (I think the updated version was V1.21).

As Graham states, there is the "ETC" limiter, in addition a traditional EFI based "Rev" limiter in all gears. 6600 is the stock setpoint in all gears for the latter, except for 5th. I have no idea what prompted GM to set the fuel shutoff at such an unrealistic "9000" rpm; which is the same as having no rev limiter at all. :screwy:

However, the ETC limiter, aka as the "soft" rev limiter, as Graham explained, does come into play at 6600, which is the key to raising the theoretical top speed of these cars. A stocker is still capable of "pulling" to a higher top speed approaching and/or exceeding 180mph, if only not for the intervention of the ETC limiter.

I use to do many of the so-called Open Road Rallye events in Nevada and this was the first thing on my list of "things to do" should I have taken my Z out there for go at top speed. Unfortunately, never got the chance. :cry:

As an aside, I don't believe TM has anything to do with this discussion. While approaching a redlined top speed in "5th", the (stock) LS6 engine has fallen well below its torque peak.
 

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Discussion Starter #19
Graham Behan said:
Frisky,
The Z06 has both a fuel injector rpm limiter and a throttle based rev limiter. In all gears with the exception of fifth the injector rev limiter is in play with the limiter set at 6600 rpm, stock. The limit is set to 9000 or so in 5th gear. The actual control of the rev limiter in 5th is the ETC based number, which for all gears except 5th is 9000 rpm, stock, 5th is set to 6600, stock.
Bingo! That is the information I needed. Thanks all! :thumb:
 

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I just found something very intersting. I have stock files from 1998-2004 M6s. autos, and M12s (Z06s).
The ETC controls are disabled on all but the Z06s, why I don't know.
The stock settings on just the Z06s closes the throttle in 5th gear at 6600 rpms.

Learn something new everyday.
If you ain't a learnin' you aint a livin'.
 
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