LT1 Rev Limiter Problem at Track

[GRSCAMARO]

I have a 95 LT1/4L60 in my 69 Camaro. It has a LT4 Hot Cam Kit.

Saturday I ran it down the ¼ mile for the first time since making some suspension upgrades. Good news is the upgrades worked. Bad news is the engine seemed to hit the rev limiter at the top end of the track shortly before going thru the traps. At least is sounded like an engine hitting the rev limiter. I made 5 passes and it did it every time. I launched with the 4L60E in 3rd. On the 3rd thru 5th pass I shifted into OD when it started “popping” but it seemed to hit the rev limiter anyway. I believe I saw the tach reading above 6000 RPM which is why I thought the problem was hitting the ECM rev limiter. I am a rookie at the track and have a difficult time taking my eyes off of the road to study the gages.

Here are the specs:
Tires: Nitto 555R size 275/50-15 (Dia = 25.75)
Differential Ratio: 3.73:1
4L60E 3rd Gear Ratio: 1.0:1
4L60E 4th Gear Ratio: 0.7:1

Trap Speed after letting off, shifting into 4th and hitting the gas again varied from 86 to 99 mph. I used several online calculators to calculate engine RPM at 100 MPH. The result is 4867 RPM which should be below the rev limiter. Again, I thought the tach was above 6000 rpm when I had the problem.


Any idea what might be wrong?

[2010 SS RS]

Sounds like you have the speed limiter still set on it. You will need to have that turned up or off to allow you to run past that speed. Does it almost seem like you blew the engine and shuts it down? If so that would be your culprit. Speed limiters were put on to match up to the speed ratings on standard tires. That 99 mph seems to be a common limiter for that year set up...

[GRSCAMARO]

Interesting, so there could be a speed limiter as well as a rev limiter. I asked my tuner (pcmforless) to advise the rev limiter. Perhaps the speed limiter is the deal.
That would explain why it acted the same after shifting into 4th although 99 mph seems like a low setting for a Z28.

Thanks for the input.

[GRSCAMARO]

Bummer. My tuner said the only limiter is the rev limiter and it is set at 6600 RPM. He suspects the opti-spark is going bad causing a spark breakup.

I guess I better start researching all of the opti-spark threads to determine to stay with GM or go with MSD.

[GRSCAMARO]

More research says it could be a spark problem at high rpm. This could be caused by the coil which is original to the car so I am replacing it. It could also be caused by low spark which can be cured with a MSD Ignition Box. First step is to replace the coil and see how it runs.

[Blueovalman]

Originally Posted by GRSCAMARO

Bummer. My tuner said the only limiter is the rev limiter and it is set at 6600 RPM. He suspects the opti-spark is going bad causing a spark breakup.

I guess I better start researching all of the opti-spark threads to determine to stay with GM or go with MSD.

You can never go wrong with MSD they make nice stuff.

[SC2150]

The 2-3 clutch pak is the weak point on the 4L60E and the first signs are it shifts late (as long as your programming is correct as far as shift points & line pressure). Do you have a trans temp gauge? The temp will spike hot as it slips if thats the issue.

[GRSCAMARO]

I do not have a temp gauge. Does it required an independant gauge or can you get that info from the ECM? If new gauge is reqd, where do you install it?

[GRSCAMARO]

Here are a couple of vids of the pass. You can hear the hiccup on the second vid.

http://youtu.be/6A6Z0c6DbWM
I listened to the second vid again and noticed the misfire is at the 2nd to 3rd gear shift i.e. the trans did not shift into 3rd. Assuming 80 mph and 2nd gear ratio of 1.63:1, the engine speed would be 6347 rpm. Since I was at 81 mph at the 1/8th and the misfire was further down the track, I probably did hit the rev limiter of 6600 rpm.

I used DataMaster to log some data from a normal run and an acceleration run today. It definitely hit the 6600 RPM rev limiter at the end of second gear.

Any Data Master experts what to help me decipher the info? I tried to post the files but the format is wrong. Send me a PM with your email and I will send them to you.

Thanks for the help.

[GRSCAMARO]

I had a response from Bryan at pcmforless (current tuner). He had some interesting comments:

The performance mode was for cars that had the performance mode switch....
Your WOT shift table is the table labeled Kickdown Mode Up/Down Shift Points (dumb name for it, should be labeled something like WOT shift MPH or something)
In there your 1-2 is 33 and 2-3 is 67, that should be right for your setup. The kickdown mode RPM trigger (wot RPM Trigger point has to be met as well as the MPH to start a shift) is at 5750 so it should be completing a shift by 6150 (tranny takes 300 to 400 RPM to complete a shift). I can lower those triggers for you to give a try. I've done that and attached the new program. I lowered that MPH as well 2 MPH just to try to force the tranny to shift earlier.

I will try to upload the new tune and try it out tonight.