2 C5 corvettes -- chassis dyno -- steady state -- same issue on both. any insight?

[turbo-charged]

question for you guys....i have put a couple of C5 corvettes, manual transmisison, onto a dynapack chassis dyno the last week or 2 and had the same issue with both cars.. i use this dynapack just about daily, and i love it (so i know its not the dyno its self)...but these c5's both were acting as if there was some sort of torque management/traction control type of condition going on.....when going full throttle only, at a fixed rpm.

-this happened on a bone stock c5 with bone stock file in the ecu. turned traction control off obviously, and also put car into competitive driving mode. same thing

-second car had cam/heads/injectors/ and we were tuning it....and it did the exact same thing.

- issue is semi intermittent. does it more often than not however. if you go anywhere from light throttle to 90% throttle or so everything is fine. if you go somewhere in the 90-100% throttle range...the car starts to shudder like its applying the abs or something is the best way to describe it. (this is only happening when holding car at constant RPM, say 2500)

- full throttle on a "sweep test" type of run works perfectly fine as well. it would be very easy to work around this issue, but i would obviously like to know why its doing it and hopefully be able to correct it if at all possible. it acts as if the computer/car can sense that you are full throttle and the car is not accelerating so its trying to get you to let off the throttle.

ive searched 100 times and have found no info - figured (and hoped) this was a common thing.

any help is appreciated. hopefully its a simple turn something off and forget about it type thing!

[turbo-charged]

and for what its worth these are the first 2 gm cars we have put on this particular dyno

[Howedeman]

I have a dynapak at work and something that I have encountered is on a Firebird that we used it on, the hub wasnt the perfect match on the center, the axle center was a little bit smaller. If we didnt dial it in with a dial indicator it would wobble. At lower speeds it wasnt too bad but at certain speeds it would shutter bad. We ended up machining spacers to center it up better. That shutter could kind of be described like abs. This may not be your problem but never know.

[blkws6]

This may be a dumb question, but did you log burst knock? When it decides to implement some radical burst knock retard, it feels like the ABS sort of thing.

[turbo-charged]

thanks for the replies.... im familiar with the uncentered hub adapters...this is not that. logged knock on both cars, was not seeing anything like that

full throttle on a sweep test, 100% perfect

90% throttle steady state, say 2500-3000 rpm 100% perfect

100% throttle steady state, say 2500-3000 rpm -- feels as if some sort of traction control is taking place...as if it can sense the car is not accelerating.

did it on a stock car, with stock calibration. id call dynapack and ask them, but im 100% sure its something going on with the cars, not the dyno. hell maybe they have gotten calls about it before and know the answer. guess ill give that a shot