Rexx

I have a weird problem that I was hoping someone else has seen. My car losses power over time, and when I took it to a dyno shop the power seems to slowly return to where it should be after 5-6 passes. I drive the car about once maybe twice a week and I do not baby it. I have a freind that has almost the exact same car and it has none of these problems. For example I drove to a drag racing event last firday and when I got there it was 8mph slower than it should be. The drive was about 2 hours at 90mph. The car sat for about an hour befpre racing so it was not like I went right from the highway to the drag strip. Has anyone else experienced something like this. The guys that i took the car to are stumped. They are not unfamiliar with ls1's either as they do about 15-20 blower installs a year.

NitrousDirect

iTrader: (1)

Well right off the bat ambient air temperature and air density can have HUGE effects on performance. Also you're racing a car that's still hot it takes 4-6 hours for a car to really cool down. Just my .01

Rexx

On a side note I drove it home on monday and dropped it off at the dyno shop this morning. The car has been run for 20min and then it hit the dyno and was about 60hp short of what it should have been. The last time that I was at the track the corrected altitude was 3200ft. and when I was at the track last friday it was 2600. I can understand that it would be hot and not happy but why would it still be down power today when it was definetly not hot. I figured it might have had something to do with the long drive but the fact that it was still down on power later on made no sense to me. It just seems like a computer problem where it does not like to hold its settings. IT should not take 5 pulls on a dyno to learn that it has 60hp more in it.


Thanks for the reply though.

redtail2426

iTrader: (10)

I just made a sort of weird observation that might help.It might be something other then the computer.Check for misfires or a bad injector possibly.Just cause you say its down about 60hp and in your sig you put out about 490.60 hp is 1/8 of your power.If one cylinder is down thats pretty much what you would be missing.just a thought

wait4me

iTrader: (10)

If, when tuned the pcm was reset and the ltrims are not final. The tune has the possibility of being way off after the ltrims have been set up... Think of this.. If on the dyno, the ltrims are reset from a tune, So they are all 0. then the car is dynoed and the fuel is right on.. Then you go and drive the car and it shows that it is having positive ltrims.. so, That means that it is now adding that amount of fuel more than what was commanded at the dyno shop.

Or, if the ltrims where negative, say -8% then the car tunes itself via the ltrims again while driveing, and they are now -3%.. So, the pcm will not add or subtract fuel if the ltrims are negative, so what does that mean for your "dynotuned" program now? It is now 5% lean!!!!

Positive ltrims are always a good thing. That way the pcm can add or subtract fuel to give you an accurate commanded pe vs rpm ratio.

If they are negative ltrims, there is no way for the pcm to correct wot. unless you tuned it for that EXACT trim.

Rexx

Thanks for the info. There was no misfires at all so I am wondering about the trims. I will talk to the guys at the shop about this and try and figure out what the problem is. The shop that I go to is the best in western Canada so I am pretty sure that they know what they are doing but you never know. I have the last srag racing even of the year next weekend so hopefully all is when by then. If not there is a long winter in which i can get things sorted out.

Once again thanks for the replys.