searching for LS1 issue. On track performance question.

[rewguy]

99 firebird. Full interior. Everything there PLUS ford nine inch. 3,680 lbs with driver. 4.56 gears, 28x10.5 slicks w front runners. (Rear tires measure 90" rollout). 4900 FTI converter, 4L60E (just been re-gone through to check it out), Shifting at 6800, crossing at 7100 in 3rd (drive). Converter slippage is high-ish at 12%, but Ive seen similar slippage not necessarily hurt anything very badly. Car is a pig. Runs 60ft/1.471, 8th-et/7.20@93, 1/4-et/11.40@116.3. I would have expected closer to 10.70@125-126. Have had two other near identical engines on dyno make between 572-585 hp @ 6400. One car at 3,440 w/driver ran 10.48@127. 383ci. 3.905 bore/4" stroke. 241 heads, cnc'd w/ also hand work. Flow 315@.650. Super vic manifold also hand ported, 4150 100 cfm throttle body. Camshaft is 244/257 on a 111+4. .646/.619. Flat top pistons, 11.1-1 final compression. I truly think something is in the tune. He has put about 6500 miles on the car since engine went in. He dealt with a local tuner that really wasn't up to par in my opinion. He ended up with more questions than answers afterward. Apparently the converter acted up on the dyno, hence the transmission and converter were both sent out to be rebuilt and inspected. I don't trust most chassis dyno numbers here locally anyway, as they almost never make the same numbers twice, even on the same dyno in the same air. Crazy differences all the time. ugh. To my knowledge the car does not push hard, and the brakes are not dragging. The alignment is current. Have you ever seen a tune so far off as to leave .6 on the table?

[user-17438]

Many things can make the car slow from a tune. Is knock being sensed? If so how many degrees is it pulling. Is it running of commanded afr. is it open loop or closed loop. if its a good converter why isn't it being locked up.

If you think its a tune, retune it.
Verify AFR and Timing. old gas, new gas,etc maybe not enough octane

[user-17438]

BTW I have seen a converter loose that much et.

[V Remian]

1/8 and 1/4 mph correlate and so do the et and mph and in my opinion rule out a converter problem as a major factor. That leaves either the power is low or its being squandered by the chassis-which I think is partially responsible.

One of the benefits of running a computerized car is wealth of data you can monitor when you log a run. If it were me, I would want to see MAP and IAT data just because of the intake configuration of the car in question.