car falling off

I bought my 94 Z28 about 3 months ago to bracket race almost every weekend. The car has been great, but it has gotten consistently slower every week. The weather here in Houston has been getting a little worse, but it doesn't explain the huge differences in my ET's. First week it ran 13.28 best, next week was in the 13.40's, next time 13.55, and this last time it had a best of 13.73. That's almost 1/2 a second. The 13.28 run was in the mid 80's temp, the 13.73 was in the low 90's. Humidity about the same. Only changes made on the car were replacing a sticking EGR and installing a Trick Flow elbow and manual fan switch. None of which should affect ET's that much, if anything, I thought it would run faster. My 60 foots were in the 1.93 range, now, they're in the 2.04 range. I'm not spinning, I have ET streets and track prep is excellent. The 4L60E shifts incredibly hard on 1-2, but is sluggish on 2-3. Is this a sign of transmission wear? Could this explain the slower ET's? The guy that sold it to me said it has a 2800 stall built by a local shop, but when I mash the brake down and ease down on the throttle, I can only get it to 1200 RPM before the tires break loose. If anyone has any advice, please share. Thanks.

Bill Arning

Most 4L60E's crap out in the 2-3 bands. If it is going soft there you are probably on your last legs. I am speaking from personal experience's!

I have a PI vigilante 2800 stall in my car. I can stall it up to 2300-2400 before creep and tire spin. One good way to judge what your stall is is to drive the car in drive at about 30 mph. accelerate without letting the tranny downshift. The trans will stall to your stall speed and your tach will read 2800 if you have a 2800 stall. It will read less if you have less.

A lot of your slower times will be effected by higher temperatures. My best time listed in sig was run on a 73 degree day. I ran a 12.5 @ 110 the other day in 95 degree heat. That is -3mph and .5 seconds! I have also added 100+#'s with a rollbar, Spohn torque arm, and subframe connectors. so I am sure the added weight had some effect. I will have to see what happens on a nice cool thick air day, 65-70*'s. High 50* low 60*'s would be even better.


Hope this helps

Ken

Thanks for the info. I guess I'm basically running a stock converter, then. Good excuse to slap in a 3200 vig and rebuild the tranny, I guess:)

I still can't figure out the loss of ET, though. 15 degrees shouldn't make .5 second difference. Guess I'll just backtrack through the things I've done. :think:

Bill Arning

It could very well be the transmission. Soft shifts could easily be something simple and cheap like your shifter needing to be adjusted, or time consumeing such as replacing worn bands, or the converter could be slipping too (in which case you could have more than one problem). Barometric pressure can have a lot to do with ET, but with your sixty foot times going the wrong way I suspect the converter and/or the tranny. Check to see if your tranny fluid is burnt and you probably want to add a good tranny cooler to your wish list (notice I said good... this is no time to cheap out).