White90GT
07-11-2005, 08:45 AM
I'm having a problem with the car on the track. I was having a problem before I rebuilt my transmission and switched converters with the motor bogging off the line. I could get off the throttle and back into it and it would perform fine. I think I got that one solved, but now I'm having a different problem launching.
Motor is a 347, ported Twisted Wedges, Holley Systemax, Lunati cam 544/560 232/242 112 lsa, MAC 1 3/4 to 2.5" offroad, 3.73 gears and 28" tires. 3100 lb raceweight.
Tranny is Performance Automatic C4, recently freshened up. Converter is a PA 10" that I had loosened up along with the tranny rebuild.
Since I put the tranny and 10" back in the car, it will not launch worth a crap on motor. It almost feels like the converter is too tight, but that can't possibly be. A Background, last year on the old motor with this converter (before re-stalling) it would hit around 3200 and pull average 1.59-1.61 sixty foot times. I lost that motor and built another 347, pretty much the same setup, but a little work done to the heads and a switch from a Victor to a Holley intake, and 1 point less compression from 11:1 to 10:1. Motor should make more power and more tq now compared to last year even with the loss of compression. When I put it back in, I used an 8" trans king converter that I had tightened up to around 3500. Converter was nice and the car cut a best 1.57 in really good weather. Lost the tranny and you get the picture from here. That converter wasn't really efficient on nitrous at the top end of the track allowing the motor to push into the factory rev limiter at 121mph. So I switched back to the 10" after having the pump changed out to gain about 500 more rpms. So the converter should be about 3700 rpm now.
Wow, thats a lot to read, but please keep going.
Fast forward to the last couple races. Since the trannys back in, the car won't launch on motor. Again the best description is that it feels like the converter is too tight. The only way that could happen is if the converter shop went with a tighter pump than a looser pump and I don't see that happening as it is a very reputable shop. One other symptom that may or may not have an effect here is that when I put the transmission into 1st gear, there is about a 4 to 5 second pause before you feel the rear wheels kick into gear. It was doing that before I had it rebuilt, so I'm wondering if the builder missed something? The sixty foots on motor are more like in the 1.80s and 1.90s and it got even worse on Saturday.
A buddy of mine suggested something that he had a problem with. He said he had a very similar issue, car just wouldn't launch. He pulled the tranny and had it gone through and it turned out that there was a stuck valve in the valve body or something for 1st gear that was not allowing the converter to pump the fluid into the transmission easily. This really sounds like a possibility and his suggestion was to pull the return line from the tranny cooler and run the car a couple minutes to see if it is flowing fluid very well.
On the nitrous, 100 shot, the car sixty footed 1.53 this weekend. But you're talking about probably 450-500 ft lbs of tq on the line when I launch, so its going to 60 ft well. With the converter looser, I would have expected more like a 1.47 sixty foot at least. Its done a 1.48 sixty on this converter before the restall and on the 100 shot.
Sorry for the long winded speech, but its the best explanation I can give.
I've tried other things motor wise to make sure nothing is out of whack in the tune. I've raised fuel pressure as high as 45 psi (no vacuum), I've raised and lowered the base timing from 18-24, I've pulled the spout and run 35 degrees flat timing across the board. Nothing really made any difference on the launch. If the track conditions were bad and no load was really put, ie spin the tires a bit, the motor would get up into its rpm band and pull on fairly well. Saturdays passes were 7.88@90-91 mph, and 7.92@92 mph. Again no tire spin on those passes, just launches soft, hits its powerband and goes. On the nitrous it went 7.15@91 mph letting off the gas about 100 ft from the end to protect my 7.10 dial in.
Thanks for reading and please give your feedback.
Motor is a 347, ported Twisted Wedges, Holley Systemax, Lunati cam 544/560 232/242 112 lsa, MAC 1 3/4 to 2.5" offroad, 3.73 gears and 28" tires. 3100 lb raceweight.
Tranny is Performance Automatic C4, recently freshened up. Converter is a PA 10" that I had loosened up along with the tranny rebuild.
Since I put the tranny and 10" back in the car, it will not launch worth a crap on motor. It almost feels like the converter is too tight, but that can't possibly be. A Background, last year on the old motor with this converter (before re-stalling) it would hit around 3200 and pull average 1.59-1.61 sixty foot times. I lost that motor and built another 347, pretty much the same setup, but a little work done to the heads and a switch from a Victor to a Holley intake, and 1 point less compression from 11:1 to 10:1. Motor should make more power and more tq now compared to last year even with the loss of compression. When I put it back in, I used an 8" trans king converter that I had tightened up to around 3500. Converter was nice and the car cut a best 1.57 in really good weather. Lost the tranny and you get the picture from here. That converter wasn't really efficient on nitrous at the top end of the track allowing the motor to push into the factory rev limiter at 121mph. So I switched back to the 10" after having the pump changed out to gain about 500 more rpms. So the converter should be about 3700 rpm now.
Wow, thats a lot to read, but please keep going.
Fast forward to the last couple races. Since the trannys back in, the car won't launch on motor. Again the best description is that it feels like the converter is too tight. The only way that could happen is if the converter shop went with a tighter pump than a looser pump and I don't see that happening as it is a very reputable shop. One other symptom that may or may not have an effect here is that when I put the transmission into 1st gear, there is about a 4 to 5 second pause before you feel the rear wheels kick into gear. It was doing that before I had it rebuilt, so I'm wondering if the builder missed something? The sixty foots on motor are more like in the 1.80s and 1.90s and it got even worse on Saturday.
A buddy of mine suggested something that he had a problem with. He said he had a very similar issue, car just wouldn't launch. He pulled the tranny and had it gone through and it turned out that there was a stuck valve in the valve body or something for 1st gear that was not allowing the converter to pump the fluid into the transmission easily. This really sounds like a possibility and his suggestion was to pull the return line from the tranny cooler and run the car a couple minutes to see if it is flowing fluid very well.
On the nitrous, 100 shot, the car sixty footed 1.53 this weekend. But you're talking about probably 450-500 ft lbs of tq on the line when I launch, so its going to 60 ft well. With the converter looser, I would have expected more like a 1.47 sixty foot at least. Its done a 1.48 sixty on this converter before the restall and on the 100 shot.
Sorry for the long winded speech, but its the best explanation I can give.
I've tried other things motor wise to make sure nothing is out of whack in the tune. I've raised fuel pressure as high as 45 psi (no vacuum), I've raised and lowered the base timing from 18-24, I've pulled the spout and run 35 degrees flat timing across the board. Nothing really made any difference on the launch. If the track conditions were bad and no load was really put, ie spin the tires a bit, the motor would get up into its rpm band and pull on fairly well. Saturdays passes were 7.88@90-91 mph, and 7.92@92 mph. Again no tire spin on those passes, just launches soft, hits its powerband and goes. On the nitrous it went 7.15@91 mph letting off the gas about 100 ft from the end to protect my 7.10 dial in.
Thanks for reading and please give your feedback.