Fox T-Bird/Cougar Forums  

I just replaced my torque converter (Precision Industries Stallion) 3700 with a Pro Torque equivalent but went from a 9.5" converter to a 8". I was having a tough time dealing with the 23% converter slippage in the 1/4 mile. It was killing my et and MPH. I am trying to get my bird into NHRA Super Gas territory of a 9.90. The best I have ran so far is a 10.08. Now I am running 6.20 1/8 mile and that should equate to a 9.80 1/4 mile. In high gear the poor PI Stallion was just not efficient enough, the problem is that upon install and optest of the new converter, I noticed quite a bit more slippage and I cannot determine if the converter is just slipping that much, or do I not have something right in the tranny? Nothing has really changed with the exception of the converter so I am a bit puzzled. These were both high end converters and I am doubting that 2 different converter shops can be so far off of their initial settings. Am I out to lunch, or should I be checking line pressure to the cooler to verify converter charge pressure? Can the pressure be adjusted? It's a full race C4 Reverse Manual Valve body, no transbrake.

How do you know it was slipping that much?

For reference I went 6.43 and 10.02 so a 6.20 should easily be in the 9.80s I would think.

I know our cars are apples to oranges but I have been happy with my Coan 8" 5500 converter.

This sounds similar to my issues. I gave up troubleshooting. Stock converter slipped quite a bit (seen after reviewing datalogs years later), but the smaller Stallion 9.5" 3000 stall unit made my transmission issues more apparent. 36% slippage at 4000rpms. Transmission stall pressures were perfect. I've had other issues with lockup in the 4r70w transmission though, so I assume that I simply have a problem in the transmission and not in the converters (both would fail to hold lockup at closed-throttle and factory tune - pressure boost at closed throttle made that issue go away). According to places like Silver Fox Transmission, the problem shouldn't be anywhere in the valvebody, and with good epc/line/etc pressures and high slippage issues with both stock and aftermarket converters, they weren't sure where I should look next. There comes a point that one must stop throwing time and money into old parts!

From what I understand about how these converters should behave, I'd assume the problem is somewhere else. Insufficient converter charge for whatever reason would cause higher slippage.

I did the math between MPH and engine RPM at the traps. Your driveshaft RPM should equate to engine RPM since it is a 1:1 ratio, so any difference between the two and viola it has to be the converter or transmission slippage.