I am in the process of rebuilding my Borg Warner gear boxes and I have heard that there is some performance mod that the racing guys used to do that would allow the installation of another clutch plate. I guess this allows less slipage for higher horsepowers. Does anybody have any details regarding this performance mod? My motors are 565hp 502's.

Do you have the BW 71's....red tag? The 72's have a green tag. If you have the 72's, you are probably good as as. If you have the 71's, you can add two additional clutch plates. We raced for a long time (500-550 HP) with modified 71's and never broke a transmission.

I have green tag's (model: 10-18-14). So it sounds like I am all set! I take it borg warner realized that the 71C were a little weak and fixed the problem with the 72?

Thanks!

Brining this to the top with another performance mod question....

I have heard that back in the day 20+ years ago you could replace the regulator spring behind the shift lever with a higher pressure spring which would bump the pressure relief pressure from 200psi to 225-235psi which appears would allow 25-35psi more when the boxes are running in the 4000-5000rpm range. I am guessing this would keep the clutches clamped together that much tighter.

Any truth to this? Anyone done it. This wold probably be more for the old school race guys??

Thanks
Jim

I have 71's and have added the 2 extra discs all carbon fiber. Don't know anything about springs but I have turned them 6000RPM's for years and my transmission builder says the are good to 700HP.
Do you have a repair manual for the transmissions? I would like to learn how to assemble one myself.

Shim the the spring in the regulator/control valve with a washer to preload it Jim.

I heard that as an alternative to replacing the spring but I have to ask why? I think all the spring does is control when the pressure bypass kicks in. The manual says at 200psi the spring allows fluid to bypass back into the sump. By changing the spring or shimming do you simple change the bypass pressure? I am not sure how this helps? Especially where based on my calculations the pressures don't start getting close to 200psi until the 5000rpm range!

Thoughts?

PM me your email and I will send it. It's a PDF!