Racers using 5 speed o/d tranny what final drive ratio?

[Tom1200]

Here's the background; I have close ratio boxes for my 1200 vintage racer but the are the smaller 56 series and not sturdy enough for the A15 that's in the car. I have currently installed a 60 series 5 speed but as you all know the 2nd to 3rd drop is huuuuuuge. I'm currently running a 4.38 R&P and have a 4.62 that I could install. It's not uncommon for people to run low gearing so that 3rd - 5th are used, in the case of the 60 series the ratios are 1.378 1.0 and .821, regardless I still feel like running the overdrive box is a compromise. The alternative is 3-4k for a proper box. I run on Hoosier Street TDs which are 20.6 and 8000 rpms in 4th is 112 mph. Slowest corner on the track is 38 mph and currently hitting 111mph on the longest straight. Motor will pull to 8200 and is safe to 8500.

 

So for anyone who has run o/d boxes what R&P are you using?

[Dime Dave]

Tom,

I ran a 1200 coupe in SCCA GTL with an A15 engine. I started with the 56 series close ratio 4 speed. I was running 20 inch tall Goodyear race slicks. With the 1 to 1 4th gear I used 4.37 ring and pinion for most tracks.

 

Needless to say the transmission failed. Ultimately I ended up buying and using the 63 series dog leg 5 speed out of a B210. I believe the fifth gear ratio is .854. I raced the car at VIR. On the back straight it would pull 8400 in 5th gear running 4.88 rear end gears. I use the same gearing and pulled about the same top RPM at Pocono as well.

 

The car has a 510 wagon H190 rear end. I purchased the third member from a 320 truck (520 and 521 with J13 engines have the same ratio). This carrier has the 4.88 gear set. All I needed to do to install it in the wagon rear end was swap the side gears with wagon side gears. I did not use an LSD and left it open. On long tracks it was not a problem.

[Tom1200]

Dave thanks for posting; I'm running the wagon / roadster 23 spline H190 as well. The car currently has a LSD that I managed to find for the low low price of $1300 a few years ago. The 4.62 has the spiders welded up (I despise locked diffs) and I just need to swap in the LSD before installing it. The 4.62 also has the 4mm spacer for the ring gear.

 

The 60L trams has a .854 5th but I'm not sure that would swap into a 60A trans (intending to investigate). Running an open diff makes sense on faster tracks. Stupidly several years back I passed on a Hall Hewland box Perer Zekert had at a good price.

 

Naturally all this tumult is brought on by the fact that my motor is belting out all of 105WHP, if took the money I'd spend on something like a Qauife Sierra 5 speed box and put it in the motor it would likely be better spent.

 

Thanks again for posting.