Autocross gearing?

[vatdevil]

Looking for suggestions on proper gear ratios for autocrossing these cars. Currently have a 3550, 3.73 gears, with 450 HP Windsor that runs best above 2000 RPM. 1st sceams and 2nd bogs on course.

[blykins]

The 1st gear ratio of the 3550 doesn't help much. If I remember correctly, it's a 3.27:1. So you are indeed correct that it will scream, then bog when you get into 2nd.

Unfortunately, if you gear higher to help 1st gear out, then 2nd will bog more. If you gear lower to help 2nd, then 1st will be useless.

What size tires are you running?

[vatdevil]

Will be running Avons 295 50. I was thinking 4.10 s. Which would make second usable from 18 to 60 MPH. First would just be good for off the line. OD is 0.68 so it would be usable from 55 and up.

[Silverback51]

Replace it with a TKO600.

[roadrod2000]

Use this link to calculate your rpms at mph in whatever gear your in Tire Size and Gear Calculator very helpful

[WardL]

I autocrossed last summer with 3.46 Rear in first and second gear never shifting. I had better times staying in 2nd gear start to finish. I have 335/35 ZR 17" tires. My TKO 600 has a 2.87 first and 1.89 2nd. I do a pretty low speed circuit. The dyno curve says I've got over 400 ft-lbs at 2,800 RPM. I don't think I had any bogging problems. At 6,000 RPM I'll be going 47 MPH in first and 72 in 2nd gear. I thought 450 HP would spin the tires in any gear. Surprised you are bogging down in second gear. Is the carb starving in a corner? I've had some of that problem, but it doesn't slow me down much.

[vatdevil]

WardL...thanks for the feedback. Using a gear calculator, My car runs a ton more revs in first and slightly more in second. Maybe once I install the Avons, I'll run faster speeds, have POS tires on now. cam just doesn't like running much below 18 mph, in second, even in straight runs. I do keep the floats low to prevent splashing fuel out the bowls, so maybe try raising up a bit.

[D-CEL]

4.10s are a great choice, Im very happy with mine.
4.30s should pull a little harder if you can keep it hooked up, depends on the tire you run.
My motor is a lot happier with the added RPM.
One of the nice things about earlier SPF’s is the 8.8 Ford diff. They are cheap, strong, easy to find and work on. I bought one complete on E-bay for less than $100.00 shipped
You can get a set of gears for about $150 and another $150-200 for set up (out of the car) if you don’t do it yourself. And 2-3 hours for the diff re-install.


jason

[fordracing65]

Don't fear the gear, 4:10 or 4:30, it will hook up with the Avons.