Many have asked about mph at rpms and what they should be. I have a TH400, 2600 stall TCI convertor, and 3.55 rear gears. Checked the speedo with a gps(within 2 mph). I don't know what the info should calculate to be but, here is reality:

2000 rpm.....40 mph
2400 rpm.....50 mph
2900 rpm.....60 mph
3300 rpm.....70 mph
3800 rpm.....80 mph

assumption is that my stock hood tach is accurate.

That sounds right for 15 inch wheels with 245 series tires. The tire circumference is critical info for accuracy in RPM to MPH conversion calculations.

Q, sorry. I left out an important detail. 15" 60 series,255's(a bit worn)...27" diameter.

How do you like your 3.55? I have the same setup (- the stall converter)? Did your car come with the 3.55 or did you swap it out? I am looking to improve my car's launch and I am currently running the stock 3.08.

I really like the 3.55's. Had 3.23's when I bought the car. Switched over to an Auburn posi and 3.55 gear set. Good launch, and doesn't wind up too high at highway speed. Only close alternative was a 3.90 gear...too steep for my street cruiser.

I wish I had an overdrive tranny

The convertor is a cam related choice, not rear gear related.

I seem to get +_ 60 (just over 55) mph at 2000 rpm , 90 (just over 85) at 3000, 2,56 rear
Th350, 14 "ims 235 tires

3300@70 is about what I turn with 3.23s. My tach may be off by a couple of hundred though. I'm running 14s w/235/60s.

Robert

I switched to 3.55 last fall and then installed the 200R4 overdrive transmission in the winter.

We ran down to Yellowstone and back (2000 miles) and I'm really happy with the results.

Speedo's not working and haven't checked with GPS yet, but I'm down from about 3300 rpm at 70 mph to about 2600 rpm.
The nice thing is you still have the good launch ratio (actually, slightly better in 1st than the TH350)

(205R14)

Trevor

I had a good website for manual transmissions. Just enter in the wheel and tire size, rear ratio and trans gears (1st. 2nd. 3rd. 4th. 5th? ) and it gave a read out of mph in each gear at various rpm's. I'll find it and post it here. For auto trans 4th gear would give you some idea if you factor in convetor drop.

Found the website. http:www.f-body.org/gears/