So I have a 37 Tudor Stock 85HP 21 stud eng. going to use T5 with .72 OD trans. Mostly in town driving with some fwy driving (prob not too long of distances.) Tire dia will prob be 29"-30" If I run a 700-16 rear tire (30") and 4.11 gears behind my T5 with .72OD and stock 21 stud flathead the chart shows at 70mph I would be at 2306RPM /650-16 tire at 2384RPM Would 4.11 be a good choice of gears to help give the old flatty some power around town and still have decent fwy driving? Considering the stock tire size, 3 speed trans, and 3.77 gears the RPM would be 2909 at 65MPH and 2462RPM at 55MPH. Does that seem like a good set up to you guys? I know it it #'s on paper, not sure how it translated to real world driving. What RPM do the flatheads like to run at? Thx
Ask Ken or Keith with the Rolling Bones, they go 3/4's across the county with that flathead/t5 combo. I'm betting they have higher gears, though; like 2.75-3.00.
You're right in the ballpark with the 4.11 cogs. You don't want that stock 85HP flatty to be pulling a gear that's too tall, somewhere between 2300 and 2400 at 70 MPH is about as slow as you'd want to turn it at highway speed pushing the wind.
I don't know about flatties, but T-5's come in a bunch of different gear ratios. Not only the o/d, but the low gear/intermediate ratios. Might list those, and let the guys who know make a better call.
The s-10 gear boxes had lower 1st gears, while the v8 camaros had 2.95 1st gear. If your not traveling across the country and occasional freeway time, 3.78 for 4.11 would be fine. Some of the World Class t5's had a .63 overdrive.
The old stock Ford Borg-Warner overdrive was a .70 with 4.10 rears and 6.70/15 or 7.10/15 tires. Seems pretty close to your setup.
If you have the stock banjo, you might be limited to 3.54, 3.78, or 4.11. I have a 4.11 '36 ford center, but no axles or bells if your interested.
You really have to pay attention to the first gear ratio as well as rpm in high hear (overdrive), especially since most of your driving will be around town. The 4.11:1 rear will probably mean that you will be shifting to second gear pretty quickly when starting, which can be a pain in city traffic. My old off topic Mustang had 3.73gears, and another had 3.55, and still another had 3.08. The 3.55 was the best compromise, although this was a heavier car with more engine than a flathead powered 37 Ford.
You can always start in second gear if you need/want to.A good friend has a T5 from an S-10 in his flatty powered 40 Ford pickup with 4-11s,loves it! He drives it almost every day and on long trips on the freeways,says it is the BEST thing he ever did for a Flatty powered old Ford,good first gear and Overdrive!!!
Let me say this I had an S-10 with a 5 speed and a banger for a while. it had 4.10:1 gears stock from the factory. On the highway I still had to drop to 4th gear on a hill @ 55. @ 70 it ran fine in 5th gear. a 4.11:1 gear or deeper is what you want with your 21 stud flatty. You need to keep it revving enough to start making torque. None of them make any torque at idle.
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