RPM and Gear Ratio's

I'm wondering what kind of rpm and mph I can expect with the rearend gears and tires I have. I'm hoping someone out there can help....Here's what I have.
I'm running a Model A rearend with 3:78's
Coker tires that are 30.5" Tall
A Flathead with a '46 model 3-speed. I'm not sure of the final gear ratio in the trans.
I know Moroso used to have a chart to figure this out but it's not available anymore.
I'm hoping that I can run down the highway OK without winding up the flathead too much. Anybody know?

see if this is what you need http://www.ringpinion.com/Calc_RPM.aspx

Thanks

That's the calcutator that I'm looking for, thanks. The only problem with it is what is the ratio of 3rd gear in my transmission. I was only told that it was a 46 model from a car. Any idea's on how to find that out without pulling the trans apart?

you should be 1:1 in high gear

You'll be right in the ballpark. Most Fords of that era ran 3:78 type gears, some were even 4:11 (generally overdrive 3 speeds though) You are running a tall tire which will bring your final ratio a little higher. The only thing you might run into is if you expect this thing to cruise down the interstate for extended periods over 70 mph. That is why a lot of flathead guys are going to 5 speed transmissions for the overdrive and deep first gear.

Don

Thanks again

Thanks for the final ratio info. I've been told that they all had a 1:1 ratio in high gear. I won't be driving it down the highway for too long, but I wanted to be able to get out there and not get run over. The calcutator showed that it will only be turning 2900 at 70mph. I 've also been corrected on the year of the tranny. It's a '37. It's a top loader and therefore it couldn't be any newer than a '39.