gear ratio for 30 model a?

hi everyone I know this topic has been beaten to death but i was wondering about the gear ratios for my model a it is powered by a sbc and will have a mild cam, a turbo 350 with shift kit, and my rear is a ford 28 spline 9 inch with nothing inside of the pumpkin.
ive been looking for 3rd members and i found one at a decent price, its gear ratio is 3.70 and has posi. will this be a decent gear for me such as freeway speeds and in town driving? not sure if this matters but im running 750 rear 600 front sized firestone super deluxe tires.

Thank you in advance.
the noob Lou.

 

Define highway speed in Nor Cal? 370 with a non lock up TH350 will be buzzing at 60-65...eating gas. Even a 4 speed stick would be a bit revved, the converter slip on an AT will make it seem worse.

 

ah ok, so what gearing should i be looking for? 3.50?
people drive about 80mph here in nor cal it gets pretty scary sometimes haha

 

I'm in the same situation, I have almost the exact same setup but I have a mutha thumper cam and a 4 speed. I have a trac lok to install but before I pay to put it together I want to get the right gear. I don't mean to steal the thread but I'm interested as well

 

get a quickchange. You should google search richmond gear calculator and play around with it. I would think anything numerically lower than a 3.08 wont be fun at slow speeds.

 

Without an AOD or T-5, you will need to get the final drive down to 3:25 or lower numerically, IMO, to get the engine RPM down to a noise level thats acceptable with some gas savings. I have a 3:55 with a T-5 in my A and I'm under 2000 RPM at 70 in 5th gear. I guess you need to decide where you will drive most, and if its the Interstate, you'll want the final drive ratio in the 3:00 to 3:25 range, maybe even lower (numercally). But, that ratio may not be what you want for in-town driving if you have a tendancy to enjoy those "jack rabbit" starts those darn hot rodders are known for. LOL

 

navy painter, no worries if we can get both answers in one thread i consider it a great success

junk yard kid, ill google it right now thank you

 

thank you boutlaw

 

so like a 3.50 gear would be a happy medium then?

 

Best to get on a online RPM calculator site. Your 750s should be about 31", maybe a bit less...those help some. I still think with those very high speeds and the TH350, it still needs to go lower number than 3.5. It's a light car, it can handle it.

I had a heavy one; 400 sbc, TH350 2.76, and it either needed a bit lower number at 75 mph, or what I really wanted was a TH350C with lockup convertor. Being heavy, it was not a tire burner with that gear.

 

i tried the calculator but for what speed should i put it at? i set mine for 65 and my rpms come back as 2389 rpm, 3.50 gear with 32 inch tire which is what i measured my firestones to be.

 

going to bump for possibly more info, so far thank you to everyone who has chimed in

 

I think that would be a good set up. 3:50 gear would give you good power for fun and even at highway speed would put your rpms in a good cruising range.

 

thank you rich

 

I think that tire it between 28 and 30 inches tall. I recommend something within a little bit of 3.00:1. I ran my roadster with that setup a long time, and it worked great.

 

Re-read the later posts. With a 32 inch tire, shoot for a gear around 3.25 or so.

 

thank you animal

 

I have a about the same setup I put in a 3.08 posi unit. Just drove the car yesterday 2000rpm at 55 29'' tall tire. I think I'm going to like it.

 

Rule of thumb: If the tire diameter and the gear ratio are the same (3.00 and 30 inches, for example), you will get almost exactly 2000 rpm at 60 mph, 3000 rpm at 90 mph.

 

sweet, thanks for the info. now i need to start looking for 3rd members which hasnt been easy so far