Final Gear Ratio

I am curious on what would be a good final gear ratio for a 65 Mustang Fastback?

Engine
347 Cubic Inches
Roush 200 heads
Comp Cams .230/.230 .528/.528 Solid Cam
Edelbrock Air Gap
750 Cfm Carb
10:1 Compression Ratio

Tranny
4-Speed Toploader

I was thinking either 3:25's or 3:55's. I think the 347 would make enough torque to get the car moving good off the line plus keep the revs down at highway speeds with the 3:25's. The 3:55's would really help the car jump of the line but I am concered that the revs would be to high at highway speeds. I have calculated both ratios using the rpm calulator. The 3.25's at 65 was 2629 and the 3:55's were 2872. Not much differance. What do you guys think is the best choice?

Well...that motor would like you to install at least a 4.11. But since you are worried about RPM on the freeway, go with the 3.25's. If the stick has a fairly low 1st gear it should run OK on the street. 3.55 would be better around town for sure.
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Is it a wide ratio or close ratio? It will make a difference.

IMO, go with 3.55 at the MINIMUM... personally, I would go 4.11's with that motor... but a very good compromise would be 3.89's.

That 347 deserves some gears!!!
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3.73 to 4.11. I wouldn't worry too much about the rpm difference. It will be minimal. I agree, give that 347 some gear.

Between a 3.25 and a 3.55, go with the 3.55. I'm planning to put 4.11 gears in my 'Stang, but I'll have an over-drive tranny. With 1:1 at the tranny tailshaft (4th gear), 3.55 should be plenty. Besides you'll have a tough time keeping the rear tires hooked up in that light car.

My $0.02.

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3.55 if thats the biggest you are willing to go. The more gear, the more you will be thrown back into your seat.

With 'mustang' sized tires, I really liked the 3.25's if I had a lot of highway driving to do. It's a good overall gear ratio to be used behind a trans that has no overdrive. 3.55's really seemed to hold the car back on the freeway.

Sure, if you just want to play around town or go to the races, install a 4.11 or something...

My advice would be to install the 3.25's if you do much highway driving, and start gathering parts to build a 4.11 or 4.30 for track use. Once you have it built, it's really easy to swap em' back and forth. [img]/phpBB/images/smiles/icon_wink.gif[/img]

I use to drive 3hrs to the track with 3.25's, switch to the racing gear once I got there, then switch back for the drive home.

Good Luck!
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