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Discussion Starter #1
Looking for a increase in acceleration (of course) and was wondering if all the expense and trouble would be worth the gear/ third member switch between the two different ratios.

70M1, 351C, toploader.
 

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you will notice a bit of change, even more with 3.70 or 4.10. If you use it as a local cruiser 4.10 would be nice. I don't know if I would invest much for the 3.25/3.55 change. Years ago I drove 4.56 on the street, made all the difference in the world from stoplight to stoplight, but that was in a time and place far far away..
 

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Shelve the toploader and add a T5 - you can have it all - deep reduction in first gear and an overdrive in 5th on the highway. I should think about taking my own advice - my car has a toploader......
 

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I think it would make a noticable difference, but won't be a major difference.

If you don't have OD, I would definitely not go with more than 3.50 gears if you drive your car alot. Anything more and highway driving with 1:1 ratio in 3rd or 4th will keep the RPMs too high.

I have a T5 with 3.50 gears and love it.
 

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I think it would make a noticable difference, but won't be a major difference.
I have to disagree. I find that .30 changes make a VERY noticeable difference especially on a manual tranny.
 

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You will notice a difference from the ratios you are refering to. Obvioucly the bigger the change the more noticable the diff.

With such a small diff in ratio, the question would be is if it is worth the money. If you can do the job yourself, or have a friend that will do it for cheap, its easier to spend the $ and make the jump you are refering to.

If you are asking opinions, I would not do it. I would save the cash, get the 5 speed, and get a set of 4.11's in there. Huge / substantial diff in acceleration, with a about the same highway cruising rpm.
 

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Discussion Starter #8
Now that is an interesting chart. Thank You.

If I can apply it to my application: At 70 mph 3.25 gears are @ 3000 rpm
3.70 gears are @ 3414 rpm

414 rpm increase on the [email protected] 70 mph

Doesn't seem to bad especially if highway driving is not a major part of my driving.

Is there a chart to demonstate possible 0-60 times, 1/4 mile w/ different ratios?

How does one figure out tire size in inches?
 

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Now that is an interesting chart. Thank You.

If I can apply it to my application: At 70 mph 3.25 gears are @ 3000 rpm
3.70 gears are @ 3414 rpm

414 rpm increase on the [email protected] 70 mph

Doesn't seem to bad especially if highway driving is not a major part of my driving.

Is there a chart to demonstate possible 0-60 times, 1/4 mile w/ different ratios?

How does one figure out tire size in inches?
You can find the tire diameter in inches with the "Tire Diameter" calculator on that website. Soon enough you'll be able to input the radial tire size to that RPM table directly. I haven't gotten around to programming that part yet.

Tire Diameter Calculator - CarCalcs.net

In order to calculate 0-60 times I'd need your engine's horsepower and torque curves as inputs. Even then, it would be only a rough approximation.

This website is still in development. I'd appreciate any feedback, suggestions, or criticism.

Good luck with your rear end selection! I plan on going T-5 with a 3.25 rear end behind my 289.

Thanks
-Matt
 

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It is interesting that you mentioned horse power and torque curves. Does anyone have these graphs available for Ford engines from the sixties era? Looking in particular for one for a "J" code 302 68. Going to use a 3.50 with an AOD (using a 3.00 now along with an AOD and it is pretty tall) but had considered a 3.25 as maybe the best option. (the AOD OD ratio is .666), making the final ratio with a 3.50 a 2.33. Anyone running this ?
 

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It is interesting that you mentioned horse power and torque curves. Does anyone have these graphs available for Ford engines from the sixties era? Looking in particular for one for a "J" code 302 68. Going to use a 3.50 with an AOD (using a 3.00 now along with an AOD and it is pretty tall) but had considered a 3.25 as maybe the best option. (the AOD OD ratio is .666), making the final ratio with a 3.50 a 2.33. Anyone running this ?
I struggled for months with what to put in mine (currently 3.00 w/4 speed toploader)...wanted highway drivability and as much stoplight to stoplight power I could get....I was looking at 3.25 or 3.50.....finally I just split the difference and went with 3.40.......hope i made the right choice (for me anyway)..... :)
Tom
 

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Difference in gears is 9%. You could get an idea in your head of how switching gears 9% sooner than you do today. I agree it will be noticable, but unless you are really dialing it in for a specific set-up or purpose or could do it real inexpensively, I wouldnt spend the $ for the change it is making.
 

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Discussion Starter #15
Yea..now I'm thinking 3.70/3.73 :1 . Seems much more $$ to replace entire 3rd member than just the ring & pinion but one can switch back to original if unhappy with the change much easier..
 

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I wouldn't run 3.70s with a non OD transmission, unless the car is never going to leave town.
 

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+1..We have 3.73's in the Yellow Foxbody and it is a blast to drive, but with the T5 highway use is tolerable...if you would drive it in 4th on the freeway it would be turning too high...
Tom
 
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