Rear end ratio change?

[jayh]

I have a Factory Five with 302 EFI with The Trick Flow Twisted Wedge top end kit. Aprox. 360 HP at the flywheel. 290 at the rear wheels.
Thinking about changing rear end gear ratio. Currently 3.27, no trac lok, 7.5 rearend (at least that's whats stamped on the outside of the unit)
Thinking about changing ratio to 3.73 with trac lok.

My question is will I end up with a noticeable and dramatic difference in acceleration. Enough to justify investment?

Thanks for your input

[bobcowan]

It will make a huge change in performance. The car will be much quicker off the line, and much more responsive to throttle input.

Keep in mind what it will do to your top end. If you spend a lot of time cruising on the highway at 80mph, you might not like it.

[Karl Bebout]

Bob is correct about the greatly improved low end. What transmission are you running? I think most 302 combo's probably run the T5 with a 5th gear somewhere around .65:1 and if so, you'll still be loafing along about 2500RPM at 80MPH, depending on tire diameter.

[keezling]

You might consider dumping the 7.5" if that's what you have and getting a complete 8.8" equipped the way you want it. Ford didn't run the 7.5" behind a V8 and neither should you. Search ffcars.com for info on which one will work. Personally I run a narrowed 9" in mine. Have fun! (3.89 is my ratio)

[RICK LAKE]

Jayh Jay the key questions about this are these,
What are you doing with the car? Cruising, Car shows,Drag racing,Autocross, looking to scary the crap out of your self??
What trans is in the car and what gear ratios does it have?
If you are going to be harder on the car, other things are going to pass there safe limit and start breaking. The rearend is a light duty one. The axle shafts are not the strongest either. Depending on tires, wear thread numbers and how soft there are also add stress to the drive train. The weakest thing will break or wear out faster.

Here the thing, IF you are going to keep the car forever, start to upgrade the drivetrain. Add a posi and goto a 8.8 reaend or a custom 9" Either are a good choice. IF you spend the extra money and go 9" you can get other center sections and change the rear gears in about 1 hour from 3.00 for cruising to 4.10 for hauling bacon. 8.8 can be made stronger with adding a rear cover support to it. This applies pressure to the carrier caps and stops the carrier from walking in the case. I use them on all my dana 44 rearends. They are not upto the abuse and torque without support and better parts like axles.

With the OD trans, alot of people goto a 3.73 or 4.10 rearend ratio for quicker acceleration with a posi, ( this is key to) No posi, 1 wheel smoking.

Last thought, leave the car alone and enjoy it as it is. The more speed or power you want the more problems happen over time. IF you sell the car down the road you will never get all the money you spent on it. Adding a better rearend may bring another $200.00 on an $750.00 investment, this is if you do all the wrenching.

I have a 600+ ft torque motor and 510 hp. Have upgraded the trans, and rearend to handle the power. Have now gone to a twin disc clutch assembly to handle the power and stop wearing out the single clutch disc setup. Cost for single setup $350.00, new setup $750+. Faster, yes. Smoking the tires more, yes. Problem is car is getting too quick for my driving skills. I have started to detune the motor and may change to a 3.07 ratio instead of the 3.31 I have now to slow down the car a little. Changing driver inputs also helps. Good luck with your choice. Rick L.
ps side thought, if you are looking for a better driving car, you might want to look at a better suspension setup of handling. IF you want straight line accell, disregard last ps

[vector1]

It will be noticeable, not going to put the world on fire. In the end, you will get used to it, and then be stuck with shifting all the time, whereas with the 3.27 you have more spacing between the gears, which is really a pretty sweet ratio imo. You just don't have the power with the 306.

[twin turbo]

If indeed that is a 7.5 rearend, I wouldn't put one penny in it. Either leave it alone or upgrade the rearend. Regarding the ratio change, the car will be peppier when comparing how it feels in each gear, but you'll be shifting sooner. Depending upon your current 1st gear ratio, 1st gear may become too short to be much fun.

[D-CEL]

At least 4.10!
Maybe 4.30
Yes swap in a 8.8,! inexpensive, available and capable

Jason

[xb-60]

Jayh,

If you go to a 3.73:1 (or lower) rear end, you might find that the overall gearing in first and second gears is way too low, resulting in lots of wheel spin and plenty of gear changes. I would think that something around 3.5:1 would be as low as you should go.
Other than that advice, I would recommend reading Rick's post thoroughly.

Cheers,
Glen

[jayh]

Thanks for all the input. Thats what I like about the forum.....it's a great source for solid information from owners that have hands on experience. Thanks to all!

[joyridin']

I would ditch the 7.5 in just about all cases. Go with the 3.70 rear gear and you will love the way it runs. You should see about 2100-2200 RPM's at about 70 mph assuming you have about a .65 5th gear.