fuelonempty

Got a 1967 fastback with a ford racing 302 crate engine thats superchaged.

Its a built c4 trans with a ford 9".

Not sure what gears are in it now, but it is way too high. there are alot of highways where I live and need to constantly be at 80mph.. and want the car to be somewhat low revving at that speed. But at the same time dont wanna kill the performance of the car.

So whats a good balance between the two? any suggestions? I was thinking of the 3.55s

Thanks.

cmanf

373 seems to be the choice gear these days. I did 325 on a supercharged 347 and 1st is still pretty much useless with my 5 speed. If you go 411 you may front tires in the air lol.
Check Kieslers site or others for a gear calculator helped me out deciding on mine.
I may go to the 355 range later but this works for now.

noroof66

I have a C4 and have 3.55's, but not much driving on highways. When I do go on highways it is revving pretty good at 70. I would go a lot closer to 3's (3.1) if I had to do more highway driving.

jspagna1

With a C4 I run 3.55's and it's just enough. You go to 3.73's the RPM's will be threw the roof.

Gun Jam

if you need to be at 80 for any given time I would suggest 3.00s

I have a 25" tall rear tire and I was never fond of the 3.00s

IF you tire is 25" Tall it would take 3300 RPM to make 80 MPH with the 3.00s

If you have 3.55s then it would take nearly 4000 RPM to make 80 ( not cool)

Now if you went 3.73 it would take 4100 RPM to make 80


SO I suggest a 3.00

IF you cant stand the thought of running such a high rear end number then your only way to have your cake and eat it too would be an OD transmission like the AOD or switch to a 5 speed of some sort.

-Gun

boogerschnot

I wouldnt go any higher than a 3.25 for the reasons that gun jam stated. But since you so have such a nice motor, why not go with an OD. My 3rd member comes out today for some 4.11's which will only run around 2300rpm at 70 with my AOD.

cfd2bc

Gun is right on. I had a mild 289 with C4 and 373's and I turned around 4000 at 70 mph. Pretty much the same with the new toploader. Luckily I don't have to be on the highway very much The car screams up to speed though.

musnicki

Slightly off topic, but could you post a few pics of your engine bay? I have my shock towers removed and I am looking to stuff a supercharger under my hood too. I just want to know what to buy or how it's all going to fit (around my AC and other things).

Oh and I have a tremec 5 spd with a 3.27 first gear and a .62 5th gear, 3.89 rear end with 25.4ish tires and I do fine on the highway, I think I had it up to 110 on I-95 a few weekends ago and was only hitting 3500rpms.

James

musnicki

Use that link, it was posted on this site a few years back but I think you can find some use out of it. Select "build your own" and put in what gears you're going to use.

http://www.5speedtransmissions.com/gear_calculator.html

LCC

Need to know your wheel diameter to be able to tell you your final rpm at speed. 3:73 and taller are better for OD trans with .65:1 finals. Yours will be 1:1 in 3rd gear, so a lower, 3:27 would be better for the open road but 3:55 would be a bit more fun.