3.55 too much?

[speedy66]

Ok heres the set up.. Roller 306. B cam. Ported E-7s. 1.6 proform roller rockers. Tri Y headers. Weiand intake. edelbrockk 600 carb. 110 gph holley fuel pump.2500 tci stall converter on a C4. rear tires are 275/60/R15.

Would going with 3.55 gears be too much? This car is a daily driver, sees a little freeway use. Im trying to decide between 3.55 and 3.27s.

 

[FIRE14142002]

.55's may be borderline. depends on how much highway use yours will see. I've got 3.70 and like them but not for much, if any, highway use

 

[SadbutTrue]

3.55s will work.

My question is how hard is it to get those 275 tires under a 66 and how do they look?

 

[12sec67]

3.55 will be great for all around performance and cruising. freeway won't be that bad-take a look a the rpm vs mph calculators on smokemup.com

 

[speedy66]

3.55s will work.

My question is how hard is it to get those 275 tires under a 66 and how do they look?

Not too bad to get back there.. had to roll the fender lips.. and do a little work on the inner fender back there.. With out airshocks or the back lifted a little.. I would rub when I hit a bump.. but I had 275/50/r15s before and those are fine.. I love the look with these tires back there

 

[65fastback]

The tires will change your gear ratio because of the size of them, but you should be O.K. just watch yourself on the freeway that your RPM`s don,t creep up on you. Those 3.55`s would be great with a 4 speed or even 3.73`s with 4 speed would be ideal. I have 3.25`s in my 65 fastback C-4 and I have 215/60r/14`s on my car and it spins the little 289 at just under 4K at 60MPH.

 

[tylers65]

289, C4, 235/45/ZR17, 3.55 and turn 3000 RPM at 61MPH. This is dyno proven RPM to speed ratio. And it is what I run.

 

[SuperDave]

As in most things in life, you are facing a compromise. 3.55's will give you more scoot but they will wear on you on the road especially if you have loud exhausts. Your mileage will suffer as well. A time-honored maxim would be "if you wanna play, you gotta pay".

My truck has 3.55's with 265x16's and a EAOD. It is a great tow vehicle for my travel trailer and in the woods but I wouldn't want it as a DD.

 

[gp001]

Ok heres the set up.. Roller 306. B cam. Ported E-7s. 1.6 proform roller rockers. Tri Y headers. Weiand intake. edelbrockk 600 carb. 110 gph holley fuel pump.2500 tci stall converter on a C4. rear tires are 275/60/R15.

Would going with 3.55 gears be too much? This car is a daily driver, sees a little freeway use. Im trying to decide between 3.55 and 3.27s.

Here are a couple charts you can compare

http://www.2mfffabshop.com/gr/c4_355_2756015.htm

http://www.2mfffabshop.com/gr/c4_327_2756015.htm

 

[jesserose17]

I have 3.25`s in my 65 fastback C-4 and I have 215/60r/14`s on my car and it spins the little 289 at just under 4K at 60MPH.

Sounds like pretty excessive RPM even with 3.25. If that's true, your C-4 must be slipping badly.

I have 3.25's in my 68 coupe, with toploader - 235/60R15 and my 289 spins 2500 at 60mph.

 

[GaPonyFarm]

Ok heres the set up.. Roller 306. B cam. Ported E-7s. 1.6 proform roller rockers. Tri Y headers. Weiand intake. edelbrockk 600 carb. 110 gph holley fuel pump.2500 tci stall converter on a C4. rear tires are 275/60/R15.

Would going with 3.55 gears be too much? This car is a daily driver, sees a little freeway use. Im trying to decide between 3.55 and 3.27s.

The 3.55 gears will have you running at around 3000 rpms at 70mph. Thats what mine do, anyway. I added the gear venders under/overdive to deal with that...

I'm concerned about the tires. My T/A Radial 245/60/15s barely fit. You better get either an 8.8" or 9" rearend with 31 spline axles too. I snapped my 28s like they were toothpicks... we have very similar setups.

 

[GaPonyFarm]

Sounds like pretty excessive RPM even with 3.25. If that's true, your C-4 must be slipping badly.

I have 3.25's in my 68 coupe, with toploader - 235/60R15 and my 289 spins 2500 at 60mph.

He's running 14 inch tires... but he should still be around 3000 or so.

 

[65fastback]

Quote:
Originally Posted by 65fastback
I have 3.25`s in my 65 fastback C-4 and I have 215/60r/14`s on my car and it spins the little 289 at just under 4K at 60MPH.






Quote:
Originally Posted by jesserose17
Sounds like pretty excessive RPM even with 3.25. If that's true, your C-4 must be slipping badly.

I have 3.25's in my 68 coupe, with toploader - 235/60R15 and my 289 spins 2500 at 60mph.

He's running 14 inch tires... but he should still be around 3000 or so.

The 215/60/14`s are what is causing my RPM`s to stay up, the lower profile 215 - 14 inch tires are the culprit. My tranny is not slipping at all, totally rebuilt with a transgo shift kit. My actual RPM`s are 3795 at 60MPH.

 

[speedy66]

I'm concerned about the tires. My T/A Radial 245/60/15s barely fit. You better get either an 8.8" or 9" rearend with 31 spline axles too. I snapped my 28s like they were toothpicks... we have very similar setups.

Tires have been on the car for about 1 year.. they fit snug but are awesome.. I will post pics tomorrow.. also depends on what backspacing you are using..mine are I think 5" or 4.5" they sit in there nice. I spent 6 hours with the guys at the tire shop finding the biggest size That would fit back there.. 295s were right at the quater panel lip and would have hit..

 

[mp67]

3.55s will work.

My question is how hard is it to get those 275 tires under a 66 and how do they look?

I have the same size on my 67 fastback without any problems, and they look good. I lowered my car some so they tuck under just a bit. I don't know how they would fit on a 66 though, cause I don't know if the wells are the same or not.

 

[speedy66]

Heres the 27/60/r15s

 

[speedy66]

and the last two pics

 

[jcp123]

Sounds like pretty excessive RPM even with 3.25. If that's true, your C-4 must be slipping badly.

I have 3.25's in my 68 coupe, with toploader - 235/60R15 and my 289 spins 2500 at 60mph.

what kind of mpg do you get? i've been looking into a set for my '68 daily driver with a C4...


and i think 3.55's will try your patience, especially with a c4. i would go with 3.25's; there are also some other gearsets out there, i've seen 3.31's and a few others between 3.25 and 3.5 for 9" axles

 

[bswor]

So which have you decided to go with? I'm considering 3.25s and 3.50's myself. I have 16" rims , i'll have to check the tire size again so what are the recommendations?

 

[speedy66]

I think I may go with something like 3.25s or along those lines