3.55 too much?

speedy66 · Jan 12, 2004

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 · Jan 12, 2004

.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 · Jan 12, 2004

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 · Jan 12, 2004

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 · Jan 13, 2004

SadbutTrue said:
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 · Jan 13, 2004

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 · Jan 13, 2004

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 · Jan 13, 2004

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 · Jan 13, 2004

speedy66 said:
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 · Jan 13, 2004

65fastback said:
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 · Jan 13, 2004

speedy66 said:
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 · Jan 13, 2004

jesserose17 said:
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 · Jan 14, 2004

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.

GaPonyFarm said:
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 · Jan 14, 2004

GaPonyFarm said:
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 · Jan 14, 2004

SadbutTrue said:
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 · Jan 17, 2004

Heres the 27/60/r15s

speedy66 · Jan 17, 2004

and the last two pics

jcp123 · Jan 17, 2004

jesserose17 said:
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 · Jan 18, 2004

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 · Jan 18, 2004

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

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