I have a mild 350 in my Chevelle. Performer intake and cam, headers, big carb, and maybe roller rocker arms soon. Right now I have a turbo 350 with 2.73 gears out back. graemlins/angry.gif My tires are short at only 24" tall and it helps with lowering gears. I just recieved a free turbo 700 from work. graemlins/hurray.gif I need to know what gear to run to keep the highway rpms a little lower than the 350 with 2.73s but still accelerate good. I was thinking going with 3.31 or 3.42 and my turbo 700. This should be killer take off with short tires, low first gear and good rear end. What do you guys think? :confused:

Also has anyone ever rebuilt a 700r4. I am a 18 year old mechanic with one year experience. Could I do it or should I take it somewhere here in Northwestern PA. Thanks guys.

im in central jersey, right over the river from EAston PA, near allentown, drop me an AIM at dragracer6900 and we'll chat bout it if youd like

mike

This is weird...I did NOT write this reply and I don't live anywhere near NJ as can be seen in the bottom line. Must have something to do with election politics..............

I have 3.08 gears with my 700 and 295/50/15 tires

I can run really well on the highway and with any more low end I'd have bad traction issues. I'm already trying to spin through first and getting wheelhop.

If you can get some 3.31 those would be good, I think someone said up to 3.55 are still great. But you might want to see how you like the 700 before doing a gear swap.

With my 3.08 and 700 I'm seeing over 20 MPG with my 350.

350 30 over
stock heads ported heavily
hyper. pistons
comp 268-h .454 lift
edelbrock performer intake
holley 650 spreadbore
HEI ign. supercoil and perf cap and rotor
MSD 8.5 mm superconductor wires
headers 2 1/4 exhaust

I think your overall gear ratio (2.73:1) would lie somewhere between using the 700r4 w/ 3.73s and 4.11s. If I recall correctly, the OD gear is .7:1 on that tranny, so 3.73 X .7 = 2.61 and the 4.11=2.87, the optimum rear would be a 3.90 gear to maintain 2.73 overall, so anything under 3.90 will be a better overall rear ratio than your current set up.

3.55=2.485
3.36=2.352
3.08=2.156

Are the trans gear ratio's the same between a 700r4 versus a TH350? That would be the starting point. Also, consider getting some taller tires. You might not want to right now. But someday you probably will end up purchasing a set of tires that are 26" tall or more, so take that into account when choosing the rear end gear. Easier to change tire size that rearend gear. (IMO) In my opinion.

TH350
2.52
1.52
1.00

TH700-R4
3.06
1.62
1.00
0.70

http://www.2quicknovas.com/tranny.html

Thanks for the replys. Is it possible for me to rebuid this tranny myself? :confused:

The decision is how fast do you cruise on the highway, and how many rpm do you want your engine to run at that speed. This can all be worked out mathematically with tire dia. and gears.

I have a 67 Chevelle with the 700R4, aprox. 310 HP 350. Tires 245x60x15. Gears 3.31 I am at 2100 RPM at 70 mph and get 19 mpg.

Another consideration is the shifter. I used a B&M hammer because it is made for a 4 speed but was a pain to install. A hot rod builder that I know always snags a steering column from an 80's Caprice or equivalent and replaces the column and wheel when using the 700 because it was made for 4 speed cable shifting. It also give a cruise control feature.

You will love the OD gear. Good luck.

Most folks feel that 3.42s are optimal for street use with a 700R4. Depends is you have an ET goal or not. If not 3.42, if so you can use up to 4.10. I'd go 3.7-3.9 for strip use.

( can't buy 3.31 gearsets for 12 bolts btw, 3.42 is closest).

the math is straight forward, 2.73 = .70X (x), where X = 3.857, Anything less than 3.90s will give you lower highway revs.
Don't bother with roller rockers unless you put a big ( .550") cam in there.

SS wannabe, love the username, being an ex SF wannbe myself. ;)