Ratio help

[Jerry M]

I am building a 388 stroker and will use a 700r4 automatic transmission. We are looking at different final drive gears. Originally we thought 3.42 would be great until we found it the overdrive would struggle hard and wouldn’t be able to use the lockup until like 85+ mph. We have found a 4.11 local and want to know if that option would be better. Or just what is the good ratio?

 

[Gary S]

A properly set up 700R4 can lock up below 50mph with gears like 3.42. I've owned a number of Caprices with 700R4 trannys and 2.56 gears. The tranny locked up at 50 mph with even those high gears.

 

[dale68z]

My 68 camaro has 3.23 and a 700 r4. This was a very common combo for caprice cop cars in the 80's. My 72 elcamino had 3.08 and 700r4, it was fine, but IMO could have used more gear. 3.42 is a sweet gear with a 700.

 

[biker]

My 1990 cop car has a 700r4 and 3.42. It is a semi gutless TBI 350, but the TH700 and 3.42 gear makes it rip. Very nice combo.

 

[ULTM8Z]

Agreed on the 3.42 / 700. Perfect combo.

Mild 350 build and no trouble accelerating in OD.

 

[CorkyE]

I have a 3.73 with 700R4, will likely change to 3.42 in the future. What is leading you to believe that you can't lock up until 85mph?

 

[ULTM8Z]

4.11 axle rationwith the 3.06 first gear is going to be a little steep IMO. 3.73 is probably about the lowest I would go.

But for a torquey engine like a 383, 3.42 would be plenty.

 

[ssupercoolss]

mild 350 with a 2004r and 3.42. 26" tire in the Camaro. really great combo. My Monte has a tired 400, 2004r and 3.08's. its great on the highway, which is like 80% of the time, but some more gear would really be a lot more fun around town.

 

[Skip Fix]

My 92 1/2 ton Pickup had a 700 and a 3.42. My current 97 has the electronic version and a 3.42. The 2015 with a 6.2 and 8 speed hauls good but the freaking computer is hunting for gears and the throttle lag is terrible.