Bob3700

I have had 308, 355 and now 370 final drives in my street BB. I have to tell you that with a Muncie or Borg 4 speed, 370 is too much if you intent to drive on the highway at all. Way too many RPMs for cruising. Around town, no sweat, you are the red light bandit.

My vote at this time would be either the 355 or the 336. In fact the 336 might just be the best compromise between acceleration and highway cruising. Now if there is a 5 speed in your future, 370s are the bomb!

Bob

JustinD

I have 4.10's not good for highway great for "extreme acceleration" I would do 3.55's.

Drew Papsun

Hello Tom,
The real question is what RPM and MPH are to the rear axle.
The 3.55 axle 3,000 RPM = 65 MPH
The 3.70 axle 3,000 RPM = 60 MPH
The difference is close but the 3.70 will give you a faster pick up to speed.
Regards,
Drew Papsun

stinger12

Like I said, decide what kind of transmission you eventually want to go with, then choose your gear ratio based on that. If you don't like the RPMs created by the new gears and old tranny, well then you have an excuse to get yourself that new tranny

BKbroiler

Yea, 5 tenths. At that time I was doing 13.9 best. After the gear change best times were 13.4s. Then I put headers on and better mufflers and looser converter and got to 12.90. ETs are erratic though due to varying wheelspin, with street tires.

ngroat7007

im glad i came across this thread i have been debating the same thing for my 82. After reading this thread ive been looking into the ford t5 and saw many of them cheap on ebay.

highest buy it now was about 750 brand new
http://cgi.ebay.com/ebaymotors/Ford-...em160217293446
and lowest was 300 out of a nissan?
anyway since your doing the same conversion what else would we need to fully convert from auto to manual?
sorry for jacking the thread but i know some people can use this info and the thread already answered most of my questions

wallifishrmn

Maybe I am calculating this wrong. Isn't FOURTH gear 1:1? If that is true then a car with 16 inch tires at 65mph with a 3.55 rear end would have 2400 rpms and same with 3.70 would be 2600 rpms. Did I calculate worng?

blckslvr79

pete.513

I'm going from 3.08 to 3.73. The Differential housing is the same on the C3 's right? I was told by someone its different, or that something was different and I could not put 3.73 in the Differential that had the 3.08. Also should I go with 3.73 or 3.70? Any help would be greatly appreciated!!!!

76strokervette

You can run the 3.70 or 3.73 on your carrier just make sure the gears are for a corvette. I have a new set of motive performance 3.70 gears I am not going to use if you are interested send pm.I also have polished carrier I am not using due to 12 bolt upgrade.

OldCarBum

I've got my TH400 with 3.36 gears. Around town drive ability is really good, however I'm turning 3071 RPM at 70 MPH on the highway. Swapping out my TH400 to a 200-4R will improve the acceleration around town because the gearing on 1st and 2nd gears on the 200-4R are slightly lower than the TH400. 3rd gear is the same for both transmissions and 4th on the 200-4R is .67 which will drop my rpm at 70 mph to 2057. 3.55 gears would put me at 2174 rpm at 70 and 3.73 gears would put me at 2284 at 70. I see that any of the gear choices would be great all around depending on what you plan to use the car for. Plan and do the gear swapping once to save $$$$. Enjoy...

terrys6t8roadster

I have 3.73s in the 6t8 with a TKO. I'm thinking of changing to the 3.55 for a couple of reasons.
First, it wont go over 145 MPH in fourth gear, didn't make any difference shifting into 5th, lack of engine power. Seems as if I need more than 411RWHP. {bucket list: exceed 160MPH].
Second, to reduce the excessive wheel spin. As you mentioned you wanted the feel of getting pushed out the back of the car under acceleration and you don't get that when your wheels are spinning. T

c3_dk

This thread startet back in 2008

jb78L-82

Maybe it did start in 2008, but the comments may be helpful to others with this question.

IMO, if you have a 3 speed auto or 4 speed with a final gear of 1:1, there is VERY little difference in day to day driving between a 3.55 and a 3.70, both are great for around town driving and neither is well suited to modern highway driving unless you drive on the highway at 55 mph. Where I live in New England the normal highway speeds are 70-80 MPH! My 78 with a 4 speed and 3.70 gears is totally unsuited for those speeds.....Back in 78 when I was in high school, a buddy's dad had a brand new silver anniversary L-82/auto (3.55 gear) and that car had the same highway issues as my L-82 4 speed 3.70 but was not as fast nor nearly as much fun as my car is even today...

If you are not going with an OD tranny some time in the future (I would love to but have a hard time justifying a 5/6 speed which are ridiculously priced for a car not driven much), the 3.36 gear is the perfect all around gear, NOT the 3.55. If you have a 400-500 GROSS HP SBC or a BB with decent power, I would go so far to prefer a 3.08 gear since you will not need revs to make big power..........

Torqued Off

So? Has the technical information changed?

gkull

you just need better rear tires. I have had OD transmi

gkull

you just need better rear tires. I have had OD trannies since the 80s in my vette. I spent a lot of time on tire diameter and gearing calculators I figured out that to be at max hp at my target speed required a 4.11 rear end

terrys6t8roadster

Thanks gKull I needed that. LOL I've gone through 4 pairs of rears to 1 set of fronts. T

fishslayer143

If your goal is to eventually go to OD trans, I would go 3.73... My 81 started with factory 2.87... a joke with 185HP .. I went to 3.31 and it helped somewhat.. I then went to 525HP and 700r4 .. 3.31 was just too low in OD .. I yanked it out, went to 3.73 and it was perfect.. very strong, and with a 26 inch tire, I m only turning 2550 RPM at 80 MILES PER HOUR ..and I get 18-19 mpg hiway

jb78L-82

Wow...sounds great!

I think with an auto, the 3.70 is probably spot on. With 525 HP with a 5/6 speed, if it was me, I would aim for 1,800-2,200 RPM @ 80 mph and some on the forum have achieved 25+ MPG.....