Thnksdad

Hi All,

Did the old gear ration check and came up with 4.10 gears in my newly acquired 1970 Corvette. I am thinking of swapping those out for 3.70 to allow for a better highway ride. Any one have any input on that?

Thanks

Derek

C3 Stroker

For a better highway ride and still have some performance, I'd go with 3.55s. If you want more highway cruising pleasure, go with 3.08. The 3.70 isn't enough change from 4.10 to warrant a change for highway IMO.

GTR1999

If you truly have Gm 411's then you will have a 4 series posi case. Changing to a 3 series gear will require a 3 series posi case as well. GM obsoleted them several years ago but there may still be some around. I bought a lot of them at the time. If you can't find a NOS case or good used one, you can buy the new aftermarket loaded cases but I don't care for those too much.

Kingtal0n

Use an online gear calculator to find optimal ratio.

take use into account. If you were 1/4 mile car only for example you would find top speed at max rpm in final non-overdrive gear and use the perfect ratio to get you there.

For daily drivers, economy cars, and for reducing wear-and-tear on an engine by reducing cruise RPM, you would go numerically lower. Much lower than what you might want for a 1/4 mile car. If your trans has overdrive I might shoot for 3.50:1 on the rear with a 26" tall tire in a 400-450rwhp car for some decent fuel mileage and powerband. However if you are stuck with 1:1 final gear (no overdrive) then you would want 2.7 or 3.2 ish for economy, longevity.

EarlyC34me

Keep the 4.11's. Drive the back roads

7T1vette

You won't get a "comfortable" highway ride with anything steeper than a 3.23 rear end ratio...unless you install an overdrive transmission. If you do install an O/D unit, you could stay with a 3.70 or less rear gear.

(I consider 'comfortable' to be 2500 rpm's (or lower) at 70 mph.)

Kingtal0n

yeah high RPM is not good for extended period of time. 4-cylinders seem to be okay at 3k but a V8 just weighs too much, you can lose more fuel turning the V8 than actually pushing the car.

7T1vette

Exactly. That's why many folks gain 15-20% on fuel mileage when they swap-in an O/D transmission (for highway driving).

bjankuski

What rpm do you want at what speed? I would suggest 3.50 is ratio, but need to know your expectations.

derekderek

Look up launch ratios too. You want about 10 to 1 for a strip car and around 9 to 1 for a road car.

jb78L-82

3.08 or 3.23's will get you a significant drop with a 1:1 final drive.

As someone mentioned, any big V8 can handle just about any rear gear but the choice will have an effect on acceleration. High numerical gears are much more crucial for 4 cylinders or small V6's to a lesser extent since these engines have low torque, especially at low RPM.

I had a mid 70's Chevy 307 V8 with 120 Net HP with a turbo 350 automatic and 3.08 gears. The car was a slug but moved just fine with the V8 low RPM torque, automatic, and 3.08 gears...X2 if the car is a manual which has much more latitude to control RPM's to overcome just about any gear ratio.

My mom's 72 Caprice had a 400 V8 with 170 Net HP, automatic, 3.08 gears, 4,200 lbs....zero driveability issues....NONE. This constant drone that any big V8 will not work properly with low numerical gears in most cases is not true, especially with a manual trans. Higher numerical gears will optimize acceleration but with many downsides as well......

Kingtal0n

Well, even with O/D sometimes its too much rear gear. For example I put a 4l80e which has .75:1 Overdrive, and a 3.70 rear gear. Its still too much. 65mph at 2700rpm? I think 75 near 3k ish. thats crazy high still. 26" tall car tire stuff. So I am dropping to 3.3 next month.

jb78L-82

A 3.70 rear gear with a .64 OD is probably about the best you can hope for with a 5 speed. A .50 6th gear would be really nice as well with a 3.70 rear. 3.36's with a .75 OD should be really fine............in my opinion.

My 10C6Z06 with 505 Net HP and 3.42/.50 6th gear is 1,800 RPM at 80 MPH...........love it....28 MPG at 80 MPH....who would have thought that was ever possible 30 years ago.

GTR1999

Jeff is correct, I would say 90% of the diff's I build for OT trans are 373 Tom's gears.

redcruz1120

Thanks guys!! Love leaning something new before my next project! don't exactly know my gear ratio but I will be looking for highway cruise for this next winter project!!

Kacyc3

Swap in a 5 speed manual here is why.

od lowers highway rpm, allows you to keep the current fun factor

700r4 - has like a 3.06 1st gear and with 410s makes first gear useless for everything other than burnouts. Its difficult to find someone that can build them to tolerate some abuse and its usually not cheap.

200-4r - not as strong as 700r4 stock and require lots of upgrades to handle power so not cheap.

4l80e - reasonable price, strength and rebuild cost but they are heavy, big and you need a computer to controller unless you have it converted to manual valve body guessing not cheap either.

Gear vendors - not sure it will fit under a vette, not cheap either.

JoeMinnesota

It's all personal preference. Just remember that you will give up SIGNIFICANT snappiness from a standing start if you are running a small block, mild motor or something with lower torque. Also depends on your trans - are you manual or automatic?

With a 355ci motor, the 3.36's weren't enough for me and didn't let the motor cruise up in the sweet spot RPM (2500-3000) so I re-geared to 3.73 over the winter. I am running the original wide ratio Muncie. It's still very good on the highway and has picked some up on the bottom, so the 3.73 was a good change. I have run 4:10's in the past on a 60's Camaro with Muncie, and it was a beast but I did want another gear on the highway. There is a compromise whichever way you go.

...Oh, and NOT as cheap as changing gears in the old GM 12-bolts, so choose carefully...

Thnksdad

I am running a M22 4 spd currently with a 350 Lt1 motor 11:1 comp with long tubes and free flowing mufflers! I am really questioning myself now to just leave the gears be!! I tested the gear ration by marking the tire and the drive shaft and the drive shaft spun 4 time to 1 full rotation of the tire.

OldCarBum

I'm currently running a 454, TH-400 and 3.36 rear end gears.
At 70 mph I'm turning about 3000 rpm, which in my opinion is way to high.
I'm stroking my 454 to 496, swapping my TH-400 for a TKO-600 close ratio (.82 final drive) and going to 3.08 rear gears.
First and second in the 5 speed are lower ratios than the TH-400 so off the line performance won't suffer with the 3.08's and I'll be cruising at 2100 rpm at 70 mph on the highway.
One other thing to consider is the operating range of your camshaft. Mine is 2000-6000 rpm, so my cruising rpm of 2100 is right where I should be.

JoeMinnesota

That rpm may seem high with your 454, but with a mid size roller cam in a 355, mine is really happy at 2750 rpm when cruising 60. At 55 I am about 2500 rpm and it sounds relaxed but anything much lower and it borderline lugging if you want to step on it without downshifting. The SB's like to hum. . You have a lot more torque at the lower rpm's. Some days I'd like to have a BB.

I think thnksdad would really see a (negative) loss at the bottom end going to 3.36 or less gear. 3.55 or 3.73 would be ideal, but no small investment with change in carriers etc.

Thnksdad - drive that badboy in the right lane at 55-60 and enjoy the snappy low end around town. Now I know why guys want O.D. For best all-around. I totally understand.