Gear Ratio Selection
Thread Starter
Intermediate
Joined: Feb 2018
Posts: 33
Likes: 1
From: Cumberland Maine
Gear Ratio Selection
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
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
Safety Car
Joined: Oct 2004
Posts: 3,926
Likes: 739
From: Youngstown Ohio
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.
Tech Contributor
Joined: Aug 1999
Posts: 15,175
Likes: 3,987
From: Connecticut, USA
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.
Safety Car
Joined: Oct 2007
Posts: 4,222
Likes: 1,080
From: South Florida
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.
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.
Parts Sherpa
Joined: Feb 2017
Posts: 520
Likes: 98
From: ICE boneyard, Pa
Team Owner
Joined: Jan 2006
Posts: 37,637
Likes: 3,118
From: Crossville TN
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.)
(I consider 'comfortable' to be 2500 rpm's (or lower) at 70 mph.)
Safety Car
Joined: Oct 2007
Posts: 4,222
Likes: 1,080
From: South Florida
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.
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Le Mans Master
Joined: Oct 2007
Posts: 7,453
Likes: 976
From: RI, Now Franklin/Nashville TN
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......
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......
Last edited by jb78L-82; May 7, 2018 at 07:47 AM.
Safety Car
Joined: Oct 2007
Posts: 4,222
Likes: 1,080
From: South Florida
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.
Le Mans Master
Joined: Oct 2007
Posts: 7,453
Likes: 976
From: RI, Now Franklin/Nashville TN
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.
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.
Drifting
Joined: Feb 2007
Posts: 1,498
Likes: 206
From: Pearland Texas
St. Jude Donor '09
ratios
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!!
Drifting
Joined: Jun 2012
Posts: 1,990
Likes: 183
From: Port St. Lucie Fl
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.
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.
Pro
Joined: May 2016
Posts: 708
Likes: 150
From: Minnesota
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...
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...
Last edited by JoeMinnesota; May 7, 2018 at 05:53 PM.
Thread Starter
Intermediate
Joined: Feb 2018
Posts: 33
Likes: 1
From: Cumberland Maine
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...
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...
Race Director
Joined: Mar 2016
Posts: 14,402
Likes: 8,209
From: Napa Valley California
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.
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.
Last edited by OldCarBum; May 9, 2018 at 06:16 PM.
Pro
Joined: May 2016
Posts: 708
Likes: 150
From: Minnesota
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.
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.
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.
Last edited by JoeMinnesota; May 10, 2018 at 09:41 PM.