Rear End Gears - Chevelle Tech
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  #1  
Old Mar 24th, 08, 7:49 PM
harley02571 harley02571 is offline
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Default Rear End Gears

I have a 70 Chevelle with a 468 that is pushing 540 horse with a built turbo 350 and 275/60/15 rear tires and 3:73 gears. My tach isn't working but at 65 to 70 mph the engine is reving too high. What gears would give me around town balls and cut down revs on the highway?
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  #2  
Old Mar 24th, 08, 8:29 PM
Mstehle Mstehle is offline
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Default Re: Rear End Gears

Harley:

Here is a link to a calculator that you can put in different gears and tire sizes and choose your RPM's http://www.f-body.org/gears/ At 70 MPH you should be turning around 3100 RPM's with your current set up. Maybe sounds high to oyur ear but should not be a problem for a well built motor. A little tough on gas though. Maybe consider a 2004r OD transmission if you do a lot of cruising? It will save a lot of $$ on go juice and give you the best of both worlds with 3.73 rear gears. Fourth gear is .67.
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  #3  
Old Mar 24th, 08, 10:46 PM
dpvoiceguy dpvoiceguy is offline
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Default Re: Rear End Gears

Quote:
Originally Posted by harley02571 View Post
I have a 70 Chevelle with a 468 that is pushing 540 horse with a built turbo 350 and 275/60/15 rear tires and 3:73 gears. My tach isn't working but at 65 to 70 mph the engine is reving too high. What gears would give me around town balls and cut down revs on the highway?
By "built TH350", do you mean it's a high stall converter? I have not seen a calculator that factors this in but I once met a driveline guru that broke this all down for me and took into account the gears, tires, converter, etc. He lost me about 5 minutes into the conversation but it seemed clear that this could play a part in the final rpms. My small block with a TH350, 3500 stall, 4:10 rear and 275/60-15s turns about 3500 at 65 mph. It's darn near annoying on the highway but has plenty of "around town balls". If I had the $ I would knock the rear down to 3:55 and start doing some highway cruising.
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  #4  
Old Mar 24th, 08, 11:01 PM
65lkey 65lkey is offline
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Default Re: Rear End Gears

overall consensus is a 3:55 gear set is the best for around town balls and highway driving.
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  #5  
Old Mar 24th, 08, 11:40 PM
eric13617 eric13617 is offline
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Default Re: Rear End Gears

Harley,what size is your cam and what does your converter stall at? 3.73 gears are not that deep.
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  #6  
Old Mar 24th, 08, 11:48 PM
72chevelle_muscle 72chevelle_muscle is offline
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Default Re: Rear End Gears

I'd say go with an overdrive, I have 3.55 gears in my car and use to hate it when all I had was 3 gears, it was way to loud and annoying. I got my 700R4 and annoyance gone and still plenty of power for around town.
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  #7  
Old Mar 24th, 08, 11:54 PM
BlueSS454 BlueSS454 is offline
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Default Re: Rear End Gears

I still don't understand why everyone in so concerned about an engine running in the 3000-3400 RPM range for any given amount of time. I run my 70 that has a healthy 454/TH400 and 3.73's up and down the I-95 corridor from Delaware to Southern Maryland on many occasions, never had a lick of trouble. The car used to have 4.10's in it when I first built it. I used to make the same runs with the 4.10's running in the 3500-3800, no problems and it got on average 12 MPG, not bad for a 454 and 4.10's. The longest drive I ever did with the 4.10 gears was from Worcester, Mass back home to South Jersey. It ran flawless while maintaining 70-75 MPH anywhere from 3400-3600 RPM's.
The way the car is setup now with the 3.73's, 275 60 15's, and a 2200 stall converter, it runs 65 MPG at 3000 RPM's.
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  #8  
Old Mar 25th, 08, 1:54 AM
BillyGman BillyGman is online now
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Default Re: Rear End Gears

I agree with most of what's been stated here so far. I had an old vette that i drove to work 2-3 days out of each week for 8 months out of the year for 6 years, and with a 26" tall rear tire, 3.73 gears, and a 4 speed manual trans (1:1 4th gear...no overdrive), my engine reved at 3,200 RPM at 70 MPH and it was fine. I thought about installing 4.11 gears in the rear, but according to my calculations, if I did that, then the engine would be reving at 3,800 RPM at 70 MPH, and that would be too much for me in a car that was driven 14 miles on the highway 2-3 days per week. It would get to be annoying after a few hundred miles for me. not only because of the constant noise the entire time I was on the highway, but also because as soon as you would let off the gas, it was like hitting the brake pedal. not comfortable at all.

But at 3,200 RPM it was fine. The engine would have a nice growl to it at 3,000- 3,200 RPM, and it sounder real nice, but not over the top. If you go from 3.73 to 3.55 gears, you'll only see a 150 RPM difference at 70 MPH from your present 3.73 gears, so don't even bother. Here's the gear calculator that I use...

http://www.richmondgear.com/101032.html

I agree that stall speed might have something to do with your issue IF it's above 3,500 RPM. But if it isn't in the 4,000 RPM range or higher, then that shouldn't have anything to do with how the engine revs when you're cruising with part throttle at any speed since the converter is only going to flash up to the full stall speed under hard acceleration when you're at full throttle or very close to it.

The only way that you're going to see a significant decrease in RPM at a 70 MPH cruise is either switch to an overdrive transmission, install one of those Gear vendors units, or do a rear gear swap to 3.08 gears. The 3.08 gears alone will drop your revs at 70 MPH by 400 RPM. But that ratio will also give you a reduction in 0-60 MPH acceleration as compared to your 3.73 gear ratio that you have now. I think that 3.73's are the best all around ratio for cars that have non-O/D transmissions.
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  #9  
Old Mar 25th, 08, 7:32 AM
mr 4 speed mr 4 speed is offline
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Default Re: Rear End Gears

Put 3.07 gears in it

or what Tom said
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  #10  
Old Mar 25th, 08, 8:28 AM
GRN69CHV GRN69CHV is offline
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Default Re: Rear End Gears

Yet another thread where it becomes evident how spoiled we all have become due to modern OD tranny's. 30+ years a go, 3.73's "WERE" considered highway gears. Street performance gears were 4.10 - 4.56.
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  #11  
Old Mar 25th, 08, 9:08 AM
71454Chevelle 71454Chevelle is offline
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Default Re: Rear End Gears

Quote:
Originally Posted by GRN69CHV View Post
Yet another thread where it becomes evident how spoiled we all have become due to modern OD tranny's.


I'm running a 4.30 gear with M/T 295/65 Drag Radials (30" diameter) and it's really not bad on the interstate. It sounds like a lot of gear, but with the cam I'm running, the engine seems to have a "Sweet Spot" (3200-3400) where the motor seems to cruise right along and doesn't seem to "strain" or act as if it's being pushed to hard. Driving at 65, the motor's turning 3100rpm. At 70, a little over 3300 rpm. I don't drive real long distances on the interstate, usually an hour or two at the most and I try and keep the speeds no more than 70 mph.

Also, I think you can get away with abit more gear on the interstate with a stick car because you don't have the torque convertor slippage to worry about.

Don't fear the Gear!
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  #12  
Old Mar 25th, 08, 9:21 AM
jeff swisher jeff swisher is offline
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Default Re: Rear End Gears

this was talked about on another thread and mufflers were meantioned ...that could get anoying i know i lived with 456 gears for a couple years 150 miles to the lake with boat in tow ,,to the race track 50 miles away..before the quieter exaust i would wear ear plugs

on a sbc i had a 9" in 308 to 370 made .7 that is 7 tenths in the 1/4 and the 308 never came out of 2nd gear in the 1/4
13.028 vs 13.75
I also wear ear plugs on my motor cycle , it makes the ride that much more enjoyable.. we normally have a lot of wind here in OK.
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  #13  
Old Mar 25th, 08, 7:11 PM
harley02571 harley02571 is offline
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Default Re: Rear End Gears

I also have a 3500 stall.
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  #14  
Old Mar 25th, 08, 7:35 PM
Chris Stanwyck Chris Stanwyck is offline
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Default Re: Rear End Gears

You could always go to a 295/65 (30" tall), hook better, and find out at the same time what a 3:55 would work like with a 275.

I did the same thing but with 4:11's...275 to 295.....difference was noticebly better.
Just get used to cruisin at 65 to 70 mph. +'s No tickets and spreading the time ya spend in your car.
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  #15  
Old Mar 25th, 08, 10:01 PM
Jerry70 Jerry70 is offline
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Default Re: Rear End Gears

As already suggested, an OD tranny (or a Gearvendor OD) would be the best for low speed "balls" and noticeably lower highway revs. A gear change that would retain most of your current low end punch (like to 3.55 or 3.42) probably wouldn't lower your hwy rpms enough to justify the cost (though it would be less). Also as already posted, the rpms you're seeing aren't that high unless compared to late model OD equipped cars.
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