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Discussion Starter · #1 ·
I'm considering dropping my current 3.73 gears to something like 3.0x. I'm not sure what the exact ratio in the 3.0x range, that's the reason for the "x" factor.

I'm trying to reduce my cruising rpm range.

I know I can go with a gear vendors unit, but I want to try the TH400 without it.

With the 3.73 gears, if I'm cruising at 3200 rpm, and if I reduce my ratio to 3.0x, how much reduction in rpm can I reduce?

I can afford to reduce my rear end ratio with the motor that I have. This is why I'm considering it. Quickness and torque will not be an issue for me. As a matter of fact, 3.73 may be too much for the blown 540 BB with street tires.

Thanks.
 

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Go to the richmond gear sight .It has real good gear calculators.Also ,what are you going to do with that 3.73?Thanx Clarence.
 

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I assume you have a 12 bolt if you are going to make that much power. The ratio you are looking for is a 3.08. If you go any farther than this you will have to get a 2 series posi. I can e-mail you a gear ratio chart if you need it.

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'69 RS/SS396 Pro Street
427 4 speed 9"
Byars Performance
High Performance Drivetrain Parts & Service
www.lubedealer.com/biggearhead
 

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How big are your tires? I seem to recal some lower profile jobber.

If you can fit a 27" or 28" tire then I'd be happy with a 3.23 rear. I think that's the right number, or close to it. So a tire change and a gear change both in the "friendlier" direction.
Maybe some better tracion tires for the added HP?

I agree with loosing the 3.73s I am putting in a GV over drive in the spring time.

Also, do you already have a stall converter picked out from when it ran before? You don't want to cruise a "3000RPM stall converter" at 2500RPM. True you can, but it will make a good deal of heat and lessen the life of the tranny. I think you had a cooling problem before right? just a thought.

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71' 3880# with me. Big Block 402, Merlin oval heads, 10.2:1CR, TH400, 3.73 posi,
1/8th: 8.0 @ 88mph
BEST 1/4: 12.5 with 1.89 sixty foot (street tires)
BEST MPH: 108mph

Picture of me roasting the tires and other guy stuff
Video of me staging (smoke of course)

[This message has been edited by BB_Mike (edited 11-04-2001).]
 

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tonyr-

A website at www.differentials.com has an RPM calculator. Just plug in a vehicle speed, tire height and a gear ratio. RPM is displayed when you click the calculate button. Then you will be able to experiment with different gear ratios & choose the best one for the RPM range you want your engine to be in during cruise. Good Luck!

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Gregg Haskin
72 Chevelle SS
ZZ502 Crated RAT
Muncie M-20 4 speed
TEAM CHEVELLE #726 ACES #4486
"PROUD TO BE AN AMERICAN!"
“What the heck are all these extra nuts & bolts for?”

Pictures of my 72 Chevelle SS Restoration: www.wcvt.com/~ghaskin
 

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BB Mike, I think with a good cooler, a 3000 stall and 2500 rpm cruise speed is fine.
I hope anyway, since that is what I have.
 

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Tony,interested in selling those 3.73's? If so,let me know.

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1970 Chevelle SS396/M20/4.10 My 70 SS396
Engine pic
1970 Chevelle SS454My 70 SS454
1968 Oldsmobile Cutlass convertible
1982 Oldsmobile Cutlass 350 Olds,TH350(daily driver)
Chris Corwel,TC Member 785
 

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Discussion Starter · #10 ·
Thank you all for your great advice.

I can't fit another inch in tire height, else it's rub.

My torque converter stall speed is not rated at 3000 rpm. It's around 2,500. I don't really need a high stall speed. I also have a pretty good size tranny cooler.

I think a 6 speed would be cool


I want a significant rpm reduction. That's why I'm leaning toward the 3.08 gears.

According to the rpm calculator, it could drop it by 500 rpm. My factors were, 3.73, 65 mph, with 26" tires.

mr 4 speed, if I do sell my 3.73, you will get the first offer.

Man, if I went with 3.08 and add an overdrive unit down the road, I can actually cruise at 100 mph


I'm trying to make my cruising speed more comfortable to drive to shows and meet some of you


Thank you all for your HELPFUL information.
 

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<BLOCKQUOTE>quote:</font><HR>Originally posted by Tonyr:
Man, if I went with 3.08 and add an overdrive unit down the road, I can actually cruise at 100 mph

<HR></BLOCKQUOTE>

I cruise 95mph at times. You just gotta be willing to turn the RPMs



Yaniz. I doubt you'll have a problem. I was just posing a worst case scenerio such as a 5 hour power tour cruise.

Tony. I like the 3.08s too. AS for the 100mph cruising, I can here it now, "But officer, the blower was whining because it wanted to go faster and faster..."
 

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OK...I'm stupid...What's a gear vendor's unit?

edit:
NEVERMIND, I guess that's what the search function is for, huh!

[This message has been edited by Barista (edited 11-04-2001).]
 
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