Gear Ratios? - Chevelle Tech
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post #1 of 26 (permalink) Old May 18th, 12, 12:09 AM Thread Starter
Andrew
 
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Gear Ratios?

So I'm looking for suggestions on a new gear ratio.

Here's the back ground: I have a 72 El Camino with a mostly stock (for now) 355, th350, 2500 stall converter, 27" tires, and 2.73 gears (open). It's way over due for having the gears upgraded, but before I have it done I want to get some feed back/input.

It's not going to be a race car, but I may take it down the track a couple of times. It's mostly a daily driver/joy rider. I would like to have good performance off the like but not be running 4000 rpms going down the free way.

I was thinking of going with 3.73s but I'm not positive. I'm new to the "re-gearing" thing. Not sure what's going to be my best bet. That's why I'm looking for feed back.
Thanks!
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post #2 of 26 (permalink) Old May 18th, 12, 12:54 AM
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Stu
 
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Re: Gear Ratios?

I would not run 3.73 without and OD trans (which I why I got one). Maybe 3.31:1, that seems like the sweet spot for a non OD setup. But I'm not an expert by any means.
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post #3 of 26 (permalink) Old May 18th, 12, 1:10 AM
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Ray
 
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Re: Gear Ratios?

3:55's are a great all around gear.

Ray
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post #4 of 26 (permalink) Old May 18th, 12, 1:16 AM Thread Starter
Andrew
 
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Re: Gear Ratios?

3.31? that would be too convenient. There's a local guy selling a complete diff. with 3.31s right now.

http://boise.craigslist.org/pts/2973266594.html

Does anyone have experience with a similar setup?
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post #5 of 26 (permalink) Old May 18th, 12, 1:42 AM
Rick
 
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Re: Gear Ratios?

Chuckd is right on!
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post #6 of 26 (permalink) Old May 18th, 12, 3:31 AM
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andy
 
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Re: Gear Ratios?

I vote for 3.42s
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post #7 of 26 (permalink) Old May 18th, 12, 6:48 AM
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Re: Gear Ratios?

10 bolt or 12 bolt?

Darren
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post #8 of 26 (permalink) Old May 18th, 12, 7:08 AM
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Derrick
 
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Re: Gear Ratios?

Quote:
Originally Posted by chuckd71 View Post
I would not run 3.73 without and OD trans (which I why I got one). Maybe 3.31:1, that seems like the sweet spot for a non OD setup. But I'm not an expert by any means.
i didn't mind the 3.70 gears in my Nova- it got to be a little much at 80mph on the interstate, but otherwise i didn't mind it..
mild small blocks seem to like ratios in the 3.42-3.55 range, too..

"Detroit hasn't felt any real pride since George Bush went to Japan and vomited on their auto executives, I tell you whut"

-Hank Hill
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post #9 of 26 (permalink) Old May 18th, 12, 7:39 AM
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Dave
 
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Re: Gear Ratios?

For a street car without OD, 3.73's would be the most gear I would want to run, but if you do a lot of highway driving, even 3.73's are a bit much.

You'll feel a performance improvement with anything steeper than the 2.73's you've got.

How much in town driving versus how much highway driving you do should weigh into your decision... 3.31's (or 3.36's if a ten bolt) will run about 400 rpm lower on the highway than 3.73's.

Which rear end do you have? You may have to buy a new carrier, too.

_____________________________________
68 Chevelle
flat top 406, AFR 195's, XR286R, RPM AirGap
750 Holley DP,TH400 w/brake, 4000 stall FTI
3.31 gear, 12 bolt
... for now.
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post #10 of 26 (permalink) Old May 18th, 12, 8:23 AM
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Re: Gear Ratios?

Without an Overdrive Transmission, 3.42 gears is the line in the sand I would not cross.

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post #11 of 26 (permalink) Old May 18th, 12, 8:47 AM Thread Starter
Andrew
 
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Re: Gear Ratios?

It's a 12 bolt. Sorry, I forgot to mention that.

My drive to work is about half highway, half in town.

So, the 12 bolt posi with 3.31s in the craigslist link I posted above might be a good way to go then? Not much experience buying rears, does that look like a good deal? Worth the $800 he's asking.
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post #12 of 26 (permalink) Old May 18th, 12, 9:36 AM
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Aaron
 
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Re: Gear Ratios?

Quote:
Originally Posted by Camaro_fever68 View Post
3:55's are a great all around gear.
Winner!

I have gone 112mph with my 355 with 355 gears at the track.
Drive great too

1971 Chevelle. 355, megasquirt efi. On3 7875 turbo. 700r4, 355 gears. C5 brakes, SC&C stg2+, hellwig bars, 04-06 gto seats. 546rwhp/450rwtq with 28% converter slip on 18psi!

Little walk around video

http://youtu.be/D_B0B1RNmcc
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post #13 of 26 (permalink) Old May 18th, 12, 9:54 AM
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Re: Gear Ratios?

I've had about everything that G.M built and like 3.31s the best. My 396/350 Chevelle got 18-19 mpg with that gear.
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post #14 of 26 (permalink) Old May 18th, 12, 10:35 AM
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jeff
 
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Re: Gear Ratios?

What no math for the boy.
336 is a given to make the math work out..but allow for converter slippage..I usually add in 10% for a sloppy converter..

336 X gear ratio X MPH, divided by tire diameter = RPM

Here is some more TH350 gear ratois 2.52 in first and 1.52 in second
1.52 X 2.73 = 4.14,, so if you drive around in second it would be like having 4.14 ratio.....
I like my 3.25's 9" ford though...the 2.75 was a tad tall and i have 29" tall tires 3.73 or 3.70 was a good all around gear but you will cruise in the fast lane at 3500 rpm at around 75mph or 2500rpm at 55 mph.
I will agree with Harold with the 3.31 being an excellent choice

Sometimes it is nice to have a complete rearend to swap out..We had a spare that had different ratio for the 64 elcamino..and about 45 minutes and you were rolling. that was a 60 dollar salvage yard part..we had 2.56's and 3.08's. With 3.08's we usually only used 1st and second in the 1/4 mile.
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post #15 of 26 (permalink) Old May 18th, 12, 1:07 PM
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Brad
 
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Re: Gear Ratios?

Quote:
Originally Posted by red72 View Post
So, the 12 bolt posi with 3.31s in the craigslist link I posted above might be a good way to go then? Not much experience buying rears, does that look like a good deal? Worth the $800 he's asking.
Looks like it might be too good of a deal?? A rear like that would fetch quite a bit more money than $800.

I question how legit the stuff/ad is when he says the second rear listed came out of a 70 Chevelle with a 454/TH400 combo and had a open 2.73 rear end.

There were A body BOP 12 bolt rears that had 12 bolts on the cover, but were more like 10 bolts internally. If that's a real deal Chevy 12 bolt for $800, it's a great deal. Do a bunch more "checking out" of that one before handing any cash over.
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