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Gear Ratios?

21K views 25 replies 21 participants last post by  dirtlips408 
#1 ·
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!
 
#8 ·
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..
 
#9 ·
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.
 
#10 ·
Without an Overdrive Transmission, 3.42 gears is the line in the sand I would not cross.
 
#11 ·
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.
 
#15 ·
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. :noway:

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.
 
#14 ·
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.
 
#16 · (Edited)
You're going to get an array of varied answers on this one. It's a matter of preference. I agree with what Derrick and some others said: 3.73's are just fine even without an overdrive trans unless you like to cruise at 80+MPH. I had 3.73's in an old Vette that i drove three days out of the week to work and back for 6 years, and I liked it. 5 miles of that commute was on the highway. But if you drive 20+ miles on the highway atleast a few times a week, having the 3.73's might get old quick. Don't get me wrong though. With the 3.73 gears, I took that car on a 150 mile interstate trip now and then, and it was fine cruising at 70 MPH with occassional 100 MPH blasts when the traffic cleared, but that was only once or twice a year. If i was cruisinf for lenghthy stretches on the highway on a regular basis, the 3.73's might have been changed for a more conservative gear ratio. But it's all about how you use your vehicle and how you drive, and what you want out of it.

I had 26.5" tall rear tires, and a 4 speed manual trans, and it reved at 3,200 RPM at 70 MPH which was tolerable for me. Another thing you have to consider is that if you'll be relying on a rear gear ratio change all by itself to improve your 0-80 MPH acceleration, then don't expect a whole lot from going from a 2.73 ratio to a 3.31. You'll notice a drifference, but it won't be a major one.

If you want a considerable acceleration difference from a gear swap alone, then going from 2.73's to 3.73's will fill the ticket. But you'll also have to consider the camshaft you presently have in the engine.

What's the dur@.050 spec? If for instance you have a very mild cam with a 215 to 219 dur@.050 spec then chances are the engine is all finished making power by 4,500 to 5,000 RPM and 3.73 gears won't be a perfect match at all.

But if for instance you have a cam with a duration spec in the 230@.050 neighborhood, then the engine should make power right up to 6,000 RPM, and in that case, a 3.73 gear ratio would be more at home. More compatible.
 
#18 ·
My small blocks don't like 3.31. Anything under 3.55 makes them weak. 3.55 to 3.73 is the sweet spot. 3.55 makes the perfect compromise. Big blocks love 3.31 and even higher. It's all about torque. My twin turbo sb has 3.15 gears and pulls better than a big block with 4.56's. Again, all about torque.
 
#19 ·
3.31's are a great gear set. They are hard to break for the average guy, great for hyway and everyday driving. 3.42's came with the towing package in my 73 Monte, and I thought they were too low for THAT 350 powered car. I've run 3.31's in hydraulic cammed 302's and was satisfied with the street performance. I'm the same guy who ran 5.57 gears on the street with a PG, so I have some general experience with a wide range of gearing. However, I consider 3.31 to be the bottom of the gear range with any kind of street/strip car. A gear that won't drive you crazy or broke. I don't think anyone makes an aftermarket 3.31, so you end up with old gears that came in GM cars. Sometimes hard to find.
 
#21 ·
3.31s or 3.55s, you will not see a difference between the two.
 
#23 ·
I have 3.08s in mine. While I don't know much about my engine, I do know it's running lean right now and that it runs 70mph at about 3000 rpm with a th350. It's great if you run around on the highways a lot. I'm hoping to get some 3.73's eventually since I run from stop light to stop light lol.
 
#24 ·
I have run 4.56's, 3.73's, 3.55's, 3.42's, 3.31's and 3.07's. I like the 3.42's in my current setup with a 454, Turbo 400 trans with 26.5" tall tires on the 14" SS wheels. Seems to get a little mpg and still have getty up go as well. I am running a 2500 stall converter as well that seems tighter than 2500. You should have that in consideration as well if you have an automatic with a high stall speed converter.
 
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