Technical Gear ratio?

ok guys when it comes to gear ratio and ****** combos, I'm ignorant. I'm putting together a coupe with a blown 331 hemi and a 2 spd power-glide and The 9" rearend has 3.50 gears. I'm Not sure of tire combo as of yet, so no info on that. With this gear and ****** combo what can I expect with this? Like I said I'm dumb when it comes to gearing. Thanks.

 

sounds like a good combo to me!

 

This calculator will let a person see how the different combinations of transmission, rears and tires behave. Just have to plug the numbers in.
https://www.teambuick.com/reference/calculators.php

 

As long as you don't put absurdly tall rear tires on it, you should be just fine.

 

I always calculate out rpms at 70 or 75 MPH and check that against what the engine I'm using would like to cruise at for extended periods of time. A 3.50 to 1 final drive is certainly doable for a Small block Chevy. I would ***ume a built 331 could live at similar RPMs

 

It's a fendered car so tires will be average.

 

I like this calculator, as it allows side by side comparisons.

http://www.grimmjeeper.com/gears.html

 

what cam does it have? Gears and stall speed need to work with the engine's RPM power band, and the camshaft is the main thing that determines that.

 

I agree with squirrel..I have a 284h cam in a 350 sb..running 4.10 rear...Cam likes 2800-6500 rpm...at 65 mph tacking 3300 rpm...th350 trans...need to know what your cam specs are to determine diff. ratio...

 

Also we need to know what you plan to do with this car....racer? Purely street car? Road trip car? Maybe a little of all?
your combination sounds like a good compromise to do all 3 pretty well.

 

If it is any help a 1955 331 powerflite came standard with a 3.54 optional 3.73.

 

I always love how guys are ready to make a gear ratio recommendation without knowing the tire height. Cause you know, why would that matter, right??

 

Pretty easy to figure out the approximate tire height, if you know what kind of car we're talking about. Which we don't..."a coupe" covers a lot of ground!

but ***uming it's a typical early hot rod coupe, 28-30" would be a good guess.

 

I have to agree with Rocky on this, without knowing your plans for what driving you intend to do in the car it is hard to suggest something. The 3.5 gears are a good compromise though.
With the 9 inch it isn't all that hard to swap pumpkins out and run a gear set that works better in the situation. I think Jim has a set for every occasion for his Chevy II.

 

Going to need a 30+ inch rear tire to keep it from screaming down the highway. I'm a fan of keeping rpm at or slightly under 2k at 60mph.

Sent from my XT1585 using The H.A.M.B. mobile app

 

I have to travel an hour to get to 4 lane. So I figure it at 60.

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Sorry for the delay, been super busy. It's a 1930 model a full fendered and is in mock up stage right now. The car is going to be built as a driver with a lot of balls. The combo I mentioned is what I have to work with but I could swap parts if need be. As for the tires im not sure what I'm going to run yet because I want the tires to be in proportion with the fenders and the chop. I'm going to play around with that until I like the way it looks. But it is a fendered car so so can get an idea of the tire size. The motor I'm gonna guess will be around 500 hp conservative. Next weekend I should be narrowing the rear end and setting up the 4 link.

 

Fortunately he said it's a 331 HEMI, not a belly ****on engine. Standard rear end gear in '55 was 3.36 with 3.54 optional. I'd think you'd be better off with a 727 instead of a P-G.

 

Do you already have the powerglide? i'd guess thats why you're looking at running it. Personally i'd aim for a 727 or an A-518. If you already have the chevy adapter, build a 200r4 up for it. You'll be a lot happier with it and you'll be able to run 4.10's, which will help you out with being a bad ***.

What cam are you running in your 331? are you going to be blown? 500hp out of it without a blower means a pretty wild cam/build. I'm looking at 400ish with a 392, 10:1 pistons, some light porting, a hot heads 4bbl intake, headers and a .470/221/110 cam from Howards cams, they rate that cam for an 1800-5400rpm powerband. Ill be running an A-518 overdrive behind it and 4.10 gears on a 27" tire. Shes going to cruise really nice and get my 3700lb Desoto off the line nicely.

 

If it is a driver set it up so the motor is happy doing what you expect to be doing the most with it. In my case, I live 30 miles from any sort of significant settlement so my cars get setup with overdrive and / or the rear ratio to cruise happily at 70-75 mph while keeping the engine rpms down to a minimum. Quarter mile times aren't a big concern. This also means getting a cam and stall convertor that is happy at 1500 to 2400 rpms, exactly where the motor will spend 95% of it's life. Now, if you live in a place like subarban Detroit and have an endless grid of Mile Roads with stop and go lights and don't have a desire to run interstates and free-ways, then a non-overdrive, and deeper rear gear would be a bunch of fun.

Bottom Line: Set it up for how you want to use it. Nothing is worse than a hot rod sitting in the garage because the owner dislikes driving it.

 

We still have no idea what cam it has.

 

Listen to Jim here , folks.
The answer to the o/p's question, as he stated it, can be as varied as all the personalities on this board.
For guys seeking advice, the more info you can provide in you initial question, the better chance you will get the answer you are needing.

 

I have a 355 SBC in my car worth about 400 HP, with a 4-speed. The last thing I want to do is lug it around town. I have a 3.70 rear now and calculated it from 30-70 mph with a 3.56, 3.90 and 4.10 rear. It looks like the 4.10 is the way to go for me. It picks up the RPMs at 30-40 nicely for around town and is reasonable at 70.

 

the motor isnt built yet, still in mock up.. looking at 6months to build the motor. thinking around 519 lift 290 duration, I know it's not all the numbers but that's what I do remember.

 

Yes I understood it was a 331 Hemi and not an over bored 327 small block.

 

^^^Ever so very much this.^^^

I am pretty sure that the guys that think that spinning at 3800+rpm at freeway speed just like the noise, and buying gas.

I am a more gears are always better guy. Both my daily and the wife's have 6-gears. When the Hemi goes in my Model A, it will have four, and only because the setup will not allow for more.

If you already have an adapter to get to SBC pattern, I would get a prepped 200-4R, and still keep the 3.50:1 rear gears. The blown 331 will be a torque monster. There is no sold reason to spin the hell out of it. So called "freeway gears" back in the day, with stock SBC's and others, were often around 2.56:1 (with a 1:1 top gear, and a car 1000-1500lbs heavier than yours). Final effective combined drive ratio with 3.50:1 rear gears and a 200-4R (in 4th) would be ~2.35:1 (0.67 x 3.50). A little taller than 2.56:1, but you will likely be in the 500-550hp range, with just over that in torque.

Since it is a full-fendered Model A, and presumably it will be fairly lowered, I would speculate the tire diameter to be about 29". Use that as a guesstimate until you lock-in the ch***is/suspension setup.

That setup would put you a tick over 2000rpm at 75mph.

I have had a lot of customers with Powerglide equipped vehicles. At almost a one-for-one ratio, they had me remove them in favor of transmissions with more gears. Nobody asked to go back. The only Powerglide installations that I was asked to do were in full-on, track-only, drag race cars.

 

Of course, without exact cam specs, and a few more, we're all just speculating.