best gear ratio

Most of my earlier days were in Trans Am and Z28. No 4 speeds yet unless you purchased the add on OD unit.

On a mild or even pukey OEM build, the highest you ever want to go is 3:08. This for Highway and pocket book (MPG)

Next is 3:42 and next is 3:55, Then 3:73.

A good torque output stock Pontiac 400, TH350 3:42 rears were nice and of course this was the WS6 package. Ok highway, strong around town. 2.25 or 2.5 duals or even Y pipe to splitters dual small can mufflers... Made no difference.

The Turbo TA was 3:08 Posi behind THM350C. About 60 MPH at you are at a little over 1800 RPM with lockup, and turbo maybe 3 pounds boost. It was good highway combination, absolute crappy around town. To high gear and too lean from OEM, not enough boost.

What you are asking for is a systems approach.

First is Static Compression and Cam Card data, ... First and foremost...

THM350 is 2.48:1, 1.48:1, 1:1, no OD.

You can do trial and error with tire height. Mathematically will help give you an idea.

The GM goodwrench engine is designed more as a stock type engine, built for reliability with gas mileage in mind.

You can get by usng a stock torque convertor and 2.73 rear gears, but if you plan on going with 3.08 or more gear, you will have to change the 2series carrier for a 3series carrier.

jcelk said:

hello ll i got a 350 gm good wrench engine proformer intake 4 barrel carb 2 1/2 inch exhaust with a 350 thm trans with a 273 rear not very peppy what gear would work the best and can i get a open rear to hook if i put in air bags with he right side inflated a little ..this is street driven thanks for your input

Click to expand...

i personally like 3.73s once had 3.42s and didn't like those maybe 3.55s might be ok.

Yes, definitely like the 3.55.

On the stock replacement is a 290 build. Short duration and I'll have to check but Melling/Elgin Cam, only opens about .230 with the normal 1.5 ratio rockers.

If that's the case, you can switch to 1.6 with out risk of damage and should liven up the engine.

In the single piece engine, 193 head is common and it's a weak swirl port.

On the 2 piece engine, 624 is common. Ok flow, 76 cc (too large) and crack prone, no 1.6 exhaust valves.

The largest problem with small block Chevy is the small exhaust valve. Then you have a manifold the looks like it was carved out of a 2 x 4. This why headers will wake this up, but it's still limited by the small 1.5.

jcelk said:

right now i have 25 1/2 tires thinking of going with 26 inch tires could go bigger i will not take it to the track a little highway not much was thinking about a 7 1/2 open rear with air bags in the springs inflated a little on the right side to get traction has anyone had luck with that ?? and to make it fun around town. the 273 rear is underwhelming

Click to expand...

While I agree with many suggestions here, some people are going down a rabbit hole with some mods I doubt will ever happen in the near term. Let's read again what he currently has and where he wants to go. Highway isn't one of them. So forget 3.08 or sticking with the 2.73. Gas mileage can't be much of a concern because again, highway isn't one of the places this car will be. A 3 series limited slip carrier (thanks for that point about a series change Ernest ) should definitely be in this car's future with 3.xx (whatever gears chosen). That, plus a 2200-2400 stall speed converter with an add on transmission fluid cooler will be the most significant bang for the buck, IMO. And all without a ton of work and no engine modificatons. As mentioned in the other posts, deep gears with no OD means any highway driving should be short or you'll be hating life. If you have plenty of money to throw at the project, and are considering more mods later down the road, an OD transmission can make deep gears a reality and able to stomach longer highway cruising.

To the OP- This is a perfect time to apply the tried and true "Plan your work, and work your plan." Think of the end goal. If all you want is a more peppier to drive in town sled but remain pretty much stock, the above 3 areas of modification is MINIMUM for low-cost fun, IMO. If you want to start adding in headers/bigger exhaust, cam, intakes, igniton, fuel delivery, suspension, etc., start planning your end goal of the car and put together packages to COMPLIMENT each other. It's fine to change your mind/plans as you go, just know once you're totally involved that changing course gets way more expensive the later you change your mind in the project as some mods are dependent on others.

I'll say anything is the mid 3's is good for the street. Not sure whats available in the 7.5, I had 3.42's and 3.73's in a 10 bolt and 3.55's in my 12 bolt 70 chevelle. I have run the passenger side airbag in my other chevelle, went 10.50's with it in there.

I've got 3.42s and 235/60/15, which are 26.1 inch tires. Works OK. I have a buick 350, so 3k at 70 is a bit scary to me, but for a sbc I wouldn't bat an eye.

I can give you real world numbers. My 84 Cutlass had a bbc with a th400 and 3.42 gears. The rear tires were 255/60r15. Just shy of 3000rpms at 60. My 80 El Camino has 3.08 gears and a th350 with a 26 inch tall tire. It's about 2700rpms at 60 and 3100 at 70mph.
I think your 3.23 idea might be pretty good. Should get you up and going without the poor thing screaming down the road.
If you use the 350c, your rpms will be lower due to the lockup, in which case a 3.42 might not be a bad idea.

Cam specs on the GM Goodwrench 290HP...

Basically a modest built 114 LSA so should idle smooth and have decent around town manners.