Gear Ratio Help

I am looking for suggestions on what gear ration do swap to. My current set up is a 1983 Chevy C10 with a built 355 small block, 3200 rpm torque converter, 700r4 trans and 3.73 posi rear. With the current engine/cam combo i can not use 4th gear unless I am running above 70 mph. The cam was originally specked for my 1975 Chevelle with a 3500 rpm converter, TH400 and 4.11 gears. Cam specs are as follows; Comp Cams 284H Hydraulic Flat Tappet, .507/.510 Lift, Duration @ .050 - 240/246, RPM Range 2300-6500. I do not want to change cams as this one sounds and runs great. I am pondering two options:

Option 1: Swap trans to a TH400 and change to 4.11 gears

Option 2: Swap the rear gears to either 4.56 or 4.88 so that I can use 4th gear in the current set up.

I am looking for information if anyone else has had this problem and what the best solution would be.

Thank you
Curtis

What is your tire size?

Do you have lockup working on the 700r4?

Are we a daily driver, auto cross, drag racing...
I need more info, pics, family history.. etc..

I do have the lock-up functioning on the 700R4.

It is a weekend driver / car chow / going to go to the strip occasionally truck. Will see minimal highway driving, mostly 65MPH and under. I can get photos but do not have them accessible at this time. I forgot to mention that I am running 28in tall tires.

Thank you
Curt

Run it in 3rd gear. A th400 high gear is the same as 3rd in your 700r4. If you feel like you need more low end than switch differential gears. But all you are doing then is improving the low end and moving the 4th gear to what you are already running in third.

Yes, I realize that. That is how I currently drive it, just a waste of an overdrive trans. But it is still not happy with the 3.73 ratio. The engine still wants deeper gears, so I am trying to figure out if the best course to go with is just deeper gears (4.56 or 4.88), or swap the trans to the TH400 and use the 700R4 is something else and go with 4.10 gears.

I'd put a 4.10 or 4.30 in it and keep the OD just in case you wanna road trip it

In that case I'd swap gears for something more usable with the 700

Aren't factory converters like 1800 rpm? I'm running 35's, 3.73's and a 700r4 with a stock wore out 350 with an intake and carb, and I can use fourth and overdrive but it won't gain speed goin uphill. It'll maintain speed on most hills but definitely not anything crazy.

That drivetrain with 28's and 3.73's should basically be optimal? I'm not an automatic or torque converter tech, but that has to be the issue.

PrairieDrifter said:

Aren't factory converters like 1800 rpm? I'm running 35's, 3.73's and a 700r4 with a stock wore out 350 with an intake and carb, and I can use fourth and overdrive but it won't gain speed goin uphill. It'll maintain speed on most hills but definitely not anything crazy.

That drivetrain with 28's and 3.73's should basically be optimal? I'm not an automatic or torque converter tech, but that has to be the issue.

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I wasn't even thinking in my earlier post,just reading and responding. My Burb was TBI 350 with a towing cam,flat tops,31x10.50s and 3.73 gear and it was always in 4th on the highway and it didn't struggle a bit.

Ricko1966 said:

I wasn't even thinking in my earlier post,just reading and responding. My Burb was TBI 350 with a towing cam,flat tops,and 31x10.50s and 3.73 gear and it was always in 4th on the highway and it didn't struggle a bit.

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I didn't think I was crazy lol. I went with a factory rated converter.

I was planning on 4.56's as my max for my setup and I was thinking that would be almost too much gear for ME, let alone 28's and a mild 350 lolol.

My truck is also peppy off the line for what it is, it gives newer rigs a run for their money... 4.56's with 350/700r4 with 35's would be an animal for being a lifted brick.

I run 4.56s with a 28" tire and 4K spragless stall she runs 2800-3000 at 55mph. I run a powerglide but hi gear is still 1:1

Yeah that cam is pretty aggressive for a 700R4 setup, that’s why it feels lazy in 4th. Honestly I’d just go steeper gears—4.56 would probably wake it up nicely without going too crazy on the highway. 4.88 might be a bit much unless it’s more of a street/strip truck.

PrairieDrifter said:

Aren't factory converters like 1800 rpm? I'm running 35's, 3.73's and a 700r4 with a stock wore out 350 with an intake and carb, and I can use fourth and overdrive but it won't gain speed goin uphill. It'll maintain speed on most hills but definitely not anything crazy.

That drivetrain with 28's and 3.73's should basically be optimal? I'm not an automatic or torque converter tech, but that has to be the issue.

Click to expand...

It's the cam. A rowdy cam doesn't like to be lugged and basically won't do anything at low speed in 4th. My daily's like that, anything below 1800-1900 and I've gotta make it downshift to get it to go anywhere

4.88's and send er, you'll never lack grunt again.