How big of a tire?

[Bob Chayer]

How large of a tire do you think I could run using 4.10 gears and still have plenty of power?

[jeffspower]

What do you have for a motor? I have a 72 k-20 w/4.10's & a pure stock 500 cad, 350 trans. It has 13/38 swampers on it now with about 8" of lift. I rarely use low range unless I am at least hub deep in major sticky gumbo. I can run 80 mph against a strong wind no sweat. DRINKS GAS doing it though! -Jeff

[Mudder]

35's would be ideal..... 38's will start robbing power. Lots run the 38's with 4.10's.

[1969 GMC]

Originally posted by jeffspower
I can run 80 mph against a strong wind no sweat. DRINKS GAS doing it though! -Jeff

I heard those 500 caddies got 8/10 mpg highway in the Cadillac they came with, what mileage you get with it?

[jeffspower]

When I first put the motor in the truck it had 255/85/16's on it (skinny 33's) and it was the only truck I had to drive. It would get 9 on the highway if i kept it under 65. Tooling around on backroads "parts spottin" at slower speeds it would get over 10. After putting on the 38's those numbers went down by about 2 mpg. But if I am out on the highway I am usually scootin along about 75 since the motor is spinning so much slower.

My 80 k-20 has a little healthier 500 w/4.10's & 235/85/16 tires. It gets about the same 8-9 mpg.

I used to have a 74 c-20 with a stock 500, 700R-4 &4.56 gears. It would get about 12. That combo was great for light trailer towing or cruising 80mph. I always joked That I could get into overdrive at 25 mph. It would!

The first cad 500 I swapped was into a 78 regal. It was a 10-1 70 eldo motor. With the stock 2.29 gears & a 400 switch pitch I could get 16 mpg! Then I put in a 2.73 posi & it got 13. Also ran a 13 flat at 96 with too tall of slicks (28's) at the dragstrip. That motor was totally stock with nothing more than a new timing chain.

Anybody want Caddy power? I can tell you what fits & what don't for many applications. It is not as hard as it looks. 73-up 2wd's are a bolt in with no cutting or drilling with a simple flat plate for the motor mounts. Just a little firewall lip clearancing on the driver's side. No crossmember or frame hacking needed when you use the right pan & oil pump.

73-up 4wd's are about the same but I take out that goofy shaped engine crossmember & replace it with a nice box tube crossmember that I make.

72-down 4wd's are a tight fit. But if you get everything just right there is no frame or crossmember hacking needed. Just some extra clearance on the driver's side of the firewall. I cut a little opening in the firewall & box it back in. People I show it to don't usually even notice it untill I point it out.

I am thinking about putting my 72 back to Chevy power when I redo the body. I picked up a 427 tall deck for pocket change! - I Just think my old favorite would be sweet with that motor! -Jeff