Hey Guys,


New to this site and Oldsmobile.
I've got a 36 Chevy truck rat rod with a 76 350 Oldsmobile in it. I'm going to be saving for a crate motor from J&S Machine.....should really make the rat fast! It has a 400 tranny and 10 bolt with what I'm guessing is around a 256 gear. I go 70 mph down the highway @ 2000rpm great for the highway but it lacks the punch I want. Open headers with baffles stuffed inside and an old time Offy dual port 360 with a 600 holley. Ignition is some stock HEI. The weight of this rat can't be much so not a lot of power will be needed to make her move all over fast.

 

Welcome to CO. Think there may be a need for a set of wings.Just keep it on the ground and between the lines painted on the road! Larry

 

Welcome Rick. Nice to see that motor choice in your rat. That would my choice too.

About your rear gear, even a step up to the lowly 308 ratio would probably feel like 50 HP in that rig.

Like that first photo, looks like it belongs in a calendar or something.

 

Welcome to the site, nice ride.

 

Awesome ride. What crate motor are you saving for? Maybe just some better gears and leave the olds in there. It looks perfect, the whole ride as is!

 

I've never messed with a 10 bolt gear change before, I can do that first and maybe I won't need a crate motor.


Don71, great guess! It had a 5 page spread in Rebel Rodz back in 2009. It wasn't mine at the time and it had plenty of previous owners. It pulled up next to me at a local Walmart and it was for sale. I bought it after the first demo ride, at this point it was rode hard and put away wet way to often and it showed. I sold my 66 Fairlane 2dr hdtp that was in excellent condition later.....it was no fun to drive anymore after driving the rat. I put new tires and mounts on her and she'll do 100 easy but that Offy intake has got to go! With the gear change and a new intake (performer rpm) and some time on a chassis dyno it should really wake her up.
I put some old style Holley VC on her with Offy breathers too.


Question: it's got an 80's Cutlass rearend, how do I tell what size ring gear it has? Right now all I know it has a 10 bolt cover and going 70mph I'm turning 2K on the tach.

 

Wow nice car. I believe to determine gear ratio you jack up one side of rear axle (open differential), rotate the tire two revolutions, and count how many times the driveline rotates, then divide. You can find more specific directions in a Google search. Good luck

 

Can you post a couple of pics of the center section? At least one good one of the rear and one from the front. Any casting numbers might be helpful, as it would be just guessing if its a 7.5'' or 8.5''

 

Don71, Got some pics of the rear but trying to take them under a slammed rat isn't easy. These might help but I didn't see any tags or numbers at all. I even tried to figure out the gear ratio. I put a mark on the drive shaft and one on the tire, I turned the tire one revolution and the drive shaft only went around 1.4 times! I think having such tall tires (28 or 29's) really changed the true ratio. Looking at the back cover it looks like a 7.5 if I'm right?

 

7.5'' Those little ears at the bottom and shape of the cover give it away.

If you really want to know the ratio for sure, you'll need to pull the cover. I've never been a fan of the chalk mark method. I'm sure there is a lot of smiles per gallons regardless.

It could be 2.14-2.29-2.41-2.73 etc.

 

If I did the chalk mark right, I got a 2.35 gear ratio with 28" tall tires. So I'm guessing I have a true 2.73 gear.


With 2 complete turns of the drive shaft I got 1.7 turns of the tire. So 1 divided by 1.7 = .588 x 4 = 2.35


Like I said earlier @ 70mph I got 2k on the tach. That's in 3rd gear in my 400 tranny.


So I'm thinking a 3.08 gear wouldn't do much but a 3.25 would be better?


I also think I should continue this subject under another forum instead of the New Guy forum.


What do you guys think?