68 Chev 3/4 4x4 overdrive trans swap

[1972RedNeck]

Originally Posted by Daimler

I've been thinking, working from a cruise rpm of 3000 with the 411's and stock four speed - why not both. Use the 27% drop with the Ranger to 2190 rpm. Then pull the O.D. on the NV4500 for another 25% - dropping to 1625 rpm. Dad's V-8 Jaguar weighs 4500 lbs. With the 700R4 he is turning about 1650 RPM at 65 MPH. Although the motor is 'built' he gets 28 to 34 mpg on the hiway. If the 500 Caddy motor was mildly tweaked the truck would also have the power to push the truck at these rpm's? Basically the same power to weight ratio? All i have to do is knock off a bank.

I think it would work. You probably couldn't use it on much of an incline or headwind, but for flat cruising I bet it would make some surprising mileage numbers. Get a good low-end mileage cam and some higher compression pistons (and maybe different heads, I don't remember what year they changed chamber types) to basically build it to 1970 specs and it will work great.

And before all the naysayers won't work and the engine will be lugging to hard, I would suggest not commenting unless you have actually been around a big block Caddy hooked to a manual transmission - the low end torque they produce is nuts. These aren't at all like small blocks or even BBC's.

[Daimler]

One might think a bigger engine would use a lot more gas. But, a buddy of mine had a 1976 Ford (spit) 3/4 ton 4X4 with the 351. He was under the impression he would gain the power he needed to easily climb the great divide. I explained to him rebuilding this engine probably wouldn't do any good. I had just rebuilt the flat head six in my /54 power wagon expecting great gains and it didn't make a lick of difference. A lump is a lump. No replacement for displacement I informed him. A 460 is what would be required in that 6000 lb truck in order to climb mountains. Four thousand dollars and an adapter plate later we had the job done. Besides a correct rebuild we ported the smog heads ( you wouldn't believe the smog exhaust p/u bumps in there) and change the timing chain and gears from stock to a set of 429 gears. This puts the cam back in the upright position instead of like 8 degrees retarded as the stock set does. ( for smog reasons) He took his truck plus a 9 foot camper to Vancouver Island. He told me even after slowing down to negotiate switch back curves, he didn't even have to shift out of fourth. It just walked up anything he threw at it. Passed everything except a gas station he told me. Same size carb (650 cfm) on the 460 as was on the 351 but instead of third gear and wide open throttle with the 351, it was fourth gear and like half throttle with the 460. His mileage went from 9 mpg to 13 mpg. Not stunning of course, but if he had sprung for the overdrive I suggested to him I am sure the numbers would be way better.

[1972RedNeck]

What are you planning on doing to bolt a manual to the Caddy's BOPC bellhousing pattern? What about a flywheel?

[Daimler]

cad500parts.com has an online catalogue and on page 29 under the heading Transmission adapters they have fly wheels for 380.00 and 480.00 with pilot bushings too. I pretty sure other companies do as well but I have'nt done the research yet.

[Daimler]

Same place has a transmission adapter plate for a 140.00. for bolting GM transmissions to the BOP block. (I just learned BOP stands for Buick, Olds, Pontiac)

[1972RedNeck]

Originally Posted by Daimler

Same place has a transmission adapter plate for a 140.00. for bolting GM transmissions to the BOP block. (I just learned BOP stands for Buick, Olds, Pontiac)

Be careful with the adapter plate. My brother and I used on behind a warmed up 472 and couldn't keep flex plates in it. 100 miles and they would be cracked. Built our own out of 1/2" plate (the boughten one was 3/16" or 1/4") and never had another problem. The only thing we could figure was that the adapter plate was allowing it to flex ever so little.