Small block to big block ?s

[see ten]

We have a buddy with a 86 4x4 who is wanting a big block installed (currently running a small block). What do we have to do to get the big block to work? Are there any clearance issues or mount problems?

[LONGHAIR]

In an '86 he shouldn't have any clearence or mount problems. 454s where available in lots of trucks from that era 73-87. The only issue that I can think of right off is in the transfercase. It is probably an NP208...lighter duty aluminum case. If he changes the rest of the drivetrain along with the big block, it should be fine.

[snj8198]

I wouldn't be scared to run a 208 behind any mild performance BBC. Granted the 208 is not the toughest t-case choice, but it's no slouch. I doubt one with 200K+ miles with lots of wear is right for the job, but I've seen plenty of stock-100K 208's survive tough 4X4 duty on a regular basis, including (worse case scenerio) a 700/208 combo behind a .100 over 454 w/ 177 Weiand blower survive daily driver duty for a few years under a heavy footed owner. -steve

[trkklr77]

you MIGHT need to change your rad, depends on the one currently in the 86
you MIGHT need to change the fan shroud aswell

change exauhst

[eedgell]

Take out SB, bolt in BB. Other issues may apply. You have to love GM. It is all the same, on 4x4's and 2wd's after 76. Cooling issues might arise, as well as bracket issues, but really no clearence problems. Really a bolt for bolt opperation. I put a 72' 402BB in my 79 GMC, slick. No problems.

[see ten]

So the motor mounts are the same? Unbolt the small block, Bolt in big block.....Drive til something breaks!

[eedgell]

As far as bolting it in, it is the same everything, or it works put it that way. Some brackets are different, you should use a higher amp starter, but pretty pain less really. Might want to go with a bigger clutch if 4 speed. No manufacturing required.

[kevinr1970]

I have been considering something similar.
I have an '86 GMC 1/2ton 4x4 and have access to an '85 3/4ton 2wd with a blown tranny.

If I were to do this I wanted to run the 454 with a rebuilt 700r4 (with heavy duty sun gears(?) and other heavy duty parts installed during rebuild including shift kit) and the stock 208 tcase.
I am not doing any four wheeling. I would mostly be using the truck for weekend and the occasional snow driving. I would like to be able to pull a car trailer (with some sort of truck on it invariably) or a small camping trailer.
Would the tranny hold up to this sort of use?

I have been told that the 1/2ton brakes might not be adequate for pulling a trailer. But the car trailer I have used and the camper trailer I looked at both had some sort of trailer brakes.

PS, I am assuming this is a used engine swap. If I understand right, the carb's on the 454 do not have a provision for a tranny kickdown that would be required with a 700r4/turbo 350. Especially if it was infront of a 4-speed manual.
So you might need a new carb?

As for exhaust mentioned earlier, a friend that did a similar swap a few years back said he bolted his existing exhaust right up to the 454. But he doesn't remember if he had a dual exhaust set-up or a single with a Y-pipe. The 80's were a long time and too many brain cells ago...