: 85 FW RWD HT4100 Engine Swap to Olds 350 help

01-13-11, 12:49 PM
I'm doing my first engine swap (I've done an engine rebuild, but never changed a motor)
I've got an 85 FW RWD with a 4100 and have found a nice 79 olds 350 to put in but am having trouble finding exhaust manifolds for it. I can get OEM exahust manifolds for the 350 Diesel option at quite a price but they wont let me see them before I buy. Does anyone know if they will bolt up to the original exhaust system for the 4100? I have a set of 350 elderbrock headers that came with the engine but I don't know if they'll fit in the car, it looks tight. The original exhaust went down and wrapped around the front of the engine and would like to use it if possible since a lot of it is brand new.
I know I need the engine mounts for the diesel option and will need to make a bracket for the throttle cable. I'll need to pull the fuse on the in tank fuel pump.
Will the original fan and fan drive shaft fit with the olds 350?
I'm expecting that I'll need to rig up a bracket to hold the power steering pump. I think I'll ditch the A/C system since it's got issues right now. What do I need to do to get belts that fit properly? Do they make custom belts for a new setup?
I'll get a tranny shop to calibrate the TV cable.
Anyone have any good advice or lessons learned to this particular swap? I'm trying to get as much prepared ahead of time since the swap will take place in my inlaw's garage and can't take too long.

01-13-11, 12:53 PM
There's a HUGE thread about someone here, Greencadillacmatt who did a 4100 to Olds 350 swap, found here:


01-13-11, 01:47 PM
Thanks for the link, there's a lot of good stuff.
Does anyone know if the olds 350 diesel exhaust manifolds will match up to the existing 4100 exhaust system?

01-13-11, 06:21 PM
Best guess - no. Completely different engines.

01-14-11, 06:12 AM
I'm with cosmo, probably not. If you buy the Olds head pipe it's just a matter of cut and splice. An exhaust shop shouldn't charge too much for something like this either.

cadillac kevin
01-14-11, 11:07 PM
you should be able to use 307 brackets, motor mounts, belts etc. the olds 307 and olds gas 350 are the same externally.
I'd also hook up the AC compressor. its easier to hook it up (or at least bolt it to the engine and not run the belt to it) than remove it. not to mention its illegal to release R12 into the atmosphere.
as for using the factory exhaust setup- what size is the single pipe on the 4100?

01-18-11, 03:08 PM
Thanks for the advice guys,
I've decided to use standard olds 350 manifolds a friend of mine has from a 70's Delta 88 and will take it to a muffler shop.
The car's under quite a bit of snow right now, so I don't feel up to digging it out to get the exhaust diameter, but It's pretty small.