425 / 368 engine swap

[PersianLimeFiremist]

Guys- planning to swap out the bad 8-6-4 368 in my 1981 Fleetwood wagon for a 1979 425. I am going to have the 425 gone through and upgraded with the MTS #5 cam, and was considering the Edlebrock intake as well. Then I got to wondering about the 368 fuel injection manifold and throttle body... would that be a simple bolt-in or not? Is it a better option than the Edlebrock and a new carb? If not which carb? I am not building a hot rod, just want a reliable daily driver with (hopefully) as much pep as my 1996 Fleetwood LT1. Am I on the right path? Any other suggestions? Thanks Bob

["Cadillac Kid" Greg Surfas 15364]

Bob,
Just going to toss this out there.  Your idea of a 425 in place of the 368 is a good one. You did not say if your car was originally FI or carbureted. If it is FI you are going to have to do a bit of electrical modifications to go to a carburetor (Quadrajet by all means) regardless of which engine you change to.  That said, since the 368, the 425 AND THE 472 ALL HAVE A 4.06 inch stroke that means your 368 oil pan and pick up, necessary for chassis clearance will fit all three of these   motors.  Parts for the 425 are no where as easily found (pistons, cylinder heads, front covers) as those for the 472. An essentially stock 8.5:1, large chamber 472 (with a #5 cam if you want) running a stock 472 intake and carb would be one of the greatest combos that would appear absolutely stone cold stock and let you pull a freight train with your car.
Just my thoughts.
That (again) said the 425 and the 368 intakes are quite restrictive and with your combination an Edlebrock 2115 would let you use your existing AC compressor (assuming you have the R-4).  If that is your decision PM me and we can talk about the intake.
Greg Surfas

[PersianLimeFiremist]

I was thinking 425 for a couple of reasons; first, I found a running 81k mile one complete, close by for $400. I had a 79 SDV and I liked that car, it was plenty quick off the line. The 81 wagon is fuel injected, that's why I was wondering about swapping those parts onto the 425

[TJ Hopland]

I believe the 368 had smaller intake ports than the 425 which was the same as the 472 and 500 so that is one possible issue.   It was the 2nd year for the DEFI injection system so there was still some learning going on.  THe 80 and 81's have several one or two year only sensors that I have read can be very hard to find today.   They were also know for electrical connection issues.  I believe in 82 when it it the 4100 plus some other GM models they changed to a completely different style of connectors that I think stayed the same till the end on the trucks in 95.

Having a 'good' 425 close is a good thing.  Another plus is weight is about the same as the 368.   The 472 was supposedly at least 100 pounds heavier.     

I have more thoughts but am out of time at the moment.   

[76eldo]

I think i'd stick with the complete 425 with the carb.

Brian

[66 Eldo]

I think i'd stick with the complete 425 with the carb.

Brian

+1 on what Brian said.

Unless going to a port FI system TBI would be a wast of time IMO.  I would stick with the carb. High cost vs return and the extra work of switching to any FI system just isn't worth it IMO.  Also the spread bore design of the Q-Jet helps to give a torquey feel off the line. Although not a spread bore, the Edelbrock (1406?) is a good performer and replacement for many older full size American cars. Its basically a repop of the Carter AFB.