Author Topic: 1981 Fleetwwod Engine Swap  (Read 621 times)

Offline 60eldo

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  • Name: Johnny.K. CLC MEMBER #27762
1981 Fleetwwod Engine Swap
« on: October 28, 2013, 01:02:32 PM »
  I have a friend whos motor in his 81 fleetwood is shot. He wants to replace it with  a 472 from a 68. Will that bolt in to his existing tranny, its a 400 I think. Or would it be easier for him to buy the 472 motor with the tranny, but then he might have a driveshaft problem? The other option would be to put a 425 engine in from a 77 cadillac. I believe the transmissions are the same so would it bolt right up? Which is easier,,, Any ideas?   thanks guys
« Last Edit: October 28, 2013, 05:20:39 PM by 60eldo »
J. Kluczynski

Offline 76eldo

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  • Name: Brian Rachlin
Re: 1981 Fleetwwod Engine Swap
« Reply #1 on: October 28, 2013, 05:38:20 PM »
I don't know for sure but I have always heard that any 368 or 425 powered car can accept a 472 or 500.  It will make a difference if the that is FWD or RWD so you want to get an engine for the same type so that you don't have to swap manifolds, brackets, and oil pans.

Sounds like it will work, but I'd check in with the guys over at the modified chapter message board.  They do these swaps frequently.

Brian Rachlin
Huntingdon Valley, Pa
CLC # 22443

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Offline 60eldo

  • Posts: 790
  • Name: Johnny.K. CLC MEMBER #27762
Re: 1981 Fleetwwod Engine Swap
« Reply #2 on: October 28, 2013, 06:24:05 PM »
Both cars are rear wheel, Im wondering if putting the 425ci from a 77 cad. will be easier cause it might bolt right up to the 400 tranny in the 81 Fleetwood
J. Kluczynski

Offline Scot Minesinger

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Re: 1981 Fleetwwod Engine Swap
« Reply #3 on: October 28, 2013, 06:59:24 PM »
It may be easier to deal with modifying the drive shaft.  Install the 1968 engine/trans combo and splice the 68 drive shaft in the middle to the 81 drive shaft.  A reputable place like "Driveline" can weld the two sections together and balance so that the rear section bolts right to the differential and the front slips right in the trans.  You would just need to specify the length.  Question is will the rear end on an 81 handle the 525lb-ft of torque that the 68 will provide?
Fairfax Station, VA  22039 (Washington DC Sub)
1970 Cadillac DeVille Convertible
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Offline TJ Hopland

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Re: 1981 Fleetwwod Engine Swap
« Reply #4 on: November 01, 2013, 09:31:50 PM »
The 81 with the 368 still had the 400 trans.   I believe the transmissions were basically the same 77-81.  Earlier I believe there were slight internal differences and they used a longer tail section. 

With the body change in 77 they changed the oil pan so if you are going with a RWD 472 you will have to swap the oil pan and pickup tube off the 368.   The earlier stuff was front sump which was basically backwards from a typical GM pan design.  77 was closer to to a more typical GM rear sump design. 

Before the 'new' motor goes in be sure to make sure the timing chain has been done.  Also a good time to do the rest of the seals and gaskets.   I would not take the heads off but I would do everything else while its out.   With the intake off you can see the cam in a few spots to get an idea of its condition.  With the pan off you can wiggle the rods and such.   When the timing cover is off I would weld some 1/4-20 nuts to the inside of the cover where the small water pump bolts go through.  They are almost always stripped.  Nut on the back will keep that from being a problem.
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