455 out of Ninety-Eight Going into 1980 Cutlass G Body

GBodyGuy

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Apr 20, 2020
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Ok I have a 1980 Cutlass Supreme that previously had a 307 in there. The 307 and transmission are both gone and I’m replacing them with a 455 Oldsmobile out of a Ninety-Eight with 21K miles on it and comes with a the TH400 Trans bolted up with and the drive shaft. I’ve been told that this isn’t a simple drag and drop due to the driveshaft or transmission needing to be modified to fit the car. What should I do ? Get a TH350? Will it take this 455 with aftermarket Headers, Intake Manifold and has been done up to push out some major HP/Torque...
 

Kennybill

Active member
Oct 3, 2018
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Braceville Ohio
Full size cars (88&98) had long shaft turbo 400. Either have new shorter driveshaft or different shorter trans. Crossmember moved back. Tube Headers that fit are pricey
 

Olds 307 and 403

Well-known member
Oct 4, 2018
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Melville, Saskatchewan
Go manifolds, the W/Z reproduction manifolds or Thorton shorties will fit. What trans do you have now? A stock TH350 with a Transgo shift kit and a few upgrades should survive.
 

TURNA

Active member
Oct 5, 2018
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NY
TH400 into a GBody

You need to cut the "ears" off the TH400
Cut the driveshaft to correct length
Use the driveshaft yoke from the donor car
Fabricate a kickdown
Get a Xmember for a TH400 along with the frame extenuation piece

And finally ditch that 7.5 rearend, because you are going to blow it up!!
 
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GBodyGuy

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Thread starter
Apr 20, 2020
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Full size cars (88&98) had long shaft turbo 400. Either have new shorter driveshaft or different shorter trans. Crossmember moved back. Tube Headers that fit are pricey
What type of shorter trans ? TH350? 200 R4?
 

GBodyGuy

New member
Thread starter
Apr 20, 2020
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Go manifolds, the W/Z reproduction manifolds or Thorton shorties will fit. What trans do you have now? A stock TH350 with a Transgo shift kit and a few upgrades should survive.
I currently only have the TH400 that came with engine
 

TURNA

Active member
Oct 5, 2018
189
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NY
I have it all wrapped up at the moment and it is raining.

If its nice out tomorrow I will
 

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