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

Rocketman269V

New member
Feb 26, 2020
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What year is the 455/T-400? A 98 would have had a medium length T-400, as stated above; however, The driveshaft would have a long yoke on the front, probably machined smooth part way on the inside to seal on an "O" ring on the output shaft, and a CV joint and a "companion flange" on the rear. None of this will work with a short shaft transmission and 7.5/8.5 G body rear end. Depending on your budget, long tube headers would be ideal. Also, be sure to use an early HEI distributor, with a single 3-wire plug. If your 455 has a points distributor, there is no provision to run one on a late model car, unless you add a ballast resistor. Good Luck! with your project.
 

GBodyGuy

New member
Apr 20, 2020
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0
1
What year is the 455/T-400? A 98 would have had a medium length T-400, as stated above; however, The driveshaft would have a long yoke on the front, probably machined smooth part way on the inside to seal on an "O" ring on the output shaft, and a CV joint and a "companion flange" on the rear. None of this will work with a short shaft transmission and 7.5/8.5 G body rear end. Depending on your budget, long tube headers would be ideal. Also, be sure to use an early HEI distributor, with a single 3-wire plug. If your 455 has a points distributor, there is no provision to run one on a late model car, unless you add a ballast resistor. Good Luck! with your project.
I have long tube headers and it came out 1975 I’m thinking of putting a TH350 down there
 

TURNA

Active member
Oct 5, 2018
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NY
You will just use the front yoke off the 88 driveshaft and have the installed on your shortened GBody Olds driveshaft
 

Intragration

Member
Apr 2, 2019
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Chicago
Are you planning to keep the 7.5" rear end? These are relatively weak, and they also came with really tall gears, possibly as high as 2.14. Neither one of these is an immediate deal-breaker, but if/when you replace it, you'll also need to shorten the driveshaft. If you're planning to go with a different rear end in the near future, you might want to wait until you get it in and measure for the correct driveshaft length.


Another thing to consider is the trans crossmember. First, the face-to-mount distance is going to be different with the TH400 than for your original trans, which I believe was a TH200. I used a TH350 in my original TH200 car, and the mounting point for the trans mount was the same. A short TH400 mount will fall 6 3/8" further back. Don't know if the long tail-shaft versions are different. The short TH400's face-to-mount distance is the same as a 2004R, which was available in later ('84+?) G-bodies, so if you went this route, you could use a crossmember from one of these.


The other thing with the factory crossmember is, they didn't have a provision for dual exhaust, and if you're using full-length headers, the left collector is going to dump IMMEDIATELY in front of the crossmember. You could spend a lot of money on an aftermarket crossmember, or you could modify yours to make room. Here are a couple pics of how I modified mine.

Picture 1650.jpg Picture 1656.jpg Picture 1657.jpg Picture 1659.jpg Picture 1667.jpg
 
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Olds 307 and 403

Active member
Oct 4, 2018
616
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Melville, Saskatchewan
Stock 7.5" spider gears are very soft. I exploded a set and it took out the gears. On the Astro van replacement spider gears that came with the gears and carrier were also quite worn and would have failed. I bought the much better hardened Yukon spider gears. Still look new despite many burn outs and heating up slicks at the track.