[cruze69gto]

I have a 78 Grand Prix with a 301 and want to replace it with a 350 or 400 what is the earlest block i can use and not have trouble with the mounts. And will the 200R4 trans. work with the 350 or 400.

Mike

[cruze69gto]

I have a 78 Grand Prix with a 301 and want to replace it with a 350 or 400 what is the earlest block i can use and not have trouble with the mounts. And will the 200R4 trans. work with the 350 or 400.

Mike

[mike nixon]

the 200 will bolt up but probably won't hold up with out some serious mods.

71 and up engines should bolt in the chassis.

the exhaust won't fit [too narrow]

i don't remember if the mounts will need to be moved or not, it's been awhile since i've done this swap.

mike

[Pontiac455]

I have a 1980 Grand Prix with a 72 455 on the stock motor mounts (301),that is until I broke both of them and went with a modified set This really depends on the type of power you plan on pushing on the stock motor mounts if it is mild they will hold up fine. I went with a turbo 400 tranny and a modified cross member.

I had to remove the heater assy under the hood and the fender wells to gain enough room but is not necessary for most pontiac engines if you stick with the low valve covers but if you step up to the tall ones then the heater assy has to come out.

Stock exhaust will not fit go with a set of headers

Have fun.......

[BradZZ]

I put a 75 400 from a TA in my 81 GP used the exhaust off the TA including Y-pipe
the strange trans brace on the G-body limits
you to a single exhaust unless you get a aftermarket crossmember or let the driver side hang down. The 200-4R will boltup but you HAVE TO lockup the torque converter on that trans or it will burn up, Several places sell a kit to hook it up to an older non-computer car. I used the TH-350 from the TA in place of a Metric 200. The motor and Trans fell right in to place of the old 265/Metric200 setup
Brad

[cruze69gto]

Thanks if you know of any thing else i should know please post. I have a 72 350 and a 72 400 i can use. what is the best trans. to use a 350 or 400 turbo and will i have to anything for it to fit.
Mike

[Ken MacNicol]

Use a dual exhaust trans. crossmember from a earlier year Grand Prix, Cutlass, Monte Carlo etc. It will bolt in, all you have to do is drill new holes.

[BradZZ]

Hey Ken sounds like a good Idea but I've never seen any on a 81-87 GP which years are you talkin about cause yard prices are better than aftermarket!

[Ken MacNicol]

I think one of them was from a 72 LeMans and the other I got from a mid 70's Cutlass and I used them both on a 81.

[BradZZ]

Ken can post a pic of how you attached the brace to the frame. My 35o trans is slowly going out. I was thinking of using a 200-4r like Mike but the 81 I've got doesn't have the perch for the OD trans. If I could mount up an early A-body trans brace (which I have) with the dual humps and relocate the trans mount Its a double winner.
What headers are you using?
PS
To mikes question about 350 vs 400
The 400 is defiantly stronger and I think it fits where the 200-4R sets, and a 350 fits inplace of a 200 with little work

[Ken MacNicol]

I do not have either car anymore. I used a 400 trans. and just drilled holes in the c-channel where the crossmember lined up. One car had 3-tube headers and the other had [1 5/8"] 70-81 Firebired Hookers then changed to [1 3/4" GTO headers. The car I have now has a custom round tube crossmember with a set of round port IA headers that are modified to fit a D-port.

[mike nixon]

if you're handy you can modify the orig crossmember to fit the duals exh.

when i put the 455 olds in my 81 diesel g/p i used a 73 cutlass crossmember. i think 74 was the last yr for true dual exhaust.

unless you're racing the car on a regular basis i'd use the th350. there are less hassels to deal with.

re the heater box, it's fiberglass and can be modified to work with tall valve covers and still keep the a/c.

if anyone runs across a non a/c unit in one of these cars i need the interior ductwork for one of my projects.i'll take a whole system if necessary.

mike

[RA462]

I would use the TH350 and RA or HO exhaust manifolds. I had an 81 with a 400 and 4 speed GP that had dual exhaust back in 93. The driver side pipe off the manifold fit between the oil pan and engine cross member like stock. After that it ran dual along the pass. floor pan and the LH pipe crossed over between the rear axle and the back seat area. Buy a cat back system for a Monte SS and modify it. Good luck and keep us posted.

Who ever thought pinewood derby cars would lead to this!