Schober Motorsports

Alright I want all advice, anything that would help me out with this. From what I've read I see that if I get the 307 motor mounts that it would work. So I'm looking to also use a Th400 trans and I know that the rear end will need to be upgraded. So anyone who has done this or done research on this, what will I have to do to make this work! Thanks!

Cameo White

Might post at Oldspower.com as well. Lots of G-body guys over there, many of whom have researched/contemplated/done a similar swap.

70 cutlass s

Yes the motor mount from the 307 will work. You will need the crossmember from one that had an 200R4 for the th400 to bolt in.

If you can find an 8.5 rear end that would be the way to go. If do find one you will also need the drive shaft because the drive shaft is one inch shorter than the 7.5 rear end.

The 8.5 are getting a little hard to find. They came in Grand Nationals and 442. If you use your rear end if it's the 7.5 you can get gears and carrier and maybe a posi unit out of an S-10 rear end and have it installed into yours.

svnt442

I had a 455/th350 in an 80 (for a month...rod bearing went...D'OH!) and it fit like a glove. It was an easy swap due to the use of the th350. I didn't have to worry about the crossmember or the driveshaft so that was a plus. It dropped down on the 260 mounts like it was finally home. Heck I even bolted it up to the stock exhaust because I didn't have the money at the time for custom work to be done to make a dual set up for it and the only headers that were out at the time were hooker super comp engine swap headers that had 2" primary tubes and required trimming of the lower control arm mounts to fit. Not to mention they were over $700 (in 1993....OUCH!!!) so that was WAY out of the budget.
All in all it's pretty straight forward, but I'm pretty sure you're at the very least looking at a custom driveshaft due to the th400, but that can be done without too much out of pocket.

racing8up

the 455 fits nice in a g body the 455 is 1.34 inches taller but not a prob it will fit nice you will need to use a bigger radiator like a 4 core or get a after market your 7.5 rear will hold up to the power ... i would run a 342 gear nice cruise and street racing gear any more q,s just ask ive put several 455s in g bodys in fact ive used about every type of gm motor in a g body the best one was a 472 caddy in a 79 cutlass

83-425

83-425

hope i can get some help ,i have a 83 hurst olds sand blasted frame,body, fenders ect . in the frame sitts a 425-m20 with those taller valve covers because of using roller rockers .i was just told be someone my HEATER AC BOX will hit . will a normal big block with factory valve covers work ? and can those taller china crome ones work to ? i just discovered the moter is in the way of putting the box in. i might just re lift the body off the frame to install box before lighning up doors,fenders ,hood ect. and paint.P.S using factory intake WILL MY HOOD CLEAR ? maby a lower air filter ? i would like to use a the factory hurst hood. thanks for the help

svnt442

You either need to modify the airbox or you can use tall gaskets with the stock valve covers to make it clear. The tall ones won't clear witht the stock airbox.
As far as the hood goes it will depend on your intake and air cleaner/filter combo. I can tell you the factory carb and manifold fit fine in the 80 I had.

Kennybill

The heater/ac doesn't "have" to be altered. There's a Toro intake for sale now that can help with hood clearance. Imo they flow good. Also imo the Oldsmobile engineers knew a little more than some give them credit for. Ken

83-425

you are telling me what i want to here ,i will lift the body install air box and lower , we will see. the intake was machined to fit the heads and block perfect .we all know when milling block and heads things change . the moter left the shop perfect .68 cast 455 intake ,68 q jet carb modified on a slightly built 425 . i hope this all comes together ...any other info would be great...

83-425

83-425

i have a 8.5 g body rear with new 410,s and posi,also have a 200r cross member that will work on your th400 ,also have new 400 drive shaft that went inbetween . e mail if you want

yjmud

For The Money Do A 9 Inch Ford Rear

J-(Chicago)

I'm here to point out that this thread is from 4 years ago.

joe_padavano

Yes, but User 83-425 resurrected it with a new question that actually is pertinent.

J-(Chicago)

Oh, now I see.....
Pertinent is good. Carry on, men.

83-425

i installed the heater box ( w ac ) .i tapped the pcv inner baffel on the valve cover to clear the rocker assy.and the corner is still in the way. these are 66 425 covers .MABY a g bodt 307 valve cover is sculpted a little different ?? and may work.i want to keep the ac going and modified the sbo brackets to work great . this is the only thing holding me back.

joe_padavano

The 307 valve covers are shaped just like any other Olds valve cover. The only difference is five bolt holes vs. 10 (the blank spots for the missing five are still there, just not drilled). Have you looked at the 68-72 notched valve covers?

83-425

i got the original 1983 307 v covers off moter and there is a big diff in shape .these covers are angled in quit a bit more on the lower ends to miss hitting the box. they fit great with the heater box , 5/16 clearence .drilling holes not a problem. Dont know why i did not think the valve covers that were made for the car would work. p.s what are notched covers ??

RetroRanger

Notch valve covers have a recess or angle at the back to add clearance at the brake booster and AC box. They were made specifically for olds BB in A bodies.

I have a pair of notch valve covers for sale if your interested pm me

joe_padavano

I'd like to see a photo of your 307 valve covers. I've got three 307 motors and the covers are the same shape as those on all my older Olds motors.

83-425

83-425

i send a photo, i guss it did not get to you .e mail me directly or tell me how to attach ? not good with computers roadliner@verizon.net

vista461

Later ones are different than early ones. I think the change was about 1973. With later ones my 455 fit fine in an 86 442 I had. No clearance issues with the a/c box.

88hurstolds

Here's my build, some info on the intake and air cleaner:

http://www.gbodyolds.com/forum/showt...hp?99-455-Swap

BigMike1228

I am trying to put a 1970 455 in a 1987 Monte Carlo SS. Do you know which mounts I would need to make this work? I am about to lose my mind trying to find the right ones. Your help and advice is greatly appreciated

joe_padavano

The Monte is the same chassis as a Cutlass. Use the frame pads for any 1978-1988 A/G-body or 1977-1990 RWD B/C body with an Olds motor (including a 307 or diesel). Note that the frame pads are different RH/LH. Use Anchor 2328 motor mounts with these frame pads.