I bought a rebuilt 425 recently and the previous owner said it has a new cam ( https://www.compcams.com/xtreme-ener...e-260-455.html) , lifters, springs, an intake, and a 750 double pumper. It is the stock bore and stroke with B heads. My question is how much power would you guess this thing makes. It also came with a set of G body headers, I was wondering if those would work on my 76 cutlass supreme. I know I can use the mounts from my 350 and that will work but I need to know if I can use these headers or if I need to order new ones before I drop it in. Thanks in advance

 

I also bought a th400 with it but I will be swapping that in later. The trans came from a 75 Pontiac from what I can tell. I haven’t done any research but I was wondering if this is a long or short tail trans. I can provide the numbers on the tag later in the day if those are necessary​​​​​​. Thanks

 

This is a short extension housing.


This is a long housing.

 

Since we have no idea which "G-body headers" you have, it's impossible to tell if they will work or not. Obviously the taller deck of the BBO requires different headers than the short deck of the 307 that came in Olds G-body cars, so if those are SBO headers you need different ones, or else a hammer to "customize" them.

 

So right now I have a turbo 350 would I need a shorter driveshaft to run the 400?

 

They guy said they where for the big block but I don’t know. I think they where headman or hooker headers. How would I be able to tell which ones I have?

 

Yes. You'll also need a new front yoke for the driveshaft. The TH400 has a larger output shaft than does the TH350. And of course, the trans crossmember moves backward because the trans is physically longer and the mount is further away from the bellhousing face.

 

If you can find a stamped P/N on the header flange or one of the tubes, that's probably the only way to tell for sure. The Hooker BBO headers for a G-body have one tube that goes around the outside of the frame on each side.




ARH sells BBO headers for a G-body that fit inside the frame rails but there is other collateral damage, like the need to trim the trans bellhousing and use a mini starter.

 

So I was looking at the headers and the only thing I can find on them is that they are headman headers

 

Well, then that's easy. Hedman doesn't make any BBO headers for a G-body. The only Olds G-body headers they make are 58070, 58073, and 58076. These are all the same header - the different part numbers are just coating type. They are for the SBO. The part number should be stamped on the flange between the tubes. Look closely, it can be very faint.

 

Thanks for the help, looks like these are 58070. I feel like I've heard somewhere that they are interchangeable or at least one set would at least work on the other size like bbo on sbo I think it was. Is that true or I'm I just making stuff up

 

BBO has a one inch taller deck height, so the exhaust ports are about 3/4" higher and further outboard than on an SBO. The headers will physically bolt up to the heads, but whether or not the pipes actually clear the chassis, starter, oil filter, etc depends on the exact routing of the tubes. Of course, SBO headers will have smaller, shorter primary tubes than you want for a BBO.

 

So with that cam and stuff is there a way you could estimate the horsepower. Another thing I forgot to add is that it was originally the high compression 4 barrel so I believe it is 10.5-1 compression

 

So if these don’t fit right what headers would you recommend using. It will be going in a 76 cutlass supreme

 

Get headers for a 1976 Cutlass with 455 Olds motor. Your choice on manufacturer.

 

There is a guy on Facebook who is selling a set of hedman headers for a very reasonable price but he can't find the part number. He had them in a 69 442. Would these work in my 76 or would things not line up right

 

Most header manufacturers show the same headers for 1968-1977 cars, so if they were installed on a BBO in a 69, they should work on a 76 also. Just be sure the seller is certain the engine was a big block and not a 350.

 

ok, thanks for all the help