Friend of mine has an 84 Delta 88 with what he says is a 307 Olds motor. Said he was thinking of buying a 350 "Rocket" engine he found, rebuilding it and putting it in his car for a little more kick in the butt.

I says why don't you go with a 400,425 or 455 as the rebuild cost would be about the same and it would really wake the car up. He's concerned the current accessory brackets on the 307 would not work on the 'big blocks" I think the engines are dimentionally the same on the outside and his concern about alt, AC, P/S brackets, pulleys and etc. would be a non-issue. Bellhousing pattern is the same too isn't it?

Could someone on here please comment?.................thanks in advance

Jerry

 

The 350 will be a drop-in. 400/425/455 blocks are both wider and taller than 260/307/330/350/403, so there would be some accessory bracket issues.


Compared to the 307 even a stock-rebuilt 350 would make it an entirely different car.

 

400/425/455 have a taller deck height and are an inch wider because of it. The bottom of the blocks are externally identical, so mounts are not the issue.
The brackets could be an issue because by that time the BBO was out of production and the 307 mounts may not have the holes to work on the BBO.

 

For ease of installation, the 350 is the way to go.........

 

Unless you find a 455 with all the brackets...

 

Should also note the exhaust manifolds from the 455 may be required... Although the 307 manifolds will bolt up to the 455 heads, the small port openings of the 307 manifolds aren't going to match up with the 455 head port openings reducing exhaust flow.... then this will lead to exhaust pipe changes etc.....

 

Which you won't because the 455 was never offered with the R4 A/C compressor used with the 307s.

In any case, the use of 307 brackets on a 455 had been done MANY times and requires only a few minor mods to the brackets. This site describes the mods.

 

Or, split the difference and go with a 403, big cubes in a small block platform.

 

Thanks much, guys........this explains why I'm a Pontiac/Chevy sort of guy!

I found out today that there is a short deck block and then a tall one..I did not know that so I appreciate this info.

I'll pass this along to my buddy and 'fess up that he was correct all along!! Brackets can get ugly when pulleys and belts don't line up like they should.

I know Pontiac used some 403's in Trans Am's for a couple years, so how hard is to find one of these complete?

thks again, Jerry

 

403's in Trans Am's would be more difficult to find then Olds 88's & Custom Cruisers which came with 403's as an option from 77/79 (IIRC).....

 

There were probably more 403s installed in Pontiacs than in Oldsmobiles. There were nearly 280,000 Trans Ams (not all Firebirds, just T/As) build from 1977-1979. About 85% of those were automatics. This doesn't count the 403s installed in Bonnevilles, either.

 

This is a no brainer. A mildly built 403 will give the required performance & is a drop in.

 

I agree with you guys..........a 403 would be the way to go if my neighbor wants to give that 88 a kick in the pants.

I'll pass this along to him and let the search begin.

thanks much, jerry

 

403 would be by far the easiest

What is your location?

dirt cheap 455 with brackets:
https://classicoldsmobile.com/forums...-400-00-a.html

 

We are located in SE Ohio