OPG advertises a HiPro set of exhaust manifolds based on the Olds big block pattern. I currently have a beat up set of headers on my 350. I like the look of stock but also like the idea of horsepower. Does anyone have any experience with these OPG's exhausts? I would appreciate any comments or advice on the stock vs. header controversy specifically for the 350. Thanks

 

Not sure on OPG, but there is also... Thornton Reproductions. I am considering them in the future. They sell on eBay as well. Perhaps they are the same ones OPG offers?

EDIT: feebay link... http://cgi.ebay.com/ebaymotors/350-3...ts_Accessories

 

I have never held these in my hand, so I shouldn't post. But I've heard that these "hi-perf" small block manifolds don't really have the full extent of "chambering" that the big block W and Z manifolds do. They might perform slightly better than stock small block manifolds, but I wouldn't expect much.

Maybe someone with first-hand experience can confirm or deny.

 

This comes up regularly. See these two threads. And yes, I have held them in my hands (well, the ones sold by Ram Air Restorations - I can't believe that there is more than one set of molds for these manifolds).

https://classicoldsmobile.com/forums...manifolds.html

https://classicoldsmobile.com/forums...manifolds.html

 

Joe,
Thanks for posting the previous threads relating to the manifolds.......I was unaware this topic had already been looked into.
Mike

 

OPG sux

Buy elsewhere

 

mike are you looking for a better cast manifold that is stock or closer to stock ? You can run the w/ z manifolds . wont be 100% correct but will look , work , and be better than any small block set up out there other than tube headers ,

 

W/Z manifolds will NOT fit on a small block Olds.

 

According to Bob Gerometta from the book Wild about cars on page 89 under exhaust /headers" The Z and W will also bolt to the small Block heads" ?? Seams to make sense if You can bolt on a set of bbo heads to a sbo if you get the combustion chamber volume set either with a pop top pistons or cut the heads down. ?? I do know with pontiac you can run the ram air gto on any 326 to 455 . Just what I have read I will be eager to hear more.

 

As to the BBO W/Z manifold onto a SBO engine...

The pass manifold WILL have major interference with the oil filter adapter.
Unless you run a different type of bolt for the adapter, AND grind the hell out of the manifold, it just plain wont mount.

Been there, done that.
Not fun.

Jim

 

I just put a set of those Thornton manifolds on my 65 this weekend, they are very heavy duty and they are considerably larger it internal volume than the stock manifolds, (makes the stock manifolds look kinds sick) they have a center divider and 2 1/4 dumps on both sides, they fit perfect and look good and last but not least they are quiet.
IMHO I think they where a good investment.

 

Pics?

Gasket needed?

 

I don't have any pics, my wife is out of town with the camera, I did use gaskets but according to Mr Thornton you don't need them. If you have more questions just call them, he answers the phone himself (Thornton Reproductions 610-282-2494) and seems to be a real nice guy, they also have a fairly decent WEB sight.

 

OPG is not making the manifolds.Chances are,they are getting them from Thornton.I would contact him for the 350 exhaust manifolds.
The large outlet W/Z manifolds from ramairestorations are real nice,but no,they will not fit a SBO,unless you get a little creative.It's not the head,it's the block & surrounding parts that are the problem.Since the deck is shorter on a SBO,it brings the manifolds down farther,thus causing interference issues.

 

Jag1886,
Did you notice any improvement in your car's performance? I would love to see someone do a before and after dyno on the Thortons to see if they are really worth the investment. Thanks for the info.
Mike

 

I haven't been able to drive it yet because it's been snowing here in Boise. They have to help performance because of the larger internal volume and being able to get a 2 1/4" pipe on the drivers side. Might not show much on my stock 330 now but they will be a good part of the equation as I continue to build.