Any input on these. I have a street build 350, wondering if I replaced my headers((rust/heat) with the Thornton manifolds would I lose much if anything?

 

From what they say, these manifolds breath pretty nice; they're a knockoff from the 455 duals. I thought long and hard about putting them on my 350 too. What changed my mind?

I want my car to be stock. The Thornton manifolds are great repros, don't get me wrong. And the price is not bad. But, instead of casting the GM manifold numbers and leaving them that way, they also cast THORNTON's onto each manifold as well.

Personally, I don't see the advantage of changing to the Thornton manifolds if you're already running headers. If you want another set that's brand new and never been installed, LMK. I've got them sitting in the garage. Not going to use them. They're Headman's I bought about 3 or 4 years ago. Not ceramic coated, but you can get that done at a powder coating shop. Everythings included: all hardware and gaskets.

 

Thornton has a reputation for solid products, but frankly I was underwhelmed with these manifolds. I inspected a set a Carlisle and while they may be pricey, there is very little difference from the stock manifolds. They are NOT fully divided manifolds like the BBO W/Z manifolds. There just isn't room on the small block to do that (which is why Olds didn't). The divider on the Thornton manifolds is only an inch or so deep from the exhaust port flange. The passenger side manifold is the same shape as the stocker and the location for the crossover pipe is simply blanked off. I doubt they flow appreciably better than stock.

 

One benefit of the Thorton manifolds is that you can buy a reproduction manifold to put dual exhaust on the B and C bodies. This manifold is near impossible to find on E-bay or at a salvage yard. I have only ever seen 1 in over 10 years of Oldsmobile fanatacism.

 

Correct, but the original question was about their SBO manifolds, which are a completely different product.

 

Indeed. However I always have to put in my $.02 about C and B bodies which are afterall, the highest form of Oldsmobile evolution.

 

I just got the 1965-70 Starfire Olds 88 98 dual exhaust "S" manifold from Thornton off eBay and it has the GM casting #'s and no 'Thornton' script on it.

 

Now if we could just get them to do the 394 LH dual manifold(s)... or at least the 63-4 part, which is worse to find than the 59-62.

 

I got the Thornton 455's w/z. I have orginal x/z, but passenger side had a crack. I did not want to chance a weld not working so I got the Thornton and had the shop port them to the gaskets. That are OK IMO, but one of the ports was very thin and it was not due to the porting process. And I think Thornton is the GM certified replacement that is way they can use the numbers. I know this is not much help, but if you get them and they are thin then you will know this is common.

I still have the driver side that is good, little pitting. I would have used them if it was not feasible to buy both for only a $75, or $100 more for new.

 

Old thread! But it came in handy today as I discovered I have a broken passenger side exhaust manifold and I am now considering purchasing a set of used Thorton Exhaust manifolds off EBay. Thanks for the info and opinions, it helped greatly in my decision making process.