When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.
I've been reading through a bunch of posts here and I think I have an answer to my first question. We were planning to build a 455 for my dads car, then covid hit and threw a giant financial wrench in his business for the last two years, so the engine is currently sitting in the garage, untouched. The car currently has an Oldsmobile 350 in it. He bought headers (with intention of using them on the 455) that he was promised would fit 350-455. Reading through here, that seems like it's not the case. They do look a lot more like the 455 style headers, than the 350 style when I compare. They are however, in the car and do fit but we're having a problem with them not sealing 100%. Is it because of a big difference in port size? or do the headers just not line up properly?
My second issue is (and honestly, what I'm leaning towards being the main leaking issue) is that the heads on the current motor, don't have a spot for a top bolt on the headers. The previous exhaust also didn't have a bolt there, but it was factory manifolds and never leaked.. What I'm assuming, is that there SHOULD be a hole for the top bolts (right above the center ports) and that someone broke bolts off and painted over it, which is a pain but I can drill and tap them if I know for sure that all SBO had exhaust bolt holes there.
I'm trying to help him finish the car up, so he can actually enjoy it given the last few years he's had, and this is one of the last steps. I don't have any real experience with Oldsmobile though. So any advice or input would be greatly appreciated.
Every Olds factory cylinder head has five bolts for the exhaust. And yes, the taller deck on the 455 means that the headers are different. They will seal on the 350 heads, but the problem is that they will likely hit somewhere else that prevents them from sitting square against the head, which is why they leak.
Here's a pair of bare heads from a 1966 425. But the 350 and 455 have the exact same holes for the exhaust manifolds. That center upper hole does not go through like the other bolt holes. That one is a pain if its broken. There's different ways to remove it, but be careful or you can turn the head into a piece of scrap metal. Yes, I have personal experience doing that! John
That top bolt is often the bolt that breaks off. Thankfully, headers still seal fine without it there. You can either double gasket or use something like Permatex Optimum Grey, high temp and very robust. What year of car? A few have used the Ebay $200 Stainless headers on an Olds 350 in 1968 to 72 Cutlass, even though they are designed for the 455. They have a very thick flange, which you want and they fit but hang low, a long as your front end sits high, like most do, you should be Ok. What brand of headers do you have? Good luck.
February 26th, 2022, 05:46 PM
