Round port header on square port head.

[Guest Anonymous]

Hey all. The thing that got me started is when i went to buy a supposedly sqaure port header for my Z. It was in fact a round port, but had obviously been used on an earlier model head because the carbon on the header was sqaure.

So i thought, why don't i use the round port header in my garage, it is 3 into 2 and bolts up to the piping i have. If you use a sqaure header gasket and some hi-temp sealant, why wouldn't this work?

I searched but there is no info on this topic. Can anyone put there 2c in?

Obviously i can expect to lose some power due to flow restrictions. any idea how much? or is this just an overall bad idea.

[Dragonfly]

Well heres my 2c worth. Next time you take a look at an intake/exhaust manifold gasket look at the shape of the exhaust ports on the gasket. They are a funny diamond shape, the reason for that is so thay can make one gasket that fits round or square port exhaust.

 

By using one of these gaskets (as far as I know they are all made like that now) you can easily mix square and round exhaust heads and manifolds. You will not get a quality port matched flow but it will not leak on you either. At this time with my spare engine in my car I have my square tube headers on a p79 head with round exhaust ports and no leaks, as far as how much power you may loose doing this take a look at my post about racing the 350Z to see my 1/8 mile times with this bone stock engine.

 

Dragonfly

[denny411]

Port matching from the head to the header is critical for peak performance. It`s not AS MUCH of an issue if the header is slightly larger, but smaller is terrible.

Compare the flow of your exhaust to a river. If the header port is too small, the flow would be similiar to whitewater, If it`s too large it would be similiar to water flowing over a dam. Obviously the closer your header matches the head, the more efficient the flow will be.

 

MY .02

[Guest Z-rific]

I share the same 2 cents as Denny. The reason you go to a header is to maximize exhaust flow (and reduce weight). People spend a ton of money porting exhuast just a little to increase flow.

 

With any kind of obstruction, you're sure to lose power.

 

But, if the way yours lines up keeps the header port larger than the manifold port, then you're fine as long is it doesn't leak.

[Mudge]

Could cause a nasty reversion effect by blocking the exaust gas, why not buy a set off eBay and fix em up.