Hi Brett,

No one has answered yet, I would say that if you open the manifold ports out to match the gaskets the hole will be bigger than the ports in the heads but the lip will be gone in the outwards direction. The exhaust passage should be at as shallow an angle as possible from the entrance to the manifold. There seems to be plenty of meat in the manifold to do this. I gather from what people say that the lip in the reverse direction from the manifold towards the heads helps to prevent backwards exhaust pulses from the exhaust system re-entering the combustion chamber. The effect of the porting should do all those things you said. I will shortly be fitting ported headers on my car too.

Maybe someone more knowledgeable will give you further advice.

Les

[Edited by Leslie - 6/3/2003 1:44:22 PM]

 

Just been reading Steven's thread re: NON DIY FMIC. And saw the porting of the headers.

What is the net result of this? Increased spool up, less turbulence around the exhaust ports, possibly causing less reversion / better filling of the cylinder?

Is there any particular angle that is recommended or just smooth it out nicely, and minimum widths of the pipe work

Sorry for so many Q's.

Thanks
Brett
MY00

 

Brett

I think Leslie sums it up quite simply IMo, and in english, instead of technical wizardry.

these may also help

Steven

 

Thanks Steven and Leslie.

I did get off of my lazy butt so to speak and did a search and found a few good threads as well. But nothing seemed to go into the technicalities of what the benefits would be, which is what I am more interested in, trying to learn as much as possible

Thanks again.

Cheers
Brett

 

I'll tell you what I find out when I get the chance to fit mine Brett.

Les

 

Going from memory here, so try bear with me

I did query the benefits at the time, but once you take off the original headers you begin to see how small the header ports are compared with the gasket and the head ports.

By flaring out the ports on the headers you should effectively remove any step or lip that the exhaust gases leaving the head would come across.

Of course any lip or step in the direction of gas flow, causes a disturbance in that flow of gas, and in some cases can cause the gas to reverse, or so i am lead to believe from the gurus.

So consequently any lip could cause gases to return to the chamber, IIRC, which is not good.

By porting the headers you remove this lip, and provide a clearer path for the gases to leave the header. At the same time you create a definate lip for between the head and headers, for when the gases are in reverse flow, ie back into the head, which i am told happens.

So by creating the lip in the reverse direction of flow, provides a benefit, as it stops more gases going back into the chamber and contaminating the charge mixture.

As David Wallis said in one of the links above, the idea is to port in the direction of flow only, as this aids gas flow in the direction it should travel, but also stops gas flow when it is going in the wrong direction.

The supposed effect of all this, is that gases move more smootly towards the turbo, and more efficeintly, i believe, thus supposedly improving spool up of the turbo.

Problem is, 90% of people that do this, do it in conjunction with other mods, eg better up pipe, etc, so can not specifically say "the improvements are XYZ"

Hope that helps, as that is how i interept the gurus, and is my attempt at putting things into english too

Steven

 

Thanks Steven,

Thats pretty much what I was thinking (in my limited experience and knowledge of engines and gas flow theory, compared to the others on here (Bob, Andy, John, Mark, David etc).

I've been given the stern word from the wife that all modifications (money spent ones that is) are to stop until we purchase our house. So I am looking at the things I can do myself that will help with current and future mods.

Cheers
Brett

 

NP Brett