I have questions about the very common 243/799 head. Why doesn't anybody "D" port or gasket match the exhaust ports and does anyone have flow bench results from doing this? I've done it tons of times even though I'm pretty sure I shouldn't because I never see anyone else do it, lol. I'm the kid the has to touch the hot stove even though I was already told it would burn me. Anybody have any experience in this?

 

All you'd be doing at that point is killing exhaust velocity where it matters.

 

Yeah I took that into consideration but then I looked at most of the cars that I've been porting heads for and they have 1 7/8"- 2" headers and I just wonder what the difference really is and would think if it was going to hurt them it would reflect in the ET which I can't see where it has. I was just kinda wondering if anyone else had some actually comparison data to show what it looks like on a bench.

 

Sure about that?
Exhaust gets a little help from the piston.

1st picture is a GMPP CNC 243
2nd is a Livernois 766
3rd is a Livernois LSA

 

Congrats! You are the only person who has ever particularly agreed with me. Lol

 

I'm sure application has a lot to do with it. A blown LSA would probably really like the larger exhaust versus a more mild NA application that a 243 head would usually go on.

Whatever you do, do not "gasket match". The gasket makers really don't know what size ports are right for your combo, so they usually make them with very large openings. Matching the ports/runners to the gaskets usually ends up in a bad mismatch or bulge at the flange and often hurts more than it helps.

 

It's too late. I've done lots of them. Haven't had any complaints yet.

 

I've thought about this myself while doing my 243 heads. I ended up raising the ceiling of the exhaust port about .060 at the gasket while maintaining the "d" and staying well within the gasket. Never touched the sides or floor except to polish.

I then feathered that .060 back to the coolant bump. I don't know if what I did hurt or helped, but it seemed to me that the exhaust would be taking a slightly more direct route to the header.

Just my $.02

 

I'll start with that I'm no professional, just a "hobbiest". Looks very similar to what I did. Leave the floor alone except to polish. I don't take it all the way to the gasket but close. I did take more around the guide than you did.

 

We have done extensive testing over the years on tons of test 243 heads.
We have tryied every port design you can imagine, from the smallest, highest velocity to the most hogged out low velcoity turd you can imagine.
There is a balance between to big and to small.

The D port works very well but it needs to be the correct size.

p.s we us our in house sf600 daily.

http://www.americanheritageperformance.com/