Matching exhaust port to headers? - to do or not to do

[106-1194218389]

I was wondering if anybody has any thoughts on matching exhaust ports to headers or to leave headers bigger than port. On my project it would be easy as I am only going to be running 1.625" od tube headers. I have seen arguments both ways. I was wondering if anybody had any dyno results or track results they could share.

John

[hdwgfx]

If possible do not match up port and pipe, you want port exit into pipe to be smaller, this is done to help prevent exhaust flow reversion into chamber on cam overlap stroke. There are several acceptable methods to accomplish this... just my 2 cents

google exhaust port site:speedtalk.com

[thomasvaught-1]

Agree!

With a Turbo Engine most leave the port and tubing the same size as they are controlling reversion with the camshaft profile vs port mismatch. The smaller tubes increase the velocity of the exhaust to the turbo.

You will always have some reversion with a turbo engine at high boost pressures but you try and contain it as much as possible. Some turbo engines will have close to the same pressures at high boost which limits the amount of reversion too.

JMO

Tom V.

[106-1194218389]

this has casued me to do some looking around and I have found some real good discussions on exhaust ports and sonic choke both on this forum and on speedtalk.com - I have a Volvo 2.2L head coming to me soon to port. Clean sheet to work with on this one.

John

[gofaster]

I am assuming that you have a port design you believe is the best shape and size for the engine you are building.

If the header pipe is significantly larger than your exhaust port, and/or you can't find a header that comes close to your port opening, I would suggest welding the header. Then you can grind the opening of the header pipe to match your port, and feather it out to blend to the tube.

[larrycavan]

For every rule, there's the exception that is contrary to established patterns.

I have a Suzuki 4V single engine that I've been modifying for several years. Among the various stages of mods, this engine is using a stock header pipe and the exhaust port is gasket matched. On tear downs, there is never a bit of reversion carbon in the intake ports. They are clean as the day they were ported and the machine is definitely fast.

I'm not saying that there isn't the possibility of some exhaust comtamination at some RPM back into the combustion chamber but it's definitely NOT making it's way into the intake port. Go figure