With the number of options for ported or extrude-honed cylinder heads steadily increasing, has anyone on the board had the opportunity to try heads from multiple companies? Just curious about the benefits of porting vs. extrude-honing, and whether the flow numbers really correspond directly to actual measured improvements in power or egt's.
Chris

 

Also, can a ported head be extrude-honed, or has too much metal already been removed in the porting process?
Chris

 

all you really gain with a port and polish job is lower egts, very little hp gained. when you have 50 plus psi pushing the air in, it tends to go in.

 

Thanks, gunracer1. Does that EGT drop correspond directly to flow numbers? For example, can we say that if flow increases 10%, we lose, for example, 100 degrees of egt, and if flow increases 20%, we lose 200 degrees egt?
Chris

 

Go4Lo: EGT is a result of very many contributing factors. Also a limit like 1250 or 1350 F is quite arbitrary. I don't think that you can quantify the effects of porting and polishing without knowledge of the other deciding facors (Injectors, fueling curve, cam, boost, backpressure, charge air temp etc etc...)
Porting the head will result in more air in the cylinder for the same boost. It will also result in less friction in the exhaust gas removal and therefore easyer scavenging for the same boost. Naturally this should lead to lower EGTs, but I don't dare to guesstimate the amount of reduction.

Just my 2c

AlpineRAM

 

I think I read somewhere that a ported head will drop the EGT's like a 100* or more. But don't quote me on that. It's been a while.

 

Another big plus is drivability, your off-idle response is better, and it helps spool bigger turbos because you are moving more air and your engine is acting like it has a few more cubic inches.

A cam has similar effects.

This is assuming proper porting and correct cam.

A member on NW Bombers ported his 1st Gen head and put in a cam and it really woke his truck up, major improvement in how it drove and was real pleased with it.

Vaughn