we've all seen what everyone does, take the manifold off, look at the soot rings on the flanges and ports them out to match the gasket (i was guilty of this on my Legacy a few years back)

my understanding now is this is the wrong way to go about it as it will create a volume bulge in the piping and decrease the speed of the gas flow, i've read alot about reversion lips to reduce back flow and was after some tips specifically for the impreza headers, how much do you take off and where etc.?

 

just out of interest, lifted from NASIOC, black line is Borla tubular headers, blue is standard P&P headers

 

Harvey is the man to speak to for this, or even get him to do a set for you He done a set for my 03WRX, work of art and they were only 5bhp down on the best set of tubular headers I tried but with non of the tube header lag.

Andy

 

Again will second harvey, He did a top job on mine.

Pete

 

Take it its cheaper to get the OE ones done?

 

dont mess about, get harvey to port the standard ones .proper job.helpfull bloke,value for money

 

I copied Bob Rawls photos. I took mine almost back to the soot line and blended gradually as far as I could go. I didn't polish as I couldn't see the point if I couldn't do all the pipe?

I figured that the reversion lip is still good off boost and helps raise torque low down. The mismatch that was possible on my headers meant that I should take mine out to the soot line just in case it didn't line up.

F

 

well i managed to do mine over the weekend, made a better job than the first lot i did a few years ago, there was definetely room for improvement on mine with some horrid bits of welding on the up pipe, will do a full write up later on and see what the experts think