Head Porting - ZR-1 Net Registry Forums

Locobob · 02-28-2009

Thought I'd share my latest project with you guys: porting or rather reporting my cylinder heads. The motor is a 368 put together by LPE back in the mid 90's. The heads are pretty gummed up, likely do in part to the car having an open loop only chip when I bought it. When we burned a new chip for it we had to be very conservative on the timing do to knock sensor activity, I suspect all the gunk in the heads may have something to do with that. Anyhow I did some measuring prior to getting started so here are the numbers:
Primary intake runners at narrowest point (just above the valve guide) 33mm high, 33.8mm wide
Secondary intake runners at same spot 33.3mm high, 35.6mm wide
Intake bowls just above the valve seat 34.8mm
Exhaust bowls just above the valve seat 33.8mm
Exhaust port at narrowest point (near union) 33mm
Exhaust port at header gasket surface 36.3mm high, 53.8mm wide

I found a few things about the prior head work suprising, one being the combustion chamber surface was pretty much left as cast - very porous. I was expecting to see a nice smooth surface below all the carbon build up. Thought smoothing and polishing the combustion chamber was standard fare for head porting. Here are a few pics of the combustion chambers before (with just a little clean-up) and after a bunch of very tedious hand work.

Here is a primary intake runner after a bit of work with a sanding drum

02-28-2009	#1
Locobob Join Date: Jan 2004 Location: Portland, OR Posts: 1,047	Head Porting Thought I'd share my latest project with you guys: porting or rather reporting my cylinder heads. The motor is a 368 put together by LPE back in the mid 90's. The heads are pretty gummed up, likely do in part to the car having an open loop only chip when I bought it. When we burned a new chip for it we had to be very conservative on the timing do to knock sensor activity, I suspect all the gunk in the heads may have something to do with that. Anyhow I did some measuring prior to getting started so here are the numbers: Primary intake runners at narrowest point (just above the valve guide) 33mm high, 33.8mm wide Secondary intake runners at same spot 33.3mm high, 35.6mm wide Intake bowls just above the valve seat 34.8mm Exhaust bowls just above the valve seat 33.8mm Exhaust port at narrowest point (near union) 33mm Exhaust port at header gasket surface 36.3mm high, 53.8mm wide I found a few things about the prior head work suprising, one being the combustion chamber surface was pretty much left as cast - very porous. I was expecting to see a nice smooth surface below all the carbon build up. Thought smoothing and polishing the combustion chamber was standard fare for head porting. Here are a few pics of the combustion chambers before (with just a little clean-up) and after a bunch of very tedious hand work. Here is a primary intake runner after a bit of work with a sanding drum __________________ Robert ZR-1 Net Registry Oregon State Director 91 ZR-1 #431 Black/Black LPE 368 Last edited by Locobob; 02-28-2009 at 11:56 PM.