Doin some porting work on a set of 1973 heads. The 2 center exhaust pockets have 2 huge egr holes in them that look to me probably messes up the flow also all 4 exhaust pockets have smaller egr holes as well, should I plug them to streamline the flow?
if i remember right it not a big deal, because the air flows mostly off the oppisite side off the valve seat seat. something like that.
The large holes in the 2 center exhaust ports are the heat cross over ports. The small holes are the air pump injector holes for th smog pump. Plugging the larger holes will help keep heat out of the intake, however, if you are trying to run the factory choke set-up, you may want to leave them open. These holes ( The large ones) will affect flow slightly, so plugging them off is a good thing to do. Jim Burek
Re: holes There are several methods, one is to melt some alum and let it flow down the passages. A much easier way is to use some 3/4 inch freeze plugs and drive them in, you can run them all the way to the bowl area. You will just need to slightly chamfer to openings on top to start the plugs. Jim burek
We are a bit excessive in plugging the heat riser holes. We drill the holes to 3/4" and plub with 3/4' mild steel rod. I takes some massaging, but you can then blend the plug to the bowl shape for best flow. We anchor the plugs with set screws drilled into the manifold gasket surface. For the EGR holes, we tap and run a threaded plug or bolt in, and grind flush. We've done this on 4 sets of heads with excellent results.
On a daily driver, anybody experiment woth blocking off the het crossover passages for good flow, and then NOT using a valley pan gasket, so the hot oil can splash on the bottom of the intake and provide some choke/carb heat?
NO NO NO! You will have excessive oil consumption due to the pcv valve being exposed to massive amounts of oil. Jim Burek
Whoops! I knew that!ou: Still, how about either using just enough valley to cover the PVC, or use an oil separator? Or is the benefit of blocking the crossover passages not big enough to worry about on a daily driver?
