Hi - gr8 forum you guys have here - just a quick question on head porting and polishing - i am currently modifying my golf with a custom profiled camshaft (306 degrees with 11.4mm lift and individual throttle bodies 40mm - does port sizes make a difference - big or small
Yes it does make a difference - big difference! The idea of a longer duration and high lift cam is to let more air into the engine, leaving the valves the same size restricts this and is kinda a false economy as you wont get the most out of the new cam.
On my Mk2 8v, the 'standard' upgrade size is 35mm exhaust and 40.5 inlet. Standard they are 33 and 40mm respectivly. I believe the mk1 is the same. But not 100% sure.
In S.A the Mk1 gti stock valve sizes are 33 exhaust and 42mm inlets - when gasflowing a head should the inlet ports be bigger or smaller Edited by: Mk1 Gti
Well bigger is always better - to a point! Usually the exhaust valves are done first as these are the smallest as standard.
Mk1 1800 GTI in Euro Spec has 38/33 valves I think....Widening out the ports will help a bit, but the valves are usually the bottleneck. When you do the ports, there's no point making them any wider than the gasket unless you're going to re-cut the holes, and then you have the same issue with the manifold. Most modders mark out the ports with a gasket to get the size to take it out to. For a really high spec you might want to go a bit further, then cut the gaskets and port out the manifolds to match. With that Cam I'd say you need to max out the inlet and exhaust valve sizes...or just buy Oakgreen88's X-Flow head, if he's still got it. He spent a mint on it, and it's hardly done any miles. It's converted for solid lifters as he had a 304 schrick cam in it.
reason I am asking is because the guy who is doing the conversions on my car sends his heads for porting and polishing to another shop - the guy that does the head p/p for him looked at my head and said that the ports were too small - he normally ports both inlet and exhaust so big that you can actually see the head bolts - he says mine wont make good power - I am at the reef and normally a good strong 20 8v dub maling good power does about 130-140 hp atw
