Messed with 1.5/6/7 Gas heads on the flow bench back in the day when I was in college working at a VW/Porsche shop.
Also played with a broken diesel head. Same valve sizes and basic layout as the small valve gasser heads of course. With the valves going down to the flat head surface instead of to a bathtub combustion chamber, there was a bit more downdraft after making the turn in the port, so all else being equal, the diesel heads flowed a touch more that the gasser. (Not a GTI 8 Valve head or anything, but the 1.5/6/7).
Nice thing is that all the info and porting techniques for the early gas heads WORK on the diesel. David Vizard wrote an article for Hot VWs in the very early 80s detailing exactly what and where to port, and it is very accurate. Don't know if there are any port differences from the early 1.5/6 I messed with and a 1.6TD or the later 1.6 hydraulic heads?
I am sure the later 1.9 and 1.9TD heads are different and with bigger valves (right?). On the gas engines, the 1.8 8V heads look very similar, but respond very differently to porting. What works on the early heads doesn't work on the later ones - you can even have flow drop off for doing the exact same thing. Anyone tried modifying and measuring the improvements on a later diesel head?
Topic: Pre cup (Read 2891 times)
