hi was just having a surf on ebay and came across this listing here seems pretty good, but what i did notice is that they are fiiting bigger inlet and standard exhaust valves, whereas the group buy thats on is fitting bigger exhaust valves. just curious really as to which is better if any and why? in my small brain it kinda makes sense for both cheers for your time Chris
The accepted wisdom is that the exhaust valves and throats need to be bigger to flow more air and get rid of the bottleneck. Stage 4 or Pack D heads use 40.5mm inlets but along with 35mm exhaust valves. I'd say 'the man' would be doing it right considering he did VW Cup and slick50 heads.
aye, which is why i thought the ebay one was a bit strange. i'm watching it to see what it goes for out of interest anyway. Chris
Big inlet valves are more important than big exhausts, it's a lot easier for an engine to force out exhaust gases than it is to inhale.. larger exhaust valves work to a point, but bigger inlets are more benificial, its getting air "into" an engine that makes more power. Getting air out faster (bigger valves) helps exhale burnt gases which is certainly good news (though longer duration and more valve lift on a performance cam do the same thing) but getting more air in to mix with more fuel to create a bigger bang is what creates more power and is even better news. A basic formula sites the exhaust valve size as only really needing to be 0.8x or 80% of the inlet valve, thus a 40mm inlet would have a 32mm exhaust (33mm standard), why the 8v Vw engine should be any different I've yet to find out. I've just stripped an ex slick 50 engine which has the fabled 35mm exhaust valve, it also has a 41mm (yes 41) inlet valve instead of the normal 40.5, all on a standard 1800 (81mm bore) bottom end. Admittedly, the standard exhaust throat is small and the seats a poor shape in standard form, but they can be made much bigger and more of the valve area can be used without going to a bigger valve. I'm not knocking "anyone" who has a bigger exhaust valve head or indeed anyone's product, but has anyone seen a valid dyno test showing a bigger exhaust valve giving a greater power increase than a bigger inlet when "all" other components on the "same" engine are unchanged ? Or is it just a product of folklore that has followed the VW engine through the years ?
Are there any marks on the casting to show it`s a different head ? I have just stripped down a spare dx head i bought for my roc,i measured the valves with my calipers the other day. My inlets are 41mm the exhausts are 35mm .But haynes say they should be 40mm in 33mm out ? I bought this head as a standard head,could it have been played with ? Valves all have T-T stamped on them,do standard valves have this ? Sorry for all the q`s never stripped a dx head before Just measured the valve seats,to check that someone had not just bunged bigger valves in,seats measure the same.
It`s just below the collet groove. Ex valve has T-T then vw audi 026611A Inlet is harder to see but it has L625 65C or could be 55C
