I'm willing to build a new head for my 8V. My 2.0 is running an Autotech 270 on STOCK (40x33) head and 12:1 pistons (runs on alcohol). Header (4x1) tubes are 38mm and 2.25in after that... I should get a Schrick stick soon...hid. 272/272/110, but not now... Now I must choose...keep 40x33 or upgrade to 41x34mm valves (both are 7mm stem). Is it worthy (considering I drive it at least 25miles everyday) and won't rev it over 6.5k rpm? I mean, is it ok to port/flow it AND use bigger valves on a street machine? Need to know pros and cons...will ya help me out?! =) Andre
I have read that going to larger valves doesnt always gain anymore power, in some cases the power went down. I'm not to sure about the VW engines as i havent tried it. Here is a link to a Vauxhall site though where some tried larger valves and didnt get the results he thought(was a 2ltr 16v engine): http://www.migweb.co.uk/forums/showthread.php?t=227241&h ighlight=bigger+valves
i had oversized inlet and exhaust valves on my old 8v and along with a crazy cam it mad some really good power.......... but if its your road car i'd stick with std and just have a bit of porting done etc my 2p
Well on the 8v VW head, the exhaust valve is restrictive.... Leave the inlet alone if its a 40mm jobbie, & go for a 35mm exhaust TurboCav....You cant really compare a 16v XE to an old 8v VW head though . In practical terms, its quite rare to fit bigger valves in a 16v head (certainly with VWs anyhow) An 8v Pack C head (40/35) is the way forward to allow the head to breathe properly. All the leading 8v tuners will reccomend it if you want the engine to rev harder..
I know, but i though it was a good read.I didnt want to mislead anyone though. I have seen people with 8v heads fit larger valves and not get what they expect, but i surpose it also depends on who does the headwork and how well.
I have seen a 2.0 8v on standard injection (k-jet)produce 131 bhp at the wheels with 40/35 valve size's @ 6,500 rpm, if thats enough power for you it may be the best way to go.
