Hi experts, I have had my TFSI (BHZ) cylinder head professionally ported (for street use). The head is now assembled with all new parts and ready to go on the fully forged block. However there's one thing that makes me a bit uneasy. I had the shop balancing the engine internals also check compression ratio and verify the head surface / deck. All okay, but the builder left me with one remark: He said because the valve guides where cut down when porting intake/exhaust, the valves would probably bend slightly, then failing to close fully, causing loss of power within just a few months of running the engine. He said he had redone several race cars (not specifically VAG) where the guy porting had removed too much of the guide. In his estimate it was general or industry wide issue: guys porting engines rarely see them run and there's not enough feedback loop on the results passed the dyno session or flow bench. And obviously porting out the valve guide is both faster AND provides greater flow, which is what a guy porting would be measured on. His approach (had he done the head also) would have been shortening the guide pre-installation to be somewhat shorter and with a symmetrical conical taper. Now, I really do not want to tear down this engine once its assembled and installed. If this is a real issue with a high likelihood of affecting my engine, then I will probably dissemble that head again (though I'd really hate to) and redo the guides. It's money and time lost, but better now than later. What's your educated opinion on this? Cylinder head (BHZ): Intake port: Exhaust port:
I'm no expert, but would always say to anybody doing a head for me to 'bullet' the guide, not flush it. Sent a head back to Longman (UK 1980's) after 2 seasons racing for a checkover, no wear found..... Jon
The Fsi / Tfsi guides are pretty short, in a std ``non ported`` head sit fully out of the airstream, after porting the valve guides stay the same lenght with only a small part removed on one side ( in most cases) but there are other engines were the guide is far more into the port as std... and when these are machined flush with the port then it harm valve guiding far more than on a TFSI ... that said, gain in flow is minimal on FSI/ TFSI heads Its like std and aftermarket valves , some flow better in lower lifts and others at higher lifts, but never seen more than 0,7 cfm @10 `` difference ( under 1% gain ) on the flowbench on N.A - FSI heads > these have the same exhaust ports as the TFSI heads, but inlet ports are different To avoid shortening the guides, would need to press them towards the valvespring before porting ... and then back after porting... and pressed even deeper incase high lift performance cams are installed, to avoid spring retainer to valveseal contact + 1 mm extra clearance as safety meassure
Thank you, I appreciate your input. At this point though, being as it is: would you suggest I redo this or just leave it be?
To finish that story of mine, that same head has a 20-25 year 'rest' on the shelf. Its now back in another motor after rebuild checkover, same guides, still no wear detectable.... Jon Not sure how many meetings its done though, maybe 50? Obviously no road miles