Minor Threat

I figure HMT is probably the best place to post this, I would search but I can't find any good terms to use.

I'm wondering if it's worth the time/money and possible machine work to retrofit some larger OEM D-series valves into my B7/A6 head. IIRC both the Z6 and Y7 have larger valves, and I have a spare Z6 head lying around.

If anyone can give me pointers, it'd be much appreciated, if it's too much work, I'm just gonna skip it for now.

ProzacOverdose

Get a valve angle job.

Bone1

the valve stems are the wrong length, and with stock bore, the smaller valves flow better.

If you were to go to a 78mm bore/sleeve, you could step up to 1mm larger valves.

Minor Threat

Why the difference in valve size between engines with the same bore then, just curious?

Foowee

Just a guess, but I'm going to go out on a limb and assume the larger diameter valve would work with a higher lift cam. Causing a sort of dynamic deshrouding...

I don't know the lift of a z6/y7 vs. b7/a6 off the top of my head. Just a thought...

Tom-Guy

Hrm. It's only a .5mm difference in size, but I guess it is a tiny bore.

Yup.

Minor Threat

Worth it if I'm still going to run stock valves due to the too long stem length?

Tom-Guy

Eh?

Minor Threat

Should I bother getting a valve angle job done?

Tom-Guy

Those pimpshit Big Name valvejobs are just moving the seat radius outward a hair, as much as they can without sucking the valve back into the head under load, and blending the bowl a little. Thusly, unported LS flows as well as stock B16/GSR.