D-series valve compatability
 

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.

Re: D-series valve compatability
 

Get a valve angle job.

Re: D-series valve compatability
 

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.

Re: D-series valve compatability
 

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

Re: D-series valve compatability
 

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...

Re: D-series valve compatability
 

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

Yup.

Re: D-series valve compatability
 

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

Re: D-series valve compatability
 

Eh?

Re: D-series valve compatability
 

Should I bother getting a valve angle job done?

Re: D-series valve compatability
 

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.

Re: D-series valve compatability
 

or also if he has a high lift cam or goes FI...

Re: D-series valve compatability
 

I know the valve stems themselves are a hair longer on the a6's vs. z6's. I've used a6 valves in a z6 head before, the valves aren't alot smaller in diamter than the z6's are, and actually sit pretty well flush with the z6 head once they're seated in. Just had to grind down the tips of the stems to keep them from binding on the z6 springs. I suppose the opposite could be done with them...get an valve angle job and they should fit in nicely. Might even be able to retain the z6 springs in conjuction with a larger cam lobe if you wanted to save on cash. I would imagine you could also have z6 valve seats machined in to make life alot simpler. It all pretty much depends on how much extra cfm you want the head to flow.

Re: D-series valve compatability
 

It's a .5 mm size difference. You can cut the existing seat to accommodate just fine.

Re: D-series valve compatability
 

Or you can do that :-* The machine shop I go to told me they won't cut the seats, only machine out and replace them with the larger ones...they're gay :P

Re: D-series valve compatability
 

Both have merits, depends on what you're doing.