Mr.D-'97 A4q 12v

Doesn't the AAH head have a slightly larger intake valve than the AFC? Do you know the difference?

VAP

Since I'm replacing guides with bronze-silicone I'm opting for the later/narrower 7mm valve stem profile for it's better flow potential but still using the under-cut ones for even better flow gains as they'll only be 5mm in the stem section protruding into the intake/exhaust ports. My exhaust valves will be stainless steel sodium-filled for even more weight shaving but spendy at $48 each.

Mr.D-'97 A4q 12v

Does it just refer to that fact that the valve stem is narrowed where it protrudes into the chamber?

Thanks.

VAP

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"Undercutting" means that the valve underside and stem have been ground down to allow better flow. The portion that protrudes from the valve guide is made dramatically smaller diameter with a much better and far more aerodynamic radius under the valve head.

The under-cut area is the part of the valve that protrudes into the intake and exhaust port. All intake air and exhaust gas must pass this part of the valve on it's way into the combustion area or to get to the exhaust manifold/header. Therefore a thin profile stem is far superior to a larger profile stem. And this is something that is not just for "racing" engines. It's good on "ALL" engines compared with non-undercut valves as it presents a smaller profile for air to get around as well as greatly enhanced airflow around the valve head and into or out of the engine. It doesn't make a weaker valve in the process. But if the valves contact a piston they bend no matter what their stem diameter as something's gonna give in that instance.

Left side of diagram is stock configured valve like Audi and right side is undercut/profiled like I'll be using. The differences in power are NOT subtle at all and it's an EASILY feelable difference. I was running these on my "B Sedan" SCCA National car all the way back in the early 70's. With better profile cams, larger valves this is a HUGE HUGE improvement!

HTH

Mr.D-'97 A4q 12v

but then I multipled 48x12 in my head. :-)

Thanks for the explanation. Can't wait until I get to the head project.

VAP

And admittedly if I coulda found the Ti valves with a 3 groove keeper system I would've. But I want the 3-groove keeprs due to it's ability to spin the valves while they're being raised/lowered more than the ultra lightweight-ness of the Ti. So I did the next best thing, ie; undercut, sodium-filled (hollow) with 3-groove keepers and Ti retainers. It's the closest I could get to my "ideal" and it saved me $1500 in the process. My original budget was between $3500-$4k for heads. Half that amount while not perfect still suits me. But admittedly I do hate giving up that last smidge of additional power in spite of the cost-savings. But not enough to have a "one-off" set of Ti valves made to my specs for $6.8k tho I did think about it... laughed about it then forgot about it.

Jretal

Buddy told me they had a '96 A4 there... so I'm gonna go see what I can find... should be fun!

VAP

at this point but they "may" not be able to tolerate dual (inner/outer) valve springs. Which is fine if you plan on using stock valves and fatally preventitive if you plan on using larger valves. There also remains the possibility that the AAH heads are the reason the AAH engine has 10.5:1 compression ratio and the AFC is only 10:1.

Too many "if's" for snagging AFC heads as once you buy em you own em. And if any of my doubts are borne out in application they're gonna be very hard to get rid of 'round these parts in the next few months. Besides, you can score AAH heads with the known-good AAH cams for $200 or less most anywhere. Thats cams AND heads for $200 or less!! Deal of the century!! You can always make an AFC-like head from an AAH head but you might not be able to make an AAH-like head from an AFC head.

Jretal

but it's quite rare of them to actually have a '96 MY Audi there... newest I saw was a '92 90. So I'm thinking they'll have a 93-94 90 there I can gut We'll see. If I don't go look at another house this afternoon that's where I'm headed! AAH heads for about 11 bucks a pop if I"m not mistaken! They were selling the IM for 10.59 if they had the car I love U-Wrench-Its! Plus maybe that A4 there will have a sunroof **** that's in better shape than mine is. We shall see, I'll take pics of my findings (if there are any)

Audidriver9

/springs/retainers/whatever else you need. Could you compose a list of what i need to make this valve job successful? TIA