Re: Audi cylinder head porting

[OorQue@aol.com]

> I think it doesn't really matter,whether the engine is normally
>  aspirated or force-fed.If a port flows well,it does it in both cases
>  giving more power.

Yes and no ... the trick in porting *any* type of head is optimizing the flow 
of the intake port flow relative to the flow of the exhaust port.  Making a 
port flow well when the valve is wide open isn't that hard; it's getting it 
to flow well at lower lifts that's the tricky bit.  This why you have to be 
careful in balancing port flow against velocity and take into account the cam 
to be used, the intake and exhaust manifolds, exhaust system, etc.

For the typical non-turbo street motor, the goal is to end up with an intake 
port that flows well across the board and an exhaust port that flows 75 to 80 
percent of the cfm the intake port flows.  For a turbo motor, however, the 
goal is to get the exhaust port flowing 85 to 90 percent (or more!) and this 
obviously means the ports will look different for each head ... this is 
especially true in the case of Audi heads, which tend to have relatively 
restrictive exhaust ports.

>  For street use I would not grind the intake port very much,only some
>  smoothing to the valve-pocket area and matching with the intake 
manifold.Exhaust side can be ported
>  little"heavier" for better scavenge.

This seems to be the consensus among those in-the-know about porting heads 
for turbo apps.

>  When you are using that Superflow,try doing a moderate back-cut to a
>  exhaust valve?Might help with the low-lift flow??

The flowbench owner told me that nearly half the increase in flow he found 
was due to reworking the back of the valves and the port area with .25" of 
the valve seat.  Of course, this was on a VW head and it's possible the Audi 
head might be different ... unfortunately, I've had to cancel this Saturday's 
session due to a personal problem that cropped up last night and needs to be 
resolved ASAP.  I'm hoping to try again next weekend.

JG