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RE: do you have any flow numbers for the audi head

Mike -
Your input and any ideas you may have are appreciated, although the head in
this case, while having a total of 20 valves, comes in a 4 valve per
cylinder x five cylinders format rather than what I'm guessing will be your
20 valves from 5 per cylinder x 4 cylinders.

With respect to your point #1 - "re: do you have any flow numbers for the
Audi head" - answer No, and apparently no one else on the list does either
although I've been asking!

The extrude honing suggestion is one that's come from Extrude Hone.  I just
had an RS/2 exhaust manifold for the engine in question done by them.  I
didn't know that they were also proponents of doing the head itself.  That
came up in a discussion about getting the intake manifold side of the engine
also done.  I'm getting different opinions about the wisdom of extrude
honing additional parts.

With respect to your point/question 2 - enlarging the cross dimensional area
of the intake port, the extrude hone, if done to the head AND intake AND
exhaust manifolds will, as I understand it, cause a defacto match up between
the manifold's intake and exhaust runners, and the heads intake and exhaust

One of my concerns however, is that I believe I do NOT want to enlarge the
valves or affect the existing valve seats in anyway that might prevent me
from using the stock valves, both intake and, in particular on the exhaust
side.  In this particular engine the exhaust valves are made of fairly
exotic materials to withstand the abuse of turbo charging and consequently
(1) rather expensive and (2) not easily substituted for.

The intake and exhaust ports are BTW on the 1992 - 1996 AAN / Audi S4/S6
engines, located on OPOSITE sides of the cylinder head.  I'm not familiar
with how the 5 valve per cylinder head you are looking at is laid out.  I
don't know just what extrude hone thinks will be the amount or material that
their process will remove, or "enlargement" of the port area that applying
their process might achieve.  I think the gentleman I spoke to may have said
@ 1mm, but I don't know for sure.  I will try to press them on that before I
commit to having this done, if at all.

In any event the Extrude Hone folks have said that they will "flow" the
assembly (the head & I'm assuming the manifolds) both BEFORE and again AFTER
their process and provide me with a chart of these flow bench results.

One line of thought has been that too "smooth" an intake will lead to "fuel
puddeling" or "laminar flow" resulting in less efficient atomization and
mixing of fuel in the intake charge.  I'm not sure I can agree, or
understand this concern based on (1) this is an individually port fuel
injected engine; (2) there is in fact no fuel mixed in the intake manifold,
the fuel is injected right at the intake port on each head; and (3) its kind
of been my understanding that one of the purposes / benefits of the fuel
injection process is to mechanically take care of this "atomization"

Second, I've noticed on a closer examination of the intake manifold, that at
the point where the fuel injectors plug into the manifold there is a slight
(?? 2-3mm) bump that actually sort of drops down into the port opening.  I'm
guessing that this slight bump which looks like it protrudes into the intake
flow path may serve to "disturb" the flow of air just as it goes into the
head and as it receives its squirt of fuel from the injectors.  Would you
have any thoughts from your classes or instructors about this?  I'm guessing
that I would want to make sure Extrude Hone, if they did the job, be told
not to mess around with these bumps or even smooth them out.

What do you know from your classes about porting and polishing a head about
maintaining or enhancing the combustion charge, in addition to improving the
systems flow?   e.g. I think its Corvette that brags in its advertising
literature about "swirl porting" and 'tumble" charging their cars fuel
mixture for more power.

It this, enhancing the mixture of fuel and air, something a person needs to
be concerned about in extrude honing an intake manifold?  How about the head
intake channels and ports themselves?  How about the exhaust runners and

Hopefully I'll be able to get some actual flow data out of this for
comparison.  FYI, I have two (2) heads available if I can work out the
logistics of getting them tested before and after modification.  One head is
brand new and in OEM stock form - that's the head I'm considering having
extrude honed, or alternatively "traditionally" port, polished and gas
flowed."  The other head has already been worked over by a shop.
Unfortunately the prior owner of the car with this head in it did not get
the people who did the work to provide "before" or "after" flow tests or
numbers.  Do you think your school (1) could; and (2) if they can, would
they be interested in running these flow tests?

Michael Pederson
Two 93 S4's -

-----Original Message-----
From: Mikehype77@aol.com [mailto:Mikehype77@aol.com]
Sent: Monday, October 25, 1999 5:02 PM
To: mlped@concentric.net
Subject: do you have any flow numbers for the audi head

i am a student a (the school of automotive machinists) in houston texas. i
looking at the audi 5 valve head as a project for my head porting class.
discussion about extrude honing is a great 1.did you  consider enlarging the
cross dimensional area on the intake (such as raising the roof, removing
the walls) ie changing port size and more cfm. extrude honing is just like
cartridge rolling (smoothing) the factory's casting. if you dont change the
port, dont expect much(turbo or not). ive seen this a million times with
customer engines, who dont want to pay for porting. i hope im not insulting
you. I just felt that your extrude hone idea was a waste of money.  thanks