Re: 5000CSQT head mods...

[QSHIPQ@aol.com]

In a message dated 97-09-23 04:36:57 EDT, you write:

<< Is there a performance gain/loss from using a latter model Closed chamber
 head on a turbo car???  
Nothing really proven, but not a lot of data either.  Using the 87 head
should be fine.  Keep the air shrouding, that really is the biggest gain over
earlier head designs.

 If bigger valves are going to be installed what is the largest head diameter
 for intake/exhaust???
3.5mm total before overlapping of seats.  The audi Rally cars got 5-5.5
total, but they had the funds to rebuild the head after every event.  The
general accepted rule of thumb is that you want at least a sliver of material
between the valve seats for longevity.  On a turbo car, Intake valve mods
tend to move the power curve up in the rpm's, exhaust flattens it out.  Make
sure you use sodium filled exhaust valves, these turbo cars get hot.   

 As far as porting goes where can the largest gains be made, the intake ports
 or the exhaust ports???
The basics are this, exhaust ports give the biggest gains, to get air in a
different turbo or more boost or higher lift give you a larger "effective"
valve area on the intake side.  Do not port match the exhaust manifold.  For
a simple anti reversion design, make the exhaust manifold ports slightly
larger than the head ports.

 What kind of cams are there to improve low end torque??
 None.  Improving low end torque can come from 2 easy sources.  EH the intake
manifold and/or installing a k24 turbo (or smaller hot side k26).  The 2
piece exhaust manifold is also a great improvement for a modded head.    The
stock cams for the audis are darn good, if you do anything with a cam, get
one with increased lift over stock, but you will give up some duration for
that.  Advancing the cam and smart use of WG spring preload and chip tuning
will outweigh most of the gains market available cams give.

HTH

Scott
QSHIPQ@aol.com
'87 5ktqwRS2 - big valve head
'87 5ktq
'86 5ktqw
'84 Urq