10v big valve conversion

Alan Pritchard apritchard at seaeye.com
Tue Aug 3 09:29:21 EDT 2004

Well ,a bit of further research suggests this...
Stick with the 40mm intake valve, and upgrade the 32??? Exhaust to 35mm ,
possibly even using the 7mm stemmed valves, or even upgrade the intake to
42mm, I have even seen a 42.5mm valve for this app.
I think I will probably go the larger exhaust valve route only, not sure...
its all dependent on cost ;)
Ill look at the head first and work out the best way forward.
Also 11:1 is the suggested cr to run on 93(us) octane. Which should be safe
for me here.
Anyone got any ideas about flywheel lightening? I know plenty of mc shops
round here, just don't know the best way to have the flywheel machined....
Also if its recommended for my na project... also, should I be thinking of a
different clutch? I will be replacing it, but will a pattern sachs unit
Best Regards,
Alan Pritchard

Network Administrator
Mechanical Design Engineer
Seaeye Marine Ltd.
+44 (0)1329 289000

 -----Original Message-----
From: 	Eric Sanborn [mailto:eric_audi.ql at mindspring.com] 
Sent:	03 August 2004 03:05
To:	Alan Pritchard
Cc:	Quattro List (E-mail)
Subject:	Re: 10v big valve conversion

Alan Pritchard wrote:

>Also may consider ceramic coating the combustion area.
>So, what is a sensible cr (thinking 10.5-10.8 ish).
>And what valves are used for the big valve conversion? 
I would also be interested to see what valves would work.  US market 
Golf II 1.8l heads were hydraulic and had 40 mm intake valves.  I had 
planned to put that in my turbo project, but my local machine shop was 
not comfortable with doing the machining.  He felt it would require new 
larger valve seats and reshaping of the combustion chamber.

If your car has the fat stem base exhaust valves I would look into 
custom stainless valves instead to increase exhaust port flow.  Take a 
look at this picture http://sofadog.net/4ktq/images/ExValves.JPG.  The 
valve on the left is out of an '83 GTI with solid lifters.  The one on 
the left is out of a KH engine.  They are both the same diameter valve 
and have the same diameter stems up by the valve guide.  See the big 
difference at the base of the stem?  Yes I know in the case of a turbo 
engine one would be giving up sodium filled, but one would also be 
giving up wieght.

As for the coating I strongly recommend it.  My KH engine has pretty 
much everything you can do except for the intake manifold (ran out of 
time).  I am not really pushing the limits yet on this engine, but I 
have seen with other cars that coatings offer a strong level of 
protection against damage from detonation.  I have not done a before and 
after comparison, but it would make sense that it would also reduce the 
engine's cooling load as more heat is kept in the combustion charge.  If 
you are adventurous and have a blast cabinet and air brush do the 
coatings yourself and save a bundle.

If you do go with big valves be sure to post the method and parts you 
use.  I would be very interested to see how it goes.

Eric Sanborn
'85 4ktq


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