Race Engine Forum UK

Hello Guy,

I am just rebuilding the head of a 1.6 Fiat Tipo, which is used in a Uno Turbo. The head is ported and blueprinted with 38 in / 33 ex valves. I am going to install new valves and guides.
How can I modify the valves for max flow? Can I do it the same way as for the DOHC valves?

Best regards
Peter

Yes, do any cc relieving first and then give it a sharp-edged 30deg top grind about 3mm wide on valve insert & adjacent cc region, 30 back grind on inlets. 45 deg x 1.75-2mm wide contact face, grind the region below the contact face to 50% of the height at sharp 70 deg, the remaining seat insert region below the 70 deg (ie: the throat) should be of a diamter worked out with a bit of geometry based on those angles/dims - and be parallel.

GC

Hi,

thanks for the fast response. The valve seats are already modified in almost the same manner as you posted.
Now I wanted to know how to modify the valves. Can you give me an advice for this?

I have also another question:
Does "cc" mean combustion chamber?

Peter

cc is chamber, yes. The valve mod can only be done in a valve grinding machine. The 30 deg back grind must be left with sharp edges. Blending it with abrasive paper will not create an optimum profile that will interact with the contact face angle and seat and thus destroy the gains. I believe there are sound aerodynamic reasons for this.


G

Hallo,

may I waist the stem to 7 mm till the valve guide?

Peter

Yes, you can but the value of this is much overstated, given that once the valve goes into lift the full stem diameter is exposed to the airstream.

Never waist exhaust valves, we need the full stem diameter to transmit the heat away from the valve head.

GC