Friday, April 13, 2007

Heads are all about details?

Obviously porting improves top end power at high valve lift / max lift.

However simply porting a head does nothing for the low lift flow which gets the the gas moving early in the lift phase.

On my old triumph head I spend ages fettling the seat area. I have seen all manner of Triumph heads, so called stage 3-4 heads great the ports are ported but the seat area is just 3 angle cut with little attention to the area just before the seat itself, sharp angles, ridges, off centre cuts, crap.

I spent this afternoon finishing off the end of the throats on my exhaust ports...As they are now complete bar a final buff the time had come to sort the seat area.

The standard seats are VERY wide, and the valves are poorly shaped. Killing low lift flow.

Above you can see the standard seats single cut angle, very wide..about 2.5mm...
After some very delicate work they are now 1.7mm and instead of getting a 3 angle seat job, which still has ridges between the angles, I have done some very neat work with sanding bands. The sharp edge that was on the edge of the seat where it heads into the throat is now very fine radius- blending with no ridge at all in a perfect convex radius into the throat.

Thats even better than a Serdi 3 angle job...Its called a proper job! I was reluctant to thin the seats any more as there is a comphremise between longevity and power here. I will reduce the inlets even more maybe 1.25mm.

Now all the exhaust valves seat areas will be degreased (they have been test lapped already to impression the seats before thinning), the valves seat area will be painted in engineers blue and lightly lapped for a few strokes...This will leave a shiney band on the exhaust valves and an area still coated in blue, all bespoke for each valve and cylinder.

Then the valves will have an extra cut made at 60degrees on the back reducing the width of the seat to only the area that is shiney and making contact with the seat in the head. This will probably double the flow just off seat...

This is the stuff that makes power and torque, no flap wheel porting bollocks...

I've got far into this head! Its now all out. I guess I can find some VVC valves, skim the heads down, insert them into the head and use then to protect the valve seats and polish and de-pocket the head too...

Blooming heck I reckon there will be 40hrs in the head when its done...Full monty.

Also ported the water ways :)

Bit scabby as supplied.
Bit larger now.

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