Here we have an alloy cyl head modified in the manner described in 'THEORY & PRACTICE OF CYLINDER HEAD MODIFICATION' by David Vizzard. THE HEAD HAS HAD THE COMBUSTION CHAMBERS MODIFIED TO THE DRAWINGS IN THE DAVID VIZZARD BOOK . THIS GIVES THE CHAMBERS A MORE KIDNEY SHAPE SIMILAR TO THE HOLBAY SHAPE.ACCORDING TO THE BOOK THIS SHOULD GIVE 10 TO 15 MORE BHP.
THIS IS AN ALLY CYLINDER HEAD OFF A 1725 BUT WILL FIT 1600 AS WELL I BELIEVE. IT HAS BRAND NEW EXHAUST VALVES & BRAND NEW TERRY DOUBLE VALVE SPRINGS. THE INLET VALVES WERE GOOD SO HAVE NOT BEEN CHANGED. THE PORTS HAVE ALL BEEN GROUND TO REMOVE ANY HIGH SPOTS AFFECTING AIR FLOW. BOTH MACHINED FACES ARE FLAT (LAPPED). NEW INLET & EXHAUST VALVE GUIDES ARE FITTED (SHRUNK IN) & REAMED TO SIZE.
These are the new Guides fitted by warming the head to 200 deg C & dipping the guides in liquid Nitrogen. They still needed hammering in - so they're tight!
So next came the lapping in of the valves using a reversible drill
Having photocopied the page in the book & cut it out it was positioned over the existing chamber then drawn round.
THE HEAD HAS HAD THE COMBUSTION CHAMBERS MODIFIED TO THE DRAWINGS IN THE DAVID VIZZARD BOOK 'THEORY & PRACTICE OF CYLINDER HEAD MODIFICATION'. THIS GIVES THE CHAMBERS A MORE KIDNEY SHAPE SIMILAR TO THE HOLBAY SHAPE.ACCORDING TO THE BOOK THIS SHOULD GIVE 10 TO 15 MORE BHP. THE WATERWAYS ARE GOOD INCLUDING THE THIMBLE ROUND CENTRAL INLET IN BRASS.
So here's the head with the ports cleaned out & the valves fitted
Well it went on eBay and had 522 views, 57 watchers , 15 bids and SOLD for £325.00. Well wasn't expecting that!!!!
Here are the valve guides fitted it also shows the steps and high spots in the ports
This is what I am aiming for. With the angles & new shape it gives a better burn pattern & directs the ignition of the gasses downwards in a swirl pattern.
Here's the Mod under way ,you can see at top right a bit more needs removing to reach the line.
Before the valves are fitted the high spots and steps are removed.
New double valve springs are fitted.
