Carl Fausett
17th April 2009, 16:07
Cylinder Head Improvements for the Porsche® 928
CNC Porting – Polishing – Milling - 3 angle Valve Job – Larger Valves
The natural progression of engine development always brings a builder into the heads at some point. Sometimes sooner, sometimes later, but ultimately no development of headers and exhaust products, camshafts and superchargers would realize their full potential until the air flow at the heads are taken into account.
Now to begin – we need to say that Porsche has blessed us with some pretty damn fine heads on the 32v 928. The combustion chamber is nearly ideal in shape, uniform, with a centered ignition source and a short flame front. The 4 valves per cylinder breathe well in the stock condition, and have already shown that they will support 500 HP without any modification at all.
Two-valve engines, on the other hand, must use intake valves more than twice the size of ours to get the same flow, and find it difficult to prevent a large pent-roof combustion chamber and long flame front as a result of the space envelope needed for those valves. They can compensate with longer camshaft durations and more valve overlap, but then they have added still more characteristics – not all of them good – to the engine.
No, our friends at Porsche engineering did us proud with this head design. But can it be better? Can they be improved? Certainly. One benefit in after-market that we have over production is we can swing the importance further towards ultimate output with less regard to cost of manufacturing than the OEM producers can. We can afford to spend more time on a set of heads than anyone in a production/manufacturing environment would think prudent.
And we have.
Take our recent development of a system to improve the air flow (measured in Cubic Feet per Minute or “CFM) of the 32v 928 heads.
Valves and Seats: Starting with the valves themselves – we looked for the largest valves the combustion chambers could carry without increasing the size of the combustion chamber itself. An upgrade from the 36mm stock 928 intake valve to the “40 mm” intake valve (which is more accurately 39.5 mm) was performed. Funny how the 39.5mm intake valve actually has a 928 part number and is used in the stock Porsche 968… raising eyebrows that the next generation of the 928 was planned – indeed larger/better intake valves had been made, when the 928 was discontinued. And those larger valves were used to improve performance in the 968.
The 968 valve is an excellent fit in the 928 head, requiring only removal of the small valve seat and milling to install the larger valve seat needed. Still, that is not to say that it cannot be improved upon. Of course, a lighter valve allows for higher rpm’s in the valve train and/or reduced timing belt tension and failures.
We have developed both a stainless steel valve and a titanium valve for the 928, both that are lighter than stock (even though they are larger), and they have smaller stem diameters than the 968 valve. The smaller stem diameter increases air flow to the cylinder, and as a result our valves flow more than the 968 model. If you are interested in reading more about these valves, please visit http://www.928motorsports.com/parts/32v_valves.php
CNC Porting – Polishing – Milling - 3 angle Valve Job – Larger Valves
The natural progression of engine development always brings a builder into the heads at some point. Sometimes sooner, sometimes later, but ultimately no development of headers and exhaust products, camshafts and superchargers would realize their full potential until the air flow at the heads are taken into account.
Now to begin – we need to say that Porsche has blessed us with some pretty damn fine heads on the 32v 928. The combustion chamber is nearly ideal in shape, uniform, with a centered ignition source and a short flame front. The 4 valves per cylinder breathe well in the stock condition, and have already shown that they will support 500 HP without any modification at all.
Two-valve engines, on the other hand, must use intake valves more than twice the size of ours to get the same flow, and find it difficult to prevent a large pent-roof combustion chamber and long flame front as a result of the space envelope needed for those valves. They can compensate with longer camshaft durations and more valve overlap, but then they have added still more characteristics – not all of them good – to the engine.
No, our friends at Porsche engineering did us proud with this head design. But can it be better? Can they be improved? Certainly. One benefit in after-market that we have over production is we can swing the importance further towards ultimate output with less regard to cost of manufacturing than the OEM producers can. We can afford to spend more time on a set of heads than anyone in a production/manufacturing environment would think prudent.
And we have.
Take our recent development of a system to improve the air flow (measured in Cubic Feet per Minute or “CFM) of the 32v 928 heads.
Valves and Seats: Starting with the valves themselves – we looked for the largest valves the combustion chambers could carry without increasing the size of the combustion chamber itself. An upgrade from the 36mm stock 928 intake valve to the “40 mm” intake valve (which is more accurately 39.5 mm) was performed. Funny how the 39.5mm intake valve actually has a 928 part number and is used in the stock Porsche 968… raising eyebrows that the next generation of the 928 was planned – indeed larger/better intake valves had been made, when the 928 was discontinued. And those larger valves were used to improve performance in the 968.
The 968 valve is an excellent fit in the 928 head, requiring only removal of the small valve seat and milling to install the larger valve seat needed. Still, that is not to say that it cannot be improved upon. Of course, a lighter valve allows for higher rpm’s in the valve train and/or reduced timing belt tension and failures.
We have developed both a stainless steel valve and a titanium valve for the 928, both that are lighter than stock (even though they are larger), and they have smaller stem diameters than the 968 valve. The smaller stem diameter increases air flow to the cylinder, and as a result our valves flow more than the 968 model. If you are interested in reading more about these valves, please visit http://www.928motorsports.com/parts/32v_valves.php