Everyone knows that quality valve seat work is essential for good engine performance. What is often overlooked is just how critical the right profile is in optimizing the flow path into & out of the combustion chamber.
Real gains are made with the right profile, but you only get one good shot at it when working with O.E. seats. It’s important to nail it the first cut.
I’m used to seeing some nice significant increases in flow throughout the entire curve, but Feb. 5 2012 the current % gain record in my shop was shattered. From a legal I.T. valve job on a ’99 1.8Miata we saw an increase in average exhaust flow (.020″lift–.400″lift) of 26.4%! Checked calibration (it was spot on) and backed it the next day to make sure it wasn’t some weird fluke and the second test was identical.
It’s a pretty safe bet that ex. gains after about 5-10% (to keep up with intake gains) will make little if any difference in torque. Going from an 85% to a 98% Ex/In flow ratio isn’t in the recipe for power on a normally aspirated engine.
But I know intake gains will make power. That’s why I was very excited by the 9.7% increase in intake flow. That’s some power right there. Click here to see the curves.
Yes a 25% gain in average flow is remarkable, but not to be expected. And that’s okay because we typically see no less than 5%, but usually more like 8-10% and sometimes even 12%.. When these gains occur on the intake side it represents real power potential.
Our testing has shown over and over that after O.E. seats are precision machined with one of our carefully selected profiles flow goes up on both sides of the head. That’s Exhaust & more importantly Intake. Which all just proves once again what every serious engine designer & builder has known since the dawn of I.C.E. performance exploration: Valve seat shape and precision are of vital importance to performance engines.
I don’t select profiles that “cheat” performance with an impractically narrow primary seat width for the application. The primary widths we use are wide enough to allow the valve to transfer heat to the seat, but are complimented by profiles that maximize flow. We utilize a variety of Serdi cutters covering a wide range of valve sizes for specific applications and even use custom Serdi cutters for some applications where the standard Serdi cutters don’t meet our needs.
At this point we have worked with so many different ports, chambers and valve profiles that we are certain to have a Serdi profile that is right for your application.
There is no typical automotive valve seat to large for us to machine and our capabilities go down to seats for valve sizes as small 25.5mm with 5.5mm stems, 26mm with 6mm stems. If your head uses more diminutive sizes than these, contact us as we may be willing to tool for them.