We have a two valve versus four valve debate currently running in our forum so I thought it would be an opportunistic time to release my patented PolyQuad head design for four valve per cylinder heads to GFN readers and the general public at large. Granted there are plenty of variations on 4 valves per cylinder and this begs the question as to what a PolyQuad head does better than a a current and typical four valve per cylinder head?
Answer – everything, and compared to Honda’s VVT and other such variable valve timing systems costs almost nothing and can be produced in a typical head shop! To best appreciate how the PolyQuad concept came into being making a start at the two versus four valve debate would be as good a place as any.
Two Versus Four.
There have been some serious debates concerning combustion efficiency going on in the rums and from these it seems that it is well understood that there is more to producing torque and power than just filling cylinders with air and fuel. At low speed the engines ability to breath is hardly a problem as relatively, there is plenty of time to fill the cylinder as full as it is ever going to get. The key to making low speed torque is how much charge is trapped at valve closure and how effectively the charge is burned. Just how effectively a charge burns is down to mixture preparation and in cylinder motion at the time of ignition.
Assuming that mixture preparation is good then, at this point, best results would be achieved by the cylinder with the best combustion dynamics stemming from appropriate in cylinder charge motion. The bottom line here is that a parallel valve two valve bath-tub or wedge chamber design has inherent swirl properties. This means a head designer would have to work hard to eliminate the heads natural advantageous tendency to swirl the mixture (and believe me some have managed to do that).
For a two valve head then the natural tendency is to swirl the mixture and this, in part, contributes to it’s normally better low speed torque. On the other hand a conventional four valve head has no natural tendency to swirl – but it does have a tendency to “tumble” the charge. The following illustration shows the difference between the two.