Calling it a short turn is almost an injustice to the term.

It's my intention to do a minimum of blending from the bowl to the port on the floor side.

 

Also miata valve sizes could be bigger but then you need to cut out and knock in new seats and double check piston to valve clearance... money people dont want to spend

 

Funny enough, Mazda BP and Honda B VTEC heads have the same valve sizes.

 

I had the same questions. Our earliest heads (2004) were just cleaned up, bowl blended. Then we started removing material. Several years of failure to improve with several port designs later, I noticed our best area under the curve was with the old cleaned up but basically stock head. Studied more and realized the BP's rod ratio plays a key role in determining intake gas mass hysteresis, peak velocity, avg velocity and ultimately, total flow. Greatly over simplified, high rod ratio (long rod) engines have a sine wave of intake velocity gradients with shallower ramps. The BP is short, sharp. Turns out it's easier to suck the gas and fill the cylinder through a smaller, higher velocity port than a larger, higher peak flow but lower velocity port. I'm not "engine guy" but the white papers and old school knowledge backed up my speculation.
So I asked Keegan to do a head with velocity in the lifts we were using as first priority. Ignore peak CFM. The result kicked ***. It also opened up new flow regimes that lead to further experimentation. That led to the +2 exhaust CNC head that we offer now.

Let us know how your experiment works out. Meaning, post A/B dynos with no other changes.

 

Long rods are good!

If I get to that, which I doubt, it's going to be a while down the road.
I appreciate you sharing your approach.

 

What does this actually mean?

 

Something I made up. I forget what the correct terminology is. The air mass behaves a bit like a slinky. Create a pressure differential at one end (piston dropping) and a pressure wave propagates up the column of gas (atmo + fuel). Takes a while for the other end of that slinky to reach the same velocity as the mass near the piston. Intake manifold, cam and port design help with resonances, mostly 2nd order in production engines. Port wall texture also plays a role in boundary layer friction. Basic HVAC design takes into account boundary layer turbulence as it increasingly occludes flow through a given length of pipe. That occlusion is why small diameter corrugated brake ducts with lots of sharp bends don't do ****.

Hysteresis = slinky. Someone that knows more about it can dig up the correct terminology. The point is short rods need port and cam designs that do not work with long rods. This is again, something I learned by failing a lot by trying to apply tech optimized for longs rods to the BP. Once I went back to square one and got my fundamental understanding more accurately aligned with the platform, we started seeing breakthroughs. My favorite stuff is the tiny mod/big gain experiments. How we get 170whp out of stock cams and intake manifold kind of thing.

 

 

 

You need one of those supertech heavy double slinkies.

--Ian

 

 

Valve inclusion angles have also narrowed. The BP has a 50 degree valve inclusion angle, which is rather wide. Narrow inclusion angles create smaller combustion chambers and better squish. They also allow for straighter, taller ports.

 

i feel personally attacked