How fast is 998cc

Bonus: they are free Like and you need a few extra for trying out additional back cuts. Things to try out are on the valve and on the seat instead of the single 30 degree on the valve. Generally the back-cut on the valve is 15 degrees less than the seat angle according to Darin Morgan of Reher Morrison up to 50 degrees seat angle.. A very very nice bit of information from Mr Graham Russell showing the differences in castings vs vs std cc head in glorious cut sections.

And the reasons why he likes one casting over an other. I must say it is very nice and enlightening.. If you look at his throat design and look at the aperture it looks quite a bit like what I would expect to work well from a theoretical standpoint. Just squint a bit and look at the negative green shape. Also note the angle of the chamber wall at the short side. Very slowly working on it a bit. I ground a minimal amount of metal out of the chamber.

Most of it is removing a bit of the beak. This all nothing new, and pretty much like is described in Vizards book, and what is shown in Gordon Russell piece on small bore tuning. My take is that the basic shape of the chamber is fine if you take a part of the beak out. As fas as de-shrouding goes, I kept it down to a minimal as in this head the distance from the valve is enough and by laying back the chamber a bit, the distance from the valve to wall will increase with valve lift.

What I think is an interesting thought is to look at the path the air takes from carb face to valve but not from a port idea but the mini plenum idea. You basically have a kind of secondary manifold which slows down the air by the enlargement of the cross sectional area CSA followed by the very very very short runner.

Another way to look at it is like a plate restrictor set-up going around a corner. If you want to have air go through a small hole, you need to do this in a manner that has a maximum of pressure recovery. Most of the time this is done by a converging-diverging duct, much like a rocket nozzle but with a very shallow exit angle. Dalhousie FSAE intake with diffusor. Just squint a bit and mentally block out the outer runners and it looks like a Siamese port….

The arrow marks the runner part. Note it is short, and the cutting back the chamber massively or removing it altogether like the design of the ancient Ford Kent engine where the chamber is in the piston and the head is totally flat you are not improving the pressure recovery shape even if you might boost raw airflow as well as substantially reducing CR. Note that the chamber is a continuum of the seat and is quite a bit like the schematic above.

The question is does it make sense to forget about the short side radius as it will never be good anyway , then sink in the valve quite a bit and focus on the area after the valve seat. Just to show that the seat area is quite critical I simply put in a 5 minute three angle seat little more than a freshen up a valve with little more than 0. Takes little more than 10 minutes if even that. Idea is to get some measure of pressure recovery and it will probably involve sinking the seat deeper in the head yup..

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