Connecting some dots.




The chamber before modification.







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. As it quickly removes about a 1 to 2 cc’s of volume it is important no to overdo it because it needs to come of the deck later ( and quite a bit extra ). 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.

do a search on restrictor intakes an you get a whole lot of essentially the same designs.




Dalhousie FSAE intake with diffusor

Dalhousie FSAE intake with diffusor. Just squint  a bit and mentally block out the outer runners and it looks like a Siamese port…



The mini port seems to act like two restrictor diffusors in series

A schematic of a straightened and single version of the path to the valve if you let go of the ” the runner starts at the beginning of the head” concept. 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 ).




Seat as cut by Graham Russell (used as an illustration done on a scrap head.. so no blending or anthing else done. The valves are very deep in the head this way, supposedly keeping the valves out of the way of the burnpath. If this is correct I can't say. From a pressure recovery standpoint it does make quite a bit of sense.  (image used without permission from Mr Russell, taken from

Again Mr Russell’s  intake seat design .. seat a bit deeper in the head as far as I can tell . 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.







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