It seems it is best to carve off as much of the cast alloy inlet manifold as possible with a disc before using a milling machine.
The cutter is only 85mm long and cannot reach the lower bits of 3 & 4 cylinders.
I bought a long reamer but that just shakes a lot, works loose in the chuck, and falls out regularly.
I go in search of a 160mm long end cutter tomorrow at a specialist milling supply shop.
When I get the cutter on to the cast ally, you have to nibble off a small bit at a time (1.0mm -1.5mm) or the ally overheats at wraps itself around and sticks to the cutter shaft, needing a hammer and screwdriver to bash off before continuing.
The R&D continues. When I have the right length cutting bit, and the right cutting method, it should be much easier.
Now on to the manifold replacement scenario.
Turbosport of Bedfordshire quoted me £1,500 + VAT to make up the mould, and £30 + VAT for each casting, and £30 + VAT to machine each casting (faces flat, 16 holes drilled and 8 tapped).
A cast ally inlet manifold is one route to follow. The other way is ally plate and tube, carefully cut and welded. I now have the plate (3/8" x 4", they measure it in inches still) , I have the tube 50mm ext diameter with a 38mm hole.
Now the technical bit.
In 1970, I helped for a very short while, to prepare a Mini Cooper S for the 1970 RAC International Rally. It had an 8 port crossflow head with 4 Amal carbs, which cost an arm and a leg. Therefore I must assume that 4 separate inlet ports are potentially better than 2 siamesed inlet ports. The airflow must be much better.
Looking at it from a geometrical point of view, the 175 Strombergs have a cross sectional area of pi times (1.75 x 25.4/2) squared, or pi times 494.17 sq mm
The Webers have a cross sectional area of either pi times 36/2 x 36/2 for 36 mm chokes or pi times 38/2 x 38/2 for 38mm chokes, both times two, as there are two chokes per 45DCOE. That equates to 648 pi or 722 pi.
So 494.17 pi for Z/S versus 648 pi for 36s or 722 pi for 38s.
It seems apart from the Y branch on the siamesed inlet ports, the twin 45DCOEs potentially let in a lot more air than the twin Z/Strombergs.
Are you with my logic so far, and do you agree with this logic?
Second question:-
If the chokes in the 45DCOE are 38s (for maximum airflow for say a 145bhp potential power level), or 36s (for a 125 bhp potential power level), what diameter should the inlet tubes be for maximum airflow?
I have bought 38mm ally tubes on the basis that if the air has been restricted to a 38mm hole in the 45DCOE choke, what is the point of a bigger tube? Plus the valve seats in the combustion chamber look like 34mm.
Is the 36mm or 38mm choke tube in the 45DCOE deliberately smaller to allow a pressure drop when it increases to 45mm as it exits the carb, to allow the fuel to get sucked into the inlet airflow?
A manifold made from plate and tube welded together is alreadt very smooth all over, so minimal machining and minimal gas flowing required.
Constructive discussion please.
Alex in Norfolk.
