Ok, on to some :
I have been sidetracked a bit and seem to have made significant headway .. yeah me.
Then the reverse 7 port head made a reappearance, And I did some runs for a head using the normal Siamese intakes of a well developed race head ( 135cfm+ @28”) but using a well flowing exhaust for each cylinder. Then I used pipemax to spit out a 4in1 exhaust using the rest of the engine data. It is a 34x650mm primary into a merge collector and a straight collector of 60mm and 360 mm long. Experience tells us that for a conventional engine what Pipemax says the engine needs is pretty close to optimal already you can sort of use it for a 5 porter but you need a kink in your brain.
1: A single exhaust per cylinder is a significant improvement over a standard LCB for the centre cylinders.
2: The use of a dedicated exhaust port will make the charge robbing worse.
Always the same engine:
1310 cc race build with a fairly long custom cam, a Weber DCOE on a long intake, power output is irrelevant for the argument and not public anyway. I changed from part 1 this as the F11 cam is not realy wild and you want to see all the nasty stuff that happens with a long cam. I forgot about the stub exhausts (they are not practical anyway) and went for a proper header design with a 7800 rpm tuning point.
So forget the numbers and never mind the silly rpm’s, and yes , it does rev to 8500 or so in real life as well.
The basic premise is that it is the same engine, but there are two types of head (5 and reverse 7 port) and 2 types of exhaust : a 4 in 1 for the 7 porter, a optimised LCB based on the data I got from Paul S of port injected turbo mini fame.
First the Rev 7 port vs the optimised lcb.
If you look at other data like the trapping efficiency, the charge efficiency and the cylinder purity the above picture gets a bit more complex. As it turns out that even with a private pipe the number 2 and 3 cylinders are actually a lot worse than the lcb at 5000 rpm.
So yes it does make more power, but if you look at the BMEP plots for nr 2&3 cylinders , the 7 porter dips down from a very fair 11 to a decidedly lowly 9 in 500 rpm while the LCB engine bravely chugs on . In contrast, the good cylinders have a BMEP of about 13.7 up to about 7000 rpm which is really remarkable.
To be honest a port this bad should not be able to do this at all, however it looks like the Siamese intakes ( as it does this even with the 4 exhaust ports) enables the outer cylinders be very efficient (even though the inners spoil the party).
more to follow in part 3.