This photo is showing the centre exhaust and the route it has to take to get out on the original 8-Port Head




It's not as bad as it looks as it flows quite well.

This is the 7 Port for comparison:

NOW I understand why a 7 port instead of an 8 port - so does the 7 port work better than the 8 port because of that, or are there other reasons?

GR,

Isnt the maxium capacity aloud under the CAMS rules for catagoy 5 in NC 1330 not 1360...

1275 plus 060. equal less than 1360ccc

1.5mm max

Just curious thats all ?
PG


Engine:
(i) Reciprocating engines: The bore may be increased by a maximum of 1.5mm, and the stroke must remain
standard as specified for the make and model.
Where increasing the bore size up to 1.5mm increases the engine cubic capacity above the original
capacity class limit, for competition purposes the vehicle will remain within its original cubic capacity
class.
Toothed belts driving engine ancillaries are permitted. Engine pulleys are free.

How much development is there on the camshafts for 7 & 8 port heads? Are they very different from the 5 port cams to get the benefit of 4 inlet ports as opposed to 2?

Dave, the 7 port head uses the standard cam used in the 5-porter -- that's the attraction of the 7-port over the 8-port, it's way cheaper as you don't need a special cam grind (and you can use your normal extractors, too).

true, but the 7 port head might allow for more aggressive valve overlap etc. given the engine doesn't have to deal with siamese ports etc. etc.

That was more the angle my thinking was going.

I don't think it'll make any difference, the two valves exhausting into the siamesed port on a 5-porter are 360º apart, so the pulses are spaced far enough apart that cam timing shouldn't come into it. I think.