SOHC.co.uk Forums > CB500/550

Inlet port matching

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McCabe-Thiele (Ted):
The book by Clive Trickey on tuning the ports on an A series engines was a big advocate of such things as port polishing etc.

Oddjob:
This isn't port polishing as such Ted, it's more to do with getting a better gas flow. Look at the picture and you can clearly see the large step where the inlet manifolds and the cylinder head machining don't match, this would cause an obstruction to the air/fuel mixture, it would hit that and cause turbulence, this slows down the intake into the cylinder. By removing this step so that the inlet manifold and the cylinder head port match better you get rid of this turbulence and the engine breathes better, this can give an increase in BHP, it's only slight but when you've only got 50bhp to start with then any extra is welcome.

Sorry if this sounded condescending, it's just so anyone else reading this with less knowledge can understand it better.

BTW, anyone wishing to try this, the way to do it is to fit a small piece of cardboard on the head, threading it onto the studs so it stays in place, like making an home made gasket. Remove it when it fits perfectly. Now fit it onto the inlet manifold matching up the bolt holes, cut the cardboard out where the inlet hole is, fit back onto the head and you can now see where you need to trim. That's my understanding of the process anyway, other ways may be better.

McCabe-Thiele (Ted):
I would include port alignment as part of the general gas flow & polishing as per Clive Trickey's book.

DomP:
I will be matching them up then, I would have thought a sanding drum on a dremel would do the job nicely.  Th only problem I always find is that aluminum blocks up any cutting or sanding product.

Bryanj:
Mike on the US forum insists on it when he does a head

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