Intake Port alignment

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GeoffW
Mariana
Posts: 43
Joined: Sat May 19, 2012 3:01 am

Intake Port alignment

Post by GeoffW » Wed Jan 22, 2014 1:52 pm

The intake port on my front cylinder head (Darmah head) is not centrally located between the manifold studs, the port is a couple of mm closer to one stud than the other - whereas the the intake manifold port is central, hence a 'step' interrupting the gas flow. Easy enough to remedy, but I was surprised to find this on an original unmodified head - was the factory sometimes 'off' with their machining of such things or is this how they were all machined on the front head?

Spagjet
Mach 3
Posts: 79
Joined: Wed Jan 08, 2014 9:07 pm

Re: Intake Port alignment

Post by Spagjet » Wed Jan 22, 2014 7:37 pm

everything metal is manufactured to an acceptable tolerance and with things like castings and machining operations only a few get checked as the manufacuring run goes along. If things look like they are slipping outside of acceptable tolerance levels changes are made to bring it back to what's 'acceptable' but there's always the chance that brumbies slip through between tolerance checks. As far as steps in intake tracts go, if the port ends up bigger than the intake manifold that's ok anyway as you don't really want a super smooth path for the fuel-air mixture. A little bit of roughness or a small step can even be seen as a positive thing as it can create turbulence that mixes the fuel and air together better (so it burns better). When you do porting work to an engine you intentionally work in a 'swirl' or a bit of scalloping to the port walls on the intake side to improve mixing of fuel, the exhaust side is the one that wants to be super smooth and clear and mirror polished to maximise exhaust gas speed (for better scavenging) and to minimise carbon build up.

the carbies are off my Darmah at the moment so I went and checked the front port, one side has got a step up of a couple of millimetres from manifold to port (bigger) and the other side lines up. All good. If there was a big step down all the way around from manifold to port (or from carbie throat to manifold) it would be a problem but a little bit on one side probably wouldn't make much difference, and like you say it's easy fixed anyway if it bugs you.

GeoffW
Mariana
Posts: 43
Joined: Sat May 19, 2012 3:01 am

Re: Intake Port alignment

Post by GeoffW » Thu Jan 23, 2014 3:46 am

Thanks for the reply spagjet - interesting your Darmah has a little step there too. I'm gonna just clean the step out of the way on that front cylinder and not get too far into the porting of this thing right now, so long as the front cylinder is firing clean and strong up and down the rev range I'll be happy.

Spagjet
Mach 3
Posts: 79
Joined: Wed Jan 08, 2014 9:07 pm

Re: Intake Port alignment

Post by Spagjet » Thu Jan 23, 2014 5:17 am

Glad to help. My Darmah hasn't had any porting work and has got 32mm carbies and goes like stink on a high wind. If you give it to it you are flat out hanging on. My GTS860 (spinger) has got sport cams, 36mm carbies, racing pipe, etc, goes very sweet but not in the same league as the 900 desmo. My other bevel (GT) has got a very souped up Darmah motor in it (bigger valves, porting work, 40mm carbies, racing clutch, no crossover, etc, etc, and is almost like hard work to ride. what I am trying to say is that a stock, well tuned Darmah motor in good nick is the best of all worlds. They don't need porting. They already go like stink.
If the step in the port is blocking the flow I would clean it up a bit too but I reckon it would affect the idle more than the power and even then by so little as to be un-noticeable anyway but yeah, I would knock the edge off it too. The step on mine goes bigger into the port so I would have to make the manifold hole bigger to match it, not worth the bother.

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