Swapping ports...
Turbo Mini Forums

Just putting it out there, but I have been thinking about charge/flow robbing in the standard head...

Has anyone ever considered using the current inlet port (siamesed) as exhaust ports, and using the 3 exhaust as inlets?
This would remove the inlet charge robbing as the inner cylinders would now be siamesed which is ok. It would require new camshaft, inlet & exhaust manifold, plus a completely different types of combustion chamber work.

Any thoughts, or am I being completely stupid...

Thanks, Rich

Valves for a start. 29mm inlets would be crap, with no way of fitting decent sized ones.

It has been done in the past I think they used to make the camshafts I read somewhere else?

I run a supercharger and I don't care the TB is on the wrong side.
VEMS + 12 PSI + Liquid Intercooler = Small Bore FUN!

probably easier to add 2 more intake ports

Yes i moved to the darkside

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better n easier to k head it and make good power

It's an interesting idea. But so many reasons that you'll end up with more issues than you solve makes it a non starter for me.

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It would just shift the problem to the exhaust port. Big pressure spike as the outer cylinder exhaust opens just as the inner cylinder exhaust is approaching overlap with the inlet.

Reverse flow into the inlet, poor scavenging and power reduction would result.

Just saying :)

Saul Bellow - "A great deal of intelligence can be invested in ignorance when the need for illusion is deep."
Stephen Hawking - "The greatest enemy of knowledge is not ignorance, it is the illusion of knowledge."

For the cost and development I would suggest a 7 port would be cheaper?

I run a supercharger and I don't care the TB is on the wrong side.
VEMS + 12 PSI + Liquid Intercooler = Small Bore FUN!

Saul Bellow - "A great deal of intelligence can be invested in ignorance when the need for illusion is deep."
Stephen Hawking - "The greatest enemy of knowledge is not ignorance, it is the illusion of knowledge."

Just some theory/science that I've been working on.

Saul Bellow - "A great deal of intelligence can be invested in ignorance when the need for illusion is deep."
Stephen Hawking - "The greatest enemy of knowledge is not ignorance, it is the illusion of knowledge."

Paul, is that about the intake/exhaust manifold length and camshaft timing you already simulated and posted? Or is there more to come?

http://www.jbperf.com/

It's continuously evolving

Saul Bellow - "A great deal of intelligence can be invested in ignorance when the need for illusion is deep."
Stephen Hawking - "The greatest enemy of knowledge is not ignorance, it is the illusion of knowledge."

Does it really matter? You can make 200bhp+ on a standard arrangement 5 port head. That's plenty for a mini.

I did some sims on a reverse 7 port so siamese in but 4 exhaust ports. There is some decidedly odd stuff happening.

I just realised that the outer cylinders of a 5 porter runs at a BMEP of about 13.5 to 14 (that is what a well fettled K1200 head would do It would also produce more than 170 bhp for a 1380)

you just loose so much on the inner cylinders

and I'm now pretty sure that is due to the shared intakes as it does this with 3 and four exhaust ports

That sir, is not rust, it is the progressive mass reduction system

http://aseriesmodifications.wordpress.com/

I'm finding that the 5 port A Series is limited by the size of the valve throat, due to the small bore/long stroke configuration for the engine capacity. The siamese port has an impact on maximum power output but, in my opinion, it is not significant. Generally what the inner cylinders lose, the outers gain.

The outer cylinders get a helping hand from the inners on the intake stroke. Just as the outer cylinder intake valve is starting to flow the inner cylinder piston is moving up the bore with the intake valve still open, providing a more accessible source of air for the outer cylinder. However, with moderate cams, the amount of charge robbing is only around 5%, but the inners loss is the outers gain with minimal net change.

So just punch more air into the inner cylinder with correct length intake runners and that benefit carries through to the outers. You get a higher useable rev band from the moderate cam and more mid-range torque than any 7/8 port with short intake runners. The short runners virtually suck air out of the intake when the rest of the engine has the potential to make peak torque.

Things get very interesting when you start looking at a bit more cam duration

All theoretical of course.

Saul Bellow - "A great deal of intelligence can be invested in ignorance when the need for illusion is deep."
Stephen Hawking - "The greatest enemy of knowledge is not ignorance, it is the illusion of knowledge."