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Matching Ports

 
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John



Joined: 09 Jan 2006
Posts: 1
Location: Canby, OR

PostPosted: Mon Jan 09, 2006 3:39 pm    Post subject: Matching Ports Reply with quote

I'm brand new on this forum, and maybe this has been answered in the past. If so, sorry to bring it up again.

Back in the "old days" one of the easiest modifications you could do was to match the ports of the intake manifold to the Intake ports in the block and the same thing with exhausts. In a street ported Rotary Engine, is that still important? As you can probably guess, I have a street ported engine using a stock intake manifold with a modified Nikki carb. The intake manifold to engine port match is terrible! The manifold is probably 30% smaller then the engine ports. The fuel/air mixture is coming down the manifold runners at whatever speed, and then is hitting this huge volume and then into the combustion chamber. I would think that at the very least the charge is slowing down and getting extremely turbulent.

So the question is back to matching the ports. In a Rotary, good or bad?

Thanks for your help!

John
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Blake
Been there, done that


Joined: 12 Jul 2005
Posts: 133
Location: Portland, OR

PostPosted: Mon Jan 09, 2006 8:00 pm    Post subject: Re: Matching Ports Reply with quote

John wrote:
I'm brand new on this forum, and maybe this has been answered in the past. If so, sorry to bring it up again.

Back in the "old days" one of the easiest modifications you could do was to match the ports of the intake manifold to the Intake ports in the block and the same thing with exhausts. In a street ported Rotary Engine, is that still important? As you can probably guess, I have a street ported engine using a stock intake manifold with a modified Nikki carb. The intake manifold to engine port match is terrible! The manifold is probably 30% smaller then the engine ports. The fuel/air mixture is coming down the manifold runners at whatever speed, and then is hitting this huge volume and then into the combustion chamber. I would think that at the very least the charge is slowing down and getting extremely turbulent.

So the question is back to matching the ports. In a Rotary, good or bad?

Thanks for your help!

John


It's generally a good idea to get it closer to a match, but the manifold should still be fractionally smaller to help minimize reversion. You should also be aware of other restrictions or sudden cross-sectional variations anywhere upstream. Some manifolds also do not flow equally, runner-to-runner. Finally, some manifolds use induction tuning to achieve certain power/torque characteristics. What many people do not realize is that crossectional area (among other things) dramatically affects the pressure waves, so changing anything could upset the intake tuning and yield contrary effects. Sometimes this actually feels faster, but that's usually because of the transition from an area lacking in power to an area that is the same or marginally improved is so abrupt. In other words, the punch in your back may be due to starting at a deficit rather than finishing at a large gain. We see this all the time with people who wire their 6-ports open...they have the same peak power but the low-end losses make the peak feel more impressive.

Basically, what I'm saying is that induction tuning is pretty complicated so, unless you have a lot of experience, a bit of trial and error is in order and sometimes less-is-more. Match porting is probably a good idea if you don't take the "match" literally, and there are many other things you could try. But just because you find a real gain from doing a little manifold porting, I would not want you to think more will necessarily be better.
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Blake Qualley
Pineapple Racing, Inc.
(503) 233-3878
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def3



Joined: 21 Nov 2006
Posts: 5

PostPosted: Sat Dec 02, 2006 11:34 am    Post subject: Re: Matching Ports Reply with quote

So what you are say in match porting the intake mans is to do a gaskit match port?

Also what is you thought on a port and polish of the TB? In another forum I asked this and there seemed to be going against this thought. I would like to hear what the thought is on this site. I tryied to see a dyno sheet from another build that states a great hp and torque incress put the sit is down.

Thanks
David

Blake wrote:
John wrote:
I'm brand new on this forum, and maybe this has been answered in the past. If so, sorry to bring it up again.

Back in the "old days" one of the easiest modifications you could do was to match the ports of the intake manifold to the Intake ports in the block and the same thing with exhausts. In a street ported Rotary Engine, is that still important? As you can probably guess, I have a street ported engine using a stock intake manifold with a modified Nikki carb. The intake manifold to engine port match is terrible! The manifold is probably 30% smaller then the engine ports. The fuel/air mixture is coming down the manifold runners at whatever speed, and then is hitting this huge volume and then into the combustion chamber. I would think that at the very least the charge is slowing down and getting extremely turbulent.

So the question is back to matching the ports. In a Rotary, good or bad?

Thanks for your help!

John


It's generally a good idea to get it closer to a match, but the manifold should still be fractionally smaller to help minimize reversion. You should also be aware of other restrictions or sudden cross-sectional variations anywhere upstream. Some manifolds also do not flow equally, runner-to-runner. Finally, some manifolds use induction tuning to achieve certain power/torque characteristics. What many people do not realize is that crossectional area (among other things) dramatically affects the pressure waves, so changing anything could upset the intake tuning and yield contrary effects. Sometimes this actually feels faster, but that's usually because of the transition from an area lacking in power to an area that is the same or marginally improved is so abrupt. In other words, the punch in your back may be due to starting at a deficit rather than finishing at a large gain. We see this all the time with people who wire their 6-ports open...they have the same peak power but the low-end losses make the peak feel more impressive.

Basically, what I'm saying is that induction tuning is pretty complicated so, unless you have a lot of experience, a bit of trial and error is in order and sometimes less-is-more. Match porting is probably a good idea if you don't take the "match" literally, and there are many other things you could try. But just because you find a real gain from doing a little manifold porting, I would not want you to think more will necessarily be better.
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