The_7

if a periphial porting adds a port to the rotor housing and is opened and closed by the apex seal....while the leading apex seal was crossing the port on the intake stroke wouldnt some of the compressed fuel/air leak into the intake stroke, dropping compression, and also when the leading apex crossed the exhaust port wouldnt some of the exhaust leak into the intake??

REVHED

I don't think so. You have to remember that compression happens on the other side of the engine. While it's true that the compression stroke has started while the trailing apex seal is closing the port it's also still drawing in air and fuel.

You're right about the exhaust though. With peripheral ports there's a large amount of port overlap which allows some exhaust gas to dilute the intake charge. It's not just pp's though, other porting styles also increase the overlap. In fact, exhuast gas dillution is what gives ported rotaries their characteristic brap, brap idle. Even standard ports (apart from the Renisis ) have some degree of overlap.

The_7

hmmm.....why doesnt exhaust leak into the intake stroke at higher rpms? why does it only happen at idle?

how does the godlike renesis not have port overlap problems?

REVHED

Exhaust gas dillution happens mainly at idle and low load when the engine is under vacuum.

I wouldn't say overlap is a problem because that's partly why porting increases hp plus you can't beat the sound of a bridgey or pp.

The Renisis uses side exhaust ports (instead of peripheral) which are placed for no overlap. I'm no expert but I think a big reason why they took the no overlap approach is for emmissions reasons. And because it has two exhaust ports for each rotor it has a lot of exhaust port area which is good for hp.

rotarygod

iTrader: (1)

The more port overlap you have, the less your volumetric efficiency will be at lower rpm's. As stated already, some exhaust will dilute the intake charge which not only leaves less room for fresh air but also heats up the intake air in the chamber. At higher rpms inertia helps keep the gasses flowing in the appropriate directions. In other words the velocity of the exhaust gasses leaving the chamber at higher rpms will help pull all the remaining gasses out of the chamber regardless of overlap. Another good side effect of this is that at high rpms because the suction through the exhaust is so good during overlap, it will create a low pressure zone in the chamber which actually helps to pull in more air through the intake. This is why it is so important to have a properly scavenging exhaust system. If it is restricive, less gasses will want to leave the chamber and will subsequently go back through the process again.

The Renesis has no overlap what so ever. It actually has 64 degrees of dwell. This is solely based on the port location. Since there is no overlap it can not get the higher amounts of dilution into the intake side. This keeps heat out of the intake as well as leaving more room for fresh oxygen rich air. Volumetric efficiency goes up. This in turn leads to better fuel economy, better emissions, and more power down low. The downside to no overlap is that at higher rpms there is not as much benefit from a good scavenging exhaust. It it still important though. It just can't help suck in more air to the intake side. It is actually a very simply concept to undestand. It is also one that should probably be seen to comprehend. When you see it you'll wonder how you didn't know it the whole time. Its pretty cool.

The_7

coool...i see how it works now....so the more overlap you have the more power at higher rpms.....what im about to say ive already posted but this was before i really understood how porting worked....what if you periphial ported your engine and then you had a sort of valve/plate mechanism that kept the overlap low enough at low rpm to have good low end power and then gradually increased overlap as rpm increased so you would have good power over a broad rpm range? im thinking about experimenting with that and my ignition idea (do a search if you want to read about it the post is "check out my idea for complete combustion in a rotary") in my 12A and if it works good ill do it do a 20B and then swap that in my 7 and then turbo it....just imagine the power

The_7

how much does periphial porting cost? also what does "64 degrees of dwell" mean?

rotarygod

iTrader: (1)

"64 degrees of dwell" is the opposite of "64 degrees of overlap". In other words overlap is the time that both intake and exhaust ports are open to the same chamber at the same time. 64 degrees is the amount of rotation that the eccentric shaft has turned during this overlap period. Dwell is the amount of time that there is a lack of overlap. The eccentric shaft rotates 64 degrees without the combustion chamber being open to either the intake or exhaust port.

More overlap isn't necessarily a good thing so don't think that it is the sole key to making power. It's not. There are too many other variables to consider.

The_7

what are the other variables?

Rotortuner

Other variables are like the intake manifold leangth, ignition set up, exhaust header tube size and leangth, another is whether you use EFI, or what type of carb. There are many different combos. A big street port in a 4 port 13b with a weber 48 IDA is an excellent engine with relatively small overlap.

CJG