adamlewis

Ive been reading some more on porting and there seems to be a steady trend...The more you port, the more HP you get uptop, but the the more torque you lose. Why is this? It seems to me like putting a bigger A/F mixture in the engine would give more power to both aspects.

Some sites even said that if you were to get a periphereal (sp?) port, you would have to bump your idle to 1.5 or something crazy like that.

vaughnc

Maby less to push against or lower pressure at lower rpms?

How bout the butterfly valve in the tailpipe closed @ 1500-3500 rpms?

Suparslinc

Porting a rotary engine increases the duration of the intake stroke. The longer the intake stoke is, the less power you have down low. However when the rotors are spinning really fast, the extended port opening raises the powerband, giving more high RPM power. Thats the basics of it. You really need to understand the whole intake/stroke/duration/ theory to see why a large port works like this. Let me get my Mazdatrix catalog out. . .

Suparslinc

Heres a paragraph that explains it somewhat. Thanks Mazdatrix!
You guys can thank me later for typing this all out. . .(hint: read this about 4 times and try to picture the rotary engine in your head as you read through. It will eventually make sense.)

The shorter the port timeing. the longer the gasses can be compressed, the longer the explosion can be contained, and the "cleaner" the chamber will be before the next charge is sucked in. These specs give you your basic "stump-puller" engine: lots of torque at the bottom, nothing at higher revs. The later the exhaust closed and the earlier the intake opens, the more intake charge is sucked out the exhaust pipe, but the earlier it can begin being sucked in . The later the intake closes, the later the engine can begin compressing the air/ful mixture. The earlier the exhaust opens, the sooner the remaing "explosion" is let out the exhaust pipe. The higher the engine needs to rev, the faster it needs to get the maximum charge (longer/bigger intake) the less time it has to "use" the "explosion", and the faster it needs to get rid of as much spent gases as it can (longer/bigger exhast timing/volume) This is your basic race engine (ignoring incredible volumes of other things going on that do matter) that makes great power at 9000rpm, but won't run below 4000. Everything is a trade-off with something else. If even this overly-simplified explanation sounds complicated - IT IS! Welcome to the world of high performance engines.

BhamBill

Remember that porting a rotary is the equivalent of changing the cam on a piston engine. The changes in the ports effectively change the "lift" and "duration" in the "valve timing".

Ever listen to a V-8 with a wild cam? Idles 1000-1500 rpm with a very lumpy idle. The engine loses low end torque but comes on strong at 2500-3000 rpm. Gee, that sounds just like what happens with a ported rotary.

adamlewis

Thanks for sorting that all out for me. You guys are the best