Exhaust Port relocation ideas.

[NoDOHC]

Originally Posted by GorillaRE

This will have a very negative effect on engine performance and consistency. The extreme amounts of exhaust reversion this port timing change will cause is something that we are trying to ovoid.

I like your attitude and thinking, but its not applied to the right issue.

-J

I agree that exhaust reversion is not our friend, but I don't see how this modification would be anywhere near as bad as a bridgeport. The significant overlap is minimal (about 10 eccentric shaft degrees). Most modern cars have significantly more overlap than that.

If you can explain why this will give terrible inconsistency, please do, as this will save me the trouble of building it.

I am curious myself as to what this mod will behave like. That is why I want to try it.

It really should act a lot more like a factory-cammed piston engine after moving the port than it does now. This should provide for better fuel economy too.

Please read my above post about the cusp on the housing shielding the exhaust port. Even at 1,000 rpm, it will be hard for air to move through a 0.050" slit. The overlap on a bridgeport occurs with the dish clearing the cusp, allowing free air flow.

[GorillaRE]

Originally Posted by NoDOHC

I agree that exhaust reversion is not our friend, but I don't see how this modification would be anywhere near as bad as a bridgeport. The significant overlap is minimal (about 10 eccentric shaft degrees). Most modern cars have significantly more overlap than that.
What modern cars? PISTON POWERED ONES! In these engines, overlap works totally different than in a rotary. During the duration of overlap in a piston engine (a properly designed modern one) the exhaust valve is "sucking" the fresh intake air across the top of the cylinder and into the exhaust. And although in a "tuned" cylinder head/exhaust/intake system it also "pulls" some exhaust back in, it does this in a perfectly timed and proportioned manner. The reason it can do this so well is because the pistons and valves are only doing "two" things: Up and down, open and close. This allows eeeveryone out...aaand eeeveryone back in.
This works very well and is a basic law of physics.

In a rotary on the other hand, it cannot and dose not have the same effect. Once the apex seal has crossed over around 50% of the exhaust port, the exhaust, back pressure from the turbine, natural engine rotation and the intake port acting like a vacuum on the smaller "squish" area on said rotor chamber during that portion of rotation, all cause a negative overlap effect. This equates to a uneven and inconsistent amount of exhaust gases being re-circulated. Since the rotor rotation is moving the chamber through the same steps over and over again, the mixture becomes more and more diluted.

Have you ever really listened to a loud un-muffled rotary idle? Do you know how the idle seems to be fairly smooth/consistent and then all of a sudden not? e.g. brrrrrrrrrruh........brrrrrrrrrrrrruh........brrrr rrrrrrrruh.........breeehhhrrruuh etc.

That is the sound of to much exhaust polution. It builds up and builds up and builds up, then breeehhhrrruuh.

If you can explain why this will give terrible inconsistency, please do, as this will save me the trouble of building it.

During Me and Barry's testing with the ICPS we noticed an UNBELIEVABLY erratic pressur/burn rate during idle, low load and a few other key moments..... can you guess what the erratic behavior was caused by
?
I am curious myself as to what this mod will behave like. That is why I want to try it.

It really should act a lot more like a factory-cammed piston engine after moving the port than it does now. This should provide for better fuel economy too.

Please read my above post about the cusp on the housing shielding the exhaust port. Even at 1,000 rpm, it will be hard for air to move through a 0.050" slit. The overlap on a bridgeport occurs with the dish clearing the cusp, allowing free air flow.

-J