So I was discussing my engine with a local fellow RX'er... He stopped me when I started talking about street porting the exhaust and chamfering the edge of my RB header to match. (The RB header has kinda like a step in it where the pipe is welded to the flange.)

He said it's be interesting to actually make the exhaust SMALLER...

This intrigued me. Power by making the exhaust SMALLER? Bullshit I thought. (Me mighta meant smaller as in smaller than a street port, but not necessarily smaller than stock.)

He continued. The exhaust port moves from an oval shape on the inside of the housing to a large round shape on the outside, kinda like a funnel.

The idea is to put a sleeve in the exhaust port that'll make it the same diameter and shape the whole length through the housing. Actually have that sleeve extend a little out of the surface of the housing so that it goes into the header/manifold. It'd actually be a smaller diameter than the pipe obviously.

The principle was that this'll limit backflow or something so that exhaust won't try and flow back into the combustion chamber. He said this might increase low end torque as well.

Thoughts?

 

hmmm...interesting. I was actually kind of think of this the other day. On the 2004 CR250R they have a component that is called a RC Valve. The valve minimises the dead spaces in the exhaust port in order to create smoother and more responsive high speed performance. And maximize top end power. If I understand correctly the RC valve controls the exhaust port(increases/decreases) by utilizing a servo motor in order to smooth out power over the complete powerband.

As you know our cars are similar to the 2-stroke cycle. Therefore I think that you are on the right track. Keep in mind that the CR's RC valve is adjusted perfectly to the engines MAP. The question is it worth it for a little more/smooth power?

~Z

 

If you fit just a smaller outlet like you dexribed, torque might be increased (possibly by only 1-2lb/ft though)

but you'd also be strangling any possibility of power higher up in the rpm range


So it's really a tradeoff, better low-end torque - or higher Bhp?

 

Yea and no. A flat surfaced plug like your suggesting would stop a reversion pulse at the end of it, but so what? There would still be a negative pulse sitting at the end of the new sleeve, all stacked up waiting to stop the next pulse of outgoing gas, but thats not the worst part. You have 2 pulses to deal with. One is a harmonic and the other is a physical reversal of flow. In this excercise we're dealing simply with the physical flow and reversion of the gasses. The harmonics are more in the lenght and collector tuning. The other downside to this idea is that the gas will have to violently change shape and volume at the exit of the new sleeve. This will induce massive turbulence that will kill velocity.

Once Im done tweaking the intake system, the exhaust is my next victim, and I have some serious ideas on blowing away anything thats out there. And its nothing from outer space. Just good old physics. The design is done on paper, just needs to be constructed and proven. And this will be alot easier than the intake/carb system with all of its intricate considerations, trade offs etc.

 

There is some turbulence on the floor of the port. What you're speaking of is out there.... I'm just not allowed to say where, he knows where I live And I've been told there was more than 5hp found there. Not the usual 5hp from bad tuning, both set-ups optimized.

 

I thought here was a good chance you'd show up in this, and I was kinda hoping you'd provide good info which you have.

As far as intake, I'm going to be starting out with Stock S5 manifolds.

I also have a RB road race header which I was planning on using with the street ported engine. That's where the idea was brought up.

As far as port, Obviously, if I go too low, I eat into the power "stroke" and if I go too high, I increase overlap.

Another thing I was thinking was about that overlap. So we have exhaust gas leaving. Could I scavenge some of that exit velocity to create a little extra suction at the beginning of the intake... But I figured it wouldnt help unless that suction was at the end of the intake "stroke"...

Flow is so... I dunno... It's so simple that it's complicated.

 

Done. It helps power by making the port flow better. Downside, is that without that giant discontinuity in the port, the exhaust gets *louder*.

At least, according to people who've done it.

 

The rotary engine is the most efficient way to convert fuel to noise. Why would I want to stifle that?

 

Amenra.

 

Yeah. It's what keeps making me think of throwing a Chevy 2.8 or a Ford 2.3 or something under the hood of the FC.

 

can i see pics of this piece u made if by chance

 

Well Ive seen plugs like what your talking about on here somewhere. I'd say they would be of great value on a turbocharged engine because the high velocity gas can be fed right to the t-wheel and make it spool quicker. Once it hits the T-wheel that game is over on a turbo car. But on an NA car youd want to maintain velocity for as long as possible. So gentle, long radius turns, gentle shape changes and area changes (if necessary at all) will net the best possible velocity. Big abrupt changes in any of these will hurt velocity, induce turbulence and reduce overall flow.

 

I made my first exhaust sleeves 7 or 8 years ago. My exhaust pipes are much smaller than 2" and the car makes great power. Even my large exhaust ports use 1 7/8" primaries. It's a great idea. There was a thread on it a few years back with pictures. I'll go take some newer pictures of one of my housings on a motor I have apart right now and post them so You can see what mine look like.

 

Went out to my storage shed and took a few pictures of my spare motor's exhaust ports. There is a little surface rust but it is very minor. The housings just need slight cleaning up but they are actually perfect. There is a little that needs to be done to the port runner shape to make them perfect but they are really close. These are my large ports. I timed their size with the degree wheel to get an open timing of 73*BBDC and a closing of 65*ATDC. If anyone has done their homework really well, they'll figure out where those timing marks have been used before.

These sleeves definitely increase exhaust velocity. Even though the header pipes are smaller than normal, the ports still flow much more. My small ports on the first engine I built were actually stock sized ports that only had sleeves to match. Flow on the flowbench went up by almost 30%. That engine used a 1 5/8" header tube yet flowed more than stock. No one can tell me that motor didn't have any top end power. These work very well on nonturbo applications but just as well on turbos. Mroe energy is kept in the exhaust system and this extra energy hits the turbo with far more force. You can run a much larger exhaust wheel and still have it spool fast. The larger wheel makes for less backpressure which means more power. It's a win/win situation. You MUST run an Inconel exhaust wheel though or you may melt the blades! I ran a turbo with no problems for a few years. That car is now gone. These are probably the easiest way to make more power everywhere. If you applied the stock exhaust port/engine exit of the rotary to a piston engine, everyone would laugh at you. They should.

 

The simple solution to this is to remove the sleeve altogether and port the crap out of the exhaust port.