Latest Crazy idea-please join in
 

Hi Guys (and girls)

A week or so ago, I started thinking about a concept, that I believe hasn’t been tried before on a Rotary engine.
Basically port timing is determined by two things: Port timing and Rotor angle at the measured time.

Naturally there is allot of overlap, and wasted intake charge on ported engine, especially looking at Bridge ported, Peripheral, and J-Bridge (Monster) ported engines.

These porting configurations work very well, but it is limited to the higher end of the Rev scale (once again depending on port shape, placement and timing).

What if the 2 Stoke exhaust principle is used?

One would build individual Exhaust for each of the Rotors, leaving them uncollected.

Benefits: There will definitely be less Intake charge dilution at lower revs, as the strong reverse sound wave will keep the intake charge from being sucked out of the exhaust peripherals.

It also seems that the Expansion chamber could be tuned for the specific RPM range at which the porting works best. Who knows, I think a few extra HP will be in order.
Might even help a little with fuel consumption.

Problem areas: It will be difficult to get the “cones” of the expansion chamber sized right for the specific application as well as the angle to be used. Allot of factors will have to be calculated, and taken into account.

Working on the Exhaust opening Degree of a Racing Beat J-Bridge Port engine: 88BBDC

Have a look at the attached example:

All of the dimensions of the Expansion are at least adequate for the Rotary to breath properly.

Except for dimension number D5 (Tail Piece) ,which is just too small. A 30mm TB have the ability to flow +- 70 CFM. Opening this up to about 50mm (2 “ ID) will be more suited for a single Rotor’s flow 50mm flowing 291 CFM.

Total length of the tuned pipe will be 42”.

Karis

I thought about this awhile ago. I think it would possibly net you gains or perhaps make for a cleaner burning rotary but I think the biggest challenge would be fitting the pipes somewhere. On most two strokes I have seen the pipes are about as large as the engine itself.

I belive i read a pretty good debate on this forum in regards to this type of set up. They went into detail why this works on a motorcycle/ 2 stroke engines and why it wouldn't result in the same gains on a rotary.

Hopefully i can find the thread for you, it had some really interesting information.

an expansion chamber in the right size and shape can make for a much quieter exhaust.

Thanks for the replies sofar!
WOuld like to see what the other thread said as well.

karis

The problem with the rotary overlap is that the exhaust port closes late AND the intake port opens late- while still having lots of overlap. Far from ideal.

There are ways to open the intake sooner (bridege, P-port), but this also increases the overlap period by the same duration.

Only the Renisis side exhaust ports solved the issue of opening the intake earlier AND closing the exhaust sooner. Much closer to ideal, but still late on intake opening.

So, on a pre Renisis we suck exhaust gasses into the expanding chamber after BDC just before the intake port opens.

Mazda cleverly used this disadvantage to their advantage by having the high pressure exhaust reversion charge (when the intake port does finally open) reflect back to the other chambers intake port just as it is about to close- ramming more air in (part of DEI affect).

So, we definitely do not need a way to keep intake charge in the chamber, but rather a way to keep exhaust out. Or rather keep exhaust going out the exhaust pipe and not up into the intake.

We do this by tuning for a negative pressure wave, which is induced by the collector in the header. You could tune a header for low rpm scavenging to help w/ exhaust dillution, but the negative pressure wave phenomenon is not as strong at low rpm/flow so you will really see the benifits at high rpm not low rpm.

We don't want a positive pressure wave in the exhaust (like a 2 stroke has) because the rotary pressure wave is so strong it will have very detrimental effects at certain rpm ranges- so we keep to inducing negative pressure wave only.

Now this is what I`am talking about!
Very well written!
Explains it very nicely!

Hmm,so now "free" hp to be gained just yet.

Karis

mufflers
 

Check these tuned mufflers out,some were tested and some are concepts.

^^Any good results with those muffler or new informtion gained ?

Very interesting concept.Going to look into it,need more info!

karis

I'll be fabbing up the exhaust for my 12a pp soon and would love some info and recommendations :)

Heath : I would recommend that you go with the Racing Beat suggested sizes and lenghts.
Questions: How high do you want the max hp to be in the RPM range?
What induction are you using? IDA or injection?

karis

Thanks, I'll be running a 48 ida. Lynn E. Hannover gave me some great recommendations as far as jets, emulsion tubes, etc. I still need to locate a 350 or 400 gross jet needle seat. I've emailed several placeswith no luck. Hell, most places don't even respond (Gene Berg, Pineapple Racing)
I'm willing to sacrifice a little hp for torque and driveability since it will see a blend of street/track use.

Those mufflers are tested on airplanes with rotary here is a link to the site ,
they have some great stuff there.



http://www.rotaryeng.net/

Ok,i see. I do believe that a no 300 needle and seat should be sufficient,but dont go smaller.Perhaps you can enlarge your float bowl,if you havent done so allready?

What fuel pump are you planning to use?

The shorter the exhaust is,the higher in the rpm range the Max hp will be.

Recommended :for PP Port.
Short primary system : 10-18"
Long Primary system : 89-94"

Primary pipe size should be between 1.9-2.0" ID.

You can go longer,if you want less HP ,and more driveability with torque at the lower end of the RPM range.

As an example: Going from 28" down to 24.5" brings the max torque RPM down from 6250rpm to 5700rpm.The amount of torque stays allmost exactly the same,the Max Hp comes down with +- 10hp.

In the end a few small adjustments in timing and air correction jets makes a nice difference.

Hope this gives you some pointers?

karis

I think this will not work for the same reason that true duals are not advantageous for a rotary. The collector in a rotary creates a low pressure pulse from rotor A that pulls the exhaust from rotor B, and vice versa. When the header is tuned right, this removes some of the reversion that is what kills rotary efficiency at low rpms. If you separate them and especially if you build a pressure chamber like a 2 stroke, you will be worsening the problem, not improving it.

Correct me if i am wrong here, becuase I sometimes get confused on this stuff, but I think that is all correct.

pat

so yeah im trying to understand this but what confuses me is the headers. Those pics you put up is that a racing beat header i saw the RB and was wondering. Im doing a bridge port so im looking into this exhaust idea.

Karis, I have indeed enlarged the bowl already.
Fuel pump is a Holley Blue
I suppose I'll just have to experiment with the primary lenghts, timing, and jets :)
Thanks for the advice Karis!

expansion chamber exhaust
 

you guys have touched on a concept that i did some design work on about 10 years ago and started testing a year and a half ago.i have been doing r+d on a exhaust that fits the description of what you guys are looking for .currently undergoing testing on 12a and 13b street port scca e-production road race cars running collected headers (2 racing beat 1 custom)with my expasion chamber mid pipe. the results so far in testing have been peak power gains of 8-10% with no changes other than retuning to compensate for the exhaust.the bigger change has been not the change in peak power but the the change in powr curve.all of the test engines made peak power just above 8000 rpm with a peak durration of about 300-400 rpm with conventinal exhaust.the same engines post Pi pipe instilation now reach peak power as low as 7200 with the power band carrying past 10300 (still rising)on the customers that will rev it thet high for testing with no drop off .i believe with a properly buit and clearanced engine the useable power band with this exhaust will be 7000-11000 rpm.the only problem encountered thus far is all preconcieved ideas on tuning need to be thrown out.every thing from fuel air ratios to timing will be different.... carb jetting how about a car that raced for years running a 48 ida with a 180 fuel and 200 air now needing a 195 fuel and a 120 air to feed it and not powder every apex seal in 5 laps!n/a rotarys running 11.2-11.3 fuel air ratios to keep from burning up everything in the motor .this pipe scavanges so hard it will lean out a motor 2-4 full fuel air ratio points if you dont change your tune. stay tunned...... more to come the header testing comes next...........

Pirsq,
I am running a 2nd gen EP in NEDIV and would be very interested in any info you can give me. I would also be interseted in doing testing if possible. I am currently running a RB header into my own fabricated collector and a mandrel bent 3" pipe to a custom muffler(5"oval in and out).

Why not just run a stepped header?

stepped header would also be a good idea,allthough it will not work as goos as on a Piston engine.

Since i had this idea i have spent alot of time reading on pulse tuning (with allot i mean more than 100 hours)

Seems i had a good idea with the expansion chamber,but it will be completely different than the one used on a 2 stroke.

pirsq : Please do tell,it sounds like you might have uncovered something very nice

Karis

Says who? A true dual setup works fine on a rotary (even though they sound like ass!). The key to it is in knowing when it is advantageous. The LESS overlap you have the better a true dual system works. The more overlap you have, the worse it is. It's crap on bridge and peripheral ports because it can't scavenge. However just because a true dual setup can't scavenge doesn't mean it can't tune. It can. This is why it can be benficial.

The biggest problem with various exhaust types, including true duals and others, is that many people take an all or nothing approach. Many assume that if it works good on a stock port motor then it must work good on a ported motor. This isn't always true. The reverse also applies. The more port overlap a motor has, the more critical a properly tuned and collected exhaust system design becomes. The more overlap you have, the more peaky and narrow of an rpm range you are also trying to tune for. When you get down into a zero overlap situation damn near any design works as good as any other as long as you meet the flow requirements.

I believe the true duals work well with the stock long runner tuned DEI manifolds (GXL-SE and later) as you have the high pressure exhaust inducing the postive pressure wave to the opposing port (like the stock manifold), but you keep the exhaust velocity up unlike stock where the exhaust mixes right out of the port for turbulence and less velocity (but better emissions).

That is why they provide good midrange torque where a collected header will be scavenging and reducing the DEI effect.

This is also why a header provides a smaller increase over the stock manifold and "race pipe" with the later DEI manifolds as opposed to the old short carb intake manifolds that only used Helmholtz effect.

Rotarygod & Blue TII : Very true indeed!I have spent some time reading on the pulse tuning of the GSLSE intake manifold,but i`am not 100% confident that I will be able to replicate the tuning employed on it,even if only on paper.(So i`ll keep quiet before I make my name ass,hahaha)

I have had a look at the lengths that Racing beat recommends for different style of porting.I believe Jim and the guys have spent allot of time on it,and it works very good.

HOWEVER!I think there is more to be gained,especially in a "special" type of porting,like BP or PP ,where you can tune for what you specifically need.

I built a header with the help of a friend for my beetle.i went with the specs that RB states, and spent allot of time getting the length the same on the pipes.The collector has a nice shallow joining angle ,at +-15Deg,with a divider plate keeping the pipes separate, without restriction. The rest of the car is not yet finished,so we will have to see the HP figures off it.

Attaching a pic of it :