Fellas,
How big a difference does using beveled rotors make in terms of output? Does doing this increase power across the powerband or is this mainly to help the engine at higher RPM? Would doing this be worth it in a street engine or is this mainly for racing? Also does doing this substantially weaken the structural integrity of the rotor?
I'm asking alot of questions right now as I have not worked on rotary engines in a very long time so please be patient with me if some of these sound redundent.
BTW this forum is a great resource for people looking for information on performance applications.
Cheers,
Peacedog

 

I can take part of this, beveled rotors allow for earlier oppenig and later closing of intake ports without inducing more overlap. They also reduce CR some. If done right there should be no substantial weekening of the rotor, however a blown apex seal can be caught in the bevel and may destroy the side housing, where as the side housings would have most likley survived with little damage.

I have never seen a dyno comparison shouwing what beveled rotors do to the HP TQ curve, but I would immagine it to be similar to comparing a mild ported engine to a stock port engine

 

Rotor beveling still adds over lap. Its the same as bridge porting, benifit being no weak bridge to crack and full corner/side seal support. Rotor beveling can open ealier OR close later OR both depending on were the bevel is added. Open timing is not as early as a bridge, but much sooner then a street port. Port closing depends on the combination of what porting was done to the port and rotor bevel. Keep in mind, realy late port closing isn't going to make more power neccessarily. It might, but it will require some major RPM and big intake runners, other wise you'll most likely loose power by reversion.

~Mike...........

 

So if beveling the rotors can change intake and exhaust timing much in the same vane as porting the side housings why is this not done more often? It would appear that beveling the rotors would take alot less work and skill than a really good porting job. Is it an issue of beveling the rotors does not generate the same amount of performance increase as a porting the side housings?

Also would beveling the rotors in combination with porting the side housings generate power along the lines of a bridgeport without the drawback of rough idle and loss of low end power?

 

For some reason I am having a real hard time envisioning how a bevel would increase overlap. I'm thinking that if only the top edge of the rotor is beveled, making the port close later, then overlap wouldn't be effected, if the mid section of the rotor is beveled, or if the rotor is beveled accross the entire or 3/4s of its edge, then overlap would be increased and the port would open earlier.

 

slo,

You have it correct, I didn't clarify it in my post although I did mention it depends WERE the bevel is placed.

Beveling has some positives and negatives. I'll start with the negatives. 1: those pockets reduce compression ratio, lowering this can be a good (if you plan on running HIGH boost, its not a bad thing), or bad thing (bad for off boost response and turbo response). 2: Those pockets also make a nice place for hydrocarbons to hide out too because its HIGHLY unlikely that during the combustion process that those relief/chamfers actually ignite. So this leaves unburned hydro carbons and raw fuel to NOT get burned leading to worse emissions and gas mileage under certain circumstances when comparing to a standard rotor. The RENISIS gets away with this because its chamfers are small, the RENISIS has a pretty lean burn (high pressure injection) and uses very little oil in the chambers when compared to the older engines. It has higher compression ratio (squeezing your mixture tighter promotes a flame front to burn more effiently and go out farther {probably far enough to possibly pick out those pockets?}). Lastly, the RENISIS has side exhaust ports, so this "pocket" of unburned crap makes its way out the exhaust port and doesn't build up. 3: Rotor beveling SHOULD require the builder to do a static balance of the rotors after beveling, then a full dynamic balance of the entire rotating assembly (READ: both rotors, counter weights and eccentric. And a good builder would include the fly wheel and pressure plate). Now for the back yard mechanic that just wants to add power, he can port the side plates and exhaust all by his lonesome, but he cannot propperly balance the rotating assembly. This would require sending it out, having more down time, and costing money when compaired to just taking a grinder to a port.

The good, can open earlier or later of the intake ports on 13b peripheral exhaust engines. Personally I'd only use it for early opening to keep the side and corner seals supported and not have to worry about a fragile bridge breaking. For late closing, I see no gain by beveling, just port up on your side plate, there’s no draw backs to doing this when comparing to late closing of a bevel. AND just as adding a bevel for late closing does NOT add overlap, neither does late closing of a side port. now porting up on a side plate and getting greedy AND beveling would be pointless. You have to really spin the engine up and have one free flowing intake system to take advantage of such a late closing intake port. It'll just cause loads of reversion, and KILL low/mid torque because a lot of your intake charge will get sqished back out the port because your combustion chamber has been getting smaller for some time now.

beveling is not new at all. It may be new to a lot of people in here, but it has been a mod used by racers getting around porting restrictions for decades. I've seen a beveled rotor in a Japanese magazine well over 15 years ago. Of corse, I couldn’t understand anything in the magazine, I can't read Japanese!

~Mike..............

 

Before you reply, re-read it, I added more....

 

what your take on beveled rotors+a Half-Bridge(only follows halve the intake port) on the secondarie ports

 

I'd say hella breathing. Make sure your turbine is rather large and big A/R and you should be making a lot of power if your cold side is up to huffing as much as your engine will want. Assumming by your last project and your name "Kabooski) you'll be artificially asperated lol.

BTW, when talking this kind of over lap on a turbo car, this is were long turbo headers start to really shine.

~Mike..............

 

So would it be worth it performance wise, cost issues excluded, to bevel the rotors on a streetported engine that was run on the street and occaisionally at an autocross event?

 

I would say no, a big streetport pushes the limits far enough. Second if your going to be turbo, then do you want a blown apex seal which normally kills a rotor and rotor housing to also kill both side housing for that rotor.

This is something you would have to decide though.

 

That would depend on what you want out of your engine and your budget, each engine build is different and someone that absolutely must get every last hp or those who would rather dial back performance a tad for reliability. Its up to the end users and i can't give a deffinate answer for you.

~Mike...........

 

Theres no differance in rotors having been beveled or not when it comes to what gets damaged in an engine be it rotors, rotor housings or side housings. You do under stand were the bevels are placed right?

Heres a well done rotor, it even looks as though the flame front from combustion might actually make it to the bevel. BTW, this is an early open bevel.

https://www.rx7club.com/attachment.p...hmentid=105343

~Mike............

 

If you shatter an apex seal and have beveled rotors apex seal chunks can go into the bevel area where they will be ground into the side housings. I have blown a few apex seals and also bought a core engine with blown apex seals. In both engines the irons where fine. There is a picture floating around somewhere of an engine with seal peices imbeded in the rotor in the bevel, and a corosponding picture of deep grooves in the side housing.

edit: it may have alot to do with the shape and size of the bevel, wether or not side housing damage is more likley.

 

I can see one more advantage to beveling rotors as opposed to porting the irons.

You are able to keep the intake ports down in size to maintain velocity= maintain lower rpm power.

This doesn't normally help in beveling for opening timing since the added overlap will work in the higher rpms where the larger ported port would still have enough velocity.

It does work if you close your exhaust port earlier (renisis) so you have more intake timing without the overlap.

It *may*work better than porting to improve midrange power where the runners are already large (4 port housing).

It would also still apply to a later closing port. You want very high intake velocity for a late closing port to help cram the air in against compression. If you port it for later closing you add port volume and lower velocity and have to wait for rpms/flow to raise the velocity back up to the point you are getting good chamber fill.

An example of this is where Mazdatrix ported their 6 port to monster 4 port (siamesed 2ndary and aux ports). They had to struggle w/ manifold design to get power to peak below 10,000rpm. This is because the larger port volume lowered velocity and only regained velocity through flow at 10,000rpm.

Note, siamesed 6 port still had the same timing- just more runner volume- an example of how port volume affects power curve.

 

Is this Big Enough?

 

Those are freakin' huge! I can see those only being used in a race motor. They have to severely affect CR and the way they break into the combustion chamber leaves me asking: Why? I would think someone could be way more conservative on a street application and still gain a benifit.

 

I saw something that mentioned carbon issues a few posts back. When I tore down my last engine with beveled rotors you could see the area of the bevel was actually cleaner than the rest of the face of the rotor. It looks like the airflow over that area keeps it clean. You could see residue and it showed "flow marks", for lack of a better term, and it showed where the air was going.

I should have taken a picture but the engine is back together now.