Is rotor beveling benefical to NA engines at all even though it lowers compression.

Also when removing weight from rotors do you also need to remove a of weight from the counter balance?

 

Yes and Yes.

~Mike.........

 

it will lower compression a little bit so start with the highest compression rotors you can afford. It is intended to open your ports earlier so there is a longer duration of intake(some also cause it to close later). This will cause more of an intake charge to enter the combustion chamber, making more power, so yes even though it lowers compression a bit, it is still beneficial(unless you have a peripheral port). The counter weights and rotors need to match, so with the weight this would remove you should have the assembly balanced when finished.

 

Not true! Read this thread very carefully! The counter weights an handle a variety of different weights without a re-balance. Remember guys the same counterweight that's used for a set of all "A" weight rotors can also be used for a set of all "E" weight rotors. If your removing material from the heaviest "A" rotors, all your doing is making the rotor weigh as much as the C,D, and E rotors (provided you re-weighed the machined rotor). If you keep the weight within the weight group of the A-E rotors, you shouldn't have to rebalance.
https://www.rx7club.com/single-turbo-rx-7s-23/my-beveled-s5-turbo-rotors-%2Apics%2A-505525/

 

I would advise that you balance your assembly afterwards. I'm going to have a set balanced here shortly...

 

Do the shops just spin balance each separate component or is it done as an assembly?

 

i've only ever seen it done as an assembly, but i've "heard" of people doing separate components.

 

This forum is sponsered by RB so they can correct me if I'm wrong. They dynamically balance the counter-weights while on the crank with bob weights on the eccentrics that equal the weight of the rotors. Plus a secret amount of added weight to compensate for the fact the rotors have oil in them.

I dont know if they spin balance each rotor and match them first or not.

 

Balancing the assembly isn't about balancing the part within itself. It's about the the balance in the circumference around it's rotational path. Again that's why the same counter weight can be used for a series of rotor weights without a re-balance.

 

I recently beveled a set of S5 turbo rotors for my engine. I had concern about the balancing issue too, this is what I came up with:

https://www.rx7club.com/showthread.p...ght+deviations

https://www.rx7club.com/showthread.p...ght+deviations

Justin

 

I rebalance my rotating assembly even when NOT doing any modifications using a STOCK assembly as it came out of an already good running engine. MAZDA allows for a lot of im-balance. I have both rotors weight matched from one another, the rotors spun balanced, the E-shaft and counter with fly wheel balanced then the entire assembly assembled (both rotors {actually these are replaced with bob weights}, both counter weights, e-shaft, fly wheel and pressure plate) and dynamically balance it. Balancing is as critical as setting seal and bearing clearance in an engine that is intended to be pushed beyond factory power levels and or RPM's. Is it completely necessary? NO, but a balanced engine runs smoother, will wear parts less and last longer. And smoother makes more power. Running a stock rotating assembly? Fine, don’t bother re-balancing but if you plan to modify it or mix rotors and counter weights get the damn thing re-balanced.

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

 

Talk to any "serious" engine builder and everything Mike has said above holds true. I keep everything matching from a motor and if it's not I get it balanced and that is just for street engines not going above 8.5K rpms. And for a race engine going over 8.5K it doesn't matter if it's totally matching set it will still be sent out to get balanced. Believe what you will about taking equal amounts of weight off a rotor but your bearings will tell you the truth once you have it running for awhile.

 

Anybody have any thoughts about beveling rotors for a half-bridge or full-bridge?

 

Opening or closing? I don' know why you would want an opening bevel On a bridge or half-bridbe. My plans for the engine I'm building now is a half-bridge with closing rotor bevels.

I really don't know if I like the opening bevel that much. I know Mazda uses it on the RX8 but the air stream has to nearly reverse its direction to enter the engine.Some sort of partial bridge, seems to me, would give better results. I don't know, could be wrong.

 

My theory regarding the opening bevel on a halfbridge is that it may result it a bit too much intake port volume at a time when the exhaust port is still fully open. The port would not open any earlier BUT it would open faster, making it more like a peripheral port in that regard but without many of the benefits of a PP. I'd just like to hear opinions from more people about bridges and bevels used together.

The opening bevel would not be a good idea on an bridged engine that would ever see street driving. On a half-bridge, a bevel on the primary ports would be a good idea. (I don't think this would hurt anything IF the rotating assembly was rebalanced) The closing bevel would work extremely well in any case. For a streetport obviously opening and closing bevels would be extremely effective, especially opening bevels because there really is very little timing advance that can be picked up from streetporting alone.

I'm interested in how your engine turns out with the half-bridge and closing bevels. Are you going turbo or NA?

 

Turbo. Iv'e done much battle in my head over this. I still don't know if I will go with a full half-bridge or a partial. Even if I go full, I want to stay conservative (very narrow, no housing cut).

I would be comfortable letting the trailing edge of the leading side seal float, but would like the leading edge of trailing side seal supported. Just cut the most perfect little eyebrow you can imagine, angled just right and everything.

You have me thinking on the primary opening chamfer. I just don't like the length of the cut,and the air flow. Advance opening with bridge seems better. change my mind.

 

A bridge will open the port MUCH earlier than a beveled edge will so the power gain will be considerably greater. That being said, a bevel on the opening edge of the rotor is a good compromise timing wise and would work better for a street engine with a streetport than a non-beveled bridgeport (particularly for an NA). The fact that it is at an opposing angle would have some effect on airflow, but remember, the beveled area would not be open at all if the rotor was not beveled so in the end you are gaining more airflow than a standard rotor setup.

I have most of what I need to build a 13BT using 9.7:1 rotors, all I need is an RB road race header to bolt up to my streetport exhaust in my 85 GSL. I'm between a halfbridge and a really nice streetport with opening and closing bevels. I know there are people pushing mid 200 range at the flywheel with an NA streetport with non-beveled rotors. It would be interesting to see what beveled rotors would accomplish on it. I will be having the entire rotating assembly dynamic balanced whether I go with the beveled streetport setup or the halfbridge non-beveled setup as a reliability and smoothness factor.

 

Sureshot has a real good thread on this and it is what convinced me to give it a try. Search his name. He is also budget concious.