scathcart

B/c the counterweights at the front and the rear have to be matched to the rotor weights in order to have a balanced rotating assembly. Without this balance, engine bearing life will decrease very rapidly.

It is impossible to gauge how much, and where, to remove metal from the counterweights without the proper equipment.

If you make the rotors lighter, you have to make the counter weights lighter. It is not just as simple as maintaining a static balance between the rotors.

Its not overthinking. Its knowing what actually happens having witnessed out of balance rotating assemblies.

sleeperfc

thats what i was thinking. thats why i wonder what plans he has with this motor. I want to see a dyno sheet before it goes

I wonder how much it would cost ot get the thing balenced like it should be. Or if there is a way to test it to see how far it is off.

RotaryEvolution

iTrader: (30)

that was my point exactly scathcart.


if i were to do this i would have the whole assembly balanced because the whole point of this mod is to gain top end performance, which is where internal engine balancing is most critical. i would build an engine like this to spin 9k RPMs in which case i would like to know it is not going to eat itself up at those RPMs.

petex

yes, but there is also problem with balancing individual rotors. there is different amount of material removed from sides of rotor. primary/secondary side.

With unbalanced assembly, you will see noticable wear on bearings if you run 8k rpms at track after 5k miles.

However it can last like regular motor if you babie it. You just can beat the hell out of it. And I think it really sux.

SureShot

The counterweight lightening was a SWAG (scientific wild *** guess).
They swing over twice the rotor eccentric so I cut a little less than half the material off the weights as it did the rotors.
I call it CBE engineering (crude but effective.)

Of course with a race motor & a race budget I’d send it out for professional balancing, but since this is just my daily driver on the stock ECU & IC, I figured WTF - I'll just go for it. This was an economy rebuild on an 85,000 mile motor (seals springs & O-rings)

My G-tech will tell me the top end, but I’m going to have to spring for a dyno pull to quantify the low end.

550rwhprex

iTrader: (1)

that diy cutting of the rotors is not going to last... as i said before ive seen it proven in a race motor (3 rotor n/a 500hp) and a street motor dynoed at 516whp just by the looks of it does look right..CLR motorsports is the only person I know that has extensive experience in modifications of scalloping the rotors there are a few people here on the forum who have had this modification done...

Aaron Cake

iTrader: (1)

Just want to throw it out there....Any machine shop can perform this operation and keep the assemblies in balance for probably only $100-$200 or so. I think people often discount their local machine shop, but you will be amazed the work they can provide for not very much cash outlay. They have the equipment and skills to make this job take abotu 30 minutes, so maybe my inital estimate was even a little high.

Good work though. I'm eager to see how it last long-term when done DIY.

Wankel7

Wow, I am with J rat...glad to see somebody stepping out of the mold here!

Some, I am sure with all this talk you can't wait to put your foot into it

ViperDude152

very very interesting. Lets see how this works out. a Bridge port will be the cheap way to go next to this.

I would in the future get the whole rotating assembly balanced. That torque vibration is probubly from the unbalanced assembly. A few ounces removed does alot as the rpms climb. Mazdatrix and rx7.com can do this for you. Also Atkins rotary and racing beat.

I think it would have been better to have a smoother transition cutout like on that single rotor pic instead of a steep angle such as you have. POssibly carry the cutout closer to the dish and toward the center of the face.
Just a thought, no idea if it would make a big difference.

Lets us know how it goes.

SureShot

I considered cutting in a bridge port, but chickened out.
The opening bevel accomplishes some of that timing without so much idle lope.
It was my trade-off for daily driving.
After 200 miles the idle purrs at 800. You have to listen real close to hear any lope.

I didn’t carry the opening bevel any further to the center of the rotor because the port is fully uncovered at that point.

RETed

Dyno graphs before and after?


-Ted

bigdv519

iTrader: (3)

I would bump that estimation up a few hundred. At least to $500. Not to many "job shops" around these parts have CNC mills waiting around for work. The hardest part about getting them machined is actually finding a CNC programmer that is good enough to program it.

bigdv519

iTrader: (3)

Its not broken in yet.

SureShot

You know I am too cheap to buy a "before" dyno run.
It was a stock block running at 11PSI.
The G-tech showed peak net HP at 220.

I am curious enough to maybe get a chart after the break-in.

Even at 0 boost & shifting at 4K it’s torquey enough to get me out in front of the traffic.

petex

Ted, forget the Dyno sheets. 20hp gain? whatever...

Sureshot, tear the engine down after 10k miles and show us the bearings, sideseals and plates.

petex

if you have no boost at 4k rpm, you drive like frikking grandma!!! C'mon man, it's been broken in or broken long time ago.

The first thing I do after motor assembly and install, let it idle for 1 hour and then BURNOUT TIME!!! That's it! Broken in, good to go.

You're not gonna feel any vibration due to unbalanced assembly. not under load, maybe little vibration when free revving at 2-3k, basicly right off idle.

I guarantee you, your bearings are not gonna last.

I thought you're building the motor to make decent amount of power and put it to USE, not babie that **** w/grandmas foot on throttle.

petex

oh, if you have stock engine mounts you wont feel thing

SureShot

If it blows up - I will.
In the meantime I'm a-drivin & a-grinnin.

bigdv519

iTrader: (3)

Where's a drunk driver when you need one?

Edit: Hey SureSHot, I just called my brother at his shop. He is a CNC programer/machinist. The first thing he questioned, was how would one follow the curve of the rotor. He said that setting it would take about 30 mins. Machine time wouldn't be very long at all, but he would have to make a program for it, and that takes a little while sometimes. He said that their shop has a $75/hour rate, and a complete job (2 rotors, 12 cuts) could take 4-6 hours.

RotaryEvolution

iTrader: (30)

why would you need a CNC mill to balance a rotating assembly? what do you think people used 40-50 years ago to build performance motors?

brent clement

I guess I should have been more specific. You shouldn't need to rebalance the rotors. Yes I totally agree with balancing the assembly,however if you scallop s4 rotors the s5 c/b should be fine. Don't know for sure though. I've done a few things to rotors that people say will unbalance the engine and have found little or no effect. Thanks for not flaming me.


Brent

SureShot

My goal is 80,000 miles of spirited driving with no tickets, some autocross, maybe some time slips.

I do plan to romp on it after the break-in (slowest 1000 miles I have ever driven.)

Digi7ech

iTrader: (1)

I just noticed you used a clear plastic rotor shape to see how your porting/layout was going. That's an awesome idea!!

bigdv519

iTrader: (3)

Obviously you don't understand what I'm talking about. I should have been more detailed. You would need a CNC to keep the rotor balanced on itself, ie, not have a heavy cornered rotor. Balancing the rotating assembly doesn't require a CNC mill.

40-50 years ago "performance motors" weren't as powerful nor reliable as todays. But you know that, so why am I telling you.

bigdv519

iTrader: (3)

Thats a different way of looking at it. If a balanced, beveled S4 rotor could lose half a pound, S5 counterweights will balance the assembly.