So yeah, a guy I know recently started getting into rotarys. He is doing an NA in a old 325i BMW.



Long story short he is an engineer and has access to some pretty cool machines.



He just milled the sides of the rotors for the whole weight reduction thing.



Came in at a whopping .498Lbs lighter per rotor.









Anyone else ever do weight reduction on a rotor?

Is the S5 stuff more dense?

 

racingbeat.com



clr performance in miami or orlando is it.

 

half a lb will make a big difference. also there is more weight to betaken out than just milling the sides.

 

Super Lightweight Rotor Assembly

1974-85 12A



Our Super Lightweight Rotor Assemblies are machined lightened using a CNC (computer numerically controlled) mill. These rotors are based on the stock 1983-85 rotors and the initial weight of each rotor is approximately 9.6 pounds, and upon completion of the machining process the weight is reduced by 1.1 lbs to approximately 8.5 pounds. (Compare these to the Mazda Comp equivalent rotors that have been lightened .44-.66 lbs each.)



http://www.racingbeat.com/resultset....rtNumber=10003

 

they drill the oil passeges too.

 

Weight reduction is not limited to just milling the sides of the rotor like you see in a certain performance catalog !

All models pre rx-8 can be lightened significantly to about the same weight. The earlier the model the more material that have to be removed to acheive the same weight reduction. The rx-8 rotors are the ones that cannot be lightened to the same weight as the earleir models. There is just not enough casting thickness to allow that safely. Trust me when I say that because I've destroyed a few in the learning process! They are now dedicated side seal cutting jigs now.

Very minimum weight reduction can be done to the rx-8 rotors though.

 

Have you seen any negative side effects to the ones you have done? Less structure stress etc..



How much extra weight loss do you gain from removing material in the ribs/inside of the rotor?

 

The point of reducing the mass of any part of a race car is to make it go faster. particularly in the rotating systems such as engine parts, drive line parts and wheels and tires. These items must be accelerated time and time again as the vehicle moves about the track.



In drag racing the drive line parts in the transmission and engine parts must be re-accelerated after each upshift. The torque lost in accelerating each peice is then missing from the calculated tire thrust (at the contact patch) and is not recovered on the next upshift. So, light weight rotating parts is free HP. And it is generally reliable HP, and it cannot be tuned out of the engine. It allways works.



If you run Hoosier tires on steel rims, and change to Goodyears on alloy rims you reduce your lap times dramatically. With no better skills or HP than you started with. Plus there is the dynamic affect of the car being lighter. Not to bad mouth Hoosiers. They are heavy, but outlast Goodyears (for us poverty racers) and can operate at very high tread temps without ill effect. They have thicker treads and suffer less from off the track operations. Not that that would ever happen.



So the deal is that two identical engines, one with just lite rotors and counterweights and one without may produce the same power on the engine dyno, in a constant RPM measurement, but not on the chassis dyno where a "time to RPM" is used to determin HP. The chassis dyno would show the lower power of the second engine where the engine dyno would not. Look at the Tilton catalogue and wonder why people would spend thousands of dollars to get a two or three disc clutch in 5 1/2 or smaller diameter and 3 pounds? Compared to your (same clamping power 8 inch 11 pound street assembly). The payoff is so big in the recurrent acceleration of that mass difference, that every serious race car has the very small diameter clutch.



I ran for years with a home made 7 1/4" button flywheel, a home made spacer, and a rebuilt Porsche super 90 cover, and a tilton single disc from a Volvo (I think). The disc is solid and very lite. New at .106" and warn out at .094". This was bolted on over a RX-2 automatic flexplate for a total of 7 pounds for everything and very little cost. The lite driven discs are also very easy on the synchronizers and allow faster shifts with less tranmission damage.



In the case of drag racing the flywheel my be very heavy in order to store enough energy for launch, but it then becomes a liability for the above reasons.



Very lite rotors tend to crack with time and hard use. If you do not peek inside now and then, a failure could occur.



Lynn E. Hanover

 

I always love reading posts by Mr. Hanover



Very nice post Lynn.........

 

Why, Thank you.



More on rotational inertia, so I didn't change the string name.



Did you wonder how to make the brakes more effective? Lower the weight of the wheel and tire assembly.



First thing is the total weight of the car is reduced. Good news. Then the wheels, that act just like really big flywheels, so reducing the weight of the 4 big flywheels reduces the ratio of swept brake pad area to rotational inertia, and presto there you are with bigger brakes. (in effect)



Also the ratio of sprung to unsprung weight goes up, and this gives you a better (smoother) ride. The tires spend more time in full contact with the pavement. You can use less spring rate and softer shock settings to control the wheels. Better handling. (can go around corners at a higher speed)



Why do formula one cars have carbon brake rotors? Nearly zero rotational inertia.



And those new wheels and tires look a lot better than the old ones.



Lynn E. Hanover