Has anyone thought about extremely lightweight titanium rotors? Machined in the same way as RBs lightweight rotors. Just a thought if its possible then that could open up a whole new range of high revving na motors. Could titanium even take the heat? I know it can take the pressure the make titanium connecting rods. I would love to see a set made and running i might try this myself.

 

Search billet rotors on the forum. I think the thread may have been closed due to the manufacturers not being a sponsor. However, Eastcoastrotary.com makes billet rotors that have ran successfully in several cars. Weigh around 8lbs.

 

Was It billet aluminum because im just looking to see if titanium can be done because that weight might be able to be lowered to 7 or even 6 pounds

 

If you search on youtube they have a few videos.

 

RBs lightweight rotors are stock rotors that have been machined. The problem with making rotors out of a different material is that because of the interior shape of the rotor it needs to be cast. It could also be made out of two pieces, but neither option is child's play.

You can make the rotor out of anything you want, how well it will work and how much will it cost are the bigger questions.

 

Aluminum is going to be lighter than titanium....

 

oh it would be it thought these rotors where machined and billet aluminum would be lighter wow never knew that. Thanks to everyone answer my question i am just searching for a good options for the Na motor im building

 

Hayward rotary in UK also has aluminium rotors in test phase

 

This is true, but the concept here, consider this from wikipedia.

Commercial (99.2% pure) grades of titanium have ultimate tensile strength of about 63,000 psi (434 MPa), equal to that of common, low-grade steel alloys, but are 45% lighter.[6] Titanium is 60% more dense than aluminium, but more than twice as strong[6] as the most commonly used 6061-T6 aluminium alloy. Certain titanium alloys (e.g., Beta C) achieve tensile strengths of over 200,000 psi (1,400 MPa).[10] However, titanium loses strength when heated above 430 °C (806 °F).

The problem isn't about the pressure that it can take, but the heat that it can take. Also if you really wanted to, you could make a titanium rotor lighter the aluminum, when you take in consideration it's strength characteristics. Although I think any rotor made with the material would "look" flimsy although it would actually be strong.

 

What you have to think is do the rotors actually get to 430 degrees celcius? If they did the steel would fail pretty quickly?

The surface temperature would be very high but the actual temperature would not be near 400 degree celcius in my opinion. Could be wrong, dont know anyone that has tested actual rotor temperature.

I know for sure that mazda test temperatures on apex seal with and without oil lubrication and the apex seal gets to around 200-250 degrees celcius with oil and up to 300 without.

Before someone can confidently make a rotor, they need to test what temperatures get up to then you can select material and machinig process.

 

Titanium wears very poorly. To be any benifit, they would need to be coated, then heavily machined to lighten. Then I think you would have seal issues and a whole new can of worms.

 

John Deere had at least worked on designing titanium rotors but I don't remember if they ever actually put them into an engine. You could look up to see if you can find some results the posted, I read some of the smaller documents but I know they had some detailed 100+ page reports on the engines. The whole thing was NASA sponsered and John Deere was just the last company to pick up the contract.

 

interesting though... at 2k a pop for the billet rotors it'd be an expensive mistake if you ended up ruining one.. or worse..

I think right now in this phase of rotor technology "lightened rotors" are the way to go.... just my opinion though..

 

mmm billet?

 

obviously the surface is going to be hotter but not much, the rotors themselves should be relatively cool or the oil in the crankcase that is hitting the inside of the rotor for cooling would instantly cook and burn through the crankcase ventilation, which isn't common even when pushing engines at higher boost levels. i have seen overheated engines that had lost all oil pressure cave in rotor faces without much difficulty so the lack of oil cooling increased the surface temperature drastically(rotors don't always cave in from just detonation) so it's really difficult to say how hot they get assuming the oil cooling system is doing it's job properly. take away the cooling and things turn into china syndrome rather quickly.

but the idea of making rotors from titanium is far fetched since it cannot be cast, it would take a rediculous amount of effort to make rotors out of titanium and cost would be astronomical without them being in mass production which would drop the price down considerably. even the billet rotors are still way jacked in price considering materials really only cost maybe $25 per rotor and once a CNC program is set the can be cranked out in no time, perhaps the rest of the cost is based on sleeving the rotors. i can't imagine that the raw aluminum holds up well in the apex seal slot or side seal or any seal slot for that matter.

billet aluminum and lightened stock rotors are the only real alternatives that people should bother discussing.

 

Super-liteweight rotors are not really the answer. Once you get too light you lose the 'flywheel effect" of the rotors and that is important, especially in a drag race launch situation. Boost, not RPM is what will make power and acceleration, not super-liteweight rotors. N/A is another story, as it is cutting a fine line between high rpm for power, and reasonable rpm for longevity.

 

Rotor weight is not the limiting factor in engine speed nowadays. It's still the good old problems of the seals, the bearings, and airflow into, out of, and through the engine.

I forget the RPM where it was tested, but someone rigged a pressure sender to measure oil pressure inside the eccentric shaft (which feeds the rotor bearings) and found that at 100psi in the engine's galleries, the eccentric shaft had only 7psi. The higher you spin the engine the harder it is to get oil to the rotor bearings.

When I heard about that, I started to seriously pay attention to in-system oiling.

Airflow through the engine is, I feel, a big problem that few people seem to touch on (publically). Everyone seems to agree that the RX-8 rotors don't make the same power as earlier rotors at high RPM. Maybe it's because the air can't move through the engine as easily when the rotor swings through TDC on the plug side. (everything that the engine takes in has to flow through the bathtub) Makes me wonder if lower compression rotors will make more top-end power, or if the bathtub was shaped differently...

At any rate, Ti is a horrible material for machine parts for a large number of reasons. Its properties are great for some things, medical implants I guess, but it seems like it is more of a fashion accessory than anything.