panda

im still new to the rotary engine....and im learning so much its amazing...i just thought id throw this out here to see what other people think...
FI cars are amazing and are so much fun, but i also think it would be a lot of fun to have a car and be able to say" yea im revving to 13 or 14"...haha maybe this is just me but when i see a FI car im like thats badass but when i find someone with a N/A car, that is revving that high i give the guy/girl major props
what im confused with is, i understand the main components in a cylinder/piston car to help you revv higher, but what would the main components be in a rotary

just thought id start a wee discussion!


andrew

wakeech

hey andrew,

yeah, the basic principles behind making more power (which is rpm X force) is that you can either make the same small amount of torque at a higher rpm (like modern F1 engines), or more juicy torque at the same rpm (like a turbo car), or if you're REALLY good more turbo torque at very high rpm (like tuners can do with the RBDETT or the F1 engines from the 80's).

to build an engine that can rev really high isn't a big deal: it's just expensive, and (to get maximum performance) would always entail a tradeoff for reliability.

in the wankel engine, you've really only got two moving parts per rotor: the eccentric shaft that is driven by the rotor, and the rotor itself. that's it. so in the 13B-MSP bi-rotor, you have three moving bits in the motor: both rotors, and the e-shaft.
to figure out how to make it rev higher, you need to understand the obstacles. although people want to say that the wankel's movement is rotational and not reciprocal, this isn't true. the movement is orbital in nature, and through its orbit of the outer gear (the gear in the middle of the rotor that determines its path inside the engine) the rotor "reciprocates" about the rotor housing. the component that bears all the load for redirecting the tragectory of the rotor is the outergear, with the e-shaft lobe floating inside the rotors.

so, as you can kind of see in your mind, at higher speeds the rotor needs a higher force to change its tragectory away from the rotor housing, and this force is supplied by the outer gear, and thus a key component would be to have stronger, harder, more heat-resistant outer gears. another aspect of this is to reduce the mass of the rotor, thus reducing the force necessary to keep the rotor on the right path (think "the straight and narrow"). another trick tuners use is "clearancing", meaning the rotor is shaved so that it doesn't hit anything in the engine as its path becomes slightly more unpredicable while speeds go up. let's all ask Paul more about this process...

another concern is the e-shaft, as it's a sausage of metal with two opposing lumps, marking the thirds of its length (more or less). as this shaft is spun (the force on those lobes), the imbalance begins to stretch it raidally and in the direction of rotation, and you can run into trouble. another trick is simply to reduce the rotating mass of the lobes, but the best solution obviously would be to have mega-trick counter balanced e-shafts, but that would be a far more involved production process (HUGE $$) and would probably sacrifice strength as well.

so, beyond those little things are comprimise issues porting (the blackest of the black arts in rotary tuning, as far as side ports go), and resonant tuning.
then you have other problems like ignition generation and delivery, cooling (more power = more heat, but with higher rpms means you need a pump that will function in normal driving and not cavetate at redline... :o), fuel delivery (not so big a deal in all-motor applications).

who wants to add more?? rotarygod i know will (if he sees this), Paul Yaw maybe (if he's got time and wants to)... anyone else?? b00gdawg??

btw, check out Rotary Engine Illustrated for the best reference around.

panda

thanks for all the info wakeech....im starting to understand now!
haha i think i may want to add a wee bit more power to the motor.....i am like trial and error type things....if it doesnt work the first time take it out and try another method!
but yea i'd love to hear what other people are thinking



andrew

ProtoConVert

someone else posted that the first obstacle to increasing RENESIS rev limit will be the alternator... doesnt like spinning that high i think he said. Do you think there would be any way to disengage it at high rpm?

panda

thats interesting to know.......is it in anyway possible to change that though??


andrew

wakeech

...change the pulley ratio?

panda

so your saying by changing the pulley ratio, i will in turn change the alternators speed basically? or am i misunderstanding? hehe

andrew

medcina

By putting a larger pulley on it, the alternator will essentially spin more slowly at any given engine RPM. However, it also means that it won't reach its peak output until a higher RPM. Not sure if this will have an impact in charging the battery but it's something to consider.

wakeech

yup, that's exactly it. and yeah, i'm pretty sure the car'd have to be running higher RPMs all the time to get comparable alternator current, but the thing about a compirmise motor (what panda's thinking about building, to some extent) is that your driving habits have to change along with the characteristics of the motor: with less low end horsepower with way more to find in the upper rpm range, you'll probably be driving the engine at a higher speed all the time. there really is no "perfect" comprimise where you can get terrific fuel efficincy and drivability at low rpm and still get rip-roarin' performance at a sky-high redline... to maximize one, you must trade off the other.

boarder

Theoretical question...

If the alternator could run at any rate (in other words act as it didn't matter), what would the max rpms the stock renesis could take ? And what do you think the net effect would be (HP and torque wise) ?

wakeech

well, boowana said that they've apparently tested the motor well over 12k rpms (yes, stock internals). PM and reconfirm that with him if you like.

because of the size of the ports, and the lenght of all the tuned runners (at least on the intake side... exhaust side needs to get some) the torque the motor would make would quickly decrease as rpms went up, and the velocities the inspired gasses would have to reach simply become impossible through the stock intake system.

so really, you can't just bump the rev limiter up to 11k rpm without first opening up the engine, doing some porting, lightening the rotors and e-shaft (why not, right?), and fabbing some re-tuned intake and exhaust manifolds. after that, it's anyone's guess, so i'll take a crack.

say you did an amazing job of it all, and could make a peak torque of 148lbft at 10k rpm = 281 hp. this is just a made-up number, but seems quite possible, in my mind... possible without a perhipheral port?? hmm... hope so :D