What exactly are the advantages of forged rotors then jus regular rotors, what are done to them to make them different?

 

Forged rotors are basically made out of solid gold. Therefore the advantage is that they can be highly profitable on the lucrative gold market...

 

well i mean, usually forged items are stronger. I know thats how it is in a piston engine, maybe same type of principal here.

 

The rotors are already pretty damn strong. They are only spinning. They are not moving up and then forcefully get pulled back down which causes a lot of stress.

The only real thing you needed to worry about is the compression ratio and how light the rotor is. Higher compression and lighter the rotor is better.

Although I think heavier rotors just like heavier flywheels can give you more torque? I dunno im just thinking to hard now.

 

Name one place where you can get forged rotors and I'll name one place that scams it's customers. I've never heard of anyone but Mazda making rotors, so that's what you're stuck with. Besides, the rotors aren't what fails, it's the seals. Stronger rotors are therefore not needed.

EDIT: Heavier rotors are just like heavier flywheels, they give LESS torque. This is a common misconception. A flywheel is only good for storing energy, it has more stored energy in it for when you let the clutch out, helping to prevent stalling, so people think it gives more torque. A lighter flywheel takes less energy to accelerate, so the engine will spin up faster, transmitting more torque to the wheels. Lighter pistons are better, so are lighter rotors.

 

Seems like it would give more high end torque not low end since once you get those rotors going round and round they may not want to stop quite so easily as if they were lighter.

But what do I know.

 

Oh I'm not looking into getting any, my friend was looking at an fc and it had orged rotors and I jus wanted to know if there was any type of benefits

 

I dont know lol leave the rotational momentum to the flywheel. aren't the rotors only spining 1/3 what the tach reads? so at 7000 rpm on the tach the rotors are spinning 2333 rpms.. not very fast

 

So with the rotors moving on a third of the tach that means it produces more power then an average piston engine? Because I have heard that the 7 can produce as much power as a 7.3l truck? Is that correct?

 

With boost (alot of it) it can...

 

With stock boost or upgraded boost and being totally tuned?

 

1.3L N/A piston engine from say a Geo Metro produces roughly 70bhp
1.3L N/A rotary engine from say a Mazda RX-7 produces about 140bhp

Both in stock trim.

Either can make more numbers then that (without boost) but the rotary will ahve more power for its displacement...the main thing that differs is torque, the rotary doesn't have much.

 

The question that really needs raised is... how would one forge a rotor?

 

expensively!

Also if you are going to go through that kind of expense you should try other materials to try to reduce the weight.

 

Well it all comes back to what "power" and "displacement" mean.

Horsepower is really a fictional number based on Torque and RPM....

(Torque x Engine speed) / 5,252 = Horsepower

High revving engines will have lots of "power". RX-7 and S2000 are good examples. High revs, high power, low torque.

An example of a low power, high torque engine would be a diesel truck. Some redline at 3k but have upwards of 800 lb/ft of torque. It'll pull anything out of anywhere, but it's not really fast.

It also has to do with the weight of a car... so power to weight ratio.... anyway.

http://auto.howstuffworks.com/horsepower.htm
http://auto.howstuffworks.com/question622.htm

On the topic of Displacement, it's measured differently for piston engines and rotary engines.

Piston engines rate the displacement by the maximum cylinder volume of all the cylinders. Rotary engines rate displacement literally. Rotor housing volume minus rotor volume. The difference comes up in racing classes, where they go by the "Double Displacement" rule... 1.3L rotary comprable to 2.6L piston.

http://auto.howstuffworks.com/question685.htm

On the issue of forced induction, the short of it is: More air, more fuel, more power, more stress on engine.

Could a 1.3L Rotary make as much "power" as a 7.3L truck? Sure, if the tuck only rev'ed to 1000 rpm.

The rotary engine isn't magical, it's just shaped wierd.

 

"magical" no, but much more efficient due to being a rotational motion rather than a reciprocating motion.

 

It is too ******* magical, damnit!!!


lol

 

I was told that some of the high power drag cars can actually dent the pockets of '89+ turbo rotors. One solution was to run 86-88 turbo rotors with 1lb more meat and lower compression. If those fail then maybe you will need forged rotors.

 

No no, seriously how would you forge them? Forged rotors would have to be a 2-piece design (basically the shell with the bearing assembly bolted to it) since there is no way you could machine all of the metal out of the inside of the rotor if you forged it with the spaces for the bearings already in place.

 

With our stellar gas milage right?

It's more efficient since parts don't have to change directions, but less efficient thermodynamically. (Where it counts.)

More contact area in the combustion chamber, more area for heat to transfer, more energy lost as heat. This is why the RX-7 has a big *** radiator and an oil cooler.

Now if they made the engine out of a material that would stand higher temperatures and lose less energy to the cooling system, then it'd be no contest.

 

Heavier rotors of the same size would give a higher moment of inertia, making it more resistant to changing speed, be it negative or positive. You can think of moment of inertia as analagous to mass. It takes a given force to accelerate a mass, right? If you increase the mass, then it won't accelerate as quickly with the same force. Moment of inertia is the same, but with moments (think like rotational "force"). In other words, a given force will accelerate a rotor with a larger moment of inertia (heavier rotor) more slowly.

The reason that you don't want lighter rotating components in a drag car is because of the launch. If you hold an engine at 4000rpm, then the engine with a lighter rotating assembly will deccelerate more quickly when the clutch is released because it has a lower moment of inertia. With a larger moment of inertia (heavier rotating assembly), the motor will be more difficult to deccelerate, so when you apply a force (slip/dump the clutch), the engine will want to stay at its current angular velocity (4000rpm or whatever). The tradeoff is that when you try to accelerate the car, it still wants to stay at its current angular velocity, so the car accelerates more slowly.

 

the FD rotors are keen to denting at the rotor faces moreso than then s5 (89-91) rotors.

S4 turbo rotors are the weapon of choice w/ high power boost mongers.

 

I wonder though, how much effect does the rotating mass of the rotors and flywheel compared to the 2500 lbs of car that it's lugging around? Once the clutch is engaged, do you accelerate any faster with a lightweight flywheel?

Anyone have any actual evidence? (0-60 or 1/4 mile times, before and after a lightweight flywheel?)

 

Thats a good question -- I know that the first place that you want to lose weight is rotating mass, then unsprung weight, then weight off of the body. I know that 5lbs off of something like the flywheel will make a much larger improvement than 5lbs off the body. Lighter engine mass is good also because you can change engine RPM's faster for things like downshifting. Lighter wheels, tires, and brakes are a huge plus because it's rotating mass (and the weight you save at each corner is x4), as well as unsprung weight.

 

There's been plenty of comparisons done on the dyno for many different cars before and after a light flywheel was installed. It doesn't make power, but it allows more of it to get to the wheels, showing higher readings on the dyno. This isn't something that needs to be tested on every car, as it's a universal thing, less rotational inertia = more power to the ground. The same thing goes for wheels and tires, smaller and lighter is "more powerful".