rx7vadim

rx7tt95

Depends on what you're trying to achieve. In my situation, I'd say yes and there's a guy right in Miami that can do them.

rx7vadim

how much will that cost, and how much performane can u expect

Mahjik

iTrader: (1)

When I looked into it (not through the same person rx7tt95 used), it was $1200 if your rotors are in good enough shape to do it. The assembly also needs to be balanced as well.

rx7tt95

CLR does the port phasing and lightening on 88 T2 rotors for $1K I believe. I'm assuming they'd come in less just to lighten the rotors. Just do a search for CLR Motorsports. They're right in Miami by the Tamiami Airport, in the industrial complex.

Ledfoot

iTrader: (1)

...if you lighten them...you're going to have to balance the assembly...might want to get the stationary gears hardened...if your intent is to rev faster and exceed 8000 rpm....next you'll want the e-shaft lightened...and a aluminum flywheel...then....good you live in FL...don't want to do this if you live where there's a lot of hills...

Ledfoot

iTrader: (1)

...oh yeah... for some reason I'm under the impression that it's preferable to lighten the n/a FC rotors...they are the same weight as FD but 9.7:1 compression...I think I read this somewhere...can't remember what the full mods were and advantages....

TT_Rex_7

https://www.rx7club.com/3rd-generation-specific-1993-2002-16/lightweight-rotors%3Dless-torque-379771/

All the info you could ever want on lightened rotors! You'll need to read through the whole thread to come up with some solid answers though. A few of the first posts are incorrect.

-Alex

rarson

What is that supposed to mean?

TT_Rex_7

Read the thread I posted above, and you'll figure it out.

When you take weight off the rotors, it has the same effect as a lighter flywheel. Have you drove your car with the stock flywheel, then a lighter flywheel?

You typically have to keep the RPM's up to keep the car from stalling when taking off from a complete stop. It's even worse on hills. Lightened rotors will have the same effect as well. When you have both, it makes it even worse.

-Alex

the_glass_man

iTrader: (2)

Has anyone done this to RX-8 rotors?

TT_Rex_7

Not that I'm aware of. I doubt you even could anyways. AFAIK, they're the lightest rotors out of all the rotary engines...Which would mean they have thinner walls than the rest as well.

-Alex

the_glass_man

iTrader: (2)

Not only the lightest, but the highest compression as well! I'm pretty sure they are the cheapest which is a plus in my book. However since you have to modify them anyways I guess the lower price is offset.

rarson

Right, I was just confirming that he was arriving at the same erroneous conclusion you just arrived at.

A lot of people don't understand the whole kinetic versus potential energy thing and the mechanism for storing energy in a flywheel. The fact of the matter is, a lighter flywheel will be a benefit whenever the flywheel is accelerating or decelerating. Which is to say, whenever performance is important. A heavier flywheel will only give a benefit in steady-state conditions such as cruising, where the stored energy can help keep the car at speed, resulting in probably better gas mileage. During transient conditions, the lightened flywheel is a benefit, hands-down. And frankly I don't mod my car for cruise conditions.

I've never had a problem with lightened flywheels on hills, and I'd suggest to anyone that does to invest in some more power mods. Nor have I ever had a problem with starting from a stop, but in that case I'd suggest driving lessons.

Lightened rotors aren't really much different. Lessening the resistance to forward motion is going to transfer energy into the crankshaft more efficiently when the engine is accelerating. There isn't any effect on torque, period. The engine will be able to rev faster, whether it's up or down. Transient conditions, just like the flywheel.

rarson

Racing Beat sells lightened RX-8 rotors, but if you check their advertised weights, you'll notice they are heavier than the lightened S5 N/A rotors.

TT_Rex_7

So I guess everyone that posted in that thread is wrong to, eh?

Maybe it's you that doesn't quite understand!?

A heavier flywheel is a benefit at launching as well. Ever notice how most professional drag racers don't use the lightest flywheel possible? Maybe you should show up to a local event and tell them how stupid they are as well...

For something like road courses, sure, a lighter flywheel is a benefit.

What I'm getting at here is it all depends on the situation. A lighter flywheel isn't better, hands down, in every situation like you seem to think.

Who said it was a problem? I simply said you had to keep the RPM's higher than with a heavier flywheel.

I'm not sure what your not getting here...A car with a lighter flywheel/rotors will be more prone to stalling when taking off from a stop because there's less stored energy, PERIOD! It's not a problem as long as you keep the RPM's a bit higher.

Hell, same thing goes for simply driving over a hill. A car with a lighter flywheel/rotors will have a harder time, than the same car with a heavier flywheel. Less energy is stored in the lighter flywheel/rotors, so there's less energy to help make it over the hill. (Keeping cars, speed, RPM, HP, TQ, etc. the same)

I'm not sure why torque was brought up here, unless your referring to the thread I posted, which has nothing to do with this thread. We all came to the conclusion that there won't be a loss of torque with lightened rotors/flywheels in that thread...



When it comes down to it, a lighter flywheel/rotors won't always be the best choice. You have to size your flywheel and rotors to what you'll be doing with the car, and conditions encountered.

-Alex

rarson

Well, rather than nitpick on small details of your reply, I'll just leave the off-topicness where it is, because I basically agree with everything you said. I did read all of that thread a while ago and there was some right and wrong info in it, and I think I posted a little hastily, sorry. Anyway, back to the subject...

TT_Rex_7

No reason to be sorry, it's just the internet!

-Alex

crispeed

Yep.
RX-8 rotors are casted very thin and you cannot remove much weight from them.
I have f..k up many trying to do so. The amount of weight that can be remove safely from RX-8 rotors in my opinion are not worth it. You're better off with a set of lightened and balanced S5 rotors and counter weights.

Whizbang

That statemnet would work but then explain why the professional teams Fidanza sponders making one-off custom flywheels to the teams specs are all VERY light. The one rotary team they sponser use a 2lb,( TWO, dos, 1+1,) pound flywheel. They must be stupid too ::

Monkman33

iTrader: (28)

Also, that rotary team you meantion... launch at very high rpm, compared to the other teams....

hmmm, lighter flywheel = higher rpm on launch to maintain stored energy... but that wouldn't prove anything...... would it?

jgrewe

iTrader: (1)

The only place a heavy flywheel helps is at launch in a drag race. After the launch the advantage is gone. Yes a lighter flywheel will help get away from a stop light smoothly and also make an engine idle smoother but (transfer less vibration to the mounts) but it won't affect going up a hill. Consider that you have four other flywheels spinning at each corner of the car. Wheels, tires, brakes. The energy stored in a flywheel at highway speeds isn't enough to carry the car very far up a hill compared to the energy in the whole chassis of "x" pounds at "y" mph.

crispeed

You cannot judge launching inertia from just the weight of the flywheel. It's the entire rotating assembly. There are clutch/flywheel combinations where the flywheel is much lighter than the clutch components for example most dragracing setups that have a huge twin disc setup. My buddies car has a total mass of 45lbs clutch+flwheel of which the flywheel only weighs 10lbs. There is also other scenarios for example where very lightweight motor components are used like in the case of a rotary lightened rotors, weights and ecentric shaft coupled to a 4.5inch twin or tripple disc where a slightly heavier flywheel to regain some inertia is used. Also the design of the flywheel/clutch also have an effect on inertia. You can take two a like clutches that weigh the same but the one with the weight more centered is going to have the lowest effect on launch. So in all it's not just the weight of the flywheel that matters. It's the entire package and it's intended use. If you're comparing apples to apples is one thing but everyone is speaking in general. Some of the worst twin disc setups I've seen come from Japan where the actual rotating assembley after the flywheel is actually heavier than the stock stuff although the flywheel that it came with is not even light enough to compensate and it's advertised as being lighter. I'm not going to name manufacturer. In case you did not know the heavier a clutch disc is the harder the factory syncros have to work.

crispeed

Believe it or not it also has a dramatic effect going down the track especially where you're using a clutch to shift. Everytime you shift with a heavy combiantion it actually pushes the car forward and accelerates the car much faster. This is seen when you do a lot of datalogging of the stuff where during shifting speed can increase by as much as 10 mph by using heavier components. I know a lot of raodracers with near to stock power levels that use this to some advantage.

jgrewe

iTrader: (1)

I'm curious if the 10mph increase is coming from shifting too late in the rpm range? I don't drag race so I can't speak of finer details that can show up in dataq but that sounds like its possible. I can see if the engine doesn't have time to wind down during the shift and the rpm difference of the drive line would then give you a kick in the butt.
It was worth waking up today, I just learned something!