nemeii

anyone know our cars top speed provided enough tq ? ( not trying to start another onslaught but im curious) i think i calculated 192.8 with our current transmissions at redline (assuming of course the e-speed limiter is removed)

as far as lightening rotors, what if you replaced the removed metal with a jacketed lightweight metal. sodium for example is in some posche valves ive heard, doing so would not stress the structural integrity of a rotor as much as just space beint there would, albeit being exotic and really expensive, sodium need not necessarily be used, just a thought

MontegoBlue

Top speed is dependent on power (remember, power is the energy per time that is dissipated to friction when there is no acceleration). Theoretically, the top speed is unlimited if you have enough power to counter the drag force, however, you also need to factor in lift forces and pitch moments (which reduce the friction between the tire and the ground and decrease the efficiency of power transfer). If anyone can find the coefficient of lift and the pitch moment coefficient of the FD, we could do this calculation, but it would still be rough.

As for lightening the rotors - sodium? Seriously - ditch the bose hose. Eat a salad. Get your car tuned by Steve Kan. There are ten million things you can do to increase power and decrease weight that are cheaper, more effective, and more reliable than removing 2 oz. of material from the most critical engine component.

EDIT: I misunderstood your question. You meant what vehicle speed is produced by redlining the engine in 5th gear, assuming you have sufficient power to do so? Your figure sounds about right, but remember that even if you got there you'd have to worry about your car flying off the road due to lift.

jimlab

This has been covered umpti-billion times, but...

Top speed is typically limited by power. A certain amount of power is required to overcome the losses at a given speed just to maintain that speed. Basically, wind resistance (aerodynamic drag), rolling resistance (friction against the road surface), and internal frictional losses in the drivetrain. If you have enough power at a given speed to overcome all of those losses and still have a surplus left over, you can accelerate further. When the losses equal the power being produced, the car stops accelerating. Losses increase as the vehicle speed increases, and blah blah blah...

That said, top speed can also be gear limited, and in the case of the FD, that's the case. You can easily make enough power to top out the car in 5th gear at redline. With a stock diameter tire, including tachometer and speedometer inaccuracies and various other factors like tire slip, you can probably top out at about 195 mph @ 8,000 rpm in 5th gear with the 4.10 ring and pinion. The only way to accelerate past that point, assuming enough power, is to A) change the ring and pinion or 5th gear ratio, B) change the tire diameter (taller), or C) exceed 8,000 rpm.

nemeii

right right right, i was just curious if i did the math right , thanks for the extra schooling and yeah i could probably figure out to make it go faster,
abt the lift issue yeah ive seen th vids of the rx take off on the salt flats, once again i was just checking my math and the sodium idea was just something i was tossing out there not that it is as farfetched as an idea as i think you make its sound i mean hell porsche thought it was good enough to put in a production car even if it did cost a decent bit =P

and how did vegetables come into this?..... 0_o "eat a salad?"

MontegoBlue

Sorry about that nemeii, my last post does sound a lot harsher than I'd intended. There's always potential for performance gain with exotic materials. My point was that, of the great number of ways to increase acceleration potential that are catalogued on this forum, attacking your rotors with an end mill is probably very close to the bottom of the list in terms of cost/benefit. The "eat a salad" comment was just a (stupid) joke - every pound the driver loses is a pound the car loses... and you don't have to worry about engine balancing, stress concentrations or thermal expansion.

JakeRotary

Lightweight rotors are lightweight in order to allow the engine to rev higher. The higher you rev the more your HP will increase while your torque won’t as much past 5252 RPMs. This is my understanding. I know for a fact that HP=(tq)x(RPMs)/5252

peejay

Light rotors don't affect torque because they don't change chamber pressure, and torque comes from chamber pressure.
They increase "felt" torque because the engine can accelerate more easily.

R-R-Rx7

iTrader: (24)

Wait for the thread to become 20 years old first before you bump it with such important information ….

CREEPENJEEPEN

iTrader: (7)

The idea that lightweight rotors would create less torque in an engine, such as in the RX-7 FD's rotary engine, stems from a fundamental misunderstanding of what torque is and how it's generated in an engine. Let's break down the concept to clarify this misunderstanding.

Torque is a measure of the twisting force that an engine can generate, and it's primarily a function of the amount of air and fuel that can be burned in the combustion chambers at any given moment, and how efficiently that combustion process can be turned into rotational force. The weight of the engine's rotating components, like rotors in a rotary engine, can influence how quickly the engine can rev up or down, but not the maximum torque it can produce.

Lightweight rotors can indeed have a few effects on an engine's performance, but reducing the engine's peak torque is not one of them. Here's why:

1. Reduced Rotational Inertia: Lightweight rotors have less mass, which means they have less rotational inertia. This allows the engine to rev up and down more quickly. It's akin to how a lighter flywheel works in a conventional piston engine. This can make the engine feel more responsive but doesn't directly increase or decrease the maximum torque output.
   
2. Improved Efficiency: By reducing the mass of the rotors, you're reducing the amount of energy needed to overcome inertia when the engine changes speed. This can potentially improve overall efficiency and performance, as less energy is wasted on moving the engine's own components around. However, this is more about how quickly the engine can deliver its power, rather than changing the total amount of power (torque) available.
   
3. Vibration and Stress Reduction: Lighter rotors can also change the dynamics of how the engine runs, potentially reducing stresses on other engine components due to lower vibration levels. This doesn't directly affect torque but can influence engine longevity and smoothness of operation.
   

So, the assertion that lightweight rotors would make an engine create less torque is not accurate. The confusion might arise from conflating torque with how quickly an engine can accelerate (which is influenced by the engine's rotating mass). Reducing the mass of rotating parts does allow the engine to accelerate more quickly, but it does not reduce the engine's capacity to generate torque. If anything, by making the engine more efficient and responsive, lightweight rotors can enhance performance in a way that is beneficial for most automotive applications, especially those where rapid changes in engine speed are desirable, like in racing or spirited driving conditions.

(What an old thread lol)

DaveW

delete

TeamRX8

iTrader: (2)

touched on a few points replying in this other thread

https://www.rx7club.com/3rd-generati.../#post12598272

in general, perhaps lighter is over-rated some for the reasons stated.
.

peejay

Lighter is always better, but as pointed out in the thread, there are also compromises relative to what parts are available and what your ultimate goals are. Sometimes you have to trade off acceleration for strength.

An interesting thing is an old (now) video about Mine's ultimate R34. He specifically said that they kept the stock bore because it accelerated better, and the goal of that particular engine wasn't "maximum power" but "maximum acceleration". Smaller bores meant (inferring) not only lighter pistons but also more detonation resistance, which were both more important than a displacement increase. From inferring his statements, they did testing for this to come to this conclusion.

Turning that around to rotary world, lower compression rotors have more detonation resistance and better internal airflow (an issue with the Wankel known as far back as the 1960s) so you should be able to make more power with a given amount of airflow due to reduced pumping losses, which is probably better than a gain made from reduced rotating mass in this case.