Mafia

I don't know if this subject has been brought up yet but what kind of gears are the RX-8s running.. has anyone for example gone from 2.29s to 3.73s?

TRZ750

The diff is already a 4.444 ratio (9-40 teeth).

Mafia

4.44s?!?!?! how come torque is so low then

zoom44

cause it's a rotary. the length of the "lever" to the "fulcrum" is very short. someone else can explain it better but that's the basic idea. careful though cause they will show you the math

Mafia

Ya im an 8 owner im only 16 so im trying to take in as much as i can learn.. im enrolled in power mechanics but they don touch on n e thing about rotaries which pisses me off.. im willing ot learn the ath :D

w2aew

The rear is 4.444 to help compensate for the low torque characteristics of the rotary engine. The reason for the low torque can be attributed primarily to the "lever and fulcrum" mentioned earlier.

Take a look at some of the websites that show the wankel engine cycle. http://www.rotaryengineillustrated.com is one decent one. Compare how the rotor pushes the eccentric shaft around and compare that to how a piston rod pushes around a crankshaft. The "push" on the eccentric shaft is closer to the axis of rotation, resulting in less mechanical advantage compared to a crankshaft.

Picture trying to apply a lot of torque to a stuck bolt. You'll typically use a long breaker bar rather than a stubby little wrench. Your same effort applies more torque with the longer tool. If you apply 100 pounds of force to the end of a 12" long breaker bar, you are applying 100 ft-lbs of torque to the bolt. Apply that same 100 pounds of force to an 18" breaker bar, and now you're applying 150 ft-lbs of torque. The longer the lever - the more torque for a given force applied.

The eccentric shaft in the rotary has a shorter "lever" and a crankshaft in a conventional engine. Hence, the rotary has lower torque. Therefore, the RX-8 is fitted with a nice short diff to get some torque at the wheels.

Mafia

Hmmmm very well put thanks i was just expecting 4.44 to be putting over atleast 162 but i guess theres no gear swaps for me.. but we were taught that the lower the gears the louder they were at high speeds + they were worse on fuel economy? also n e ideas on how to get big torque gains ?

zyran

I'm 16 too. Read around here and you'll learn so much more.
For torque gains, specifically low-end torque for of the line lift-off, a supercharger is the answer.

Or bigger rotors.

wakeech

you're young so i'll clarify this for you:

quoted outputs from a motor are always measured at the flywheel when from a manufacturer. the torque at the wheels in first gear is in the 1000's of lb.ft. of torque.

zryan, a supercharger is definitely not "The Answer", and "bigger rotors" aren't something you can bolt on.

...aw, what the hell, i'll just keep going.

when you say "torque", what you're actually talking about is low-end horsepower, simply incorrectly percieved. (do the math, it makes sence).

it is fact that if you build a motor for a good bottom end, you are not maximizing the top end, and thus sacrificing the maximum amount of power the motor can make (adn thus limiting its potential for acceleration). if you build a motor for the top end, it's now very ineffective at making power at the bottom end.
when car companies create an engine, what they often do, even for performance cars, is come up with a comprimise that they believe will satisfy the most customers: have enough bottom end for those that just doodle around the city, and enough kick at the top end for the more adventurous.

basically, if you want serious performance, stop being silly and forget about the low end, 'cuase it doesn't matter how little power your engine makes at the bottom end when you're redlining it. using an engine with a sharper power curve is more difficult than an engine with a flabby low-end oreinted one, but certianly not necessarily slower.