MintyFresh

Anybody know how many HP a lightened flywheel (act prolite/mazdaspeed/Rb) is expected to free up?

Hightshoe

I dont think its going to free up any hp. It will just allow the engine to rev quicker, which may give you .1 - .4 fast quarter mile time.

staticlag

A long time ago somone said about 10 hp in 1st gear, 6-8 in second, 4-5 iin third, 2-3 in fourth and about 1 in fifth.

Being able to rev quicker does free up horse power. and a .1-.4 faster quarter mile is a heck of a huge difference.

MintyFresh

thanks

18bsTiRX8

It doesn't free up any horsepower at all..........the car just revs quicker due to less inertia meaning you hit the powerband sooner. It does have side effects though....when I had one in my last car, the car didn't like to idle with the A/C on. You need that inertia to keep the motor running smoothly so there comes a point where lighter isn't always better, but shedding a few pounds won't hurt!

staticlag

I'm not going to bother explaining it, take a physics course at your local cc or something, you can begin reading here:

http://auto.howstuffworks.com/gear-ratio.htm

dmp

I had a .xls spreadsheet - one could enter variables and show "the car would accelerate as if it had 'x' much power in 'x' gear...I've forgotten who created the spreadsheet - but it was made for a miata; you'll have to adjust stuff.

http://www.d-mphotos.com/movies/flywheelcalculator.xls

r0tor

iTrader: (1)

i think that was me... and i stand by them


on another note...
also, if your car "revs faster" and its in gear while its "revving faster", then you are accelerating faster because of putting more power to the wheels/pavement or have a slipping clutch

samsong

Interesting question. My 2-cents (flame suit ON)

From an dyno perspective, you might not see see any (some dyno testing is done at a constant rpm, or only slightly changing rpm where the flywheel's inertia wouldn''t affect the resulting torque much). Practically speaking, the engine is able to increase rpm faster which does translate into getting more energy to the rest of the drivetrain (vs the flywheel) during acceleration, so could be converted into a net hp difference. The effect is more pronounced at lower gearing, because the engine is accelerating faster (you go through the rpm range faster). The results will very with the weight/inertia of the car and drivetrain, including the flywheel.

The folks above seem to have some practical experience...it's a good start.

Maybe I should build a mathmatical model for this to see how pronounced it would be. Hmmm....

Razz1

Lot's of discussion on this.

I believe at least 1-2 more HP is freed up to the rear wheel just from the fact of the reduced weight and the power need to move the fly wheel.

Quicker acceleration and 1/4 mile times are great improvements.

Unfortunately, there is a reduction of torque. Torque is needed on the top end and to pull a heavy load. Load increase as speed increases.

Many drag racers and track guys will take torque over HP.

Then others will tell you you don't need athe fly wheel if you increase your HP through other means such as FI.

Oh yea, do a search it's worht the reading.

mlx8

You don't have to guess. Theres a complete set of dyno charts for "before" and "after" LWFW, and in several gears posted somewhere in this forum. Try searching on "LWFW" for lighe weight flywheel etc.

Paul_in_DC

Question for those with the lightweight flywheel... I've heard that switching to the LWFW makes the car shudder or jerk more as you change gears? Do you find this to be the case? Any other day-to-day impacts?

carbonRX8

iTrader: (1)

None. After you adapt as a driver. (I will admit that nearly every one that drives my car stalls it the first time they try it. And my fly is not mega light. But you quickly adapt.)

MintyFresh

ah!

here's the one...

https://www.rx8club.com/showthread.p...light=flywheel

dmp

Did nobody look at that spreadsheet?



FWIW - Torque is worthless in terms of winning races. HP is where it's at.

:D

samsong

Thanks.

BTW, if the reduced rotating inertial losses due to lighter flywheelscan be translated to HP gains, would lighter weight/tires wheels also show up similarly on a dyno? I'd think it would.

Ericok

Horsepower=(Torque X RPM/5252). I don't see any flywheel weight in that formula. Might help in engine response, making the car marginally lighter, but no HP increase.

Brice-RX8

Right, no hp increase in the motor, but allows for more of that hp to get to the wheels which can be thought of an increase in hp.

Paul_in_DC

I don't have the lightened flywheel, but I think those that do report it as "revving faster." So, using your formula, if the engine reaches a given RPM in less time than before, that would mean that you'd reach that horsepower in less time as well. That should result in faster acceleration, even though actual horsepower hasn't changed.

Ericok

Yes, that's basically the benefit. The same horsepower is available sooner because you can spin the engine quicker. Keep in mind that the flywheel does serve a usefull purpose - it keeps the engine spinning between power pulses from the combustion chamber. If you go too light, the engine will have a problem idling smoothly.

r0tor

iTrader: (1)

here's another good equation...

HP at wheels = HP at crank - flywheel inertial - transmission inertia - transmission friction - driveshaft inertia - differential inertia - differential friction - axel inertia - wheel bearing friction - brake inertia - wheel/tire inertia - tire rolling resistance

Paul_in_DC

Still, my favorite equation is:

Gas Pedal + Foot = ZOOM!

rotarygod

I'm going to just pose this scenario for those who don't think that a lighter weight flywheel frees up horsepower to the wheels. Technically you gain no power as the engine makes no more power. You are reducing drivetrain loss though which means more power goes to the ground so in terms of what gets to where it counts, you do have more. If you don't believe me, think about this.

Let's say that instead of a 20 lb flywheel, you have a 200 lb flywheel. Now lets also say that we pulled off 200 lbs from somewhere else on the vehicle just to keep the total weight the same. The car weighs the same and has the same total flywheel horsepower. Which one will win in a race? Of course it's not the one with the 200 lb flywheel. As someone pointed out, it can't rev as fast. That's because it lacks the power to get it moving as fast. Power is being functionally absorbed by the flywheel. This is seen as the effort to turn it. That means that less power is making it to the ground. Once you get it up to speed, you don't see that much loss as it takes far more energy to get it turning initially than it does to keep it going but it still does take power never the less. This weight is stored energy which is also harder to slow down.

The lower the gear you are in, the larger the gain will be perceived as. This has to do with the amount of "leverage" that the gearing gives you.

Agent008

I think the best way to explain to people that a LWFW is a good thing is to simply point them to real race cars and professionals. I bet a F1 car's flywheel is almost non-existent.

The real questions to ask yourself:
1. Is the gain worth the cost?
2. What weight do I want?

For question 1 the answer is a resounding maybe.

For question 2 I can only say that I went with the RB 12lb flywheel because I was a bit worried about drivability issues but I was 100% back to normal with my takeoff after just 15min in the car with the new flywheel.

Skythe

can you elaborate on this plz? i don't understando