93redFD

ok, I have heared that a lw flywheel reduces torque, is that true or false??? Why do poeple use lieght wieght flywheel??? I know they are for keeping rpm up but you loose lots of torqe. Is it hard to keep built up boost while shifting??? Im am considering 8.5lb..

93redFD

does reduce the turbo lag???

peejay

I just posted something on this recently... it was indepth enough to be an article

In a nutshell, lightweight flywheel does not affect static engine output. It DOES reduce rotating inertia. This allows the engine to accelerate quicker. It also allows the car to accelerate quicker because the engine spends less energy on accelerating itself, so more is available to accelerate the car.

The flip side is that it also DEcelerates quicker. If you rely on the engine's inertia to accelerate from a stop, or maintain speed up short hills, you will have problems. This is not a lack of torque, it is a driver habits problem.

turbostreetfighter

not being an ******* or anything , and just for the sake of arguing...how is that everyone agrees that lighter rotors makes lower torque but lighter FW does not? it has been my experience that lightened f/w's spool slower for the same reason that you just explained. in a NA situation where the engine is all that is there they work great! but in a turbo situation a LFW makes less boost in the lower gears and usually will not make full boost until third gear ( this is single turbo info) and are a total bitch to launch in drag racing, in one of my other race cars i consistently lost .4 in ET and 8 mph by changing nothing but the FW..i switched back to the normal FW and everything came back!! turbos work off of load which is also why you get that feeling that your car seems to pull harder in the fourth gear than it does in second, lighten the load and you lose pulling power..so to speak. i run the heaviest FW i could get and a 9.5" TC full of fluid!! i gained 6 mph in the 1/8 by adding 4 lbs to the FW! you can argue if you want but these are facts. ya gotta remember that your engine is not actually making the power , the turbo is supplying the air and ya gotta make the turbo happy most of the people that use LFW do so for the quick shifting that is needed in autocrossing and road racing..it is alot easier to match downshift with a lightened FW.

MWW

peejay

Lighter rotors don't make lower torque either.

93redFD

so a lwf is not great fir everyday car or drag racing right..

Jeff20B

iTrader: (13)

Hey peejay, could you point me to your mini article?

I will be going from auto to manual in my Cosmo as soon as the auto dies. The diff is geared 3.636. That's the highest of Mazda's rotary cars. It is also their heaviest rotary car from the '70s. This means I'd be stupid if I installed an aluminum flywheel from RB. I also think a light steel flywheel might be a little too light for this car. Of course if I had more power, it wouldn't matter as much.

Anyway, my REPU is geared 4.6xx and has the stock thick flywheel. The REPU was also very heavy (the same weight as a cosmo, give or take). It's really great for what it's for- truckin'! However my friend has an REPU with the same diff gearing and a light steel flywheel and it works quite well. I mention this because he needed to get an auto counterweight so he could install the flywheel, and my Cosmo already has an auto counterweight on it.

I'm thinking I ought to get a light steel flywheel and put it and the Cosmo's engine in the REPU, and put the truck's engine in the Cosmo.

peejay

The LW flywheel might be great for the REPU (thanks to its low gearing) but if you actually use it for hauling anything it might be a good idea to keep the stock heavy thing to help compensate for any insufficient torque with rotating inertia.

j9fd3s

iTrader: (3)

the 20b has a lot more low rpm torque than the 2 rotor does. for the rx7's i like the rb 17# flywheel, it feels like the one the car should have from the factory

mike

Satan's RX7

iTrader: (6)

its is my opinion that a lighter flywheel would reduce torque, because torque is based on the rotational force of a moving object, and less mass rotating around means less force, hence less torque.
just my .02

peejay

Torque has nothing to do with moving objects.

Do not confuse rotational inertia with torque!

Satan's RX7

iTrader: (6)

i dont mean to argue or make problems, but torque has everything to with movement and moving objects. without moving objects this stuff wouldnt mean anything. torque is the magnitude of the force and the perpindicular distance from the force to the point the movement is being calculated about multiplied together. feel free to prove me wrong.

NO3FAN

He is right!!!!!

peejay

Torque does not have any motion attached to it. You could put 50 pounds of force on the end of a 1 foot wrench and not even budge the bolt, but you would be applying 50 lb-ft of torque.

Once you have motion, then you are performing work. Work is commonly expressed as horsepower. Work times motion is power.

The heavier flywheel (or rotors, or any other part of the rotating assembly) doesn't "add torque". It adds rotational inertia. You can USE this rotational inertia to your benefit, like, say, if you have a strong clutch and good traction, you can dump the clutch at high RPM and get a harder launch. This harder launch is not due to the engine's torque, it's due to the engine's torque PLUS its rotational inertia.

fdracer

marcus, you have a point. but, how is it that all the big name manual dragsters are switching to the lightest flywheel combos out there and are being more succesful? i see a lot of the guys switching to the tilton triple plate carbon cluth, and that weighs 9 lbs. w/ flywheel. almost all of the quick supra guys run that clutch, and most of the top honda guys do too. these guys are all turbo, are you saying they all don't know what they're doing? you look at all the records being broken this year, and some of it has to be attributed to the tilton and lwfw.

Satan's RX7

iTrader: (6)

ok, thanks for the clarification peejay, i dont really know what im talking about, and im sure you do, so thanks for helping out with the problem.

Jeff20B

iTrader: (13)

peejay, I think I'll be keeping the REPU's engine in it for now. I still want to haul things and I have a few ideas for how to up the HP and torque and benefit from the heavy flywheel.

j9df3s, the auto in my Cosmo seems to be ok so far. The next engine it gets will be a 20B, regardless if the auto is still functioning or not .

turbostreetfighter

PeeJay, light weight rotors do make less torque to the ground , it has been proven. i took mine out for that reason. but i am sure you are right and my et and MPH is just a coincidence.


there is a happy medium on FW weights for any setup and alot of the extremely fast guys that run the lightend FW and clutch setups are leaving the line in excess of 12k rpm's !!!the rotational weight at that high of an rpm is not the same as the rotational weight of 7k rpms. i am only shifting my car at 9k and leaving the line on the trans brake at 6.5k so the heavier FW worked in my situation. if i were to build a different setup that moved my powerband higher than i MAY go to a lighter setup.

Fd racer, what was the biggest problems with the supras in the past? .....too much torque and wheel spin out of the hole. and guess what cured that? the LFW!!! think about it..it seems to have tamed them hasnt it? and as far as the g-force trannied guys are concerned those cars do not need to worry about loading the turbo because they are in fourth gear within 5 seconds!!! they have shifted 3 times to my one shift, this is why i need more rotational mass to keep going than they do. i am not hear to argue with anyone i am just sharing my personal experiences with y'all, there is no textbook for experience and no math formula for the track!! if you are not "in the trenches" then you dont know

turbostreetfighter

Fdracer, ditto for the hondas, they were having the same problem...blowing the **** out of the tires for the first 1/8 mile..hell, most of the hondas were beating the supras half track!!


MWW

peejay

If your ET's are hurting after a switch to lightweight rotating parts, that just means your gearing is too tall and/or your clutch is too strong You've been relying on rotational inertia to launch the car.

Lighteight rotating parts have been PROVEN to not affect HP or torque one bit, BUT allow faster lap times/1/4mi times due to the fact that the engine can accelerate quicker.

fdracer

marcus, do you use heavier wheels and heavier brakes as well? that would have the same effect as a heavier flywheel.

turbostreetfighter

PeeJay, my car is automatic (th350) and my gearing is 5.13 so that is not correct. of course you have to rely on inertia to launch the car!! how else do yo do it? how is the engine going to accelerate faster if there is no boost? in NA cars and small turbo cars this is true. judging by what you are saying it would not matter what turbo you use? you got me ( and my car) confused. i have been drag racing for half of my life and most of it was on the domestic side. how fast is your car and how much power do you make?

FD racer, what do you think happens when you bolt on a set of 33x14" tires? they are taller and stickier therefore make more traction load. the brakes and such are a different story that would get us into sprung and unsprung weight. once your power gets to the wheels it had already gone through drivetrain loss.......clutch/convertor....tranny....diff......and finally the wheels.

MWW

SPOautos

I read somewhere that a light flywheel actually made more tq on a dyno at the wheels due to not having as much drive train loss. That the engine tq/power is the same but you gain at the wheels but that the prob is you loose rotational inertia.

Is this pretty much what you guys are saying???

Seemed like someone a long time ago on the forum did a before and after on the dyno with just a flywheel change....thats what I'm basing this info on.

I guess my main question is about how the lwf affects tq at the wheels. Seems to make sense to me that it would go up because of less drive train loss.

STEPHEN

SPOautos

Also isnt the difference between rotational tq like some of you guys mentioned and tq the way Peejay mentioned the reason for foot pounds verus pounds feet......I think I read somewhere that the two different ways of saying it were from rotational tq verus applied tq or something along those lines.

STEPHEN

peejay

If you use an inertial dyno, you will see a HP difference at the wheels, because inertial dynos measure the engine's ability to accelerate a known mass.

If you tested on a steady state dyno, you would see no difference.

Therefore the engine doesn't make any more power, but it can accelerate quicker.

This is why I don't trust inertial dynos to give HP figures... they can be easily fooled like this. However, knowing how fast your engine can accelerate against a known load is important, because unless you're only interested in top speed or hauling ability, you use full throttle under acceleration. It's probably more important than HP figures, actually, again unless you're more interested in steady state conditions like top speed or hauling the horses up a mountainside

Foot pounds vs. pound feet is simple... Foot pounds is the correct way of saying it, pound feet is wrong It's confusing because you say foot pounds but abbreviate is as lb/ft. Hey, I didn't create the language, I just try to speak it