ratio411

One thing you say is totally contrary to what I was told by a guy at a show with an aluminum flywheel...
He said that there is little to no engine braking with a light flywheel. <img border="0" title="" alt="[Confused]" src="images/icons/confused.gif" />
Had something to do with the engine being easier to spin, therefore had less effect against the weight of the car when decellerating.
Dave

ratio411

Okay, so I don't road race, I don't drag race...
I drive on the streets, not even daily... but very 'spirited' driving.
So now we've established that a heavy flywheel and super deep gears would help me at the drags, but that is not where I am at. Again, we got all the cons and all the drag tips.
What are the pros for aluminum flywheels?
How do they apply to street driving. Driving that is a little grandma, a little road race, a little drag race.
I am more interested in shifting as well as the improved operation of the clutch.
Dave

Boo Yeah

That is true and untrue. At high rpm the engine works as a huge brake, while at low rpm 2500 or less it works the oposite way. Once again, i do both drag, street, and auto x. And I love my flywheel.

Stick only

I would agree with Boo - at lower rpm it is not going to have as much affect. But if you are, say, autocrossing, what engine RPM is normal going into or out of a turn? Or in a road race situation? If you run an engine up to 5K and let off with both a steel and aluminum wheel, which will slow the car faster?

I'm not trying to talk anyone out of an aluminum wheel, don't get me wrong. But I talk to customers everyday with these questions or who put aluminum in and are disappointed. We also have found some 'newer' flywheel companies who are just not telling the truth to their customers. Just friendly $.02 for fellow LS1 folks.

Boo Yeah

Well if i was you customer I would be satisfied. <img border="0" title="" alt="[Big Grin]" src="gr_grin.gif" />

taqwache

ok so tell me this. i have a 2002 M6 Z28 with 4.10s and convo pros with BFG DR as my only mods. right now my car does 12.80's all day long and has pretty good traction with out any bog. i shift around 6200 and the motor will go down to 4800 or so on the next gear and then back up to 6200 for all four gears. i end the 1/4 around 6300 or so. now i dont care about driveability, how quick my engine can accelerate/deccelerate, clutch wear, RWHP, launch speed, or anything exept ETs. also i only launch a 3000 or so to save the rear and only get 2.00 60f because of it. now if i install an aluminum flywheel, will my car do a 12.79 or better? remember, that is all i care about. do you think that since my clutch is engaged most of the time down the strip and only disengaged to shift gears that the quicker acceleration would offset the loss inertia imbetween shifts and my car will run a faster ETs. i completely understand the physics of inertia and mass but i would like to know if the pros and cons of an aluminum flywheel will acually help or hurt me down the 1/4 mile. does anyone have any time slips before and after this mod without any other changes to the car?

Boo Yeah

OK from all my experiences that is both a yes and no. At your point yes. Because you can hook in first. I think you can turn the same 60ft launching a little higher rpm. And then yes once you get going the freed rotational mass wil allow you to make more rwhp and propel you better. And then no because it is all up to you, no part will make you car faster only you can drive it faster with your parts. At the same time if you are going only for drag car then you need to wait, soon it will be at your disadvantage to have this mod. It is up to you.

NB99Z

iTrader: (9)

I went to the track with the factory flywheel and went back the next week with my Fidanza. Nothing else was changed. I even used the same clutch. My 60 was up .03(1.69 with steel/1.72 with alum.) MPH was up 1 and I dropped .1 off my ET with the Fidanza. Weather was about 10 degrees cooler on the first trip(steel flywheel). Tires were 8.5 wide ET Drags for both trips.
The Fidanza does not like DRs. I've tried to run on BFGs and Nittos many times and if you dump it and floor it the engine revs so fast that your on the rev limter instantly. If you roll into the the gas on DRs your 60 still sucks and you lose MPH.
SO if you have a low gear and Drag tires you can lower your ET a little. Stop light to stop light racing will be worse(unless you run ET streets on the street).
And if I had it to do over again I would of spent the money on something else.

trackbird

iTrader: (4)

If you have a 50 lb flywheel at 6000 rpm and you are in gear and stopping the car, you now have to stop the energy stored in that flywheel (would you want to grab 50 lbs at 6000 rpm, of course not...that is alot of energy). If you have 1 lb (extreme case I know) at 6000 rpm, it is much easier to slow down (and accelerate).

Now, for the "illusion" of horsepower.

Horsepower is "torque over time" (torque x rpm / 5252 = HP). The faster you can accelerate the engine through the powerband, the more horsepower you will make. When you install a cam (heads, headers, etc) you hope to be able to make more power (to get through the gears faster). The faster you can run through the gears, the more horsepower you are making (all things being equal) and the quicker your ET (for the drag guys). Accelerating a heavy flywheel takes horsepower, you are accelerating mass, more mass takes more power. If you add 100 lbs to your car, you will likely slow down at the track since you have to accelerate the extra mass. Now, if you add 100 lbs to the flywheel, not only do you have to move it forward, you have to spin it (grab a 10 speed, put it in first and crank the pedals, not too hard to spin, put it in 10th, or add 50 lbs to the wheel, and spin it again....it is more difficult). This is why rotating weight is so important. For street and track use, you'll see that your brakes works slightly better (when they don't have to slow extra rotating weight). You are correct, flywheels don't make horsepower, they absorb it. Some absorb less than others. A light flywheel is easier to spin and takes less horsepower to do so, A heavier flywheel takes more horsepower to spin (to accelerate at the same rate as a lighter flywheel) and uses more horsepower in the process. Also, I can see the engine braking arguement, but that is what brakes are for. Engines and transmissions accelerate the car, brakes stop it. The transmission is not primarily a braking device, it can be used as one, but mostly when the brakes are not adequate for the job.

Ok, A flywheels primary job is to keep the motor spinning between firing pulses. When a motor fires a cylinder, it makes power. It then has to "coast" until another cylinder fires. If there was not a flywheel to store energy, it would either stop due to the compression stroke of the other cylinder or it would need to idle at a very high RPM to use the stored energy in the crank, rods, etc to compress the next intake charge. If you think of a "non-automotive" application it will make sense (lawnmowers do not have to get anything moving, but it has to spin until it fires again, remove the blade from a mower and it will not run, at least not well).

The heavier the flywheel, the more stored energy you have to work with. As for slippage, it depends. On the street, the motor is doing 700 rpm and the transmission (and clutch disk) are stopped, the "slippage" will be the same, you need to "find" 700 rpm and add it to the clutch. If you are "launching" the car, it will be tire spin that handles the slippage in most cases and a light flywheel will cause less of it (and possibly a bog).

I still contend that the RPM difference is the same and the "slip time" will be so as well. Now, if you feel the need to spin the motor to 3000 rpm to get moving with the lighter flywheel, you may have a case for clucth wear. In my personal street experience with light flywheels, I found the car drove just like stock, just better. I didn't need to spin the motor any more or less to get it to move. So, bacically, this is a factor of driving style. Aggressive drivers will be harder on clutches (is that not almost always true?)


As for the drag guys.

If you have enough power to "drive through" the launch, a light flywheel will help you everywhere else. You may lose some 60ft time, but you will be faster from the 60ft to the finish line with a light flywheel, 100% of the time. Force equals mass times acceleration, less mass has the same effect as more force, and there is the magic of a light flywheel.

I ran a 15 lb on the street in my 89 Formula Firebird for years, I recommend them (the car went quicker with the flywheel).


Just my thoughts,

Kevin

Zeta

Mostly wrong...

Its main purpose is storing rotational inertia to smooth the idle. The rest of the statement is not relevant to the question posted. Nor does the flywheel create inertia.

The stored energy can be helpful in overcoming the shortcomings of the drivers’ abilities or high friction clutch material that can result in stalling the engine. The rotational inertia is helpful in a drag race to accelerate the car from a stop.


Flywheel choice effects gear choice is an ok summation?

Quicker acceleration comes at a cost of a lighter flywheel is agreeable. With the exception of a standing start that takes advantage of the higher rotational inertia that a heavy flywheel can deliver of course.


A lighter flywheel absolutely positively will increase HP. Math will show that it is not an illusion. Mentioning drivability does not support the claim about horsepower.

Please see trackbird's commentary for other well made points, and of course math to help with understanding what horsepower is.


Hopefully the above commentary is clear.

trackbird

iTrader: (4)

I will clarify my comments about horsepower.

You will not see any increase in horsepower on a "brake" style dyno. This type of dyno measures an engine by loading it to a certain rpm and the weight of the rotating parts becomes almost insignifigant. Now, unless you have a car with a continiously variable transmission, it will not be "held" at one RPM. So, an acceleration type dyno seems to be a more acceptable measure of "driving" power, the way the car runs on the street. On a dynojet (an acceleration based dyno), you will see an increase in horsepower with a lighter flywheel. You are simply wasting less horsepower accelerating the weight of the flywheel, and using more of it to turn the dyno rollers (or to move the car). I was not sure that I was very clear on that in my last post.

Thanks,

Kevin

Joe Kizzire

Good info Mike... Hope everything's going ok with you. Clutch still working great.

2001CamaroGuy

iTrader: (6)

you will "see" more hp at the rear tires with an aluminum flywheel, but your not "making" more.....

the steel flywheel stores energy (hp) which is why it can help you launch harder and is often needed on large cams.....when the engine sees a sudden load (dump the clutch), the inertia of the flywheel starts to release its stored energy thus helping the engine to contenue running......

BUT....


once your moving, the lighter flywheel becomes an advantage for three reasons:

1) its lower mass is alowing more of the engines power to be used towards pushing the car (instead of being stored in the heavy mass of iron)....

2) the faster the engine can rev up in each gear, the faster you can get to the next gear and the faster you will go........

3) thats 30+lbs off the entire weigh of the car.....remember....weight reduction....its a good thing.....



so....if you can launch with the aluminum flywheel (either have the torque or would spin anyways....), you will actually go faster in the end....but...if you don't have the torque to get good 60' times then the iron is better.....


finally....if your car is a road car or even a street car with a "reasonable" cam, then the lighter flywheel will make the car perform from a roll MUCH better (can't tell you how much more passing performance I have at highway speeds with the aluminum.....just downshift and I'm at 95 almost instantly.....)

trackbird

iTrader: (4)

You are correct. You are simply "wasting less HP".

LiquidSword

iTrader: (1)

Was this ever a sticky? or linked from the FAQ? Took me a while to find it, but very good info. I've been seeing others making new threads on this subject. Figured a bump 7 years later might help the new wave of owners.