This was posted by VaporTrail on ClubSi...I thought it was very cool!



Peak gain of 2.5 HP and 3 TQ but with even bigger gains in other parts of the powerband.
This is on a boosted car...I hope teh same stands true for NA motors. (Cant wait to get my 9 LB flywheel next week!)

 

What type of Flywheel you getting?

 

I ordered the Clutchmasters 9 LB aluminum flywheel.

 

Someone please correct me if I'm wrong, but power gains using a lighter flywheel is deceptive. The flywheel stores power through momentum, so using a lighter flywheel will allow revs to build up quicker and looks good on the dyno, but the revs drop like a tons of bricks when taking your foot off the accelerator and shifting.

No real gains to be had here

 

I always thought that too, but at the same time on M3's when you replace their stock 26lb flywheel (!) w/ a 12 pound one, they all say it makes a big difference in their acceleration.

It also seems like a lighter flywheel would help accelration because the engine would not have to work as hard to rotate the wheel. Inertia is defined as the mass that resists acceleration, and less rotating inertia means less mass to resist acceleration. We all want lighter rims for better acceleration, no one questions that, but how is a flywheel any different?

Accoring to this argument, then a 50 pound flywheel would have no negative effects on acceleration as well. I find this hard to believe.

Hell, the entire car stores momentum (p=mv) , not only the flywheel, but then according to the argument that mass doesn't matter, then the weight of our car wouldn't matter either.

 

where is the argument you speak of that says mass has nothing to do with it? I dont think anyone said that. Revs build up faster cause there is less intertia, but this also means it drops faster for the same reason, intertia is the resistance to speed changes (accelerations)

 

I've always said that lightened flywheels help to free up lost HP. And now the dyno sheet proves it.

 

That doesnt really tell me anything. I can dyno my car, and make say 200whp. Then wait 15min, dyno after the car has cooled and make 204whp. With 4 hp gain across the whole rpm band. Sure a lightened flywheel helps, but how much it does is anyones guess. The point is, its really hard to compare a dyno sheet on sessions that were made on different days, or made between a 3-4 hour variable.

I run a lightened flywheel btw, it does make the car free rev alot faster both up and down. Thats were the biggest difference is IMO.

 

A lightened flywheel works kinda like changing out your pulleys. It's less work for the engine to do. Everything that the engine has to do affects power. The harder it works to push exhaust gasses out affects power. The harder it has to suck in air affects power. The more it has to power your accessories affects power. The harder it is to turn your wheels affects power (therefore, lightened flywheels and featherweight rims). It does recover the lost horsepower. The reason that there is a difference between bhp (depending on manufacturer, some do test with accessories but some don't) and whp is because of everything extra being put on the engine making it work harder. The more you can do to help it out, the closer you get back to that bhp level.

 

Well guys, if the engine revs faster (which it does) aren't you accelerating faster? It does slow down faster, but that doesn't mean it doesn't help accelerate the car faster?

The conventional wisdom is that drag racers may not want a light flywheel since it makes the car harder to launch or hurts low end.

I have a Spoon flywheel and don't really notice much loss in low end or difficulty launching, but I changed quite a few things at the same time. Car def revs faster, both up and down... Rev matching is just so much fun, hehe.

Since I don't really notice the detrimental affects, I'm very happy with the flywheel. The Spoon one is like 10 or 11 lbs, so it's not like the 6 lbs flywheel which may be harder to deal with? I would not be surprised if it produces a repeatable/consistent gain on the dyno, since there is less rotational inertia.

Thoughts?

FB

BTW, In the past I dynoed my car with and without PS belt attached and made 3HP and 1TQ across the board in back to back runs within a few minutes of eachother, and this would prob be a similar type of concept. Takes longer to swap the flywheel out though, heh.

 

Like someone else said here, you need the extra weight for momentum to get off the line especially for drag racing unless your engine makes enough power and torque to overcome it.
I had a JUN ultralight flywheel in my car and I'd literally come off the line at 7-8k rpm and the car would still bog. I put my stock flywheel on and I come off the line hard.

Lightened flywheels are more for road racing. It really depends if your n/a or fi. The cars with the turbos gain spool up time, and other forced induction cars benefit by allowing less load on the engine.

Yea the graph shows a pick of a few hp but dont be misled by what its use is intended for. If your drag racing stay with the stock if you're road racing this is for you, if you're a guy that mainly drives on the street maybe you want something like this .. Its just my opinion sorry for the long boring post.

 

Good god...was this in a B18C1? I would think the GSR engine has a little more torque then that.

Im making 135 ft-lbs of torque to the wheels..so hopefully it will be enough to overcomes this..Ill have to see.

 

Actually...now that I think about it...this might be a good thing. First gear is useless to me pretty much..because of wheel spin...especially at the track. If this will have less inertia then maybe wheelspin wont be as big a problem.

 

[QUOTE]
I had a JUN ultralight flywheel in my car and I'd literally come off the line at 7-8k rpm and the car would still bog. I put my stock flywheel on and I come off the line hard.
QUOTE]

yeah this has to do with the small intertia of the flywheel, and the momentum it has (or lack there of). Since it changes speed so easily, when you let the clutch go, the momentum of the flywheel is so little that when it transfers to the wheels and effectively the whole car it slows down big time. mv=mv . With the little intertia, the force it takes to move the wheels will slow down the flywheel and then the engine (unless you got power).

In theory, if you had a big *** flywheel like 35lbs, and held it at 3k and dropped the clutch, the wheels would be nothing to that and they will just spin like crazy while the tach would porbably drop like 100rpm if anything. but once that intial launch is complete it's gonna take a lot of time to accelerate the flywheel from that pt up more so than a light flywheel.
Light flywheels are good for road racing like mentioned above cause, revv matching and stuff. and if you have enough power i guess drag racing would benefit too.

After every flywheel post i get a thought in my head, and perhasp when im really really bored this summer (perhasp on a 6.5 hour drive) i will try to relate momentum, speed, friction, intertia, torque, force, acceleration all together...to hopfully explain the flywheel's weight and it's effect and wheels' weight and launch rpms and stuff since im pretty sure all of them can be tied together in one long winded post, perhasp some guys out there already figured it out and can enlighten us.

 

Well, when you say lightening the flywheel has no acceleration gains, that's the same as saying the mass of the flywheel has nothing to do with acceleration of the car since what we are changing here is the mass.

Now as for your argument about the momentum of the drive train versus the momentum of the flywheel/engine, that sounds very valid for a car standing still, since the car will have no momentum (v=0) but the wheel will and when engage the clutch, the momentum will be transferred. Thus a bigger flywheel will spin the wheels more easily than a lighter one. However, that is when we are holding rpms at a fixed level to launch the car.

However, what we are taking about is a car that is in motion, which already has momentum in it's drivetrain and thus the difference in momentum between the flywheel and drivestrain are much smaller. Either way, once the clutch is engaged, this difference in momentum will not matter because the masses will have combined together.

Truth is if you go back to F=ma, when you increase the mass, keeping acceleration constant, you need correspondingly more force. Or if you decrease mass, keeping force constant, you increase acceleration.

Ricehornet, would you care to comment?

 

Lightned flywheels definitely allow you to accelerate more quickly. They dont add horsepower, just free some up, but I'm sure its quite evicent that the benefits greately outweigh the quicker dropping revs, so long as you dont go too light for your application. They must be chosen accurately or you will not attain the gains you seek and you will probably be very disappointed.

 

Hey guys!

Interesting, from what Rice, Fast, and you are saying, I see how a heavier flywheel could help launches, since there's more "oomph" as it kicks in and gets everything going. I didn't really have a grasp on that till now.

However, as stated, I think that once it's engaged and you're spinning the flywheel engaged to the tranny, a lighter one will def be easier to accelerate. Obviously, things with less rotational inertia are easier to get accelerate. I would bet that if you have two cars rolling at 30 mph side by side and one has a 10 lbs flywheel vs a 15 lbs flywheel for the other car ceteribus paribus, the car with the lighter flywheel would accelerate faster if they both floored it at the same time. If both cars were launched side by side, the one with heavier flywheel may get a better start. Note that I said ceteribus paribus, so all else is = between the two, which may not be realistic, but necessary for comparisons...

Thanks,

FB

 

whoa nelly. Thats EXACTLY what im trying to figure out. Cause arguments can be made for both F=ma and p=mv. Anyone who has taken calculas based physics will realize that almost everything dynamic is related, blah blah is the derivative of blah blah while this is the integra of that and whatever.

I NEVER said lightening up the flywheel has no acceleration gains, i always believed it helps, but i think it hurts launching.

Ein, thats what has been keeping me thinking, how momentum plays a role in launching, but at speed, it doesnt play that big of a role. Since at speed like you said the difference in momentum is quite less, especially since the car is zero, you can say it's infinetly less. So in that case, a big flywheel is good, but like you said, the engine produces more torque and energy to build speed, because conservation of momentum will only bring the vehicle to X speed. Without any more energy being brought in from an outside source (combustion), you launch, and thats about it. So, once everything is momentumized() F=ma comes into play , well sorta, more like torqueangular acceleration)(rotational inertia) so light flywheels accelerate faster, inturn less load on engine, and accelerating the wheels faster since they are connected,wheels then use friction to propel the car.

Basically, heavier flywheels like big *** 18 wheelers, keep speed well (see if crashing into a civic really matters to them ). Light things like a motorcycle accelerates much more violently.

Momentum, torque, linear force, friction,dynamics of rolling ,mass, inertia, speed, rotational speed, are all related, and all have somthing to do with why a car moves. Im gonna try to link them together in a nice little long winded post. Anyone want to work with me via IM/email/phone(i'll call u (no long distance fees)?? So i wont look like an *** when i overlook somthing?

I shall write up my thesis soon.

BUT it is the weekend, and im apartment shopping so no work this weekend, perhasp monday i'll start work. Like i said, if someone wants to help me, or wants me to help them as a consultant im glad to.


Berkel - yup thats what i think too.


Edit - I just reread my post and i realized somthing...maybe im looking too deep into it, and it just lies in somthing as simple as the inertia. Heavier - hard to accelerate (hard to slow down too), so it launches hard, but build up speed slow. Lighter - easier to accelerate, and therefore conservation of momentum makes it stall easier too. But less force needed to build speed.


-k,b0t -- who thinks he might be making a mountian out of a mole hill and just say " it does because it does"




[Modified by Ricehornet, 6:06 PM 7/27/2001]

 

i had my OEM flywheel machined to about 12lbs too. very nice. accels much quicker.

it just takes a little time getting used to taking off from a stop sign or light. you gotta kinda ride it a little more. after that it's just like normal. the revs drop quicker than before but not by that much.

10lbs would be perfect for the street..........

 

Damn, you guys get complicated to explain a damn flywheel question ! We should call this the popular science corner ....heh heh... Look.... in caveman terms....just so EVERYONE understands : Heavy FW (flywheel)= more momentum.... able to transfer more torque to clutch plate faster with minimal power lloss... once higher accleration increased.... it get harder to accelerate heavy FW, lose potential power in high end of tach....
Lighter FW cannot transfer as much torque on engagement with clutch, (slower takeoff)... but once acceleration increased, lighter weight of this FW allows acceleration to come on easier with less energy. The engine has to use less energy to create more power...

Just think about how easy it is to slow a plastic bladed fan (with your hand) and how hard it is to slow the heavier metal bladed fans.

Is school out for summer ??

BTW, very impressive scholastic explainations of the flywheel issue !

 

hahaha, I know I'm making a big deal outta nothing, the only reason why I've said so much is because I read on the board before that flywheels do nothing other than allowing you to match revs more easily and make starting off the line a lil harder, so I just accepted it as that. It did seem odd that flywheels didn't help acceleration, but at the time I just assumed that these people were more knowledgeable than me about it and accepted it.

 

Theories are great and X2BOARD explains it very well.

Now let me tell you my personal experience. I use the CM 9lb flywheel on my GSR. Results:

- No more bogging at low rpms, as the stocker did (painfull 2000rpm, get beat by a stationwagon, 2nd gear -- oh the agony)
- Rev's don't drop noticeably more (I think this is due to the comprimise weight of the CM FW)
- Idle is unaffected (car never stalls)

Overall, this mod kicks ***. I recommend upgrading your clutch when you do it to save install costs and avoid surface matching problems. I also recommend upgrading your tranny to ITR spec -- but then that's a whole different story.

 

Nice review Ninjaman

I went with the Clutchmasnters 9 lb unit as well
Also Im having a GSR tranny installed to replace my LS one.
And Ill probably be getting anew clutch as well. The car should feel VERY different after everything is all done...damn I cant wait for the faster revs...the LS tranny is a DOG in 3rd an 4th!

 

And now for my personal experiance. I love my JUN UL flywheel. I was weary at the whole launching issue but after some practice I can get mad tire spin on drag radials when launching from 6500 rpm. Slopoke uses an UL flywheel in his b18b powered hatch and it is simply awesome. With the torque output of the motor coupled with the lightweight of his hatch the car launches aggresively from 3500 rpm and any higher it smokes them.

 

Alot of people like the comptech units too... which is sorta weird since their weight of 6.75 pounds seems too light for street use.