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PostPosted: Wed Feb 11, 2004 3:35 am 
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What amount should I machine off to help top end power?

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PostPosted: Wed Feb 11, 2004 7:22 am 
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Remove weight from your flywheel will not give you any extra horsepower. All it does is let you rev your engine faster. Your power band never changes it just gets there faster.

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PostPosted: Wed Feb 11, 2004 7:34 am 
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i don't think it'll help the top end, but letting you accelerate faster sounds an aweful lot like increased power .. not really increased power from the engine, but more of it should be making it's way to the wheels through the midrange ... as for how much to remove, you'd have to ask someone like liam/murr

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PostPosted: Wed Feb 11, 2004 8:52 am 
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lightening the flywheel will makes your rev faster due to the lower inertia and your pick up timming will be better, feel as if you had lighten the car tremendously. However on the other hand due to the lightening of your flywheel, u lost some inertia and will sacrifice your top speed and mid-top end power. its a balancing act on how much to machine off and depend on what you want your car's performance to be like. a 1/4 mile pick up spec or a highway spec?


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PostPosted: Wed Feb 11, 2004 8:58 am 
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Also because you're reducing the flywheel's ability to store kinetic energy you may find it bogging at RPMs it didn't before.

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 Post subject: flywheel
PostPosted: Wed Feb 11, 2004 3:17 pm 
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lightening flywheels should be done after you build a high hp motor.. on my 68 pontiac with a 455 (gobs and gobs of torque) helps the engine get to the torque curve quicker...on a car with no torque it just dosen't have enough effect to justify the expense. let me put it another way... would you run a 3" exhaust(the whole system incl. cat) on a stock swift? no way! the loss of low end grunt would offset any top end gains. now on a turbo, then you would see the benefit. same with a lighter flywheel, helps build revs, that in turn helps build boost etc....no doubt it would allow the motor to reach high rpms in a shorter ammount of time, which would make the car seem that much more "peakier" in its power delivery.

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PostPosted: Wed Feb 11, 2004 3:42 pm 
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Hello ppl!

This is my first post here. I just found out about this forum today; i've been scroling through and reading the posts and i think you ppl are great! (I mean the forum is great!) Okay, you are great too. Almost as much as the forum. Okay maybe just as much as the forum. Probably because the greatness of forum has been achieved through greatness of your posts. Therefore everithing is great. :P Anywho i would just like to say hello to everybody! Hello (to everybody)..

I would just like to point out one thing tho. Power is actually "how fast can the work be done" right? Remember the "definition" of horse power (ponies pulling cargo (coal) out of the mine - So one HP was the work that was done by one pony in one hour.) I think it was like that.. :razz: Anywhat, if lightning the flywheel makes the engne rev-up the powerband faster it means that it makes more power (but same torque). No? I dunno this is how i explain it to myself.. Please correct me if im wrong! :razz:

Greetings from Slovenia! (its far away).

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PostPosted: Wed Feb 11, 2004 4:09 pm 
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Well, i believe it would show up on a dyno, like an under-drive pulley. It takes HP to turn a heavy flywheel, so if you make it lighter, that's that much more HP that will get to the wheels, instead of using that energy to turn the flywheel. So in theory, you'll "gain" horsepower, it's just a matter of where on the powerband it'll land. And you'll have a harder time in bad traffic, or getting moving from stop lights during regular driving.


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 Post subject: lite wheel?
PostPosted: Wed Feb 11, 2004 4:20 pm 
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this is the same as light weight wheels, underdrive pulleys,

in lower gears the light flywheels will dramatically increase response. which in turn, makes you go faster, approx every pound off the outer most edge of a flywheel is like taking 100lbs off your weight off the car. which is very noticable on our cars which weight 1700lbs...

light weight wheels are usually used in displacement challenged cars. unless you have a hi reving v-8 then its common to have a light weight flywheel.

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PostPosted: Wed Feb 11, 2004 4:56 pm 
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murr, I agree with you to a degree... but, the original question was how much to take off for "top end power" making the fly wheel lighter won't increase top end power even a little bit. now it will get the engine to peak power quicker, but it will probably "wind" right through the torque curve just as fast. wouldn't that take away some of the low end responsiveness? wouldn't you get more out of that modification if you had other mods already done?(like turbo, nitrous and the like?) I know guys who run a slightly lighter flywheel on big blocks because of high lift cams and such. since the torque curve is table top flat, they want the motor to ge to peak h.p. as fast as possible. but were only talking 12-18 oz. total.

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PostPosted: Wed Feb 11, 2004 5:19 pm 
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i don't see where you get torque out of a flywheel .. a flywheel just carries inertia, it affects how quickly the engine can rev up & how long it takes to slow it down, it's effectively a dampener between your engine & gearbox ..

it works much like a capacitor in your stereo system, when you run into a hill, or even when you're just letting the clutch out, it transfers some of it's inertia or kinetic energy to the driveline, just like a capacitor will do when you get a phat bass note ..
when you're talking about it affecting your torque or top end speed, that's bogus, it doesn't provide anything but a buffering effect against acceleration/decelleration .. what you're trading off is the stored energy you have when you drop the clutch for the ability to accellerate for the rest of the quarter mile

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 Post subject: Flywheel
PostPosted: Wed Feb 11, 2004 5:27 pm 
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I have a light flywheel. I have only noticed a very very little more shifting. Not enough to even consider. If anything I think it has been one of the better investments. I have made. Oh it is a AASCO. Aluminum 3pc. It is only 6 lbs. The tech people at the factory said " It can go as light as 4 lbs. But it would be only useful for track use at high RPM's. As in constant high R's. " The aluminum one is not cheap. But in my view. Lighter is better.


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PostPosted: Wed Feb 11, 2004 7:22 pm 
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that stored energy you talk about is torque. torque is what provides the inertia to turn the fly wheel. if you dyno a car that has a lightened fly wheel the h.p. of the motor doesn't change.. just how fast the engine turns. I do have to apologize about an earlier comment in which I was wrong... in years past ( read: musclecars) the cars that were the quickest(stock) had the most torque. the heavier the flywheel was the better to transfer the engines torque to the trans. ( thats the buffer effect you spoke of) the trans is essentially a torque multiplier. a lighter flywheel in a car like the swift requires less torque to turn it, therfore letting the trans do a better job of multipling the little torque we have. ergo better response, ergo this is a good thing. I think the stock fly wheel weighs 9 lbs. so taking 2-3 lbs is a good rule of thumb.

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PostPosted: Wed Feb 11, 2004 7:37 pm 
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i really thought torque was the product of an extended burn, eg. the power generated vs the length of time that it's generated during the power stroke as opposed to hp being the overall power an engine puts out ..
this is why engines with longer strokes or a compressed intake charge produce so much more torque.
to be completely honest, defining torque vs. hp is one of those subjects that doesn't make a whole lot of sense to me ..

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PostPosted: Thu Feb 12, 2004 12:21 am 
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me neither.. all I can tell you is what a very trusted mechanic told me a long time ago... if you want to go fast you want to make h.p. If you want to run quick you want torque. example: 1970 buick gs stage 1. Buick listed this car @375 sae gross h.p. (not much for the day) but listed torque @ a mountain moving 510 ftlbs! these cars ran easily low 13's from the factory. I know I saw an article in scc magazine that adressed the difference from an engineer's point of view, I'll see if I can find it.

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PostPosted: Thu Feb 12, 2004 1:32 am 
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the wrc peugot 206's from last year were making something like 570ft/lbs ..
enough to rip the rear axle out of a v10 dodge in a tug-o-war =)
i found this writeup, it seems to be the clearest of the ones i've dug up ...
http://vettenet.org/torquehp.html
there's also this one
http://www.allpar.com/eek/hp-vs-torque.html
but it may make your brain hurt a little more ..
Quote:
Awhile back, a gentleman by the name of Watt (the same gent who did all that neat stuff with steam engines) made some observations, and concluded that the average horse of the time could lift a 550 pound weight one foot in one second, thereby performing work at the rate of 550 foot pounds per second, or 33,000 foot pounds per minute, for an eight hour shift, more or less. He then published those observations, and stated that 33,000 foot pounds per minute of work was equivalent to the power of one horse, or, one horsepower.

Quote:
Torque and power are (almost) flip sides of the same coin. Increasing the torque of an engine at a particular RPM is the same as increasing the power output at the same RPM.

Power is just as useful and relevant in determining vehicle performance as is torque. In some situations it's more useful, because you may not have to play with gear ratios and a calculator to understand what's going on.

A car accelerates hardest with gearing selected to stay as close as possible to the engine *power* peak, subject to the traction capability of the tires.

Not all cars should be shifted at the redline for maximum performance. But it's true for many cars. You can determine optimal shift points by graphing horsepower vs. velocity or transmission torque vs. RPM. Engine torque alone will not determine shift points.

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 Post subject: my brain hurts...NOT!!
PostPosted: Thu Feb 12, 2004 3:40 pm 
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by the time the wrc pugeot got to its torque peak i'm afraid the dodge would have pulled it apart. the wrc car , while making higher torque numbers, does it at a much higher r.p.m.. if you made a graph of the torque curve you'd see that the wrc car doesn't start to really build torque until the boost comes on. I'm guessing but I think that's around 4500-5000 r.p.m.'s. the dodge probably makes 350 ft.lbs @ idle and then climbs to its peak in a hurry. but then a funny thing happens, it doesn't drop off as near as dramatic as the wrc car's builds, so the graph would look like a table or mesa. the wrc car would look alot like a mountain. all this means is that by the time the pugeot started to over power the dodge, it couldn't overcome the dodge and the inertia. this of course is assuming both vehicles are the same weight. and have the same traction. to awnser the original question, shaving the flywheel won't add h.p. just changes the way it's delivered to the drive wheels. what would be great is if someone baselined 1/4 mile times before and after the flywheel was lightened. but since it doesn't change power output of the engine...top speed would stay the same, it just might get there slightly quicker. whew! :blackeye:

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 Post subject: wrc
PostPosted: Thu Feb 12, 2004 4:16 pm 
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Idon't have the graphs
but a WRC rally car is very flat tq curve. they pull from low revs. and are not peaky. usually max revs is around 6500ish. no 8000 screamers...

Remember the WRC cars have a 40mm <1.57"> diameter intake restrictor.

I have heard the tq curve is very similar to a new deisel truck.... lots of power everywhere

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 Post subject: Re: wrc
PostPosted: Thu Feb 12, 2004 4:54 pm 
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MURR wrote:
Idon't have the graphs
but a WRC rally car is very flat tq curve. they pull from low revs. and are not peaky. usually max revs is around 6500ish. no 8000 screamers...

Remember the WRC cars have a 40mm <1.57"> diameter intake restrictor.

I have heard the tq curve is very similar to a new deisel truck.... lots of power everywhere


Seen my dynochart with lightened everything (flywhell by 30%) and ported head? Ohh it's like OzMidnight said a low compression slug....

http://www.teamswift.net/files/colin.jpg

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 Post subject: flywheel...
PostPosted: Thu Feb 12, 2004 8:04 pm 
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a lightened flywheel on a gti WILL result in quicker ets..

on the topic of wrc,
the new 307 is making GOBS of torque, and they now have 4 speed boxes...so it will pull like a mofo no matter what gear...

TGstring

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 Post subject: wrc cars
PostPosted: Fri Feb 13, 2004 7:10 am 
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Quote:
Idon't have the graphs
but a WRC rally car is very flat tq curve. they pull from low revs. and are not peaky. usually max revs is around 6500ish. no 8000 screamers...

Remember the WRC cars have a 40mm <1.57"> diameter intake restrictor.

I have heard the tq curve is very similar to a new deisel truck.... lots of power everywhere


MURR is 100% correct. Their power is limited to 300 HP due to restrictor, but if you look at the tech data through the years you'll see that torque is getting a bit higher every year, or at least peak torque is at lower RPM. You can see that in the fact that WRC cars are getting faster every year (and aerodynamic improvements are not so big to be tha main cause for this). Their power curve is actually better then the one on diesel engines, almost totally flat...

BTW, on electric engines there is a direct connection between power and torque, like this:
T=x*P

where T is torque, and P is power. On electric engine you can have the same torque through all the powerband if you want (you can even have max torque before it starts turning). On car engines that would be something like this:

T=f(P)

The function f(P) is different from one type of engine to another, and you can't just express it that easilly (I think that this would be actually impossible) and this is why torque and power are taken as two very different things...


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PostPosted: Sat Feb 14, 2004 2:39 am 
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stillshedswift wrote:
...what would be great is if someone baselined 1/4 mile times before and after the flywheel was lightened. but since it doesn't change power output of the engine...top speed would stay the same, it just might get there slightly quicker. whew! :blackeye:


Grassroots Motorsports once did an article on this. According to their math, two identical Mustangs, one with a stock flywheel, the other lightened, the difference at the end of a quarter mile I think was something like a car-length and a half. I believe their math was only calculating just the reduced rotating weight.

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 Post subject: Flywheel lightening
PostPosted: Sun Feb 15, 2004 7:15 am 
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Thought Id do some research and found a section on Rotating Inertia in Chassis Engineering by Herb Adams. He states:
Reducing weight of a car will increase acceleration.
Reducing the weight of rotating components about its centre of rotation will also increase acceleration.

If a car had a flywheel that had most of its weight concentrated around the rim, it would have greater resistance to revving quickly than a flywheel that had its weight concentrated around its centre. The later would have less rotational inertia.

Vehicle Acceleration = Force / Weight , Weight = Mass x Gravity

Force =Engine torque x Axle Ratio / Rear tire static radius

Velocity = Acceleration x Time

In his example he compares the difference between simply reducing the weight of the car by 15lbs against reducing 15lbs from the rotating components.
Reducing 15lbs of the weight of the car gives an improvement of 0.5% in horsepower and 0.02% in speed at the end of the straight.

Reducing 15lbs of the rotating weight of components gives an improvement of 1.5% in horsepower and improvement of 0.5% in speed at the end of the straight.

Rotating components include crankshaft, flywheel, clutch, wheels, discs, etc.

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PostPosted: Sun Feb 15, 2004 5:28 pm 
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you'd think reducing rotating mass would also vary depending on the rate @ which you have to spin the various parts of the assembly .. eg .. your tires/wheels travel between 0-1800rpm (@200km/hr), while your engine revs between 800-8000rpm
or if you want to really break it down, simply use your gear ratios, even in 5th gear, your engine is still revving about 4 times faster then your engine @ whatever rate it's accelerating .. so reducing mass from the engine should be ~4 times as effective as removing it from the wheels .. ???

this is a cool thread :)

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 Post subject: Rotating mass
PostPosted: Sun Feb 15, 2004 8:39 pm 
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Herb also examines rotating mass at engine RPM.

The greatest gains in HP can be made in this area.

The figures in his example show a 15lb reduction in engine rotating mass gave a 7.5% HP improvement and 5% speed increase at the end of the straight. (this is on a 400Hp engine).

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