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      02-20-2011, 01:01 PM   #23
pbonsalb
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Lighter flywheels and lighter wheels have been dyno proven to add power and dragstrip proven to reduce acceleration times. Muscle Mustangs & Fast Fords, Grassroots Motorsports and other magazines have done the tests. Expect nothing dramatic -- maybe 1/10 of a second or 10 hp.

The best explanation I read for the effect of a lightweight flywheel was that in 1st gear, it would be like making the car 300 lbs lighter. In 2nd gear, it would be like making the car 200 lbs lighter. In 3rd gear, it would be like making the car 100 lbs lighter. The benefit would be pretty much gone by 4th gear. I like LTW flywheels for naturally aspirated and centrifugally supercharged cars that need rpm to make power.
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      02-20-2011, 01:19 PM   #24
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Quote:
Originally Posted by pbonsalb View Post
The best explanation I read for the effect of a lightweight flywheel was that in 1st gear, it would be like making the car 300 lbs lighter. In 2nd gear, it would be like making the car 200 lbs lighter. In 3rd gear, it would be like making the car 100 lbs lighter. The benefit would be pretty much gone by 4th gear.
Yep, that concept is true for wheels too, the less you're trying to change the speed of the wheel (or most anything that moves) the less it matters how heavy it is.
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      02-20-2011, 06:38 PM   #25
Tim B.
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found this interesting....

Going through some old magazines i came across an article in BMW Car(july '09) with a G-power supercharged M3 with 600hp........"we have new 19in wheels that weight aroung 8kg each. Together with carbon-ceramic brakes, we calculated we can remove over 50kg from the car's unsprung weight. So why is this important? Apart from improving ride and suspension control, we found that it reduces the energy required to move the car. Rotational mass is equivalent to over THREE times static weight, so with the lightweight wheels and brakes fitted, the 0-124mph time of the standard M3 was reduced from 20.7 sec to 18.5 sec. That is equivalent to adding another 20bhp!"--Christian Stober

Thought this was a pretty good story with some "real world" results.
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      02-21-2011, 12:26 AM   #26
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The notion that reducing mass, either fixed or rotating mass adds any power is 100% positively false.

Now it can appear on certain dynos to show more power, but it does not add power. Think about it - the engine produces the power, lossy components like gears and bearing waste power turning it into heat. Thats it. Rotating components only store energy. This was discussed extensively recently in a post about CF drive shafts. Please read that one. In short just remember Newton's law:

F = m x a , force equals mass time acceleration

Reducing mass, normal sprung mass or even rotating mass is simply lowering the m term. If F (basically the force from the engine at the rear wheels) is constant than a the acceleration goes up. It is slightly more complex for a system with translating and rotating mass like a car but that is the correct concept. You can increase the force or lower the weight to get faster but they are entirely different things physically.
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      02-21-2011, 07:05 AM   #27
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You are correct that we are not changing the power of the engine in isolation. The engine in my car, however, is not in isolation. When I change the flywheel or rear wheels, I am changing the drivetrain attached to the engine. The dyno reflects rear wheel power after all driveline losses, including the flywheel. Lighter or heavier front wheels, no, but the lighter or heavier rear wheels or flywheel are lighter or heavier on the dyno drum and the engine has to turn them so the dyno can compute the power that is eventually put to the drum.

To avoid offending Newton, we could call it adding rear wheel power or reducing parasitic or drivetrain loss. The bottom line to a non-engineer like me is that my car is putting down more at the rear wheels and is going faster. Same concept applies to underdrive pullies, catless midpipes, and aftermarket rear exhausts -- they increase rear wheel power, but no one questions those mods.

The differential is more interesting to me, because you don't see any change on the dyno when you change the rear gears. Supposedly the same goes for testing the engine in 3rd versus 4th versus 5th though in practice, as opposed to theory, I have seen better numbers in higher gears that load the engine more during my dyno runs.

Maybe as the engineer or engineering student, you could explain this: I know that in reality, the 3.64 that I swapped in place of the 3.23 in my E36M3 had the effect of increasing torque through gearing by about 13%, but that this was not reflected on the dyno. It seems like turning a bigger or smaller gear at the end of the driveshaft is much like turning a lighter or heavier wheel, but I am just a hotrodder and not an engineer.
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      02-21-2011, 09:29 AM   #28
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Like you said a shorter rear gear increases torque multiplication, but this is usually compensated for by the gearing inputs in the dyno software and/or the software itself which does a wheel speed/rpm correlation to determine effective gear ratio. If anything, the physically bigger ring gear adds mass to the drivetrain, but it's a relatively small change in MOI.
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      02-21-2011, 07:02 PM   #29
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Sorry absolutely wrong.

Quote:
Originally Posted by pbonsalb View Post
You are correct that we are not changing the power of the engine in isolation. The engine in my car, however, is not in isolation. When I change the flywheel or rear wheels, I am changing the drivetrain attached to the engine. The dyno reflects rear wheel power after all driveline losses, including the flywheel. Lighter or heavier front wheels, no, but the lighter or heavier rear wheels or flywheel are lighter or heavier on the dyno drum and the engine has to turn them so the dyno can compute the power that is eventually put to the drum.

To avoid offending Newton, we could call it adding rear wheel power or reducing parasitic or drivetrain loss. The bottom line to a non-engineer like me is that my car is putting down more at the rear wheels and is going faster. Same concept applies to underdrive pullies, catless midpipes, and aftermarket rear exhausts -- they increase rear wheel power, but no one questions those mods.
Nothing you do to the weight of drivetrain components gives you more power, it simply improves your power to weight and makes the car appear to have more power. It will be faster but it WILL NOT have more power. You do not reduce PARASITIC drivetrain losses by reducing the weight of rotating drivetrain components.

Underdrive pulleys, exhaust mods and the like absolutely do increase power. The pulley by reducing electrical/pumping system parastic losses. Less loss in the engine system means more power at the wheels. Exhaust mods similarly by making the engine system breathe better and simply pump more easily also actually increase power output.

Quote:
Originally Posted by pbonsalb View Post
Maybe as the engineer or engineering student, you could explain this: I know that in reality, the 3.64 that I swapped in place of the 3.23 in my E36M3 had the effect of increasing torque through gearing by about 13%, but that this was not reflected on the dyno. It seems like turning a bigger or smaller gear at the end of the driveshaft is much like turning a lighter or heavier wheel, but I am just a hotrodder and not an engineer.
It's obvious you are taking a "hot rodding approach" here. By the way, just for your info I am not a student. I have 3 degrees all science/math and worked at a Mechanical Engineer for many years. Just FYI.

It is good you ask about final drive modifications this is ultimately just like the torque/gearing/hp discussion we are having in another thread. What folks fail to realize about FD mods is that by getting more torque multiplication you also spend less time in each gear (you get to redline at a lower speed and have to shift earlier). Often time this torque multiplication benefit is equally or more so reduced by this inability to stay in lower gears longer. Think about how much more acceleration you get in 1st as opposed to 2nd or 2nd opposed to 3rd. This adds up. With modern sports/GT cars such as the M3 the FD ratios are pretty well optimized. However, if you only want better results in a single gear and you can end your test before the shift is required FD mods will deliver this. Across multiple gears - not likely.

Here are more threads for some good FD debates (arguments)...

http://www.m3post.com/forums/showthread.php?t=379139
http://www.m3post.com/forums/showthread.php?t=287873

P.S. Last but not least, don't worry about respecting or offending Newton. If you proved him wrong (of course for classical problem) you would be the most famous scientist around and you would most likely win the Nobel Prize.
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      02-21-2011, 11:58 PM   #30
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Lighter wheels should help w/ handling not speed right? That's what I love most about the driving experience, just like "lightening" the ride, making it more nimble, this is what I would hope for.
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      02-22-2011, 11:49 AM   #31
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There are several advantages to lighter AND strong wheels. Running a lighter wheel which is weaker than the recommended load for your car will actually reduce performance due to increased flex during hard acceleration/cornering. A light and strong wheel will have a higher rigidity than your OEM wheel and will result in minimal to no flex under stress compared to your OEM setup. You also reduce rotational mass and unsprung weight which help increase acceleration. On our designs this has its greatest advantages since the weight savings are usually concentrated toward the outer flange of the wheel, where it matters most. Due to lighter weight the suspension also has less effort controlling its components which makes the vehicle more adaptable to road changes, improves braking, improves grip/traction and steering input is more precise. In essence your overall vehicle dynamics are improved.

Some of this changes are very tough to notice unless is as drastic as one case I once had. One customer took out a set of OEM 18" 162 on his 335 that the wheels alone weighted 32lbs. Yes, 32lbs OEM wheels. He installed a set of 19" VS7 that weight 19lbs. That's a unsprung weight reduction of approx. 13 lbs per corner. Whether this is equal to 2x, 4x, 8x or 10x makes no difference on the effect it`ll have on your vehicle. The customer called and said he was loosing traction while shifting to 3rd gear. Did he gain power? No. The power the vehicle makes is constant. What improved was the efficiency on which the power was delivered to the wheels.

Lately the trend is to buy wheels based on perception or how "cool" they are. I have had a chance to examine some of these wheels in person and is comical the lack of engineering on these designs. A wheel is supposed to be stronger and lighter than your OEM setup, and if possible, without sacrificing strength and weight, improve your vehicle aesthetics. A $5,000 set of wheels that weights the same as your OEM setup or more is a mockery. When making a wheel purchase you must choose a product that will give you an improvement in performance unless the case is you only care about looks.
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