Lighter flywheel bad for drag racing?
03-20-2007, 01:15 PM
#1
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Lighter flywheel bad for drag racing? Can anyone explain how using a lighter flywheel hurts launches when drag racing?
It it a moment of intertia thing or a strength issue?
For example, why would I not want to use an aluminum flywheel that works
well for circle track and street racing at the dragstrip?
It it a moment of intertia thing or a strength issue?
For example, why would I not want to use an aluminum flywheel that works
well for circle track and street racing at the dragstrip?
03-20-2007, 01:48 PM
#2
I assume you are talking about a stick car. The reason is that the weight of a spinning flywheel is part of what gets a stick car moving out of the hole. Think about how much energy is stored in say a 12 lb spinning flywheel at 6800 rpm, vs a 25 lb flywheel spinning the same RPM. I'm not a math guy, but I can tell you it's a shitload more energy, making for a way better launch.
Circle track and road course cars don't use heavy flywheels because they are up to speed, not trying to accellerate from a stop. They want the motor to rev as fast as possible, hence the lighter flywheel. A quick revving motor in a drag car will work too, but the added energy for launching the car, will make for a bigger gain.
Circle track and road course cars don't use heavy flywheels because they are up to speed, not trying to accellerate from a stop. They want the motor to rev as fast as possible, hence the lighter flywheel. A quick revving motor in a drag car will work too, but the added energy for launching the car, will make for a bigger gain.
03-20-2007, 01:50 PM
#3
while the theory is correct(and I always thought too and that was what i had when my car was a 6speed)
there was a magazine article that tested the difference between the two, and the lighter one still pulled a better e.t.
god i wish i could remember which one it was in. coulda sworn it was an old GMHTP, maybe car craft though
there was a magazine article that tested the difference between the two, and the lighter one still pulled a better e.t.
god i wish i could remember which one it was in. coulda sworn it was an old GMHTP, maybe car craft though
03-20-2007, 02:06 PM
#4
I'll bet the Et was better because they couldn't leave at a high enough RPM ot really get the heavier flywheel to carry th car out of the gate. If you were to leave off idle I bet a lighter flywheel would be better, but if you had a killer suspension setup and a big tire that dead hooks and can leave at say 7200 with either flywheel and have the car dead hook, I'm sure the heavier one would be better..... less bog and the 300 foot #'s would for sure show that. Lighter flywheel might get a little more mph, but if it causes the car to bog, it's gonna run slower.
I think the test could be skewed either way... if LW flywheel manufacturer wanted to make it look that way, they certainly could. Same with a heavy flywheel manufacturer.
I think the test could be skewed either way... if LW flywheel manufacturer wanted to make it look that way, they certainly could. Same with a heavy flywheel manufacturer.
it's those damn "magazine articles" 
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03-20-2007, 04:49 PM
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In my opionion it is not quite black and white. My wife had a stick Camaro (1968) with a 350 engine. It was fastest with a light flywheel but used a drag racing slider clutch. If you are using a street clutch or a low power engine stored energy might be your friend.
Kurt
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03-20-2007, 05:18 PM
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I would beleive there is more to it than flywheel mass alone. For a relatively stock Lt1 car, I would assume my experience would be applicable...
I used a 32 lb flywheel behind a 13.40's stock 350 in my 55 Chevy with a 2.52 low Munice and 3.70 gears. The car ran as well as could be expected. I had to slip the clutch some out of the hole with such an insufficient starting ratio. When I did this correclty it would run the 13.40.
I tried a 45 lb wheel with the same setup and the car DROVE so much nicer on the street and in traffic in first gear. At the drags... well... the car still bogged unless I slipped the clutch a little not much improvement and it killed me at the big end. Couldnt run quicker than 13.55.
The same car now with a .480 lift cam installed and 4.11 rear with the 32 lb wheel will turn 12.90s when I slip the clutch out just right and bad if I don't. I will not try the heavy wheel again. I have already proven the result of that.
Now, I would thinik the more powerfull the motor the less it will need the flywheel mass and the more the light wheel will benefit the e.t. My old 283 would not leave with the lighter wheel and didn't accelorate well with the heavy one.
I know the SERIOUS drag racing crowd back in the day would use a long style 3 lever pressure plate with a sintered iron disk and only about 900 lbs of static. They used as much weight on the levers as could be tolorated and a light flywheel with serious rear end gears in the neiborhood of 5.57 to 6.17.
From my experience with the 55 Chevy, I would think the light variable pressure plate plate with an iron disk and a 15 to 32 lb wheel would work best. I have also seen some guys leave real hard with those ls1 motors 4.30 gears and a light wheel. I don't know how they work the clutch though.
I used a 32 lb flywheel behind a 13.40's stock 350 in my 55 Chevy with a 2.52 low Munice and 3.70 gears. The car ran as well as could be expected. I had to slip the clutch some out of the hole with such an insufficient starting ratio. When I did this correclty it would run the 13.40.
I tried a 45 lb wheel with the same setup and the car DROVE so much nicer on the street and in traffic in first gear. At the drags... well... the car still bogged unless I slipped the clutch a little not much improvement and it killed me at the big end. Couldnt run quicker than 13.55.
The same car now with a .480 lift cam installed and 4.11 rear with the 32 lb wheel will turn 12.90s when I slip the clutch out just right and bad if I don't. I will not try the heavy wheel again. I have already proven the result of that.
Now, I would thinik the more powerfull the motor the less it will need the flywheel mass and the more the light wheel will benefit the e.t. My old 283 would not leave with the lighter wheel and didn't accelorate well with the heavy one.
I know the SERIOUS drag racing crowd back in the day would use a long style 3 lever pressure plate with a sintered iron disk and only about 900 lbs of static. They used as much weight on the levers as could be tolorated and a light flywheel with serious rear end gears in the neiborhood of 5.57 to 6.17.
From my experience with the 55 Chevy, I would think the light variable pressure plate plate with an iron disk and a 15 to 32 lb wheel would work best. I have also seen some guys leave real hard with those ls1 motors 4.30 gears and a light wheel. I don't know how they work the clutch though.
