roverman Art Gertz Winchester, CA. (3188 posts) Registered: 04/24/2009 11:02AM Main British Car: 74' Jensen Healy, 79 Huff. GT 1, 74 MGB Lotus 907,2L |
aluminum flywheel worth it ?
Jensen Healy Hell Fire, 2,400 lbs/loaded. Turbo Supra 5spd. Theory says it should grab rpm's quicker ? Approx. 15 lbs with steel insert. I will probably build it, don't find one new. Thoughts? roverman.
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DC Townsend David Townsend Vermont (406 posts) Registered: 11/21/2007 12:22PM Main British Car: '78 B (almost done) 30-over SBF, dry sump |
Re: aluminum flywheel worth it ?
Can't speak to your specific combination but can say that comparing the stock steel flywheel to a Fridenza aluminum wheel on my 340HP Ford 302 there was a pronounced difference in how crisp the throttle response was. With the alloy flywheel it revved both up and down much more quickly than with the stock wheel. I know most of the flywheel suppliers are quick to tout the horsepower gains but I'm not so sure that's true based on my 'seat of the pants' measuring. While the motor revved quicker, I can't say I noticed any difference in hard acceleration although time between shifts was reduced.
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roverman Art Gertz Winchester, CA. (3188 posts) Registered: 04/24/2009 11:02AM Main British Car: 74' Jensen Healy, 79 Huff. GT 1, 74 MGB Lotus 907,2L |
Re: aluminum flywheel worth it ?
David and clan, were this a pure drag car, where-in I could make pedal-to-metal shifts, a lighter flywheel, should make for "slower" times,(less stored energy/more rpm drop between shifts). With conventional syncro's, and more towards road-course work, slaloms/track days/etc., the lighter flywheel, should have merit. Cool the disk better ? Light car/light flywheel ? roverman.
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DC Townsend David Townsend Vermont (406 posts) Registered: 11/21/2007 12:22PM Main British Car: '78 B (almost done) 30-over SBF, dry sump |
Re: aluminum flywheel worth it ?
I think the gain in throttle response would be well worth it on a road course. Bottom line is it simply takes less effort to spin the alloy wheel. I could behind the "light/light flywheel" idea as well. FWIW, I bought my off a guy on e-bay who decided to go AOD with his car. Nice mid-line Fridenza for $150, NIB. With a stock steel 302 flywheel going for around $100-$125, didn't seem to be much a decision to go aluminum.
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Dan Jones Dan Jones St. Louis, Missouri (280 posts) Registered: 07/21/2008 03:32PM Main British Car: 1980 Triumph TR8 3.5L Rover V8 |
Re: aluminum flywheel worth it ?
A while back I ran the numbers for switching from an iron to aluminum
flywheel for my Triumph TR8. The effect was surprisingly large. There are a couple of approaches to doing the math. The more rigorous approach is to calculate the polar moment of inertia for the two different flywheels, adjust for the square of the overall gearing (transmission, final drive and tires) and convert to an equivalent linear inertia. The second method (the one I chose) is to start with a known linear to rotational equivalent and ratio from there. The known relationship I used is a solid disk rolling on its edge. It has an effective inertia exactly 1.5 times what it would be if it wasn't rotating. That means the rotational component is 50% of the linear component. Adjust for the square in gearing and you have the answer. I wrote a little Fortran program to do the calculations. I assumed a 12" diameter flywheel which is the Buick/Rover diameter, less the ring gear. The circumference of a circle is the diameter multiplied by pi. So if you roll the flywheel along the ground it will move 37.7 linear inches per revolution (= pi * 12). A 205/50/15 has a diameter of approximately 23.1 inches. My TR8's final drive ratio is 3.45:1 and first gear is 3.32:1 so one revolution of the flywheel results in the Triumph TR8 moving around 6.3 inches. Ratio the squares and take half ((37.7/6.3)**2)/2 = 17.9. So each pound removed from the flywheel (equally across the face) is the same as about 18 pounds of weight removed from the car when in first gear. So if you remove ten pounds from the flywheel (equally across the face), the result is equivalent to removing 180 pounds of vehicle weight in first gear. The effect goes down for each higher gear, of course. Removing weight farther from the rotational axis has a more pronounced effect. If the weight is removed from the outside of the flywheel only, the effect is about 2.78 times as strong since a solid disk has a radius of gyration of 0.6 times the radius (1.0/0.6)**2 is 2.78). 2.78 * 180 is 500 lbs equivalent weight reduction. A non-trivial effect, particularly in a lightweight car. I ran the numbers a couple of ways to illustrate. For my TR8, assuming a 3.45:1 final drive ratio, 205/50/15 tires and LT77 gear ratios of: 1st 3.32:1 2nd 2.09:1 3rd 1.40:1 4th 1.00:1 5th 0.83:1 along with flywheel weights of: stock flywheel - 32 lbs lightened steel - 22 lbs aluminum - 11 lbs The engine in the TR8 is essentially a Buick 215 aluminum V8 from the early 1960's. The stock flywheels in those had a big ring around the perimeter. Lightening the flywheel by milling off the ring is similar to removing the mass from the perimeter (from 32 to 22 lbs). In the numbers below, I didn't do it that way but a more accurate approach for the aluminum flywheel would be to assume a reduction of 22 to 11 lbs equally across the face and add that to the difference of the 32 to 22 lbs across the perimeter. In any event, a lighter flywheel looks like a good thing to do for performance. Here are the numbers: 32 to 22 lbs (across face assumption): 1st 177.5 lbs 2nd 70.3 lbs 3rd 31.6 lbs 4th 16.1 lbs 5th 11.1 lbs 32 to 22 lbs (perimeter reduction assumption): 1st 493.4 lbs 2nd 195.5 lbs 3rd 87.7 lbs 4th 44.8 lbs 5th 30.8 lbs 32 to 11 lbs (across face assumption): 1st 372.7 lbs 2nd 147.7 lbs 3rd 66.3 lbs 4th 33.8 lbs 5th 23.3 lbs 32 to 11 lbs (perimeter reduction assumption): 1st 1036.1 lbs 2nd 410.6 lbs 3rd 184.2 lbs 4th 94.0 lbs 5th 64.8 lbs Rotational inertia is mass multiplied by the distance from the rotational axis (integrated over the surface). The effect is stronger farther away from the hub. The best is from the perimeter. Equally across the face is less effective and near the hub is the least effective. In my example, dropping 21 lbs from the perimeter is equivalent to over 1000 lbs reduction in weight in first gear. Dropping the same mass the face is equivalent to 372.7 lbs. Reducing the flywheel inertia does reduce the stored energy for start from a stop. Torque follows displacement. Little engine in big car with tall gearing needs more stored inertia at start. Big engine in little car with short gearing can get away with much less stored inertia. On the street with a lighter flywheel, you may need to use more RPM and clutch slip. On the strip, you may bog if you don't have enough excess torque at the rear tires (more traction than engine/gearing). Remember that HP is the measure of how much potential torque you can have at the rear tires via gearing. If you have enough power to overcome your traction, then a heavy flywheel is a loser. Dan Jones |
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roverman Art Gertz Winchester, CA. (3188 posts) Registered: 04/24/2009 11:02AM Main British Car: 74' Jensen Healy, 79 Huff. GT 1, 74 MGB Lotus 907,2L |
Re: aluminum flywheel worth it ?
Dan and clan, seems like a more complete picture of M.xV.will include clutch cover and disk ? Partially explains why many pure race cars use small dia., multiple disk. I suspect shift times and syncronizing loads are reduced, as well. Greatly reduced, "explosion" risk. Kennedy Engineering makes alum. covers. Perhaps there are others. Thanks for science, roverman.
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DC Townsend David Townsend Vermont (406 posts) Registered: 11/21/2007 12:22PM Main British Car: '78 B (almost done) 30-over SBF, dry sump |
Re: aluminum flywheel worth it ?
If you're going with Ford power, Gordon Levy at Levy Racing has some great flywheel/clutch/bellhousing combinations that are race car specific. I think his bread and butter trade is the Cobra and Mustang racing scene but seems to be a wonderful source for go-fast parts for the Blue Oval crowd.
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roverman Art Gertz Winchester, CA. (3188 posts) Registered: 04/24/2009 11:02AM Main British Car: 74' Jensen Healy, 79 Huff. GT 1, 74 MGB Lotus 907,2L |
Re: aluminum flywheel worth it / light ring gear ?
Update, If your putting the flywheel on a diet, don't forget a "light" ring gear, hung on that alum. flywheel. For instance, a 130 C, will weigh approx. double of a 130 T, only because the id. is 1" smaller, preventing a larger clutch bolt pattern to clear it, ie. a 10.5" clutch package. This set-up will likely go on a "stroker" motor, needing this, "Center Force" gripper. Slip tires not clutch, roverman.
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roverman Art Gertz Winchester, CA. (3188 posts) Registered: 04/24/2009 11:02AM Main British Car: 74' Jensen Healy, 79 Huff. GT 1, 74 MGB Lotus 907,2L |
Re: aluminum flywheel wo$th it ?
Wow ! $380-$700, for alum. flywheel. Ring gear $23. New insert $44,(with screws). Satisfaction from making it-priceless. roverman.
Edited 1 time(s). Last edit at 07/08/2010 08:18PM by roverman. |
roverman Art Gertz Winchester, CA. (3188 posts) Registered: 04/24/2009 11:02AM Main British Car: 74' Jensen Healy, 79 Huff. GT 1, 74 MGB Lotus 907,2L |
Re: aluminum flywheel worth it ?
Update, 10.5" steel insert with screws/nuts = 520 grams+/- . roverman
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MGB-FV8 Jacques Mathieu Alexandria, VA (299 posts) Registered: 09/11/2009 08:55PM Main British Car: 1977 MGB Small Block Ford, 331 Stroker |
Re: aluminum flywheel worth it ?
I have used an aluminum flywheel in three different cars and it seemed to have different results in each car; however, each one behaved the same at the start of each gear shift. The surge after the shift seemed softer for a split second but the quicker engine revving attribute (from the aluminum flywheel) seemed to close the time gap in between. The pros and cons are different with each car depending on engine built, vehicle weight, gearing, camshaft and a lot more. My idea of horsepower gain is through combustion efficiency and savvy rotating mass application which will always yield better MPG.
On this 331 stroker built, since I’m using a light weight rotating mass, I feel that my aluminum flywheel may not cause as much "take off" lost on start because of the extra torque generated by the stroker kit. I wish that someone would make an aluminum flywheel that would have the ability to have (removable) calibrating weights added in progression, something as simple as playing around with tire seizes. As it stands, I have no way of telling if it will benefit the car since this is a new power-train with no history to compare it against itself. I feel that the minimal advantages I could gain from it would be fuel mileage, engine braking deceleration, better clutch heat dissipation and I could easily replace the friction insert instead of losing material through the re-facing process. I'm not that smart at doing complex calculations, therefore I'll take my chances with basic rules of thumb; sometimes it's beneficial and sometimes I wish that I could get my money back, most of us have been there. Forums like this one are the heart beat for us gear-heads as we all look for proven engineering. If I'm going to be the "guinea pig" for a major modification, I feel a camaraderie’s obligation to share my findings with others. It may open debates on my findings, but it's all for the best. |
roverman Art Gertz Winchester, CA. (3188 posts) Registered: 04/24/2009 11:02AM Main British Car: 74' Jensen Healy, 79 Huff. GT 1, 74 MGB Lotus 907,2L |
Re: aluminum flywheel ,worth the weight ?
Jacques, Well put. I consider, this one, the best I know of. We are fortunate to have a skilled,"Science and Engineering Department" , by the name of Dan Jones. This alone, alows me to be less "pig" and more savy , Thanks Dan. Regarding "tuning weights", just so happens, one I'm building has that potential. Screws and nuts that secure the insert,(9.45" bc.). Nuts could be substitited for nut plates(weights), nested in a counterbore, on engine side. How much weight ? roverman.
Edited 2 time(s). Last edit at 07/26/2010 01:42PM by roverman. |