BOOTLEG Gary Rosema Wisconsin (47 posts) Registered: 11/18/2013 07:26PM Main British Car: 1978 MGB Rover 3.5L |
Ideal Flywheel Weight?
I weighed my flywheel to see how much I'd have to remove to meet the Roger William's 22lb. ideal weight. I was surprised to find mine weighed only 17.4 lbs. I weighed it again to be sure, then I consider that perhaps Roger was including his clutch plate or....
Anybody have a flywheel this light? (Moderator: split this message from a thread in the classified section, renamed it, and moved it.) Edited 2 time(s). Last edit at 01/21/2014 04:51AM by BOOTLEG. |
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: Ideal Flywheel Weight?
> I weighed my flywheel to see how much I'd have to remove to meet the Roger William's 22lb. ideal weight.
> I was surprised to find mine weighed only 17.4 lbs. I weighed it again to be sure, then I consider that > perhaps Roger was including his clutch plate or.... A friend has an older BMW M5 that came with a 12 lb flywheel from the factory. The car weighs 3800 lb, has the same size engine as my TR8 (215 cubes) had, has a 264 degree cam on 110 deg center and has a 3.53 1st and 3.91 axle. It gets off the line very easily and, thanks to the IR EFI, can spin the rear tires (275/35R18) at will in first gear on dry pavement. Hooks just fine in second, though. Gary also had a Buick 215 powered Vega. It weighed about the same as the TR8, had a 3.36 axle and a 3.41 first. He lightened the 32 lb flywheel to 22 lb (mostly from the perimeter) and said the result was wonderful. He said he would have gone lighter if he could. Of course, there is a point of diminishing returns and a combination of a very light flywheel and a digital on/off type race clutch can make street driving less than pleasant. A while back I ran the numbers for switching from an iron to aluminum flywheel for my Triumph TR8 with Rover V8. 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 tire diameter) 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 circumerence 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 tire has a diameter of approximately 23.1 inches. My TR8's final drive ratio is currently 3.45:1 and first gear is 3.32:1, so one revolution of the flywheel results in the TR8 moving approximately 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 from 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 ligter 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 |
DiDueColpi Fred Key West coast - Canada (1365 posts) Registered: 05/14/2010 03:06AM Main British Car: I really thought that I'd be an action figure by now! |
Re: Ideal Flywheel Weight?
Excellent article Dan.
But don't forget to factor in the rotational mass of the engines rotating assy. Also engine stroke and # of firing impulses per revolution influence flywheel choice. Cheers Fred |
t-100 Glenn Towery (31 posts) Registered: 09/09/2009 10:55PM Main British Car: 1974 1/2 MGBGT 3.9 Rover V8 |
Re: Ideal Flywheel Weight?
For 30 years I have used a 15 lb. alu. fly. to a cut down Rover/GM fly to 20-22 lbs. more to take the BIG BANG that a heavy fly can/will put on the rear axel. At one time I had a 35lb fly & I would hear the tires when I would go into 4rh. With the light fly I have to work to hear the tires in 2nd. Hits RPM faster comes out of the hole real good (even when pulling a trailer) Start it up & it sits at a smooth 600 RPM. Just turned 599,000 miles on my 74.5 GT with a Rover 3.9 & & a 3.07 C rear & I have only twisted 2 rear axels.
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DiDueColpi Fred Key West coast - Canada (1365 posts) Registered: 05/14/2010 03:06AM Main British Car: I really thought that I'd be an action figure by now! |
Re: Ideal Flywheel Weight?
Gary,
I didn't have the picture available earlier. You have a flex plate for an automatic trans pictured. Absolutely no relationship to a manual trans flywheel. Cheers Fred |
Dan B Dan Blackwood South Charleston, WV (1007 posts) Registered: 11/06/2007 01:55PM Main British Car: 1966 TR4A, 1980 TR7 Multiport EFI MegaSquirt on the TR4A. Lexus V8 pl |
Re: Ideal Flywheel Weight?
In October when we were building motor mounts and test fitting the Lexus 1uz into my TR7, we weighed the flywheel I got with the craigslist package I bought. It weighs 16 pounds.
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ex-tyke Graham Creswick Chatham, Ontario, Canada (1165 posts) Registered: 10/25/2007 11:17AM Main British Car: 1976 MGB Ford 302 |
Re: Ideal Flywheel Weight?
Just weighed the Fidenza aluminum flywheel from my 302 (as it happens to be disassembled) at 12 lb.
Interesting to note that when Curtis drove my car in Omaha last year, he immediately recognized that I had an aluminum flywheel installed - so the engine response difference from a heavier flywheel must be evident. |
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74ls1tr6 Calvin Grannis Elk Grove,CA (1151 posts) Registered: 11/10/2007 10:05AM Main British Car: 74 TR6 / 71 MGB GT TR6/Ls1 71 MGB GT/Ls1 |
Re: Ideal Flywheel Weight?
I sure like my 12lbs aluminum flywheel. The rpm comes up very fast and goes down very fast also. It is great for autocross.
I will use a 12lbs flywheel in the GT build too! Our cars seem to be light enough for them. Edited 1 time(s). Last edit at 01/21/2014 03:30PM by 74ls1tr6. |
kstevusa kelly stevenson Southern Middle Tennessee (985 posts) Registered: 10/25/2007 09:37AM Main British Car: 2003 Jaguar XK8 Coupe 4.2L DOHC/ VVT / 6sp. AT |
Re: Ideal Flywheel Weight?
WHAT? Do the still make steel flywheels? :-) I am happy with the Ram installed back in 04.
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BlownMGB-V8 Jim Blackwood 9406 Gunpowder Rd., Florence, KY 41042 (6468 posts) Registered: 10/23/2007 12:59PM Main British Car: 1971 MGB Blown,Injected,Intercooled Buick 340/AA80E/JagIRS |
Re: Ideal Flywheel Weight?
That Lexus flywheel was a smaller diameter too. Same effect as being lighter. I think some more weight could probably be taken off at the rim as well.
Another thing to remember is that the pressure plate is half the rotating weight with a fairly typical figure of 18 lbs for one with a ductile iron pressure ring. All of the major manufacturers make them with aluminum pressure rings, dropping that number to about 12 lbs. So with the right choice of parts you can easily go from nearly 50 lbs down to around 25 or less. That's going to make a big difference in the responsiveness of the engine, and with the displacement we have there's no need whatsoever for more. Jim |
88v8 Ivor Duarte Gloucestershire UK (1041 posts) Registered: 02/11/2010 04:29AM Main British Car: 1974 Land Rover Lightweight V8 |
Re: Ideal Flywheel Weight?
Remarkable post by Dan.
Worth remembering that a positive or negative effect on acceleration is also seen when fitting larger/smaller tyres. And likewise an effect on braking. Ivor |
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: Ideal Flywheel Weight?
Yea aluminum flywheels ! Now, has anyone measured how thick is the aluminum, under the steel insert ?? Thanks, Art.
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Re: Ideal Flywheel Weight?
D&D sells approx. 10lb aluminum flywheels using one it with my 4.6 in a less than 2000lb mgb many years ago used a 10lb wheel with a 289 stroked to 327 inches with a 2.20 t10 4.88 narrowed 57 Pontiac rear 1200lbs front 1000lbs rear weight all in a 100/6 2 seat healey never a problem with getting out of its own way light wheels grab rpms so easily
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BlownMGB-V8 Jim Blackwood 9406 Gunpowder Rd., Florence, KY 41042 (6468 posts) Registered: 10/23/2007 12:59PM Main British Car: 1971 MGB Blown,Injected,Intercooled Buick 340/AA80E/JagIRS |
Re: Ideal Flywheel Weight?
Think about bike engines. The flywheel on a 500+ lb bike is made as light as possible, using a multi-disc clutch. Most of the flywheel effect comes from the crankshaft. We all know how quickly a bike engine will rev up and throttle down.
Now scale that up by a factor of 4 or 5 to the V8 MGB. To have parity we would still have to use a triple disc small diameter clutch with an ultra-light pressure plate and a skeleton flywheel, with a total weight of well under 20 lbs, maybe close to 10 lbs combined including the flywheel, pressure plate and clutch package, all shrunk down into the 6-8" diameter range. The crankshaft alone weighs 60 lbs, but with the small diameter that would get us close. The torque for getting off the line would still be quite adequate and the throttle response would be exceptional. So assuming you don't want to go sourcing exotic racing parts to get the weight down (although honestly I think some judicious shopping in the racecarparts forums could find what you'd need at fair prices) the reasonable approach would seem to be to use the lightest flywheel available. Then use the smallest diameter clutch that will handle the torque, and finally, a matching pressure plate. But not just any pressure plate, since average weight for those can easily hit 18 lbs. No, if you shop around you will find PPs with an aluminum pressure ring that will weigh about half of that. Maybe even some with an aluminum hat as well. There can be no doubt that if you drop 20 or 30 lbs off the rotating assembly you will feel the difference immediately. Now, are you driving twisty roads, or drag racing? If drag racing maybe you don't want to get rid of all the rotating weight, but if driving the twisties, lightning response and light speed transitions are your new best friends and any rotating weight you can eliminate will make you faster. Jim |
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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: Ideal Flywheel Weight? Thickness please ?
Still fishing for thickness need, under the steel insert. I'm ready to make chips and I don't want to guess . Anybody ? Thanks, roverman.
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DiDueColpi Fred Key West coast - Canada (1365 posts) Registered: 05/14/2010 03:06AM Main British Car: I really thought that I'd be an action figure by now! |
Re: Ideal Flywheel Weight?
I have 3 aluminium flywheels from three different manufacturers here Art.
Two of them measure at 0.575" under the insert. The remaining one is 0.550" From the looks of it I wouldn't go any thinner. Also all three have nutted screws for the insert. No threads into the aluminium anywhere. FYI the thinnest mounting hub is 0.750" Cheers Fred |
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: Ideal Flywheel Weight?
Thanks Fred, just what I needed. Any suggestions for a lightweight 9.5" cover ? My Kennedy unit is quite heavy,(iron/steel). Onward, art.
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Re: Ideal Flywheel Weight?
I have a McLeod double plated clutch,with the fingers,on a steel flywheel,
The metal plate between the clutch plates,can this be lightened ? As it is,the clutch and flywheel are quite heavy,if anybody is interested,I'll weigh it Bryan |
Nexxussian Erik Johnson Alaska (62 posts) Registered: 04/20/2015 10:32PM Main British Car: 1974, MGB, Citroen Color Rover V8 |
Re: Ideal Flywheel Weight?
Brian, I for one am interested in what your McCleod setup weighs, especially with component weights and dimensions (diameters, tape measure is good enough).
As to "can you lighten?" the floater, McCleod are the ones to ask, if it can be safely lightened, they likely sell one that already is. Awaiting details on what monstrous engine you have to require a twin disc. :) Just out of curiosity, do you know if McCleod sells a lightweight version of yours with an aluminum flywheel? |