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tips, technology, tools and techniques related to vehicle driveline components

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BOOTLEG
Gary Rosema
Wisconsin
(47 posts)

Registered:
11/18/2013 07:26PM

Main British Car:
1978 MGB Rover 3.5L

Ideal Flywheel Weight?
Posted by: BOOTLEG
Date: January 19, 2014 04:22PM

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.)
flywheel.JPG



Edited 2 time(s). Last edit at 01/21/2014 04:51AM by BOOTLEG.


Dan Jones
Dan Jones
St. Louis, Missouri
(268 posts)

Registered:
07/21/2008 03:32PM

Main British Car:
1980 Triumph TR8 3.5L Rover V8

Re: Ideal Flywheel Weight?
Posted by: Dan Jones
Date: January 20, 2014 01:26PM

> 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
(1259 posts)

Registered:
05/14/2010 03:06AM

Main British Car:
What if the Hokey Pokey really is what it's all about?

authors avatar
Re: Ideal Flywheel Weight?
Posted by: DiDueColpi
Date: January 20, 2014 05:08PM

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

(30 posts)

Registered:
09/09/2009 10:55PM

Main British Car:
1974 1/2 MGBGT 3.9 Rover V8

Re: Ideal Flywheel Weight?
Posted by: t-100
Date: January 20, 2014 09:30PM

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.


DiDueColpi
Fred Key
West coast - Canada
(1259 posts)

Registered:
05/14/2010 03:06AM

Main British Car:
What if the Hokey Pokey really is what it's all about?

authors avatar
Re: Ideal Flywheel Weight?
Posted by: DiDueColpi
Date: January 21, 2014 04:59AM

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
(967 posts)

Registered:
11/06/2007 01:55PM

Main British Car:
1966 TR4A, 1980 TR7 Multiport EFI MegaSquirt on the TR4A. Lexus V8 pl

authors avatar
Re: Ideal Flywheel Weight?
Posted by: Dan B
Date: January 21, 2014 08:38AM

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.


ex-tyke
Graham Creswick
Chatham, Ontario, Canada
(1066 posts)

Registered:
10/25/2007 11:17AM

Main British Car:
1976 MGB Ford 302

authors avatar
Re: Ideal Flywheel Weight?
Posted by: ex-tyke
Date: January 21, 2014 01:40PM

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.

302 flywheel.jpg



74ls1tr6
Calvin Grannis
Elk Grove,CA
(1145 posts)

Registered:
11/10/2007 10:05AM

Main British Car:
74 TR6 / 71 MGB GT TR6/Ls1 71 MGB GT/Ls1

authors avatar
Re: Ideal Flywheel Weight?
Posted by: 74ls1tr6
Date: January 21, 2014 03:25PM

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
(914 posts)

Registered:
10/25/2007 09:37AM

Main British Car:
2003 Jaguar XK8 Coupe 4.2L DOHC/ VVT / 6sp. AT

authors avatar
Re: Ideal Flywheel Weight?
Posted by: kstevusa
Date: January 21, 2014 04:15PM

WHAT? Do the still make steel flywheels? :-) I am happy with the Ram installed back in 04.


MGBV8
Carl Floyd
Kingsport, TN
(3680 posts)

Registered:
10/23/2007 11:32PM

Main British Car:
79 MGB, Buick 215

authors avatar
Re: Ideal Flywheel Weight?
Posted by: MGBV8
Date: January 21, 2014 06:14PM

Y'all are killin' me. I'm ready to yank my flywheel back out & carve on it some more!


BlownMGB-V8
Jim Blackwood
9406 Gunpowder Rd., Florence, KY 41042
(5779 posts)

Registered:
10/23/2007 12:59PM

Main British Car:
1971 MGB Blown,Injected,Intercooled Buick 340/AA80E/JagIRS

authors avatar
Re: Ideal Flywheel Weight?
Posted by: BlownMGB-V8
Date: January 22, 2014 05:36PM

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
(647 posts)

Registered:
02/11/2010 04:29AM

Main British Car:
1974 Land Rover Lightweight V8

Re: Ideal Flywheel Weight?
Posted by: 88v8
Date: January 26, 2014 04:31AM

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.
(2975 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?
Posted by: roverman
Date: September 28, 2015 07:22PM

Yea aluminum flywheels ! Now, has anyone measured how thick is the aluminum, under the steel insert ?? Thanks, Art.


40indianss
don foote

(46 posts)

Registered:
08/01/2013 04:35PM

Main British Car:


Re: Ideal Flywheel Weight?
Posted by: 40indianss
Date: September 29, 2015 12:25AM

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


BlownMGB-V8
Jim Blackwood
9406 Gunpowder Rd., Florence, KY 41042
(5779 posts)

Registered:
10/23/2007 12:59PM

Main British Car:
1971 MGB Blown,Injected,Intercooled Buick 340/AA80E/JagIRS

authors avatar
Re: Ideal Flywheel Weight?
Posted by: BlownMGB-V8
Date: September 29, 2015 12:03PM

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



roverman
Art Gertz
Winchester, CA.
(2975 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 ?
Posted by: roverman
Date: September 29, 2015 04:48PM

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.


DiDueColpi
Fred Key
West coast - Canada
(1259 posts)

Registered:
05/14/2010 03:06AM

Main British Car:
What if the Hokey Pokey really is what it's all about?

authors avatar
Re: Ideal Flywheel Weight?
Posted by: DiDueColpi
Date: September 29, 2015 05:43PM

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.
(2975 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?
Posted by: roverman
Date: September 30, 2015 11:53AM

Thanks Fred, just what I needed. Any suggestions for a lightweight 9.5" cover ? My Kennedy unit is quite heavy,(iron/steel). Onward, art.


Blown v8
Bryan Phipps

(49 posts)

Registered:
03/10/2013 04:52PM

Main British Car:


Re: Ideal Flywheel Weight?
Posted by: Blown v8
Date: October 21, 2015 11:41AM

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?
Posted by: Nexxussian
Date: October 21, 2015 07:09PM

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?
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