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I am with M on this one. There is no doubt that where the metal mass is
removed is important. The moment of inertia is proportional to the square
of the radius. I removed 6.8 lbs from my BJ8 one mostly around the
periphery. This is a 23% reduction in weight but must be a higher %
reduction in inertia - perhaps 30% - who knows !
Next issue being discussed is the potential improvements (if any) with this
mod. No doubt when in neutral the engine will accelerate faster as less
inertia to get moving. Total inertia is engine plus flywheel (ignoring
drive train) inertias. So the relevant fact is the CHANGE/REDUCTION in
total inertia. I have no idea what the engine inertia is.
When the engine torque accelerates the flywheel, and the engine mechanical
components, energy is added to the flywheel. This is proportional to change
in angular velocity (RPM) and Inertia.
So, with a lightened flywheel, less engine torque (energy) is used to
accelerate the flywheel to a new speed and thus more energy (engine output)
is available to accelerate the car.
Very difficult to estimate. - may or may not be insignificant.
So until someone does some bench tests to measure these inertias we will
just have to rely on anecdotes !
On my car the engine now shuts off pronto and no fear of the dreaded
dieseling.
rg
On Tue, Sep 7, 2021 at 6:10 PM Michael Salter <michaelsalter@gmail.com>
wrote:
> Perhaps another way to look at this question is with respect tp engine
> power.
> It takes a certain amount of horsepower to accelerate a mass (car) at a
> certain rate.
> Taking weight off the flywheel decreases the amount of horsepower require=
d
> to accelerate the car and for that matter the engine's speed of rotation
> but the change in the amount of horsepower required is very small.
> Sure engines with light flywheels sound racey but they aren't more
> powerful.
>
> M
>
> On Tue., Sep. 7, 2021, 6:22 p.m. richard mayor, <boyracer466@gmail.com>
> wrote:
>
>> I should add one more thing for clarification. The general rule of
>> thumb for comparing rotational weight to other weight (sprung or unsprun=
g)
>> is 10 to 1. So, using that rule, 5 pounds of weight removed from
>> rotational mass would equal 50 pounds of fuel. As Michael pointed out.
>> But, it doesn't alway work out that way. If you removed one pound from
>> the flywheel in the area where the bolt pattern is then the 10 to 1 rule
>> may apply. But if you remove one pound of material out near the ring ge=
ar
>> then it is more like a factor of 30 to 1. Any rotational weight removed
>> further away from its axis will have a much greater effect. And when you
>> lighten a Healey flywheel the place where the meat comes off first is ou=
t
>> near the ring gear. Removing 3 or 4 pounds has a big effect on
>> acceleration.
>>
>> On Tue, Sep 7, 2021 at 2:24 PM Michael Salter <michaelsalter@gmail.com>
>> wrote:
>>
>>> The total mass of the flywheel is not completely relevant insofar as
>>> engine moment of inertia is concerned.
>>> What is important is the mass removed times the square of the radius, s=
o
>>> just how much weight has been removed per se is not important.
>>> Secondly removing rotational inertia is not always the best thing to do=
,
>>> if it was you can be assured that manufacturers would be all over it as=
a
>>> way to save money.
>>> The rotational mass is often designed in to protect the drive train, in
>>> particular the gearbox.
>>> Read this:
>>> https://www.netbug.net/blogmichael/2017/01/03/austin-healey-100-crank-f=
ailures/
>>> Thirdly lightening a flywheel in of itself has very little effect on
>>> acceleration. An engine with a lightened flywheel may accelerate to 60=
00
>>> RPM 1 - 2 seconds more quickly but that doesn't necessarily equate to 1=
-2
>>> seconds faster to 60 MPH. You may be able to shift marginally faster if=
the
>>> gearbox can stand the extra loads and the 4 to 5 pounds off vehicle wei=
ght
>>> is really only the equivalent of half a tank of fuel. (Who ever notices
>>> that their car accelerates more quickly with a half full gas tank).
>>>
>>> Just sayin'
>>>
>>> M
>>>
>>> On Tue., Sep. 7, 2021, 4:17 p.m. Earl Kagna via Healeys, <
>>> healeys@autox.team.net> wrote:
>>>
>>>> I have Bill Bolton lightened flywheels in both my Healeys. According
>>>> to Kent Lambert, who took over Bills Healey business awhile back, the =
stock
>>>> weight (6 cyl) is 28.5 pounds, and Bills machining program reduced the=
m to
>>>> 24.
>>>>
>>>>
>>>>
>>>> Both of my cars run just fine, no problems at all in the 20 + or so
>>>> years that I=E2=80=99ve had them installed.
>>>>
>>>>
>>>>
>>>> Earl Kagna
>>>>
>>>> Victoria BC
>>>>
>>>> BJ8, BT7 tri-carb
>>>>
>>>>
>>>>
>>>>
>>>>
>>>>
>>>>
>>>> *From:* Healeys <healeys-bounces@autox.team.net> *On Behalf Of *richar=
d
>>>> mayor
>>>> *Sent:* Tuesday, September 7, 2021 10:23 AM
>>>> *To:* healeys <healeys@autox.team.net>
>>>> *Subject:* [Healeys] Lightened flywheels
>>>>
>>>>
>>>>
>>>> 6 cylinder flywheels vary slightly but are all generally in the 29
>>>> pound range. Very aggressive machine work can get the weight down to t=
he
>>>> 22-23 pound range.
>>>>
>>>> How much weight you take off will affect your driving style. To
>>>> maintain the feel of a stock Healey while still improving the engines
>>>> response, I suggest removing no more than 3 pounds.
>>>>
>>>>
>>>>
>>>> Richard
>>>>
>>>>
>>>> <https://www.avast.com/sig-email?utm_medium=3Demail&utm_source=3Dlink&=
utm_campaign=3Dsig-email&utm_content=3Demailclient> Virus-free.
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--000000000000256e9905cb7f2fb0
Content-Transfer-Encoding: quoted-printable
<div dir=3D"ltr"><div>I am with M on this one. There is no doubt that where=
the metal mass is removed is important. The moment of inertia is proportio=
nal to the square of the radius. I removed 6.8 lbs from my BJ8 one mostly a=
round the periphery. This is a 23% reduction in weight but must be a higher=
% reduction in inertia - perhaps 30% - who knows !</div><div>Next issue be=
ing discussed is the potential improvements (if any) with this mod. No doub=
t=C2=A0 when in neutral the engine will accelerate faster as less inertia t=
o get moving. Total inertia is engine plus flywheel (ignoring drive train) =
inertias. So the relevant fact is the CHANGE/REDUCTION in total inertia. I =
have no idea what the engine inertia is.</div><div>When the engine torque a=
ccelerates the flywheel, and the engine mechanical components, energy is ad=
ded to the flywheel. This is proportional to change in angular velocity (RP=
M) and Inertia. <br></div><div>So, with a lightened flywheel, less engine t=
orque (energy) is used to accelerate the flywheel to a new speed and thus m=
ore energy (engine output) is available to accelerate the car.</div><div>Ve=
ry difficult to estimate. - may or may not be insignificant. <br></div><div=
>So until someone does some bench tests to measure these inertias we will j=
ust have to rely on anecdotes !</div><div>On my car the engine now shuts of=
f pronto and no fear of the dreaded dieseling.</div><div>rg<br></div><div><=
br></div></div><br><div class=3D"gmail_quote"><div dir=3D"ltr" class=3D"gma=
il_attr">On Tue, Sep 7, 2021 at 6:10 PM Michael Salter <<a href=3D"mailt=
o:michaelsalter@gmail.com" target=3D"_blank">michaelsalter@gmail.com</a>>=
; wrote:<br></div><blockquote class=3D"gmail_quote" style=3D"margin:0px 0px=
0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex"><div di=
r=3D"auto">Perhaps another way to look at this question is with respect tp =
engine power.=C2=A0<div dir=3D"auto">It takes a certain amount of horsepowe=
r to accelerate a mass (car) at a certain rate.=C2=A0</div><div dir=3D"auto=
">Taking weight off the flywheel decreases the amount of horsepower require=
d to accelerate the car and for that matter the engine's speed of rotat=
ion but the change in the amount of horsepower required is very small.</div=
><div dir=3D"auto">Sure engines with light flywheels sound racey but they a=
ren't more powerful.</div><div dir=3D"auto"><br></div><div dir=3D"auto"=
>M</div></div><br><div class=3D"gmail_quote"><div dir=3D"ltr" class=3D"gmai=
l_attr">On Tue., Sep. 7, 2021, 6:22 p.m. richard mayor, <<a href=3D"mail=
to:boyracer466@gmail.com" target=3D"_blank">boyracer466@gmail.com</a>> w=
rote:<br></div><blockquote class=3D"gmail_quote" style=3D"margin:0px 0px 0p=
x 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex"><div dir=
=3D"ltr"><div>I should add=C2=A0 one more thing for clarification.=C2=A0 Th=
e general rule of thumb for comparing rotational weight to other weight (sp=
rung or unsprung) is 10 to 1.=C2=A0 So, using that rule, 5 pounds of weight=
removed from rotational mass would equal 50 pounds of fuel. As Michael poi=
nted out.</div><div>But, it doesn't alway work out that way.=C2=A0 If y=
ou removed one pound from the flywheel in the area where the bolt pattern i=
s then the 10 to 1 rule may apply.=C2=A0 But if you remove one pound of mat=
erial out near the ring gear then it is more like a factor of 30 to 1.=C2=
=A0 Any rotational weight removed further away from its axis will have a mu=
ch greater effect. And when you lighten a Healey flywheel the place where t=
he meat comes off first is out near the ring gear.=C2=A0 Removing 3 or 4 po=
unds has a big effect on acceleration.=C2=A0 <br></div></div><br><div class=
=3D"gmail_quote"><div dir=3D"ltr" class=3D"gmail_attr">On Tue, Sep 7, 2021 =
at 2:24 PM Michael Salter <<a href=3D"mailto:michaelsalter@gmail.com"; re=
l=3D"noreferrer" target=3D"_blank">michaelsalter@gmail.com</a>> wrote:<b=
r></div><blockquote class=3D"gmail_quote" style=3D"margin:0px 0px 0px 0.8ex=
;border-left:1px solid rgb(204,204,204);padding-left:1ex"><div dir=3D"auto"=
>The total mass of the flywheel is not completely relevant insofar as engin=
e moment of inertia is concerned.<div dir=3D"auto">What is important is the=
mass removed times the square of the radius, so just how much weight has b=
een removed per se is not important.=C2=A0</div><div dir=3D"auto">Secondly =
removing rotational inertia is not always the best thing to do, if it was y=
ou can be assured that manufacturers would be all over it as a way to save =
money.</div><div dir=3D"auto">The rotational mass is often designed in to p=
rotect the drive train, in particular the gearbox.</div><div dir=3D"auto">R=
ead this:=C2=A0 <a href=3D"https://www.netbug.net/blogmichael/2017/01/03/au=
stin-healey-100-crank-failures/" rel=3D"noreferrer" target=3D"_blank">https=
://www.netbug.net/blogmichael/2017/01/03/austin-healey-100-crank-failures/<=
/a></div><div dir=3D"auto">Thirdly lightening a flywheel in of itself has v=
ery little effect on acceleration.=C2=A0 An engine with a lightened flywhee=
l may accelerate to 6000 RPM 1 - 2 seconds more quickly but that doesn'=
t necessarily equate to 1-2 seconds faster to 60 MPH. You may be able to sh=
ift marginally faster if the gearbox can stand the extra loads and the 4 to=
5 pounds off vehicle weight is really only the equivalent of half a tank o=
f fuel. (Who ever notices that their car accelerates more quickly with a ha=
lf full gas tank).</div><div dir=3D"auto"><br></div><div dir=3D"auto">Just =
sayin'</div><div dir=3D"auto"><br></div><div dir=3D"auto">M</div></div>=
<br><div class=3D"gmail_quote"><div dir=3D"ltr" class=3D"gmail_attr">On Tue=
., Sep. 7, 2021, 4:17 p.m. Earl Kagna via Healeys, <<a href=3D"mailto:he=
aleys@autox.team.net" rel=3D"noreferrer noreferrer" target=3D"_blank">heale=
ys@autox.team.net</a>> wrote:<br></div><blockquote class=3D"gmail_quote"=
style=3D"margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);p=
adding-left:1ex"><div lang=3D"EN-US"><div><p class=3D"MsoNormal">I have Bil=
l Bolton lightened flywheels in both my Healeys.=C2=A0 According to Kent La=
mbert, who took over Bills Healey business awhile back, the stock weight (6=
cyl) is 28.5 pounds, and Bills machining program reduced them to 24.<u></u=
><u></u></p><p class=3D"MsoNormal"><u></u>=C2=A0<u></u></p><p class=3D"MsoN=
ormal">Both of my cars run just fine, no problems at all in the 20 + or so =
years that I=E2=80=99ve had them installed.<u></u><u></u></p><p class=3D"Ms=
oNormal"><u></u>=C2=A0<u></u></p><p class=3D"MsoNormal">Earl Kagna<u></u><u=
></u></p><p class=3D"MsoNormal">Victoria BC<u></u><u></u></p><p class=3D"Ms=
oNormal">BJ8, BT7 tri-carb<u></u><u></u></p><p class=3D"MsoNormal"><u></u>=
=C2=A0<u></u></p><p class=3D"MsoNormal"><u></u>=C2=A0<u></u></p><p class=3D=
"MsoNormal"><u></u>=C2=A0<u></u></p><div style=3D"border-color:rgb(225,225,=
225) currentcolor currentcolor;border-style:solid none none;border-width:1p=
t medium medium;padding:3pt 0in 0in"><p class=3D"MsoNormal"><b>From:</b> He=
aleys <<a href=3D"mailto:healeys-bounces@autox.team.net"; rel=3D"noreferr=
er noreferrer noreferrer" target=3D"_blank">healeys-bounces@autox.team.net<=
/a>> <b>On Behalf Of </b>richard mayor<br><b>Sent:</b> Tuesday, Septembe=
r 7, 2021 10:23 AM<br><b>To:</b> healeys <<a href=3D"mailto:healeys@auto=
x.team.net" rel=3D"noreferrer noreferrer noreferrer" target=3D"_blank">heal=
eys@autox.team.net</a>><br><b>Subject:</b> [Healeys] Lightened flywheels=
<u></u><u></u></p></div><p class=3D"MsoNormal"><u></u>=C2=A0<u></u></p><div=
><div><p class=3D"MsoNormal">6 cylinder flywheels vary slightly but are all=
generally in the 29 pound range. Very aggressive machine work can get the =
weight down to the 22-23 pound range. <u></u><u></u></p></div><div><p class=
=3D"MsoNormal">How much weight you take off will affect your driving style.=
To maintain the feel of a stock Healey while still improving the engines r=
esponse, I suggest removing no more than 3 pounds. <u></u><u></u></p></div>=
<div><p class=3D"MsoNormal"><u></u>=C2=A0<u></u></p></div><div><p class=3D"=
MsoNormal">Richard =C2=A0 <u></u><u></u></p></div></div></div><div id=3D"gm=
ail-m_-4327506918077947763gmail-m_7168537835214182875m_573075059829985210gm=
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