<div dir="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 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 !</div><div>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.</div><div>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. <br></div><div>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.</div><div>Very 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 just have to rely on anecdotes !</div><div>On my car the engine now shuts off pronto and no fear of the dreaded dieseling.</div><div>rg<br></div><div><br></div></div><br><div class="gmail_quote"><div dir="ltr" class="gmail_attr">On Tue, Sep 7, 2021 at 6:10 PM Michael Salter <<a href="mailto:michaelsalter@gmail.com" target="_blank">michaelsalter@gmail.com</a>> wrote:<br></div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex"><div dir="auto">Perhaps another way to look at this question is with respect tp engine power. <div dir="auto">It takes a certain amount of horsepower to accelerate a mass (car) at a certain rate. </div><div dir="auto">Taking weight off the flywheel decreases the amount of horsepower required 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.</div><div dir="auto">Sure engines with light flywheels sound racey but they aren't more powerful.</div><div dir="auto"><br></div><div dir="auto">M</div></div><br><div class="gmail_quote"><div dir="ltr" class="gmail_attr">On Tue., Sep. 7, 2021, 6:22 p.m. richard mayor, <<a href="mailto:boyracer466@gmail.com" target="_blank">boyracer466@gmail.com</a>> wrote:<br></div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex"><div dir="ltr"><div>I should add one more thing for clarification. The general rule of thumb for comparing rotational weight to other weight (sprung or unsprung) 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.</div><div>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 gear 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 out near the ring gear. Removing 3 or 4 pounds has a big effect on acceleration. <br></div></div><br><div class="gmail_quote"><div dir="ltr" class="gmail_attr">On Tue, Sep 7, 2021 at 2:24 PM Michael Salter <<a href="mailto:michaelsalter@gmail.com" rel="noreferrer" target="_blank">michaelsalter@gmail.com</a>> wrote:<br></div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex"><div dir="auto">The total mass of the flywheel is not completely relevant insofar as engine moment of inertia is concerned.<div dir="auto">What is important is the mass removed times the square of the radius, so just how much weight has been removed per se is not important. </div><div dir="auto">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.</div><div dir="auto">The rotational mass is often designed in to protect the drive train, in particular the gearbox.</div><div dir="auto">Read this: <a href="https://www.netbug.net/blogmichael/2017/01/03/austin-healey-100-crank-failures/" rel="noreferrer" target="_blank">https://www.netbug.net/blogmichael/2017/01/03/austin-healey-100-crank-failures/</a></div><div dir="auto">Thirdly lightening a flywheel in of itself has very little effect on acceleration. An engine with a lightened flywheel 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 shift 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 of fuel. (Who ever notices that their car accelerates more quickly with a half full gas tank).</div><div dir="auto"><br></div><div dir="auto">Just sayin'</div><div dir="auto"><br></div><div dir="auto">M</div></div><br><div class="gmail_quote"><div dir="ltr" class="gmail_attr">On Tue., Sep. 7, 2021, 4:17 p.m. Earl Kagna via Healeys, <<a href="mailto:healeys@autox.team.net" rel="noreferrer noreferrer" target="_blank">healeys@autox.team.net</a>> wrote:<br></div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex"><div lang="EN-US"><div><p class="MsoNormal">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 them to 24.<u></u><u></u></p><p class="MsoNormal"><u></u> <u></u></p><p class="MsoNormal">Both of my cars run just fine, no problems at all in the 20 + or so years that I’ve had them installed.<u></u><u></u></p><p class="MsoNormal"><u></u> <u></u></p><p class="MsoNormal">Earl Kagna<u></u><u></u></p><p class="MsoNormal">Victoria BC<u></u><u></u></p><p class="MsoNormal">BJ8, BT7 tri-carb<u></u><u></u></p><p class="MsoNormal"><u></u> <u></u></p><p class="MsoNormal"><u></u> <u></u></p><p class="MsoNormal"><u></u> <u></u></p><div style="border-color:rgb(225,225,225) currentcolor currentcolor;border-style:solid none none;border-width:1pt medium medium;padding:3pt 0in 0in"><p class="MsoNormal"><b>From:</b> Healeys <<a href="mailto:healeys-bounces@autox.team.net" rel="noreferrer noreferrer noreferrer" target="_blank">healeys-bounces@autox.team.net</a>> <b>On Behalf Of </b>richard mayor<br><b>Sent:</b> Tuesday, September 7, 2021 10:23 AM<br><b>To:</b> healeys <<a href="mailto:healeys@autox.team.net" rel="noreferrer noreferrer noreferrer" target="_blank">healeys@autox.team.net</a>><br><b>Subject:</b> [Healeys] Lightened flywheels<u></u><u></u></p></div><p class="MsoNormal"><u></u> <u></u></p><div><div><p class="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="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 response, I suggest removing no more than 3 pounds. <u></u><u></u></p></div><div><p class="MsoNormal"><u></u> <u></u></p></div><div><p class="MsoNormal">Richard <u></u><u></u></p></div></div></div><div id="gmail-m_-4327506918077947763gmail-m_7168537835214182875m_573075059829985210gmail-m_-5451347567706541358m_4102748135953362380m_-1299543942381278781DAB4FAD8-2DD7-40BB-A1B8-4E2AA1F9FDF2"><br>
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