56 replies to this topic

[racingbob]

just put it on dont take any advice on a BACK TO BACK test i done

do you have any figures or anything to prove what you're saying?

yes me, feel of the drive, car had no real go to it
raced minis for 8 years

[adam davies]

Woahhh , lets calm this down a bit. I didn't mean to start any arguments. At the moment I still think I'll get one no disrespect to you racing bob. I appreciate the advice you have given me. If I fit one to my car I'll say whether I think it's a good idea to install one or not

[racingbob]

Woahhh , lets calm this down a bit. I didn't mean to start any arguments. At the moment I still think I'll get one no disrespect to you racing bob. I appreciate the advice you have given me. If I fit one to my car I'll say whether I think it's a good idea to install one or not

just to say you know you will have to compare

your set up with standard and then the lightened one

or you wont know the difference in a back to back test

its torque you want for a road car

make a decision what rev range you will be using

TORQUE IS WHAT ACCELERATION IS ALL ABOUT
TORQUE ACCELERATES THE CAR

[skoughi]

Surely it's all down to momentum. With a standard weight flywheel it will take power to get it spinning but it'll take an equal if not more effort to stop it so therefore thats where the torque comes from as there is more mass on the move. So if the engine is a big v8 say then it'll have bags of torque as there is a larger mass on the move whereas a bike engine with low mass, moving parts, has low torque but maybe high bhp and an ability to spin up quickly. So with a very light flywheel then there will be less mass spining at low revs and maybe a tendency to stall so you'll have to rev it a lot to get it moving. On my wreck of an engine it has a verto clutch, from what I can make out is heavy, but I'm thinking to leave it on as my car will hopefully be a daily driver so I'll be using it at lower revs. Plus fuel is bloody expensive up here and I'm tight with the cash!

[oltonlad]

Woahhh , lets calm this down a bit. I didn't mean to start any arguments. At the moment I still think I'll get one no disrespect to you racing bob. I appreciate the advice you have given me. If I fit one to my car I'll say whether I think it's a good idea to install one or not

so what was the point of this thread then?..............to ask peoples advice and then to completely ignore what anyone says..........seems a bit pointless to me!

[adam davies]

Woahhh , lets calm this down a bit. I didn't mean to start any arguments. At the moment I still think I'll get one no disrespect to you racing bob. I appreciate the advice you have given me. If I fit one to my car I'll say whether I think it's a good idea to install one or not

so what was the point of this thread then?..............to ask peoples advice and then to completely ignore what anyone says..........seems a bit pointless to me!

Not really. I took in everyone's opinions and the majority of members have said that a lightened flywheel is a good idea. Therefore I'll go with majority and see how it turns out for me

[MiniHead95]

 

 

Woahhh , lets calm this down a bit. I didn't mean to start any arguments. At the moment I still think I'll get one no disrespect to you racing bob. I appreciate the advice you have given me. If I fit one to my car I'll say whether I think it's a good idea to install one or not

so what was the point of this thread then?..............to ask peoples advice and then to completely ignore what anyone says..........seems a bit pointless to me!

 

Not really. I took in everyone's opinions and the majority of members have said that a lightened flywheel is a good idea. Therefore I'll go with majority and see how it turns out for me

 

 Heya  Did you go for a lightened flywheel in the end? What was it like ? 

[Dr s]

Regardless of flywheel the engine makes the same power. That's a function of valve size lift etc etc.
A heavy flywheel stores power this makes the engine feels torquier in gear. You get that engine power + stored fly power. However that flywheel had to get power from somewhere. Which was slowing down the acceleration of the car until the fly had spun up.

So a heavy fly smooths things out costing power until the fly is spinning. A light fly doesn't smooth it out but doesn't take much spinning up. Try blipping the throttle between the two types. Light fly rips up the rev range compares to normal.

I like my light fly for round the lanes

[Captain Mainwaring]

You'll have less low down torque, especially with the 276.
Its is good for acceleration though.

 

 

Haaaa? Why? 

Oh and unless the car has a very high power to weight ratio then a lightened flywheel won't make any difference to acceleration, and even then, in the low gears.

[Captain Mainwaring]

Surely it's all down to momentum. With a standard weight flywheel it will take power to get it spinning but it'll take an equal if not more effort to stop it so therefore thats where the torque comes from as there is more mass on the move. So if the engine is a big v8 say then it'll have bags of torque as there is a larger mass on the move whereas a bike engine with low mass, moving parts, has low torque but maybe high bhp and an ability to spin up quickly. So with a very light flywheel then there will be less mass spining at low revs and maybe a tendency to stall so you'll have to rev it a lot to get it moving. On my wreck of an engine it has a verto clutch, from what I can make out is heavy, but I'm thinking to leave it on as my car will hopefully be a daily driver so I'll be using it at lower revs. Plus fuel is bloody expensive up here and I'm tight with the cash!

 

 

There is an element of truth here - yes, an engine that can rev up to 13,000 rpm from idle in a split second like a big bike engine (hehehe my CBX) will benefit from a lightened flywheel, and an improvement will be noticed in the lower gears only - you're also right in stating that an engine that has a nice torque curve will be less effected by flywheel weight.

Also correct that the engine will be more forgiving for rough clutch use at low speed and throttle openings.

 

Flywheel weight isn't the be all and end all - it's all about weight x diameter. Google polar moment of inertia.

[Captain Mainwaring]

how would your car be slower it doesnt change ratios or any thing with the lightened flywheel? It will just spin up faster, i havent done testing but am speaking from what i have in my motor, you will loose abit of torque but i think you will be fine

 

It will do with the clutch dipped, but in gear, particularly the higher gears then the only effect will be in your pocket and bragging rights in the pub.

You certainly won't lose any torque - torque is nothing until you do work with it over a time increment then it becomes power - 

Edited by Captain Mainwaring, 08 May 2014 - 07:34 AM.

[Captain Mainwaring]

Let's knock a few myths on the head.

Take a 300mm flywheel with uniform density spinning at 5000 rpm, the total stored energy in slowing the flywheel from 5000 rpm to stop is around 15000 joules....

Nahh, power = rpm x ftlbs torque/5252 and 1hp is 746 joules/second sooo

 

if we stop the flywheel dead in 1 second then....

 

15000/746 = about 20hp expended in 1 second

 

using a constant torque of 5250/5000 = ftlbs/power

or 1.05 = ftlbs/power or 20*1.05 = 21 ftlbs of torque available at 5000 rpm

 

So there is your maths - you need 20 odd horse power 21 ftlbs of torque to accelerate a 10kg flywheel (sorry for the mixed units) up to 5000 rpm in 1 second.