v8 fly wheel

v8 fly wheel

Author
Discussion

tcpc

Original Poster:

166 posts

226 months

Friday 3rd October 2003
quotequote all
could some one tell me what the beneifit or down side off having a aliminiun or lightend fly wheel on a 350i v8,

i have got to have the gear box out next week for some repaires so this could be the idea time to change the fly wheel

look forward to anyones though on this


Thankyou

Tony

p.s sorry about the spellings

jmorgan

36,010 posts

252 months

Friday 3rd October 2003
quotequote all
Had mine lightened on the rebuild. Told it adds (?) less mass so quicker on the acceleration. But have to careful on how much it is lightened as too light it can fracture and break, not nice.

Am I right? Standing by for the shoot down


>> Edited by jmorgan on Friday 3rd October 21:43

joospeed

4,473 posts

246 months

Saturday 4th October 2003
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you're dead right. because the torque multiplication of the gearbox, in a low gear your engine effectively "sees" a lower mass car than you actually have, this means that
1) any weight you save on the car has more effect in a low gear than a high gear and
2) because the flywheel requires effort to actually accelerate it through the rev range lightening it helps acceleration because it then becomes a significant proportion of the total mass being accelerated.

You're supposed to have the whole crank and flywheel and clutch assembly balanced, but TVR dealers swap flywheels around all the time with no ill-effects. Sometimes I wonder just how critical engine balancing is on engine life (yes it'l make it smoother, but will it last significantly longer if it's all balanced together, enough to justify stripping the engine and rebuilding?). Certainly there's alot of V8Ss out there that had to have flyhweels swapped becasue of a machining issue that don't seem to be affected, mines got 92k on it and was one of those affected!! it's turbine smooth too. Early cerberas have the flywheel changed on the clutch upgrade package too. Do it I say

gdr

571 posts

228 months

Saturday 4th October 2003
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joospeed said:
in a low gear your engine effectively "sees" a lower mass car than you actually have


Hmm, not sure if this strictly complies with laws of physics, acceleration = force/mass. Force is equivalent to torque at wheel and g/box effectively multiplies the torque available from engine. So in theory cut the car weight by half and you double the acceleration in any gear.
But the lighter flywheel does reduce overall mass of the car and lets the engine spin up faster. However the flywheel is a device to store the energy of each explosion (4 per rev in a V8) and smooth it out, especially important at low rpm - too light will make the engine unpleasant on the road.

MGBV8

160 posts

224 months

Saturday 4th October 2003
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joospeed

4,473 posts

246 months

Saturday 4th October 2003
quotequote all
gdr said:

joospeed said:
in a low gear your engine effectively "sees" a lower mass car than you actually have



Hmm, not sure if this strictly complies with laws of physics, acceleration = force/mass. Force is equivalent to torque at wheel and g/box effectively multiplies the torque available from engine. So in theory cut the car weight by half and you double the acceleration in any gear.
But the lighter flywheel does reduce overall mass of the car and lets the engine spin up faster. However the flywheel is a device to store the energy of each explosion (4 per rev in a V8) and smooth it out, especially important at low rpm - too light will make the engine unpleasant on the road.



that's cos you're not considering it from the viewpoint of the engine though. The engine still produces the same torque, it's then multiplied by the gearbox and final drive.
Puy yourself in the position of the engine, you can feel how much effort you're putting in to accelerate the car .. then someone moves from 4th say to 1st, all of a sudden you can feel that the effort required is less, if you didn't know the gear had been reduced then you'd think the car had less mass (same effort, greater accleration or less effort for same acceleration) .. see? If 1st has twice the reduction of 4th you'd accelrate twice as fast all things being equal, or as if you'd halved the mass, so the effect of lightening the flywheel is greater in a lower gear to the engine. No re-writing physics..
For every reduction of gearing and consequent torque multiplication there's an trade and in this case it's engine revs.

tcpc

Original Poster:

166 posts

226 months

Saturday 4th October 2003
quotequote all
read the link and thanks all for your replys,

where or who is the best people to send the fly wheel too

Thanks again
Tony

Boosted LS1

20,087 posts

228 months

Saturday 4th October 2003
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A downside with a lightened flywheel could be at cruising speeds. As said, it stores inertia so when you tickle the gas the car will respond smoothly and accellerate nicely. With a light flywheel you may have to keep touching the throttle to hold a given speed which could be a pain. If it was to light you'd never be able to keep a fixed speed. I wouldn't lighten by very much. I think drag cars like the heavy flywheel to get a really great launch.

jmorgan

36,010 posts

252 months

Saturday 4th October 2003
quotequote all
tcpc said:
read the link and thanks all for your replys,

where or who is the best people to send the fly wheel too

Thanks again
Tony


DJE in Nuneaton did mine but then it was all in bits and the rest matched up and balanced.
www.djev8.com/

My sheet shows around 60 but that was a while ago. Best speak to him first if you decide to try him.

Boosted LS1

20,087 posts

228 months

Saturday 4th October 2003
quotequote all
Any engineering firm with a lathe can do it. Take the weight from the outside but don't compromise thickness. I have taken 5-8 lbs off rover flywheels without problems.

v8 jago

982 posts

221 months

Tuesday 14th October 2003
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tcpc, i am selling a mcleod steel flywheel (lightened and ballanced) a mcleod full clutch and a rover sd1 gear box that has been strengthend and has taken 600 bhp without any problems it also has ARP bolts with it. the clutch and fly wheel cost over 500 alone. will sell everything with gearbox for around 350. i may sell the clutch and steel flywheel if the price is OK.

HarryW

14,911 posts

237 months

Tuesday 14th October 2003
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v8 jago said:
tcpc, i am selling a mcleod steel flywheel (lightened and ballanced) a mcleod full clutch and a rover sd1 gear box that has been strengthend and has taken 600 bhp without any problems it also has ARP bolts with it. the clutch and fly wheel cost over 500 alone. will sell everything with gearbox for around 350. i may sell the clutch and steel flywheel if the price is OK.

Sounds like you could save Mr shpub a fortune in his next winter upgrade project there with that little lot .
When you say the box has taken 600bhp what was it rated at with the strengthening by the builder. As being able to take 600bhp doesn't mean it nots going to break next time around due to a previous very hard life IMHO

[back on topic]
Re lightening rover flywheels, I understood that not a lot actually comes off them in terms of overall weight 1-3lbs but it is sufficient to make a difference but not make the car undriveable on the public highway.
V8 developments do lightened flywheels if you check out their parts section here www.v8developments.co.uk/parts.asp give them a ring and speak to either Ray or Sean to talk it through.

Harry

Harry

harry

Boosted LS1

20,087 posts

228 months

Tuesday 14th October 2003
quotequote all
Any car engineering firm will do it. It's very straight forward. Take the weight from the outside and don't compromise strength. 5-8 lbs is ok for a rover and probably more can be removed on a chevy as their stuff is heavy. Thing is, not to get greedy. Having stored up mass is great for a hard launch.

wedg1e

26,736 posts

233 months

Wednesday 15th October 2003
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Arse. My lathe can only take brake discs....

Ian

v8 jago

982 posts

221 months

Wednesday 15th October 2003
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To what extent it has been strengthend i arnt sure. when the gear box was bought i was verbally told it had been uprated same as most of the parts on the rally car my mate used it for 2 years then i bought it then the clutch set up ive used it all year and it is as good as the day i bought it and every gearbox ive used previously has only lasted several months on the strip. The only reason im selling it is cause ive got diffrent ideas. OH extras include 2 clutch cylinders and a carbon fiber look gear knob. maybe a fluffy dice.

RichB

45,530 posts

252 months

Wednesday 15th October 2003
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Boosted LS1 said:
A downside with a lightened flywheel could be at cruising speeds.
Doubt it - at crusing speed it is the momentum of the car that keeps the speed smooth, not the flywheel, the flywheel only has effect at idle speeds. Rich...

Boosted LS1

20,087 posts

228 months

Wednesday 15th October 2003
quotequote all
RichB said:

Boosted LS1 said:
A downside with a lightened flywheel could be at cruising speeds.

Doubt it - at crusing speed it is the momentum of the car that keeps the speed smooth, not the flywheel, the flywheel only has effect at idle speeds. Rich...


When your cruising on a light throttle a heavy flywheel has plenty of stored mass which allows you to touch the gas and go smoothly. Same thing happens at idle. The opposite would be if you had a 5lb flywheel (just for example). I doubt you would be able to stick to a steady speed as the revs would be going all over the place as would your right foot.