Aluminiun Flywheels

[AndyV]

Dear All

I've acquired an aluminium flywheel which I was intending to fit into my Triumph Spitfire race engine to improve pickup and acceleration. However I've been advised by a couple of guys in the UK racing paddock that they are not a good idea with a possibility of disintegration. To broaden my knowledge on ally flywheels and help me make a informed decision on fitting it (or not) does anybody else out there run one or have any experiences with them. Do they last, do they make a performance difference, would I need to think about fitting protective shielding etc etc

Many thanks
Andy

[zefarelly]

It needs to be billet aluminium and not cast, it'll need a steel facing, very well screwed on, and a nice light clutch as well to get the benefit

If you stick a clunky great cast iron clutch on a direct aluminium replacement and rev it high, your asking for trouble.

as a rough idea, aluminium is half the strength and a third of the weight, so unless you get it right the benefit on all but a screaming ultra race engine is going to be negligible.

another consideration is the balance of the engine . . .does it need some weight there ?

[graham bahr]

re balence, on most engines unless were talking V's with odd shapes cast into the flywheel the a lightened flywheel wont have an adverse effect on engine balence, although its advisable to have the crank and flywheel balenced as an assemblly, that said on many occasions i've fitted a lighter flywheel than the engine was origonally built with without rebalencing and seen no ill effects.

i've not heard of any relability issues with alloy flywheels, dont forget the main reason aost iron ones fail is either they have been machined in the wrong places or just are too brittle to stand the rpm in question.

[Al Weyman]

I use one on the Black Chevy in my Avatar infact it is bearly a flywheel more a spoked wheel and is complete with a two plate clutch assembly and it does have steel friction surfaces rivited to it, it makes for very crisp gear changes as the engine dies instantanouesly you lift off the gas. It is a ***** to negotiate around the paddock though especially with a first gear that will hit 80 mph. It does not effect the balance of the engine as it was all balanced as an assembly but I did use a Tilton clutch once and still have it actually and all that used for a flywheel was an automatic gearbox starter ring carrier plate and I bolted that on to a previously balanced V8 and it was OK.

[zefarelly]

I run an 8 1/2 Lotus TC steel flywheel and clutch with sintered plate, the only downside is its size and weight . . . .I had been advised an AP racing clutch wonyt work . . .but I've already started drawing up plans for an ally one with the correct offset for the AP clutch withing my bell housing and retaining the std starter and ring gear, hopefully the weight saving will go hand in hand with a hotter cam, higher revs and more power . . .and not hand in hand with exploding, unreliability and stalling on the grid !!!

[NiG_21]

Andy,

One thing that tends to happen with these things is that the ringgear can become 'loose' after some use and spin freely on the flywheel.

A fix would be to locate it with dowels/screws fitted around the circumference that will 'nip' into the ringgear and so hold it in place.

Of course, I would reccomend fitting helicoils to any threads cut into the flywheel to allow greater torque figures for the clutch.

BTW - if you thought you'd be able to sneak this modification on us by posting here then you've been found out!!

[AndyV]

Thanks for all your advice, It is a billet ally wheel with a steel friction plate so seems to meet all the requirements.
I think I'll give it a go as the engine is pretty revvy already so more lumpyness below 4K revs is not going to make much difference if I make some gains in the upper rev band. I will make sure I get it crack tested, threads helicoiled, and the whole thing balanced before use though. And as a bit of a safety measure to start with I'll retain the weedy standard clutch as a week link until I gain confidence in the ally wheel.

NiG
Theres nothing 'sneaky' about trying to stay one step ahead. Minimising the amount of guys I race against knowing exactly what I'm up to is a fine way of keeping an edge. And the rules do say 'type of material for rotating components' is free, so there.

Cheers
Andy

[Richy_Rich]

No, it's rubbish. You should give it back to the person you got it off and demand a full refund

[R59]

I've got one for a Chevy too Al, but I use the Quartermaster 7.25" triple plate clutch on my engine, with a reverse mount geared starter. Lift off, it almost stops!!! That's what you get with a gallon and a half of engine capacity!

Rob.

[zefarelly]

a gallon and a half ! blimy, I'd only just be over the limit on my little engine, its not even three pints !

[Al Weyman]

In the Historic ca,aro I am finishing off I have a lightweight steel flyweel as it can be a bit hard to live with these ultra light jobs, if the clutch is not up to the job I have the tilton and the auto flex or an American 10,000 rpm (proper name I swear!) ali flywheel and triple plate I can stick in. On my black car I have a twin plate McCloud with ali flywheel curtesy of Real Steel.

[bugs]

found this at cosworth cgi.ebay.com/ebaymotors/ws/eBayISAPI.dll?ViewItem&item=7955579756&category=33732
cheers bugs.

[boyracer]

My two cents worth.
Have spun down several cast flywheels, some we have milled around the bolt holes to take it even further. Anyone who's seen a toyota flywheel will have a rough idea what I'm on about, except think more.
Have them all balanced as a matter of course, with generally only VERY small dipples evident after balancing. The bid trick is to take the weight off equally. Little harder with a casting due to unequal spread of material, but if you're dodgy you could throw it back on and it will PROBABLY never bother you.

Aluminium, have seen several installed on street cars (who think they're racers) haven't heard of a complaint yet. Some nut and bolt the pressure plate on rather than rely on threads/helicoils in the flywheel itself... but I think Loctite would be a necessity rather than an optional extra.

Biggest stresses the flywheel is exposed to would be when it's under expansion (radially) as the mass in the centre tries to out accelerate the outer edges and this is fatigue so aluminium not so flash for this, but I've never seen any comparos to a cast flywheel (remember people like chev and ford are going to over engineer it to withstand a lot of abuse) so maybe stress is fine. Next would be the torque applied to the wheel by the clutch plate as you attempt a standing start, but unless the load comes in at an angle (not going to happen unless you've got some really loose bolts) the only thing being stressed is the friction the bolts generate between the crank and the flywheel, and this should be similar CI to ally.
Third and one I have my biggest concerns about is, the pressure plate applies it's load thru the bolts on the outer edge of the flywheel and this introduces a bending moment. Kinda like a cap on a pressurised pipe, ie it tries to bulge the middle even though the edges are constrained.

Have seen what we think is this on a road car (WRX) with a really wafer thin flywheel as there were shimmy marks as though the clutch didn't have even pressure across the face. Whether this was due to the bending of the flywheel or abuse from the driver, not so sure.

Probably no help, but throws a few more ideas into the mix

[Al Weyman]

Boyracer, I think you are crazy to cut down a cast flywheel, I was at Snetterton once when one of the ModProd cars exploded in front of me or at least that is what I thought had happened, right at the end of the Pitlane straight. Anyhow what had caused this spectacular pyrotechnic display was the flywheel (a weight reduced cast unit) on this Manta 400 had exploded, it shattered the bell housing, lifted the bonnet 6 inches in the air puting a huge dent and gash in it, severed the oilcooler hose which spilled oil over the hot exhaust causing the firey explosion. The driver was lucky not to lose a foot in the incident, the previously immaculate car looked a very sorry state and this was all because he had been a bit liberal with the old metal removal on the flywheel. You can be thousands of an inch away from exposing a casting blow hole creating a potemtial foot removing grenade and never be aware of it, stick to proprietory steel billet or aluminuim stuff by guys who know what they are doing.

PS the driver/preparer of this car was actually a very competant professional race car preparer who I won't name as it may embarress him.

[zefarelly]

I know of an MG 1100 race car . . .the driver has a 6mm thick plate welded to the floor under his toes for exactly the reasons stated above

I only use cast iron flywheels in road cars and never rejmove anything from them

[boyracer]

It's all about exercising restraint. And yes I have seen flywheels explode on other vehicles as well.
But these flywheels I'm talking about are out there in cars pulling 8k+ every time they get driven and have been doing it for several years now.
Reducing the weight probably helps the life of the flywheel as you lose alot of the inertial forces from quick rotational speed changes.

I tend to think you are both under-estimating the strength of cast iron.
You can buy continuous cast iron bar from the states for +5000psi hydraulic manifolds and when you cut a flywheel it handles and even smells exactly the same.
And Hydraulics is definitely a fatigue application.

Of course if you'd rather use steel or ally, by all means. I'm certainly not going to stop you