Auto flywheel and lighter crankshaft

[JagsK1981]

Hi All

Need some advice, as my e30 325i sport is completely stripped and work has started on the auto box and engine. People's input has now started to confuse me, so please help.

One person is saying to have the flywheel lightened and another saying no point to do that.....help.

Another saying to put in lighter camshaft, but this is costly does it make much difference?

Thank you


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[Brianmoooore]

Lightened flywheel: If your car has an auto. gearbox, then you don't have one to even consider lightening!
Lighter camshaft: This is probably supposed to read "lighter crankshaft". There are extremely small gains to be had - the sort of thing you would do when chasing every last fraction of a bhp and reduction in rotating mass when building a serious competition engine. Not remotely worth considering on a road engine.

[steve_k]

are you converting the car from auto to manual?? if so then yes a lightened flywheel will make a (slight) difference but not a massive one on it's own.

as brian says do you mean lighter cranks shaft?? if so then you have a few options open to you.

lighten, balance & knife edge the crank, the latter can be expensive & there's not a lot of places in the uk that do it, but it HAS to be down correctly otherwise it's bye bye engine, but when coupled with lighter fly wheel, lighter rods (all balanced together) will really wake up the engine.

or use the m52b25 crank with matching rods & m20 pistons (again all balanced together with lighter fly wheel) with a decent chip/remap.

all this costs & in time leads to other supporting mods (head work, cam, inlet work, exhaust etc etc)

choice is your's, but before you go down any of those routes you need to make sure the engine is in fine form/fettle & running as best as it can.

[JagsK1981]

Ok thank you both I will just leave as it is. Appreciate the advice a˜a

[steve_k]

[Simon13]

Lightened flywheel: If your car has an auto. gearbox, then you don't have one to even consider lightening!
Lighter camshaft: This is probably supposed to read "lighter crankshaft". There are extremely small gains to be had - the sort of thing you would do when chasing every last fraction of a bhp and reduction in rotating mass when building a serious competition engine. Not remotely worth considering on a road engine.

I'd disagree i fitted an M52B25 crank to a stock M20 engine (manual) along with a lighter flywheel and took 7 KGS off the rotating mass on the bottom end. It made a huge difference to how the car drove felt. Otherwise a totally stock engine

[Brianmoooore]

It's not the total amount of mass removed that's important, it's where that mass was located. The further from the centre of rotational mass, the more effect it will have. The longer the stroke of the crankshaft, the greater chance you have of metal removal from it being effective, but it's just not of a big enough diameter for machining to have anything like the effect that removal of metal from near the rim of the flywheel has.
There's also the problem that metal removal from the crank will affect it's natural harmonic frequency, leading to possible unwanted harmonic vibrations, which in turn could lead to fatigue.

[reggid]

truth is taking a 8.5kg stock flywheel down to 5.7kg removes as much inertia as deleting an entire 84mm stroker crank.

so a slighty lighter crank doesn't do much in the grand scheme so IMO pick the low hanging fruit first e.g. you can get 3.2kg flywheels these days if you want low inertia.....

[tomson]

a lightened flywheel will make a (slight) difference but not a massive one on it's own.

Absolute cobblers, a lightened flywheel is one of the best mods you can do to an M20 and makes a huge difference to the way the car drives.