Engine Guru's: lighter crank for a 3.2?

[Arlo911]

I'm thinking about getting my 3.2 rebuilt, but I want something a bit different
Is there a possibility of using an SC or GT3 crank (or other) whilst keeping the Motronic? I guess I would need custom rods and/or pistons.
My goal would be a very responsive engine, not looking for top HP, and it needs to be reliable too.

[chris_seven]

I am sure you could modify the 3.2 crank to reduce the inertia.

Knife edging and lightening the big end pins would help and comparing counterwight sizes might lead the way to further intertia reductions.

A light flywheel would help significantly as would piston and rod masses.

A rod with a smaller diameter wrist pin and matching slipper pistons would be good.

This impact on responsiveness will probably only be noticeable in the lower gears possibly 1st, 2nd and to a limited extent 3rd. In 4th and 5th total inertia of the vehicle will dominate. (Engine Inertia is likely to be 0.1kgm^2 and the car could be as much as 50kgm^2)

I am not sure that you can easily disassociate responsiveness from Horsepower and Gear Ratios, particularly in the taller gears, and to optimise behaviour I think you have to take all these aspects into account.

[piggdekk]

I think if You look for a crispy engine rather than lightening the rotating masses (or on top of that) I would go for high compression, properly ported heads (for flow velocity, not only big flow numbers), and as much advance as You can get away with. That means probably dual plugging the heads, but probably cheaper (and more reliable) anyway of what Chris is suggesting.
luca

[johndaroza]

SO that was in 2008 did you do the rebuild?

I took off over 12 pounds the rotating mass .

SSI Steave wong chip cut air box 20/21 cam's put it with a new LS trans Lots of crank work done

new stock heads 9.3 -1 pistions redone rods new bolts, stock head studs. Steel RSR fly wheel and clutch

Fun vary fun ! It lights up the tires in first all the time both just will rip it up second hold on becase it will light it up too if you want up at 90mph it is pulling like mad never took it past 100.

[KTL]

If you use the SC crank, which is lighter than the Carrera/930 crank by a considerable amount, to keep it simple you would use SC pistons & rods. Then you'd end up with a 3.0L Motronic

You can use the GT3 crank. Supertec makes their own version that's already crossdrilled and grooved. But you do need the rods & pistons spec'd specially since the GT3 crank is 76.4mm stroke vs. your Carrera's 74.4mm stroke. GT3 also uses SC-spec rod journals, which is nice.

Your '87 3.2L has a clutch on it that is a whopper of a boat anchor. There is a lot of weight to be lost there, which goes a long way toward improving throttle response. I replaced the stock clutch with a light aluminum alloy unit and it made a very noticeable improvement in the throttle response. The original clutch weighs approximately 25 lbs. Alloy clutch removed 8 lbs. That is a LARGE amount of rotational mass reduction. I know of an even lighter clutch that is twice as light. 17 lbs. of rotational mass loss makes for a snappy throttle response.

[Henry Schmidt]

If you're serious, you can order a Supertec SuperCrank.
Combined with Pankl GT3 titanium rods, you can spin it as high as you like.