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 Posted: 06-02-2021 10:30 pm
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Esprit2

 

Joined: 05-01-2005
Location: Minneapolis, Minnesota USA
Posts: 536
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The 2.2 stroker crank will require pistons with higher wrist pin locations. Once you make the committment to different pistons, then you should also give a little thought to increasing the compression ratio.

With the long-stroke crank, and all the reciprocating bits flailing about in a larger circle, the 2.0 block assembly is marginally stiff enough to contain all the inertia. That's why the 2.2 912 was given a wider, stiffer block assembly. The "block" is the same, and it's a larger, wider, stiffer main bearing panel assembly that adds the stiffness. But a wide 912 doesn't fit into a J-H without cut & weld modifications to the chassis. Doable, but do you want to...

The alternative is to keep the 2.0 block assembly, and 10-pin the block and main bearing assembly. Stock, there's only one ring dowel at the front, and one at the rear. 10-Pinning puts a ring dowel at the base of each of the 10 large studs on each side of all five main bearing journals. Ten studs = 10 ring dowels = "Ten Pinning".

That will also require that the block assembly be align bored after the 10-pinning. If you just align bore to the next oversize bearing shell, you may find that they're now rare and difficult to find. Have a set of bearings in hand before you commit to that option.

Alternatively, fly cut a few thousandths of an inch off the mating faces (both faces) of the block and the main bearing panel. That will make the main journals slightly football shaped. Now align bore them back to round using the original inside diameter on the original centerline.

"Lotus" cranks (both 2.0 and 2.2) were available as crossdrilled and non-crossdrilled. And the main bearing configurations were different for each one. It's important that you use the correct bearings for the type of crank used.

If you intend to drive the car in a civilized, commuter traffic sort of way and short-shift before 4000 rpm, then the non-crossdrilled crank is adequate. If you intend to put your foot into it and use all it has, then go with a crossdrilled crank and the appropriate bearing shells.

Have all the rotating & reciprocating mass BALANCED together.

After that, it's the same old questions/ decisions about what you want the engine to be. Easier to drive with more low end torque? Or a hotrod? All other decisions spin-off from there.

It's not reasonable for you to ask others to tell you which woman you should marry. Okay, same thing... some decisions you have to make for yourself. So, what do you want the finished stroker engine to be?

And while you're pondering stroking the 907, know that Lotusbits also sells billet stroker crank kits to take it to 2.5 or 2.6 litres. Expensive, but powerful.

Regards,
Tim Engel

Last edited on 06-02-2021 10:36 pm by Esprit2