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Custom stroker crank

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Joined: 16 Sep 2009
Posts: 23
Location: Kogsbølle, Denmark

PostPosted: Fri Feb 21, 2014 7:59 pm    Post subject: Custom stroker crank Reply with quote

I'f you could make a custom stroker crank. What would the dimensions be?
I have CAD software available and access to cnc lathe/milling machines.

I want:
The longest possible rods, to decrease piston acceleration.
Optimal piston dimension for turbo applications (i have a 931).
Rod and piston should be affordable aftermarket or OEM parts.

I know there are some bright heads in the 924 community, so please share your thoughts.

931 Current status: bits and pieces
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Joined: 01 Oct 2004
Posts: 15544
Location: Woodstock IL

PostPosted: Sat Feb 22, 2014 1:51 am    Post subject: Reply with quote

Some tools to help:

To net it out, the longest off-the-shelf rod I have found that will work is 150mm, only 6mm longer than stock. If you do anything more than the 2.1L stroker described above, you will have a very difficult time finding off-the-shelf pistons that will work for a turbo car because none of the off-the-shelf pistons will have proper crown-to-deck distance to provide suitable quench area. So for pistons, you would be best to go with completely custom slugs where you can spec out the compression height, quench ring, and dish volume.

The other big factor to be concerned with is that as you move the crank journal out, you will experience rod-to-cylinder and rod-to-block interference. The largest stroker I've ever heard of is Dave Dennet's 2.4L. However, when I plugged the specs in that were listed for that motor, it actually came out to 2.2L. The Ottinger stroker was purported to be 2.3L, but we don't have all the specs to validate the authenticity of that claim. On my 2.2L stroker, I experienced very minor interference at the #2 rod where the shoulder would slightly rub on the oil galleys that run inside the block (these are the galleys that transport oil to the filter console). And that was with the custom Crower rods we developed that have a much smaller profile than stock rods and the aftermarket off-the-shelf rods that I used in the cheap-a$$ stroker described above.

Good luck. I'll be interested to see what you come up with.
erstwhile owner of just about every 924 variant ever made
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