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66mm racing crank (aka 906/910) vs. 66mm production crank

I have only just found out that they’re almost identical and one of the differences is the racing version had their rod journals turned down an additional one to two thousandth of an inch (necessitating special bearings) to further reduce bearing friction and allow it to spin even faster, more freely.

So, do you know if it’s suitable for street use? Logic tells me such a crank is noisier… Am I assuming right or not? Have you tried this?
If it’s that good, why didn’t Porsche do the same to their production cranks?

TIA

Last edited by blue72s; 01-05-2005 at 07:12 AM..
Old 01-05-2005, 05:43 AM
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noisier? I certainly haven't tried this, but it seems like one of those small tweaks that all add up to something in a race car, but likely isn't worth the brain damage unless you're at the top levels. Unless you already have one of these cranks, in which case I don't see why it would be a problem in a street car with the proper bearings. You might be able to sell it for a good sum to someone trying to put together an original motor, or who has spun a bearing and damaged their crank.
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Old 01-05-2005, 09:58 AM
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Weren't the special bearings for fillet clearance?
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Old 01-05-2005, 05:11 PM
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There is no metal to metal contact on the bearing surfaces in normal operation , the crank rides on a film of oil, so the only sound diffrence would be what the oil might make Now I am not a porsche expert , but in my experinces with racing engines of other brands it is common to run losser tolarances on race engines than street virsions, My guess is the racing bearings or of
the same size but have diffrent qualitiys better suited for racing. Race engine have a very narrow ( and narrower the higher level of tune ) specific use and alot of their aspects I would not want in my hot rod street car.
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Old 01-05-2005, 05:15 PM
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