327 crankshaft question
10-09-2007, 11:12 AM
#1
Burning Brakes
Thread Starter
327 crankshaft question
I was wondering which crankshaft was stronger and which crankshaft was lighter between the large journal 327 steel crank of 1968 or the small journal steel 327 cranks before 1968.
Which is better for higher RPM? The small journal will of course have a smaller friction surface but the large journal has a large over lap between the rod journals and the main journals.
What are yalls feelings on this?
Thanks!
James
Which is better for higher RPM? The small journal will of course have a smaller friction surface but the large journal has a large over lap between the rod journals and the main journals.
What are yalls feelings on this?
Thanks!
James
10-09-2007, 11:35 AM
#2
Race Director
I would take a forged SJ crank over a cast LG crank any day.
if both are forged, I would use the LG crank.
Doug
if both are forged, I would use the LG crank.
Doug
10-09-2007, 11:38 AM
#3
Team Owner
Member Since: Oct 2000
Location: Washington Michigan
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Engineering logic says the large-journal crank is stronger due to the increased journal overlap, but the difference is very minute; in the real world, probably wouldn't matter much. 
10-09-2007, 04:01 PM
#7
Le Mans Master
It might be slightly heavier due to the corresponding larger journal sizes but I'm not looking up the density of cast vs forged steel either. However if that is a concern, lightweight rifle drilled cranks are readily available. If you are looking to run a high RPM large journal crank, I would look into buying a forged lightweight 4340 piece.
Nitriding is a very common form of hardening cranks, I recently had two nitrided. I believe the depth of penetration is around .010" or less.
Nitriding is a very common form of hardening cranks, I recently had two nitrided. I believe the depth of penetration is around .010" or less.
Last edited by Scott Marzahl; 10-09-2007 at 04:04 PM.
