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Old 10-03-2021, 08:45 AM   #39
vintagewrench
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Join Date: May 2016
Location: Paradise
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A six-bolt crank will work just as well as an eight bolt as least up to 200hp and more with a light flywheel. The one issue with them is the torsional vibration inherent in a four cylinder engine will break the stock flywheel bolts. Switch to new Dana 30 diff ring gear bolts or get a set of ARP flywheel bolts and you should be ok.

Eight bolt cranks use narrower and very heavy rods and narrower crank journals.

This photo shows our B18B crank (same as a 6-bolt B20) after removing all of the external stress risers and semi-polishing it for race prep. In the photo the flywheel runout (in this case a 8.5lb aluminum piece - the original is 22 lbs), and the runout of the center main bearing (only .0005) are being checked. Then it was then reground followed by rebalancing and cryogenic treating

For what you are shooting for the rods should be replaced with aftermarket pieces; either Pauter rods, or Asian. Carrillo rods and bolts are the strongest on the market.

If you use a steel cam gear it can lightened (this one by one pound) and if you use an early steel gear it should be balanced. The recessed hub area and the original lightening holes in these gears usually are not concentric with the bore or the teeth, but machining both of them will remove the imbalance. This gear and others we have checked are off as much a .060"




Last edited by vintagewrench; 10-03-2021 at 08:54 AM..
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