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Jul 7, 2008 | 08:31 PM

todds69

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From: Dallas,GA

421 questions

i recently picked up a 04 6.0 truck long block and i want to build a 421 stroker,4.125 stroke 4.030 bore.i just want to know your experiences with this combo any thing i should look out for and mainly wondering how much if any clearancing is going to be needed on the block.i am more than likely going to buy a complete 421 rotating assy.also what is the most compression some of you guys run on pump gas 93 octane? i've heard as high as 12 to 1.any help or advice is appreciated.

Jul 8, 2008 | 09:22 PM

todds69

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Staging Lane

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no one knows anything about a 421?

Jul 9, 2008 | 07:03 PM

Shawn MacAnanny

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I have heard that the bottom of the cylinders will have to be notched to run the 4.125 stroke and have also heard negave thing of such a long stroke in terms of durability. Static compression ratio of 11.5 or less i would say but really it's your dynamic that determines how much you detonate, i.e. cam selection. That displacement could take a 250s duration cam no problem.

Jul 9, 2008 | 08:53 PM

KCFormula

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I have that setup in my Firebird. But mine is 15:1cr.

Jul 10, 2008 | 12:10 PM

A_VAS

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From: Harrisburg PA

unless you run a shorter rod, that piston design has to be ugly....pins would be way up on the oil rings. Have you looked into pistons for this combo, I'm curious as well....?