FrontEngineDragsters.Org Forum
Technical => Matt Shaff's Engine Shop => Topic started by: spitzerscott on March 18, 2018, 09:18:00 AM
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What would be the factors that would make you need to run longer pushrods? Some are obvious but thought you guys have ran into many, just looking for info. Thanks
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Many things combine to change the push rod length needed
On any new build you use and adjustable checker push rod--sharpie tip of the valve--roll it over observe pattern on =valve tip--adjust length--re-sharpie--roll her over --check pattern--when the average back yard guy gets a pattern in center of valve tip about wide as a third of stem diameter he should stop measure--order push=rods and never look back
This does not address every situation but covers about 90 % of them for average racer
On a small block Chevy longer valves equals longer push rods in most cases
Most folks use a .100 long valve so they gain installed height for valve springs usually those engines will use a .100 longer push rod
My advice above does not get into a bunch of math and all of the details but it will work for most guys
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spitzerscott - probably not expected answer to your question, it’s info though. Switching from a V8 sbc to an inline 6 cylinder needs longer pushrod. A stock sbc pushrod is 7.900” compared to 10.140” length for a Ford 300 six. Anything you do to reduce weight for the moving parts in your valvetrain helps your springs be more reliable and allows your engine to rpm easier. Think about a stock engine’s valvetrain at 5000 rpms and adding even a fraction of weight (e.g. longer pushrod) is a negative. In this instance the stock V8 sbc has huge advantage over the Ford inline 6 cylinder. Alan
p.s. Some aftermarket sbc have raised cam location which may require different than stock pushrod length.
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If you have engine where you might change head gaskets for more or less compression start in middle. I made up a set for Hemi with .080 gaskets and when got in lousy air switched to .030 and had cpl pushrods that where just long enough to be problem. Probably not issue for most combos but it happens.