high lift cam in olds 350 question about Push Rod length

Asked by Guru3WY7S Jun 30, 2020 at 10:24 PM about the 1971 Oldsmobile Cutlass

Question type: General

I put a higher lift cam (RV type) into my 1971 olds cutlass. bone stock engine with only about 3000 miles on it) For them to make a "higher lift" to fit into the olds block, the Base cirlce's of the lobes have to be smaller (by .150") so the lifters are now .075" down in the hole, making the distance from the lifter to the rocker are .075 longer. it seems I need push rods that are .075" LONGER to keep the geometry straight and the valves to not open .075" short.  am I explaining this right ?? since putting in this cam, the car has no bottom end (it is only 205/214 @ 50, .448/467 lift. I am thinking because of the Stock Shorter pushrods, I am gaining the duration but not the lift. get it ?? cam is installed straight up, not advanced) (also 2.56 gears don't help the matter).   any educated opinions on this will be appreciated.   Thank you

6 Answers

Guru3WY7S answered 3 years ago

the cam came ALONE (Elgin). I used new aftermarket crane lifters. was lubed properly, not my first rodeo. the lobes are fine, but SENSE tells me when a lifter and push rod goes .075 Farther down in the hole than it originally was, SOMETHING has to"make up" the difference. and the "Middling" of the hydraulic lifter will NOT take up .075".

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F_O_R answered 3 years ago

Read this. http://victorylibrary.com/mopar/regrind-c.htm

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F_O_R answered 3 years ago

And this. https://blog.trendperform.com/how-to-measure-pushrod-length-and-optimize- valvetrain- geometry#:~:text=Inspect%20the%20position%20of%20the,pushrod%20length%20for%20str eet%20engines.

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F_O_R answered 3 years ago

Lastly. https://www.hotrod.com/articles/how-to-measure-for-correct-length-pushrods/

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KenF answered 3 years ago

Your instinct is right, any change in the diameter of the base circle will affect pushrod length. Some old cam books I had showed how to measure for new pushrod length but I don't have those anymore. Try this compcams guide, starting around page 6. http://www.compcams.com/pub/media/productattach/1/4/145.pdf

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