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Discussion Starter · #1 ·
Could you guys fill me at least in alittle more on piston speed.
I put that 4000 fps out hopeing for someone to correct it./wwwthreads_images/icons/smile.gif
I think 4000FPS is close. I know that like honda had some raceing
engines on motorcycles way way above that figer./wwwthreads_images/icons/blush.gif
 

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/wwwthreads_images/icons/tongue.gif The factory rates my 4.0 Max BHP at 4600 RPM, which puts the piston speed at 2612 FPS.
At 3500 I am moving those little ringed rascals at 1988 FPS. I have always heard the engine life begins to be reduced at over 2400 FPS, and can easily buy that theory. You do know that heavy pistons will stretch the rods if the engine is over revved, like if a Diesel engine gets an unplanned sniff of natural gas (when a dozer rips open an underground gas line) and revs into never-never land, so heavy pistons have to go slow./wwwthreads_images/icons/wink.gif

CJDave
 
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Discussion Starter · #3 ·
94 YJ with 4.0: 3.44" stroke X 2 (up & down) X 5000 RPM = 34,400 inches per minute divided by 12 = 2866.66667 feet per minute divided by 60 seconds = 47.77778 feet per second. Is this the same FPS you are talking about? Or does it stand for something else? Or am I forgetting something? (THAT never has happened before!)(not)
please explain, Dave.
sln

 
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Discussion Starter · #4 ·
Just wanted to let you know for sure... Stroke dist. x RPM x 2 = mean piston speed
Oh yeah, I don't know the exact number, but the max safe mean piston speed is about 4000 feet per minute (not seconds)
Thanks JP

Sully

 

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/wwwthreads_images/icons/smile.gif Uh....don't make it harder than it is....the stroke is 3.41"....moves UP and DOWN so that's 6.82"...OR. .5683333333 feet....times five grand......gives you 2841.666666666 Feet Per Min. Hey...did I saw Feet Per SECOND in my other post??? NO WONDER! Sheesh!/wwwthreads_images/icons/blush.gif Oh well...../wwwthreads_images/icons/blush.gif

CJDave
 

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Here is some information I have from an old Car Craft Magazine, (Nov, 93). 4000 fpm is considered the safe upper limit when using forged pistons.
According to the Car Craft article piston speed is determined with the formula stroke X rpm / 6

The example was given for a Chevy 350. 3.48" X 6500 RPM / 6 = 3770 FPM

The formula for Max Safe RPM is piston speed X 6 / stroke

The example was give for a Chevy 350. 4000 X 6 / 3.48 = 6896 RPM

Hope this helps

 
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