Piston speed and rotating assembly longevity.
02-14-2010, 11:49 PM
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Piston speed and rotating assembly longevity. I’ve been playing around with several calculators for piston speed, engine volumetric flow, and another equasion that calculates the amount of air in lb/min the engine is flowing under boost and at temperature. Using these I’ve figured out that a 540 BBC, shifting at 6200 would have a relatively safe piston speed of 4391.6 feet per minute, or 73.194 feet per second. Also having a EVF of 970.5, with a properly sized turbo at ~15psi and running pump gas (A2A intercooler and water/alchy injection) would make the power I’m looking for.
With big power, comes rebuilds which I would like to avoid as much as possible. Although I know some items would have to be replaced from time to time, like valve springs and lifters.
My question is that if I build the rotating assembly beyond my needs, say with a piston speed around 5500 feet per minute (92 feet per second), would that allow the bottom end to live longer between rebuilds? Or am I completely off my rocker for thinking so?
Thanks for the input!
With big power, comes rebuilds which I would like to avoid as much as possible. Although I know some items would have to be replaced from time to time, like valve springs and lifters.
My question is that if I build the rotating assembly beyond my needs, say with a piston speed around 5500 feet per minute (92 feet per second), would that allow the bottom end to live longer between rebuilds? Or am I completely off my rocker for thinking so?
Thanks for the input!
02-15-2010, 08:37 AM
#2
TECH Regular
The funny thing about piston speed AND a power adder is you "scare" the piston, rod, and crank manufacturers into giving you bricks...which will make your maincaps, bearings, and block unhappy no matter what the actual running conditions are.
The "rock on the end of the sling" is the best way to think about it. This is where institutional knowledge comes into play. If you speak to the piston guy first to determine the lightest piston that will do the job, the wristpin will come next, the rods after that, and the crank next. You will have an optimized combination.
Comparing quality based on gram weights and price doesn't work because good design (cross-section and radii) doesn't necessarily cost anything more. Quality machining is a must but it can't overcome a poor design.
The "rock on the end of the sling" is the best way to think about it. This is where institutional knowledge comes into play. If you speak to the piston guy first to determine the lightest piston that will do the job, the wristpin will come next, the rods after that, and the crank next. You will have an optimized combination.
Comparing quality based on gram weights and price doesn't work because good design (cross-section and radii) doesn't necessarily cost anything more. Quality machining is a must but it can't overcome a poor design.
