Re: 4cyl,6cyl,8cyl max rpms
a few of the 8.1 and 8.2 marine engines operate at 46-5K and there were a few merc 454 motors with a 56K operating range.
we spun our 427 regularly at 8200. most cast pistons wont tolerate sustained use above a piston speed of around 3000FPM without coming apart at the wristpins.
a lot of factors comme into play at the maximum sustained RPM/load.
valvetrain design,reciprocating assy design,main bearing/block design.
but without a ratio selectable transmission, most marine engines dont need more than 4500 or so.
ya gotta remember the piston comes to a dead stop then accelerates to a dead stop twice per stroke. my poor 455 olds had a 4.185 bore and a 4.250" stroke with 3"dia main bearings. at 7200 RPM my bearing speeds were aproaching limits and the piston speed really was borderline.
eventually you have to take into account the laws of physics.
thats why most small bore short stroke EFI 4 stroke outboards with direct acting overhead cams and 4 valves per cyl can run at 6000 RPM as long as they have fuel and cooling water.
the inertia in an older detroit V8 is rather high.
to keep the valvetrain stable while still moving a big heavy 2.5" or larger valve is horrendous.
to keep the lifter on the cam we had to use rev kits. a rev kit is another set of springs between the head and the lifter to make the lifter follow the cam, that coupled with triple valve springs and crazy spring pressures. this also required special retainer/keepers to prevent,sometimes, the spring from pushing the retainer off the stem and allowing the valve to free fall into the combustion chamber which is somewhat messy at 7000 RPM.
neatest thing I ever saw was a kit to convert a SBC to a 4 cam,4 valve per cyl overhead direct acting valvetrain.
talk about waking up a package.
