Is there any way to semi-easily calculate the maximum RPM that the engine can operate in....? meaning based on cams, stroke, bore, etc.... How did the factory come up with 6900 RPM redline when we know that 7300 RPM is safe... how could we know 7500-7700 isstill safe

pistons and rods are relatively lightweight ... i wouldnt push past 7300 - 7400 rpm though

there is a rough formula for calculating piston speeds

stroke (inches) * rpm / 6 = 4000 max

ie. 82.7/25.4 * 7400 / 6 = 4015.6 (a little over)

titanium or lightweight aluminium conrods and you could aim for 5000 max

ie. 9200 rpm

BUT ... the valvetrain would limit the peak power rpm anyway so there would be no point pushing past 7400 rpm anyway

Wes,

I'm sure there's a way to determine it, but you'd have to take a lot of things into account like the valve spring rate, guide strength, etc..

the way I understand it, a VQ motor can spin to 7400 (according to a article a while back in r&r or C&d where they tested the "nismo long nose" Z) because the crank and other componenets are balanced from the factory

BUT: The heads/manifold (not sure which) limits the flow past 6500, and running that close to where valve float occurs may be a very, very bad idea, since most nissans run interference heads.

Likewise, a conversation with JWT told me that a KA24De could rev to 7200, no higher unless someone went totally ape-crap and rebuild the valvetrain completely(balanced, etc) and still wouldn't net much higher...

I'm planning on getting a new mani, cams and have my rev-limited set to 7200, 200rpm before vavle float, but high enough for me to run 7k and hear what a VQ sounds like.

-Chet

For the VH45DE? It's in one of Q45tech's posts.