Whats the perfect size cam for our jet boats? and how fast well our pumps max out at? 5500? 6000?

First off, what are you going to put it in

2sav

yes, 19 foot dana, 454 bored 60 over, all roller parats, aluminum bow tie heads, headers, single dominator 1150, berkeley jet done by jack. skid plate, droop snoop, jetovator, ruffly 11 1/2 to 1 compression.

What is the impeller cut. I am running a Comp Cams. Hyd Roller CCA-11-456-8.
It runs good. Spins to 5950 RPMs with a tight pump with B-cut impeller.
T.J.

IMO the XM270H is a fairly mild cam, especially with the compression ratio you're running. I believe you could get away with a little more duration and lift, however with the manifolds you will find yourself limited do to possible reversion (water being pulled into the engine via the exhaust pulse) you did say something about "for now" on the exhaust, I do like the Exteme Marine line from Comp, good stuff at a fair price (been using them for 15+years). I  like that cam if you want it to be mild, the limiting factor for me is the exhaust manifolds.

This combo will make good power to probably about  5,000 rpm, which will get after it and live forever, it also keeps valve components cheap, which brings me to point two, stock ratio rockers? you could replace the rockers and get that little bit more lift which will help wake up the big end, but for that matter go up one cam size and stay with stock ratio's (you can always change rockers later).

My 468 has the XM278H and I really like it, but I'm running Bassetts and roller rockers and a 10.5:1 CR

But it turns a stainless "A" to 5200 RPM like its hitting a wall.

Hope I didn't confuse the matter...I tend to get verbal diarreah.

The duration at .050 is what matters, that sets the rpm range of the engine.

This is why duration to impeller is important, as well as limitations such as logs to the engine.

If you have a 280 degree @ .050 cam that sets the rpm range to 4500-8000 rpm, and then you use logs, and a AA impeller - the engine will never spin high enough to make the rpm range. That is over camming.

From what I've experianced a 225-235 degree duration cam is probably as much as you want to go on a stock engine (lower duration for taller impellor A4, A3, etc) , and up to 250 for a modified engine (better heads and such with a looser impellor). Start getting into headers, loose impellors, big heads, etc, and the duration can go up even further into the big HP numbers - BUT you have to be able to spin it up there. 


I personally am running 246 duration with logs and a 4.5 inch exhaust with an A. 


While my engine could physically handle a much bigger cam (duration), the logs will keep it from spinning in the sweet zone.


Duration @ .050 = rpm range
Adv duration - duration @ .050 = ramp velocity (smaller number makes more power)
Lift = HP

I look for the highest lift in the duration I want with the steepest ramp.

Thanks guys!

Sorry about the duration.  I stated the "advertised" in the first post, at 0.050" it is a 226/236 degree cam.  It's very close to the Crane cam I run in my boat (an old man's cruiser  )

Basic long slot 1.72:1 rockers are being used.

As far as max RPM the lower end is built to take a bit.  Forged steel crank, "H" beam rods, recip assembly fully balanced.  I don't want to have to worry about the abuse an 18 and 20 year old will give it.  It should be perfectly safe at 5,500-6,000 RPM.

Log exhaust for now but we do have a set of Bassetts hanging from the rafters, perhaps later on.  These logs reduce down to 2.75" ID hoses so they're a bit more restrictive than the ones on my boat.

Cheers, Mark