p4-33

Just getting back into this, what a weekend. Between St Pats day and the OPA Kart 2 Kart bash, I just woke up from a nap.

Thanks for the input guys. Here's the problem I'm trying to solve; my current cam setup makes great power, tq comes on strong with 550+ at 3000 rpm. It also stays fairly flat with a peak of 625 at 4700, peak hp at 5400. This torque band was my stated goal with my the 04/05 winter upgrades, and I was and still am satisfied with the results. After all, I run P-class, and I am right at peak performance for my class. Just for clarification, hydraulic roller, spinning at 54-5600 rpm.

Ok, so that's not a problem... the real issue here is I had a problem last fall where a lifter tie bar rivet popped off, lifters rotated in the bore, lobes knocked off the rollers, lifters dug into cam, cam dust through motor, and All Bad from there. In trying to analyze the failure, there was a contingent from the various manufacturers and engine folks involved (let's leave names and brands out of this) looking at my numbers, and the concensus was I needed to make changes due to the "agressiveness" of the Xtreme Energy lobe profile (inverted ramp). There was no real evidence of valve float or lifter toss, so the solution was a theoretical one. The gist of those changes were to change springs to a pacalloy(sp?) based design, lighten up sprung weight with titanium retainer hardware, and increase spring pressures to 175 on seat and 415 over the nose. They were originally set to 150 on seat and 390 open. Of course, both motors had these changes applied.

Now that I'm putting things back together for the season, I'm revisiting my cam selection. Things to consider are moving away from the inverted radius ramp profile to ease valve train abuse, but my main question is what changes would need to be made in duration and lift to "make up" for less aggressive lobe profile. Avoiding another valve train meltdown is now my primary goal, preferrably without sacrificing my torque band.

And there's another option: be happy with how it runs now, and write off the previous incident as a fluke, which has since been adjusted and corrected. Pucker factor has set in, however.

I've got about 2 weeks before dyno sessions begin, so I'll be making a decision what to do this week. The cobwebs should be cleared out by the morning, so I'll call a few of your suggestions tomorrow.

Thanks again for the help,
Brian

p4-33

XFI profiles are going the opposite direction in agressiveness from what I'm trying to accomplish. Was anything special done to your top end? Do you know your spring pressures? What rocker setup and spring hardware are you using? How many hours on it so far?

And thanks for the Summit tip. Good to know.

Brian

p4-33

I'm using Pro Topline 320 runner aluminum heads, Jesel Sportsman rocker hardware. Some port work has been done and I can get you flow numbers if necessary. Also running a Dart rect port single plane intake manifold, port matched to the intake runners of the heads.

Please explain what you mean about 2 different intake lobes for "good runner and bad runner".

Thanks,
Brian

p4-33

Dave will be one of my calls. Having someone with specific marine knowledge is a big benefit. Often times when you call the tech hotlines of some of the bigger cam companies, you get folks that know how to make power in a straight line or a 1/2 mile track, but don't understand why I don't want to run a 106 LSA.

I've chased your boat while you were spending "significant time above 6000 rpm" If your valve train is staying together, that speaks volumes. But keep in mind I'm running hydraulic, not solid. Nor am I dry sumped, nor vacuum scavenged, etc, etc.

Thanks for the tip,
Brian

p4-33

I've talked with Bob on a number of occasions, and he will be another call tomorrow,

Thanks,
Brian

p4-33

My engine builder has recommended Bullet as well. Does anyone have any experience with these guys? Website?

Thanks,
Brian

p4-33

Ok one last question, then I'm done post-whoring for the evening...

What does swapping 4 and 7 do for you?

Thanks,
Brian

KAAMA

Bob/rmbuilder of Marine Kinetics engineered the valve train set-up for my engines, and did a nice job of working closely with the person who assembled my engines (Dave of WESCO). I am very pleased with the results. Plus he gives wise, straight forward instruction. I hope all goes well for you this year.

cstraub

Now I remember this project. Brian as much as RMbuilder helped you last year with your issues with the one engine I would highly suggest working with him.

BBC have 2 intake runners. These runners are different from each other. Grinding a specific lobe for each style runner can optimize the combination.