O.S. Max 81 VR-M setup help

[Flyin Rat Sass]

any info about pipes, props ect. but mostly about the stuff i may not know that i dont know.(i can ask about the stuff i know i dont know)

 

[Don Ferrette]

Let's start with what it's going in ... mono?, hydro?, skateboard? ...

 

[AndyBrown]

Don, RATSass has an OS 81 in the Flattie pitured above.

RAT, R U on a budget? (lots of good used pipes out there) or R U looking for a New pipe?

How much Nitro do you plan to run?

 

[Flyin Rat Sass]

I'm running a 36" long 15" wide flatbottom.the contact area of the hull has been modified into what the full size dragboat racers call a runner bottom(two very shallow chanels ) l_/-------------l___________l---------------\_l.Prop depth, a little deeper than true surface drive (3/4) submerged .To get the benifits of surface drive,with reduced prop walk.The hull has a slight rocker in it (convex front to rear) to allow greater trim control,as opposed to two modes--too wet with the bow plowing,or massive wheelies.These are things I learned with my first flat ten years ago,it had a k&b 7.5.I had so much fun, and enjoyed the challenge and learning experience, I'm trying it again with a fresh hull and a lil bit more motor.Any experience (real or simulated) would help me to be aware of factors I have probably not entered into the mess. Thanks

Ummm,yea i need a pipe.price is no object.Well,Ok ,not exactly but i wont be trying to barter with food stamps or bits of driftwood.fridays are good for me...lol whatcha got, Andy? Nitro 10 to25%

 

[Don Ferrette]

Well if you are going with new stuff, try one of Andy's parabolic pipes. Good power curve, it's muffled & what I like best is it's rather short in overall length, especially for a muffled pipe, easier to conceal. I'm sure you don't want to take away from that Keith Black hemi mock up in the rear! To start out I'd try a X455/3 blade since it's semi submerged, them go from there. You'll probably wind up with a x457/3 on it. I've always liked the 3 blades, a touch more lift & a bit smoother overall.

 

[Flyin Rat Sass]

Thanks Thats the stuff i'm looking for.how much of a performance drop if the header/pipe snakes around a lil, to keep it below deck?

 

[Don Ferrette]

A little snakin' won't kill you, look what the little Nova Rossi's do, 180 degrees right off the motor. What you need to stay focused on is overall length. .... h34r:

 

[Flyin Rat Sass]

......And that would take special math skills or restrained hacksaw skills?

 

[Don Ferrette]

Nah, just a flexible tape measure................

 

[Flyin Rat Sass]

would you average the outside and inside circumference of a curve or just measure down the middle?

 

[Flyin Rat Sass]

wouldnt a curve widen the band some as well?

 

[Don Ferrette]

wouldnt a curve widen the band some as well?

I don't think so, overall length is the key.

would you average the outside and inside circumference of a curve or just measure down the middle?

Down the middle.

 

[Flyin Rat Sass]

i could be wrong, but it seems that a curved header and a steep convergent cone would be close to the same as, a straight header and a longer,or more gradual cone.the curve giving a short or a long path just like the cone does.

 

[Don Ferrette]

i could be wrong, but it seems that a curved header and a steep convergent cone would be close to the same as, a straight header and a longer,or more gradual cone.the curve giving a short or a long path just like the cone does.

Not quite. The divergent cone affects the return exhaust pulse & the overall length affects when it reaches the motor. Now the design of said divergent cone can & will play a part in the overall timing (pipe length). For example the Irwin quiet pipes typically ran one inch longer in length because of the very short divergent cone that would send the pulse back sooner. This is why so many people were convinced they didn't work, they were running them too short. On the other hand, Andy's parabolic pipe throws all that out the window as it runs shorter that you are used to. Preston Hall runs a parabolic on his 45 Crapshooter at something like 8 3/4" & the boat is ballistic & throttles beautifully.

 

[Flyin Rat Sass]

Thanks for setting Me straight,there's a lot of principles(stuff) at work here and I find the physics aspect of optimal operation more rewarding than having someone sell me a fully setup proven runner.

 

[Flyin Rat Sass]

Oh yea, Where might I find those "Andys Parabolic Pipes"?

 

[Don Ferrette]

Right here-

http://www.cmdracing.com/updated/tuned_pipes.htm

 

[Flyin Rat Sass]

Thanks ...Cool site B)

 

[Flyin Rat Sass]

Are there any problems with turning the carb manifold 90%,placing the needle pointing straight up and the throttle linkage easier to set up?