Refining Pipe Length for CMB 1.0

[BradV]

I'm still trying to get this motor to rev a little harder, have tried pipe length (unsilenced CMB pipe) in the range of 12 1/4-13 inches.

Can those who are running this motor let me know what pipe length has worked best for them?

 

[John Knight]

Brad,

What boat hull and prop are you running? They have a lot to do with it.

 

[Tofastformellow]

you can get those to fire up on a really short pipe if you try it....

i had a mono that liked a fat pipe more like 9 or 10 inches...

Jason

 

[BradV]

SprintCat with a Prather S265 prop. Having tried a number of props this seems to be the best so far.

Just found it unusual that going from over 13 inchs to 12 1/4 didn't make as much difference as I would have liked.

Motor really sounds like it is a few 1000 rpm short of its optimum.

 

[John Knight]

Consider dropping down a size or two in prop and shorten the pipe even more. I have a 90 rigger that has a pipe length of 11 3/4 to 12".

 

[NAMBA860]

shorten it about 1.5 inches it should really come alive i found that engine will make no power on a long pipe.

 

[nigel]

shorten it about 1.5 inches it should really come alive i found that engine will make no power on a long pipe.

I I used to run my 1.0 CMB on a K pipe at 31cm with a Octura X465 (moded) and it had no problem revving.

 

[gil sonsino]

I'm running my 101RS on my 90 rigger using a .84 parabolic(drilled) at 11,5(85mph).I do know that a cat offers more drag than a rigger but seems that 12-13" is good for you.what mods did you do to your props?Barr cut and tongue cut usually work well for the X serie in a cat.

Gill

 

[BradV]

I'm running my 101RS on my 90 rigger using a .84 parabolic(drilled) at 11,5(85mph).I do know that a cat offers more drag than a rigger but seems that 12-13" is good for you.what mods did you do to your props?Barr cut and tongue cut usually work well for the X serie in a cat.

Gill

Thanks

The props are just sharpened and balanced. Yes the Cat has quite a bit of drag as I found out last week swimming after it for 50m and pushing it back to shore!!

As suggested I will take more out of the pipe. I think part of my problem is perception as I'm used to a 7.5cc that has been fully worked and revs close to 35k, these bigger CMB obviously aren't going to get there.

 

[BigChuck]

Some CMB's will not get to 35K others will. I would suggest a pipe change. RPM's are what you may be looking for. But if a pipe change pulls the 265 with authority and makes the boat fast, do you still want the RPM. 265 is not a big prop on a cat with a 1.0. 15cc Mac pipe and you will have fun trying all of the lenghts that you have just been given.