Cmb gas engines

[Drew St. Amant]

I am very seriously considering a cmb gas engine for my next gas mono what's the general consensus on them compared to modded zenoahs and quickdraws I know one big disadvantage is parts availability but my main concern is power are they any more powerful?

 

[Kevin Sheren]

They are roughly about a pound heavier.

Kevin

 

[K F Wheeler]

Scott Myers, M5, in one of his pit tours talks with someone that has one in a hydro. Don't remember which vedio... I do remember the turbine scoop covered the spark plug.
Think it was a little taller as well.

Ken

 

[Roxyflash]

There taller and the drive line has a taller center line.On my seaducer I had to use a custom radio box but if you use a exposed servo be easier.There heavy.You have to use a belt and starter.I have a evo 27 and used a vision pipe for gizmo.The cmb pipe is almost two foot long.Here’s a picture of my boat.

 

[John Seybold]

Are you a square drive in the Seaducer? If not have you had any issues with the rear bearing?

Thanks

 

[Roxyflash]

It came with a collect for round shaft so far no issues.

 

[RaceMechaniX]

Bruce there was an issue in the gas RS motors as the engine was a small end guided design and there was too much axial clearance on the crank. This allowed the crank to push and tilt the connecting rod leading to scuff's and bearing failures. It was more of an issue with the 35RS, but I believe it occurred in the 27RS was well. The simple solution was to always use a square drive to remove the thrust component and allow the crank to self center. If you can, I would recommend switching to a square drive.

 

[Drew St. Amant]

So I see all these other disadvantages with the crank play the size and the weight so after all that can it turn a bigger prop turn more rpms or something like that I like that it's rear exhaust but so far thats the only advantage I see

 

[RaceMechaniX]

Drew,
It's hard to beat a good modified Zenoah. The weight and packaging advantage plus the availability of spare parts is a big reason why they are popular. In some specific boats like gas scale the inline rear exhaust is a big packaging plus which outweighs the other disadvantages.

If you are into the nitty gritty details of modding motors you should be able to push more power through the CMB disc motor compared to a piston port Zenoah.

 

[Drew St. Amant]

OK so to really see the advantages of the cmb design you'd have tweak the engine after purchasing it like a zenoah but theoretically because it's a better design for power it should have a higher ceiling than the zenoah but stock they are not way more powerful

 

[Roxyflash]

You would be surprised the stock cmb 27 evo in my mono pushed it 73 stock and there was much more to be had it would pull a bigger prop don’t think there’s too many stock zenoahs that would do that.The mono I have is a handful but was the only boat I had that I could fit the cmb without redisignin the boat.I was gifted the motor and wanted to test it to see how it ran.Im going to build a couple riggers for the cmb over the winter.I was very pleased with the performance easy to tune idles great starts easy and runs very strong.

 

[Andy Nightingale]

A box stock CMB is considerably higher revving than a tuned zen. They tend to turn smaller props than something like a TK but at much higher speeds

 

[Mike Cathey]

There taller and the drive line has a taller center line.On my seaducer I had to use a custom radio box but if you use a exposed servo be easier.There heavy.You have to use a belt and starter.I have a evo 27 and used a vision pipe for gizmo.The cmb pipe is almost two foot long.Here’s a picture of my boat.

I bought a big block Zenoah with the Zenoah case instead of their billet case because it would sit power in the boat. Only good things come in terms of the boat ride by lowering the CG.