CMB 27GPX

[Timbo Whalen]

Is CMB recommending methanol and oil for the AAC spark engines instead of gasoline? That would make a lot of sense, but most of those engines go into endurance FSR hulls where I think they would run into issues having to carry 2x the amount of methanol over gasoline. The issue I know of with AAC and gasoline is the higher combustion temps lead to hotter piston temps. The piston grows beyond allowable fit and the oil film breaks down leading to scuffing. It does not help if we overcool the head which leads to more taper in the liner and tighter interference near TDC.

The aluminum sleeve expands more than brass over the temperature range trying to keep the taper and fit optimal, but it's tricky.

Aluminum also has a faster heat dissipating time, soooo...

Methanol does mix with certain synthetic lubricants available. The Klotz Techniplate line being one.
Red Line did produce one, too, but we're not sure of it's present availability status.

Modern synthetics and castors are impervious to the condition you mention related to heat.
If you look at the tribology specs on modern synthetics, they are virtually immune to the operating conditions our engines run in, even very high nitro %'s. Modern synthetics even out perform castors, and leave behind castors negative attributes.

As far as the CMB gassers ability to function on straight methanol, there's no reason it shouldn't... however, methanol requires a much higher CR and jetting increase due to A/F ratio stoichiometrics.

 

[Wasted wages]

Any update on the CMB 27 GPX gas motors?
Anyone having success running them ?

It's been a few months, and was just wondering if the jury is still out ..

 

[Buckshot]

Pretty sure they won O-27, H-27 and V-27 at the Worlds in Poland

 

[DON MAHER]

Does anyone know what the “safe” RPM range is?

 

[DON MAHER]

Wow a week later and no one has any information about the RPM range of this engine?

 

[Buckshot]

Wow a week later and no one has any information about the RPM range of this engine?

When I ran the black head Evo version in an outrigger, it liked to be at +/-19k. I ran ~20% oil to help it live. I was told by factory racer to let it rev.

 

[DON MAHER]

Hey Buckshot, thanks for the info. 18,500 for my zen’s!

 

[ianfolkson]

You can run it safely to 20000rpm it will run at 21000 but then you need lots of oil to stop big end bearing breaking.
I run 20% Motul go kart oil fully synthetic in ringed and aac version. No loss of power with the high oil and safer on the big end bearing.

 

[ianfolkson]

Green Head GPX AAC over 2 hours running in a Endurance boat. 20500rpm 20% Motul go Kart oil new head design with 6 M4 bolts for better spread of clamping head. Running on powerspark ignition. Important on AAC water cooling in head first and out on case.
4th place in iMBRA world championships Endurance
First 6 places in Endurance CMB GPX
Hydro 1st 27cc CMB GPX
Offshore 1st 27cc CMB GPX

 

[SayMikey]

Currently IMPBA does not allow Methanol in spark ignition motors

 

[ALLAN YUEN]

Currently IMPBA does not allow Methanol in spark ignition motors

someone “ Cheat” mixed gas & methanol into the red tank how to find proof smell or gas tester device before fill up ?

 

[Buckshot]

You can run it safely to 20000rpm it will run at 21000 but then you need lots of oil to stop big end bearing breaking.
I run 20% Motul go kart oil fully synthetic in ringed and aac version. No loss of power with the high oil and safer on the big end bearing.

Currently IMPBA does not allow Methanol in spark ignition motors

Pump gas dose not have methanol in it. I believe the EU guys like Shell V-Power.

 

[ianfolkson]

Pump gas dose not have methanol in it. I believe the EU guys like Shell V-Power.

Any 100 octane petrol works well in the CMB motors they are not set up for higher octane

 

[David Bryant]

apparently Stu Barr runs like 110 - 112 octane