CMB .21 Greenhead

[GRand]

can someone give me an approximate pipe length (and where your measurements are taken) for a CMB .21 outboard..........40%, .007 head clearance.

 

[TimD]

Maybe you should list what type of pipe you are using.

 

[GRand]

sorry...........its an irwin pipe

 

[ggillman]

Got these specs from Prestwich Models in England:

CMB Greenhead

2.8hp@40000 rpm

Suggested pipe length 185 mm.

Gene ;D

Most seem to measure from center of cylinder to end of diversion cone.

 

[Jerry Dunlap]

Greetings,

On my CMB Greenhead 21 with the new Irwin muffled 3.5 pipe, the distance from the end of the header to the weld on the pipe is 7"(is that close to 185mm)? When it comes to "pipe length," once size doesn't fit all. But, that 7" length should be a good starting point.

.007 head clearance should be fine. I think I'm running .010 on mine and it's working great. A propeller that seems to work well for me is an Octura X640 cut down to 37 mm in diameter.

Jerry Dunlap

 

[ggillman]

Dug out my conversion chart:

7"= 177.8mm

7.2" = 182.88mm

7.5" = 190.5mm

I would say 7 to 7 1/4 inches would be real close.

Gene ;D

 

[Alan Elzer]

Greetings,
On my CMB Greenhead 21 with the new Irwin muffled 3.5 pipe, the distance from the end of the header to the weld on the pipe is 7"(is that close to 185mm)? When it comes to "pipe length," once size doesn't fit all. But, that 7" length should be a good starting point.

.007 head clearance should be fine. I think I'm running .010 on mine and it's working great. A propeller that seems to work well for me is an Octura X640 cut down to 37 mm in diameter.

Jerry Dunlap

Jerry

Have you rad your 36 in. wolf boat yet?

Alan

 

[dougaldy]

Greetings,
On my CMB Greenhead 21 with the new Irwin muffled 3.5 pipe, the distance from the end of the header to the weld on the pipe is 7"(is that close to 185mm)? When it comes to "pipe length," once size doesn't fit all. But, that 7" length should be a good starting point.

.007 head clearance should be fine. I think I'm running .010 on mine and it's working great. A propeller that seems to work well for me is an Octura X640 cut down to 37 mm in diameter.

Jerry Dunlap

Jerry,

Who did your X640? I have a Sholund X438 on my HTB 290/greenhead combo and was wondering if maybe the X640 might be a bit better.

Scott

 

[topfuel443]

Wow, this was an OLD thread

~James

 

[dougaldy]

Wow, this was an OLD thread
~James

James, youre right. I didnt even notice this was that old. Oh well. Jerry what have you found to be the best prop for your CMB?

Scott

 

[Jerry Dunlap]

Wow, this was an OLD thread
~James

James, youre right. I didnt even notice this was that old. Oh well. Jerry what have you found to be the best prop for your CMB?

Scott

The props I've had the best luck with on CMB/MAC OBs have been: X438, Y537(I think that's the correct number), and X437/3. There's a couple of props from the Grim Racer Series that might work, but I haven't had the opportunity to try them yet.

Alan, I didn't build a WOF 36 this winter. Had to build another WOF 34 to replace one that was apparently stolen from our front porch after the National OB Championships back in March.

JD

 

[Mike Larson]

I'm running my greenie with the spp nova pipe header to pipe, mine only likes the small dia, too, I have a tweaked 215 on it reduced, a little, it spools and pipes well, the top end is unreal....... kinda Mac like... the 437/3 will test next... my clearance is down to .008, i like it...... mike