Hello Don,
My name is Tom David, and I am the boater that Chris is referring to from Indiana.
First let me say that I agree with Chris and Steve Wood about the possibility of RPM
harmonics causing some of the sleeves on the RS 80’s to crack at the finger port.
I am not a well known boater from Evansville, Indiana. But I have many years
of experience setting up 80 size nitro engines in Mono Hulls. About one year ago
I set up a new CMB 80 RS in a Seaducer 60/80 Mono Hull. I never was able to
obtain the performance level I was looking for with this stock engine turning a
X462 on the Seaducer hull.
After spending many hours at the lake testing and cracking several sleeves, I went to
the work shop and put on my thinking cap for a solution. I decided to drop the high
exhaust timing of the RS sleeve down to 181 degrees. I did this by cutting .016 off
of bottom of the flange on the sleeve. This dropped the sleeve in the case and brought
my exhaust between 181-182. I did NOT change anything else on the sleeve. Using
Steve Wood’s .68cc head button with a flat squish band I set the deck at .011. On
my engine it took .020 of shims to reach the .011 deck clearance. By the way,
this timing now is almost the same as the CMB Green Head 80. (intake and exhaust)
I am using the new Cooper muffled pipe for my testing. The fuel is 50%, 18% oil.
On a very humid day I tested my set-up. Pipe set at 11.5 turning an X462 I was able to
Clock in with several 12 second laps. What really made me happy -- I never replaced
The MC-9 glow plug after five runs. Also never cracked the sleeve.
Of coarse this is a mono and not a hydro. But I am convinced if you make this mod
I described, you can reach the same level of performance as the green 80. Maybe even
better because of the geometry at the transfer and boost ports and the added finger port of the 80 RS sleeve.
Happy Boating