CMB 21 LS Black Case

[akilbar]

Has anyone run the new black case CMB 21 LS. I know Bobby from Tidewater ran one at the SGRA race in October. It seemed pretty good but he is always pretty fast. Anyone know the differences between it and the silver? I heard higher timing?? I am replacing a worn out CMB red head 21 in a Jaguar 2 rigger.

Tony

 

[izitbrokeyet?]

As far as I know the timing isn’t raised unless he cut it (stock is around 178 if I remember correctly). If the Sleeve was a buggy sleeve, he may have raised the sleeve a hair to run it in a boat. The Black case has reduced crankcase interior volume relative to the silver case. This is mostly because the boost and transfer canals are separate canals to the liner in lieu of the huge canals feeding 2 ports on each side of the piston. The front boost canal bottom lobe is much smaller than black case than on the greenhead.

There is a LS and a SS version of the black case motors. I'm not certain, but I'm thinking it's like the TT where the difference is only in the P/l, head button and crankshaft with most other parts being compatible.

 

[DaveMarles]

I just compared the latest black case to the last silver case and as far as I can see the internal difference is only the exhaust port shape in the casting. The side transfer passage is still one big passage for both ports and everything looks exactly the same size. I don't know about the port timings because they change with every batch of engines. Externally the case is slightly different but you would need to look closely to see that.

 

[izitbrokeyet?]

Dave is right...I was looking at one of the older Black Cased motors.

My Bad..

 

[akilbar]

I ordered it yesterday. Thanks for the input. Guess we'll see. I have two friends with the same boat (21 Jag 2). One is running a 2 year old greenhead LS. The other is putting a new NovaRossi in his. Mine was ok with the redhead but the greenhead in my buddies was faster.

Should be a fun comparison.

 

[izitbrokeyet?]

another point of interest...the new Black case motors are timed stock at 180 in lieu of the greenheads 178 all parts are compatible between the new black case and silver case.