All I can tell is the cylinder has been to someones porting salon and it has had the sand cast finish removed and possibly more. The port window dimensions,the port tunnel dimensions and exhaust system being used have to be known to make any type of assessment as to what application would best suit this engine.
I do not know what size engine and power level the "B" pipe is best suited for, but I have tested both versions of the TRX 5 and both versions of the TRX 5B on the 250s and the 310 big bore cylinders and the TRX 5 ( pipe with the small diameter head pipe) performed the best during my test.
On the 250 engine that we did the pipe testing on had our porting, head, carburetor, and intake system, the out of frame version of the ESR TRX 5 (TRX 5 with the out of frame pipe body and out of frame silencer) made the most power everywhere when compared to the TRX 5 center mount (TRX 5 with the centermount pipe body and center mount silencer), TRX 5B center mount (TRX 5B with the centermount pipe body and center mount silencer) and the TRX 5B out of frame (TRX 5B with the out of frame pipe body and out of frame silencer)
On the ESR 310 (level of porting unknown) the TRX 5 centermount version made the most power everywhere over the TRX 5 out of frame, TRX 5B center mount, and the TRX 5B out of frame version.
