91 v 91b v 91b1
Posted: Wed Jan 23, 2008 10:44 pm
Is there a difference in performance between these models?
Dennis,
The biggest peformance difference in the models you mentioned is the switch from the Mac Big Bore carb to the BDC 14 model. Put a BDC 14 on all three motors and you will have a hard time noticing a performance difference in them. They all have the same bore, stroke, intake tract, ignition etc. The exhaust and transfers are the same and only the boost port in the back varies. The 91 and 91A use the single square boost port with the removable cover while the 91B, B1, 92, 93 all use the two acorn shaped boost ports. To give you an idea of how close the motors are in performance, back in the 70s they were all legal in the American Reed classes and you could put the newer manifold and carb on a Mac 90 and that motor could run right with the later models when fitted with the BDC 14 carb. The 90 has one exhaust instead of two and it has a completley different boost port arrangement..... still ran with the other motors in the hands of the right driver.
Regards,
Steve O'Hara