by Bill Jurgenson » Mon Aug 02, 2010 12:17 am
just for the books.
My SZR is one of the quieter ones at meetings altho I use an absorber can (straight-thru) without a DB eater, a SR-Racing can with E-4 for the XT660R.
I have remained quiet; the BSM is not a good can, regardless of price. Their only would-be advantage, aprt from being light and looking good, is that they have certification for MZ models. Admittedly, this is an advantage in continental Europe. By what means they got certification is anybody's guess. They are too loud brand new with the DB eater installed. I measured one, new out of the box with 106DB. On my own Skorpion. A byproduct of their being light: the damper wool burns out quickly, so that they get louder and louder. You end up removing the end caps and repacking.
beenther-doonit- I've had three BSMs. Also three original L&Ws, a L&W modified by L&W, two BOSs, Two Remuses, the OEM LaFranconi of the SZR and the SR-Racing, All on my three different Skorpions and the Yamaha so all on the same basic engine.
What is important are larger headers. BSM does not and neither does anyine else offer a complete system with headers for the Skorpion. Or the SZR. There some larger headers for the Baggi as has been noted elsewhere here in the forum.
Assuming your shop made larger headers (whcih they apparently did not), the increase you note is easily explained. Otherwise it is wishful thinking.
My own experience with reflector cans(those with internal baffles) has been varied. On the Skorpion it is hard to beat the OEM L&W which is a reflector, a very expensive one into which many hours of dyno testing were invested. It was all of 1hp down on a very good straight-thru BOS (with 108BD): 58 instead of 59. It was 4-5hp down in midrange, tho, where MOT measuring is done and where it is quietest. I was unable to get the jetting right after weeks of testing on my TM42 and a baffled Remus mated to my Remus Cup system so I bought the look-alike straight-thru from them and - voila! - the carb was great with the jetting I started with- at a just tolerable noise level, much louder than the baffled can. I had no such problems with the L$W, either, altho it has baffles because it is designed specifically for the XTZ engine. The baffled Remus simply had way too much backpressure.
In real-world car racing, reflectors are the rule. But they must be calculated to match the system and also the use. Because they have baffles,reflectors, they can be designed, tuned to aid scavenging for a given RPM range. this is not really possible with straight-thrus. Within the design range the backpressure is vey low at the right times. At other RPM it increases markedly. That is why the BOS had so much more ( 45 instead of 40) at 4000: the absorber has less to very little back pressure but also very little to no reflection. The L$W is tuned for 6000 where it creates no practical loss. In fact at that speed it is up on the BSM by 3-4hp!!!
bottom line: don't waste a cent on a BSM. It is cheap crap sold at a premium price. Last week I was truely shocked to hear to hear the present retail price which is higher than the that of my high-end SR Racing.
A good can costs money. It is not just a stainless cylinder with caps. One size fits all stuff like the BSM is just a cylinder with endcaps. Most aftermarket cans are. Not all. As i noted at the top, the purpose designed SR is quiet while being straight-thru and without an eater. Here, too, many hours of testing and experience went into the design specifically for the Yamaha engine and getting it certified. It is conceited to assume one does not have to pay for other peoples work and experience. OTOH, Inferior stuff like the BSM show that it is possible to sell junk at a premium. The only way to avoid this is to learn.