Pipe Tests, Sound Limits and Deceptive Dynos Letter to the Editor - Feature Review - Dirt Rider Magazine

I recently read your article featuring full exhaust systems for the Honda and Suzuki 450s (June 2005). Will you be having tests of the quieter performance pipes (below 98db)? If so, I—and many others—look forward to it!Also, it was noticed by many on Thumpertalk.com that the stock CRF horsepower and torque curves where less than what other tests have previously shown (including your own magazine's). In a previous 450 shootout it showed over 50 horsepower while the stock CRF 450 in your pipe test only reported about 45. Some on Thumpertalk.com guessed that the stock CRF450 had rings that may not have seated well when it was broken in, causing low compression and lower ratings. Was this the case?

I enjoyed the test, but I'm looking forward to the quieter pipe test (96-98db, and possible quieter inserts that can be removed).

Todd Papora**Todd,Sure, some day we will have another pipe test. When exactly? I don't know. But we will definitely have a lower sound limit.We started with the AMA Professional sound limit (102 decibels) because that seemed to be what all the pipe manufacturers were shooting for at the time. It also gave us the most pipes available for a shootout—we wanted to have more than two in the test! In fact, about half of the pipe companies didn't even send us exhaust systems because they knew they wouldn't pass the 102 limit!I agree, 102db is still too loud, but it is a start and we will go to a lower level next time... maybe the AMA sound limit of 99db for amateur motocross. There are only about 100 guys in the US who truly race at the AMA professional limit, so for now 102 can be for them. But we should limit our test to at least 99db next time. Personally, I race motocross with a 96db system.Hopefully the majority of exhaust manufacturers will get on board with the sound limits or we will lose our right to ride in a LOT of places real soon. But we have to speak with our wallets as well. They continue to make loud systems because people continue to buy them. As the Editor of Dirt Rider, I know we have to lead by example. But if we jump too quickly, we will only take along those who already understand the problem. We want everyone to understand the sound issue. If we can get guys running 107db systems down to 102, that's a start. And hopefully next time we'll see another improvement. Racing organizations and tracks also need to start enforcing sound limits. We're on the right track. We wish it was faster too, but we're working on it.As for the horsepower rating, please forget what number a dyno puts out. Everyone is so hung up on that number, but it means nothing unless all bikes are run on the same day, same dyno, in a relatively close period of time. People do not ride a bike like a dyno reads it: Full throttle from the earliest possible point with a 100% load on the wheel without (much) spin. In fact you can't really feel horsepower, only torque. The dyno run in the test was used for comparison purposes between the bikes on that particular day, and as a reference to see what the pipes were doing. We did not use the dyno charts one bit in our rating; it was entirely based on track impression.I'm sure the Yamaha crowd on Thumpertalk was saying the Honda rings wore out on the fourth dyno run, but you should know it was the valves going soft, causing the power to drop. Actually that Honda 450 (now four months after the shootout) is running better than ever—despite what a dyno says.–Jimmy Lewis