- Joined
- Oct 25, 2021
- Messages
- 203
- Location
- USA
That's a pretty good dyno run. . .
The problem is not the fuel curve tuning. it how inefficiently the exhaust 'works' at certain rpm. The exhaust has a resonance, based on the exhaust cam timing. At every rpm point the exhaust pulse resonance is a certain length. Lower rpm has a longer resonance event versus high rpm, so the resonance point occurs further along the exhaust header pipes. In the case of the 1199 and 1299, the resonance point at about 3500-4000 rpm is INSIDE the catalytic convertors . .AFTER going through a very restrictive 2-1 merge of the two head pipes, and an additional 1-2 separation back into the convertor/muffler assemblies. I won't even start to opine on what happens as it passes the restrictor valve assembly. Let's just say it can't be very efficient. This resonance disruption continues up to about 6,000 rpm, which is just before the 2-1 joint, at which time it starts to work properly as the rpm increase. By 7,000 the exhaust is 'working' properly again and the engine just takes off like a rocket ship. So, to get rid of the 'dip' the only solution is to get rid of everything that is causing the resonance mismatch problem. First step (and cheapest if done correctly) is to ditch the stock mufflers. You could just run straight pipes off the two head pipes and ditch everything from the 2-1 assembly onwards. Just get some 56-60mm stainless with bends and weld up a straight exhaust that wraps around the oil pan and exist on either side of the bike. This is called LOUD. but it will give you the best performance. This is a Race only setup, however, since the rear cylinder would have to ditch the loop under the seat, turn straight down in front of the swingarm and then around the oil pan sump to exit on the right side of the bike, while the front exhaust would just dump directly to the left side in front of the tire. That would keep both pipes short, very efficient, and light. A flame catcher mesh at the exit would be necessary. Very loud, very efficient, and the exhaust pulses would be separated which would improve the scavenging for each cylinder (since they wouldn't be interfering with eachother) and could be individualy tuned for best performance.
Barring that, though, I'm of the opinion that the quietest option is to used a single-tube slip-on, like mine, or a the Competition Werks or AR versions. They all do basically the same thing. The only real difference is the cost and materials used. You could get rid of the incredibly bad 2-1 interface by making a custom one out of stainless, and have it taper the two pipes more smoothly together, sort of like an exhaust header on a car, so that the pulses complement eachother, rather than running into eachother at that joint. It would require ditching the first glass pack, but the flow and performance increase at that juncture would probably get rid of the torque variance shown in the Dyno printout. Noisier, yes, but how much is the question. You might get some off-throttle popping because of the removal of the first glass pack. I ran mine without the second glass pack in place, and it was spitting out flames constantly, just running in the driveway. Of course this was with the lower farings off, so it's not an option for the street. Having the complete length, however, would probably reduce this a bit. I'm considering making this modification over the Winter, when I do my 2nd Desmo Service on the bike (Yes I do all my own work on it).
If you need any more information let me know. Thanks for your comments.
