What I/you did today on the bike
#21
Research on Powerbomb and Megabomb cross-sectional views produces only a little information.. Turns out the Powerbomb simply contains a densely perforated section of header piping.. I didn't find enough on the Megabombs' internal config to comment - but it does not produce TRQ, idle to 6.5K, as well as the stock header. It does significantly increase TRQ from 6.5k to redline though..
#22
Research on Powerbomb and Megabomb cross-sectional views produces only a little information.. Turns out the Powerbomb simply contains a densely perforated section of header piping.. I didn't find enough on the Megabombs' internal config to comment - but it does not produce TRQ, idle to 6.5K, as well as the stock header. It does significantly increase TRQ from 6.5k to redline though..
That's a characteristic of any header that goes up in ID though isn't it? I know on cars it sure is.
#23
15T front
I went +1 to 15T on my SF for commuting. Still can lift the front wheel no prob. Rode off a 2 ft drop today and front lifted up ok. Had to rush down to the LBS and get a chain because the PO cut the one on the bike to a minimum length and was too short for the 15T front sprocket. He also ran it bone dry. Can't believe they did not have a 520 size O-ring chain on the shelf. I might as well order everything online cause the bike shop usually has to order it anyway. Hey, anyone have troubles with the metal piece in the sprocket guard running a 15T? Any interference? Chain looks pretty close to it and other engine case structures. 14T was wore out. Suspect the chain too. Will order a good chain and sprocket set soon but the cheapo chain should last a few weeks. And my home-brew tubeless rear tire is holding pressure now. Like on my mtb tubeless wheels, there was leakage for a few days but a few miles/hours of use and the Stan's did it's magic and now there was no pressure loss after my commute today including 40 miles of interstate highway. Maybe I will do the front wheel next week.
#24
Yes Pwjm, that's right.. I expected - due to its' high price - that the Megabomb would produce a better TRQ curve, from off idle to redline, than the stock header.. Imagine my disappointment.
#25
I didn't read everything, but FWIW, I found it interesting that FMF did the power bomb set up which is a mini-expansion chamber on the bike as is a reverse cone megaphone, a seldom used set up on off roaders these days, but common on the MotoGP pipes. All are apparently dealing with exhaust wave acoustics to work flow. How, I don't know. I knew and understood more about two stroke chambers, courtesy of Gordon Jennings' Two Stroke Tuner's Handbook, back in the 80s, but never really followed up with the 4 strokes.
Unfortunately there is no 4 stroke "Gordon Jennings" on the horizon...
Unfortunately there is no 4 stroke "Gordon Jennings" on the horizon...
Along with any mod you'd need to be able to do accurate testing. That stop watch bolted to a plate on the R.H. mirror base and activated by a piece of metal affixed temporarily to the throttle was a huge advance for me in knowing if something worked or not.
On my XR200 I found it a bit quicker with a vertical divider in its intake; then I sawed about an inch and half off the Al muffler case-shortening the OAL of the exhaust, and picked up a little more sprint power. Times dropped from 6.53 to 6.41 with those two mods. That's a nice gain in a short distance sprint.
But, removing the choke slowed the bike to mid 6.50s again!
Your brain says it'd have to be quicker without all that junk in the air stream, but the automatic on/off stop watch doesn't lie, and it allowed me to do testing by myself without the expensive instrumentation I'd been eyeballing. There's a change in pavement level at the end of where I test, so I back off the throttle when the bike hits the dip. Testing starts from a 17 kph roll at a specific point on the hwy in 1st btw.
Having an a/f meter to check ratios accurately saves a ton of time and avoids mistakes due to brain lapse as well. But then again if you have accurate timing you can compare WOT jetting results that way.
Last edited by Richard Avatar; 05-31-2015 at 07:21 AM.