Check out this cb750 chopper senior has, saw it on one of the shows in the background and googled it and came across this video on youtube. Boy that thing sounds strong as hell! Wish they showed the dyno results...
@FastCletus552 aka Jimmy C, buildin' rides out of Napa CA
Current Build 1980 CB 750 F
Finished Build 1975 CB 500T Cafe Racer - SOLD
2002 Ducati 998 Biposto
2005 Rossi #46 Scooter
I think he meant "American Choppers",the TV show. I know I'm not a big fan of the showBut if they are fooling with some SOHC bikes I may have to tune in!
Hellbilly,thats what Fred sound like at full song I've seen alot of engines dyno'd.Both on engine dyno's and chassis dyno's,but I've never seen anyone pull one for that long!!! I counted 11 seconds at full pull on that vid! Thats just kinda abusive IMO. Love the tank on that bike.
I don't think Sr. is hurting for money. Many's the time him or his boys/employees blew stuff up, and they just changed it out. Remember the supercharged chopper (Shelby Cobra, maybe? can't recall) they said had to hold up to full throttle runs, so they dyno'd it and it went boom? Next segment, there's a new engine in there.
Luke M
Used to have a 1979 CB750L, sold it as a parts bike, now riding a slightly modified 1984 VT700C. Network/Field Engineer. Central OH, USA, Earth, Sol System, Milky Way Galaxy, Universe.
Yes I meant the show. This bike is one of Senior's old bikes, before he got rich and famous, now it sits on a lift in his f*&$ing huge garage at his non-vacation home. That poor bike deserves a lot better than that....
Wish you would get a video of that thing running at full song! Talk about me being selfish, lol
Buddy, if I had a decent camera I would. It don't sound like much just dead revving it, but it has a nice, deep growl when cruising. Pleasant surprise. But oddly, at WOT, it gets much quieter. I dunno. More physics I don't understand :(
Yeah, that's how my accord was when I put an aftermarket cat back exhaust on it, when I had the removable "silencer" (baffle) it still had a nice low tone to it, but when at WOT it would seem almost like there was no noise coming from the exhaust. Must be the back pressure from the baffle really affects the air flow at WOT and the sound waves get caught and cancel each other out before exiting the exhaust?
Correct me if I'm wrong, really just a theory, but if you had a 4-4 exhaust it would stay loud because there is only one cylinder firing per pipe so there aren't any contradicting sound waves to cancel out the noise, right?
If the firing order on the CB750 is 1-3-4-2, and based on the observation that it operates like a parallel twin x 2 (2 pistons going up, one fires, same 2 pistons go up, other one fires), and if cylinders 1 and 2 are on the same side of the bike, then you would get 2 exhaust impulses per side:
1 - left
3 - right
4 - right
2 - left
and so on. I was originally thinking they would alternate in a left/right/left/right pattern, but the firing order determines that.
I like machines. They are fun to figure out.
Luke M
Used to have a 1979 CB750L, sold it as a parts bike, now riding a slightly modified 1984 VT700C. Network/Field Engineer. Central OH, USA, Earth, Sol System, Milky Way Galaxy, Universe.
Sound wave cancellation is real, but only happens in discrete locations/times. Sound waves are literally waves of pressure in the air. An easy way to think of it is to use water as an analogy.
When there is a wave in the ocean there is a depression in the water immediately before the wave. If wave A overtakes wave B the depression of A will temporarily cancel out the peak of wave B (at least partially, depending on the size of the wave). However, as wave A passes through wave B there will be a point where the peak of A and B line up. At this point the size of the peak is A+B so the it will be significantly higher.
Once wave A passes all the way through wave b, then the two waves are now independent and non-interfering again.
So yes sound wave cancellation is real, but with a moving motorcycle it can't account for a decrease in sound volume. It would only have an impact if the bike was stationary and your sensor (e.g. your ear or a mic) was in one of those cancellation zones. If you moved your sensor a bit, then you would hit a peak.
True wave cancellation is a real phenomenon, but only in standing 2-D waves, and even then they are mostly just possible as mathematical models and difficult to create in real life.
Sound is a 3D wave that radiates from a point source. Here is a 2D representation showing how 2 point sources would interfere with each other. Notice the areas of maximum pressure and minimum pressure. These will correspond to the peaks and troughs I am talking about.
Now, none of this explains why you're getting a quieter exhaust at WOT, but I thought it might help.
I love how they did the "you wanna see that,,,,but you dont"" part in that video!!! Dane Cook had got to be one the funniest guys ever. I've almost wrecked while listening to that CD.
Locked
But if they are fooling with some SOHC bikes I may have to tune in!
I've seen alot of engines dyno'd.Both on engine dyno's and chassis dyno's,but I've never seen anyone pull one for that long!!! I counted 11 seconds at full pull on that vid! Thats just kinda abusive IMO. Love the tank on that bike.
I love how they did the "you wanna see that,,,,but you dont"" part in that video!!! Dane Cook had got to be one the funniest guys ever. I've almost wrecked while listening to that CD.