Exhaust - Page 2 - Kawasaki Vulcan 750 Forum : Kawasaki VN750 Forums
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post #11 of 16 (permalink) Old 12-25-2018, 10:33 PM
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Originally Posted by Jason Pittenger View Post
I just pulled the mufflers off, running straight out of the goat. Love the sound! Cheap, and easy to reverse.
I did this last night and drive it today. Sound is good, drones going down the road, need some extensions to carry the sound out the back. Actually feels like it has more power on the top end, doesn’t feel like I lost anything on the bottom end either.

- 1999 Kawasaki Vulcan 750
Ear shaved
Mufflers removed / 38/140 + 2 shims
Relay coil mod
Pick-up coil mod
Emissions removed
Lowered rear
Rear blinkers located in tail light housing
Petcock gutted

- Wife's: 2018 Can-am Spyder F3 Limited Pearl White
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post #12 of 16 (permalink) Old 12-26-2018, 04:48 PM
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Some people drill out the baffles and keep the stock mufflers on. I haven't tried this as its not reversible. I get enough wind noise that I need ear plugs anyways, so the droning doesn't bother me.

I want to put in short (few inches) of straight pipe after the goats belly, just to regain the rear clamp on the heat shield. The left side rattles with the missing clamp.

As far as more power, the bike feels faster when I ride without earplugs. Clearly my perception is not reliable 😄.

I am doing an ear shave and rejet over the winter. Also going to adjust ignition timing a bit. Stock without mufflers, I run equal to a Harley V-Rod all through 1st gear. He loses me in 2nd, as he doesn't hit 2nd until 60 mph. If I can pull ahead after the changes, I'll let you know.


'89 Vulcan 750 Purchased 4/12/18 @ 17805.9 miles $800
Purchased stock except for K&N Filters. Wrecked once
20969.2 miles & counting

Completed modifications:
Removed mufflers, running straight out of goats belly
Pick-up coil re-gapped to .020"
Compufire 55402 r/r series regulator
USB Outlet + Voltmeter
Repainted Metallic Blue w/ new tank bages

Planned modifications:
Ear Shave (without coasters)
Custom LED turn signals
Windshield
Highway Pegs
(Possible) ignition advance
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post #13 of 16 (permalink) Old 12-26-2018, 11:04 PM
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Drilling is totally reversible! Ever Heard of bolts or a welder? Lol

And the dude on the V-rod is going easy on you... Just saying

Even with "just" drilling I would consider adjusting the carbs. At least the air/fuel mix if not shimming the needle(s). Probably won't need a rejet if you keep the stock airbox and filter(s).
Easy enough to pull a spark plug after a few miles to see if it's running too lean.

Straight pipes are definitely too loud for most!

Don't just ditch the mufflers. Short pipes raise the power band so you have to almost redline it just to get out of your own way. Or worse, you end up lugging the motor and beating up the rotating assembly and trans gears... And shaft splines!

Do ditch the crossover and get slip-on, free flow mufflers. "Screeching beagle" is Harley's "stage-one" label. And yes they flow well yet are not obnoxious.

I think Cobra makes full pipe setups for the VN and many Jap makes/models.
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post #14 of 16 (permalink) Old 12-27-2018, 09:58 AM
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I ran the numbers from a dyno chart of both bikes (in stock form), and the VN750 (red graph) pulls just under the V-Rod (green graph) from 0-40. The graph is adjusted for bike weight, gearing, tire size etc. He is running an oversized front sprocket (30 vs 28) for lower highway RPMs, which is also in the graph. It basically shows how hard you will be pushed forward at a given speed. He hits his torque peak in 1st just as I'm hitting 2nd gear. I also show a Buell (yellow) and a Suzuki V-Strom (black) in that graph.

If the open pipes after the goats belly help the top end, that would keep me even just a bit longer. I don't have access to a dyno to measure changes, so that VRod will be my gage. I'll post my holeshot results this spring, after an earshave and rejet.

Open pipes after goats belly isn't too terribly loud. I do make an effort to be light on the throttle during morning or evening hours in town. Sundays, when riding to church, I push my bike to the street before starting, as a courtesy to my neighbors.

The straight pipes I was referencing was going to be after the goats belly, simply to give the heat shields something to clamp onto. I wasn't considering full straight pipes! YIKES! Others will tell you that full straight pipes without some sort of crossover causes you to lose low end torque. And that it's stupid loud. I don't need it THAT loud.
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'89 Vulcan 750 Purchased 4/12/18 @ 17805.9 miles $800
Purchased stock except for K&N Filters. Wrecked once
20969.2 miles & counting

Completed modifications:
Removed mufflers, running straight out of goats belly
Pick-up coil re-gapped to .020"
Compufire 55402 r/r series regulator
USB Outlet + Voltmeter
Repainted Metallic Blue w/ new tank bages

Planned modifications:
Ear Shave (without coasters)
Custom LED turn signals
Windshield
Highway Pegs
(Possible) ignition advance
Jason Pittenger is offline  
post #15 of 16 (permalink) Old 12-27-2018, 01:52 PM
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Neat!
Got a link to that calculator? Or is it a program?

Straight open pipes usually have reversion problems and can only be tuned for a very narrow RPM band.
Bends, baffles, "lollipops" and the like are great for fighting that reverse shockwave. As long as they don't impeed flow...
Of course there's always a compromise.
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post #16 of 16 (permalink) Old 12-27-2018, 05:15 PM
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https://www.dropbox.com/sh/940m9ihpv...oz67zxuHa?dl=0

That will get you to the folder with all the Excel documents. The posted graph is in the Vulcan Excel file. It pulls the data from the other files.

The graph was also useful for gaging optimal shifting RPM. 8500 from these graphs. Notice how the 1st gear line basically touches the 2nd gear line? I've heard some say to run to 9000-9500 for best acceleration, but the power falls off quickly after 8000. Maybe with intake/exhaust mods it retains power above 8000? I'm not sure I want to push a vtwin past red line.


'89 Vulcan 750 Purchased 4/12/18 @ 17805.9 miles $800
Purchased stock except for K&N Filters. Wrecked once
20969.2 miles & counting

Completed modifications:
Removed mufflers, running straight out of goats belly
Pick-up coil re-gapped to .020"
Compufire 55402 r/r series regulator
USB Outlet + Voltmeter
Repainted Metallic Blue w/ new tank bages

Planned modifications:
Ear Shave (without coasters)
Custom LED turn signals
Windshield
Highway Pegs
(Possible) ignition advance
Jason Pittenger is offline  
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