Outboard exhaust?

This topic has 9 replies, 8 voices, and was last updated 15 years, 2 months ago by kent7351.

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March 23, 2011 at 11:22 am #273411

sthomas2
Participant

This may be a dumb question but ive always noticed the different sounds from different outboards idling around before a blastoff. I realize why an EFI sounds different but why do some optimax and xs motors sound completely different? I have a 2008 optimax and its very quiet idling with a small “loping” sound. Ive noticed some other opitmax outboards that have more of a “popping” sound. Also noted alot with the XS motors but have still heard some XS motors sound like mine. Hopefully i am describing this right. Can anyone explain why? are they modifying the exhaust? is that even possible? is this anything that helps performance if they are changing something?

March 23, 2011 at 1:30 pm #273412

poopsdream
Participant

Maybe they have made some small modifications on their motorOn my XR6 I have installed a Modified Tuner pipe , Boyesen Power Reeds , Changed the timing and rejeted the carbs. And my motor has a different sound than most XR6s.

March 23, 2011 at 2:07 pm #273413

Bass Cat Boats
Keymaster

Difference in exhaust tube

March 23, 2011 at 2:29 pm #273414

Bass Cat Boats
Keymaster

We dont think most folks modify engines today, nor are the technicians really able to understand at the home town level the impact those changes make. Thus we feel the different tones or pops you hear are just differences in those engines from the factory. The Pro XS and XS engines do have a different sound than the sewing machine sounds of the straight Opti engines. Though often that is from the different air pump (compressor) in the cowling also which has nothing to do with exhaust. The tuners in the exhaust buckets are different. The sound attenuation differences when one is reaching up to plane out are also impact by different exhaust hubs on the propeller and combinations of PVS plugs.

March 23, 2011 at 3:13 pm #273415

ischnell
Participant

Im betting it is different boats and the engines mounted differently. Higher or lower, more submerged or less, different trim etc. I think all these will make the engine sound different. I know it does on my opti 225

March 23, 2011 at 3:29 pm #273416

Tideman
Participant

I LIKE TO HERE THEM SOUND LIKE THEY ARE CRACKING WALNUTS….LIKE A AUTO WITHA BIG RACING CAM INSIDE………THE LOUDER THE BETTER, BUT IM ALMOST DEAF…

March 23, 2011 at 3:40 pm #273417

poopsdream
Participant

TideMan:Light Car+LS7+Big Cam+ Good Headers= GO FAST

March 23, 2011 at 5:09 pm #273418

Jstew
Participant

Nothing in the world sounds as good as a loped up big block trying to idle at 1200 rpms. Close was a very warmed over Merc Pro Max last weekend with relieved exhaust and a good tuner. That motor sounded absolutely wicked just idling – when he hammered it – huge adrenaline rush.

March 23, 2011 at 6:20 pm #273419

tswanson
Participant

Tones are the result of velocity of air moving thru the exhaust.I would say that if you have the exact same motor side by side and they sound different, then the idle speed is probably higher on one than the other.One may also be just a bit leaner and the other just a bit richer. Rich will be muffed or warm, lean will crack because it is hotter.All 2 strokes have tuned exhaust. The exhaust tube creates a super charged effect. Unburned fuel is sucked thru the motor then is reflected back in into the engine just before the exhaust port is shut off by the piston.A tone is a sine wave. The length of the sine wave is a function of rpm. Higher rpm-higher tone (shorter sine wave).A natural aspirated automobile engine has around 78% volumetric efficiency. A blower will push volume well over 100%.Tuned exhaust does the same thing as a blower in terms of increasing volumetric efficiency.You are packing more air/fuel into the cylinder to get more power and better efficiency by reflecting the sine wave back to where it came from.It is easy for engineers to figure this out these days using computers.I am impressed that the early racers in the 50’s figured out how to do this largely by trial and error.

March 23, 2011 at 8:42 pm #273420

kent7351
Participant

LIKE TO HERE THEM SOUND LIKE THEY ARE CRACKING WALNUTS….LIKE A AUTO WITHA BIG RACING CAM INSIDE………THE LOUDER THE BETTER, BUT IM ALMOST DEAF… Is that why youre always YELLING on here?
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