Why no crossover on an airboat?

A discussion on ways to reduce it.
rost495
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Why no crossover on an airboat?

Postby rost495 » Thu Jun 23, 2011 11:52 am

Dave says no crossovers on an airboat? Why?

Right about now I"m really hard thinking about a crossover for torque, and then into a dual in dual out RV muffler, largest I can find and then tail pipe all the way out.... Could then add 2 more mufflers later if needed.

So many different answers....

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BigJakesrq
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Re: Why no crossover on an airboat?

Postby BigJakesrq » Thu Jun 23, 2011 12:21 pm

It's been done there was a thread on it a while back. Do a search you can probably find it.

Really in the end what you are taking about doing seems excessive when you'll still have the prop making a bunch of dbs more then your stealth exhaust setup. Unless you running a lot of gear in your reduction, big wide blades, and keeping you tip speed WAY DOWN.

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Re: Why no crossover on an airboat?

Postby machinestles » Thu Jun 23, 2011 12:54 pm

Get the magnaflow muffler. I believe the 2.5 inch part # is 12468 less than 100.00 at summit. All stainless with a crossover in it. Some folks say its overkill, and in some setups I think they may be correct. What I can tell you is this: I had a buddy swear that my muffler was holding me back on the high end. As I have faith in his opinions I pulled my flex pipe off the headers and ran it on the trailer at my shop. As a control we ran it with the muffler hooked up first, and let the engine warm to 160 deg. We got 5050 rpm with 2.68 box and 3 blade r set a little past the 2.5 mark. With open headers I only got 4900 to 4950 rpm. The prop setting was unchanged as I only removed the flex between the headers and muffler. On my setup, there is something to be said about a little back pressure.
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cntry141iq
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Re: Why no crossover on an airboat?

Postby cntry141iq » Thu Jun 23, 2011 1:14 pm

:salute: Takes a brave person to say back pressure helped them on here LOL ... I have had to increase the pitch in every application to which I added real mufflers that have some back pressure in them ... every one of them from 35 hp briggs to a/c engines to small blocks ... and having to increase the pitch only happens because the engine made more power ...
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scorbin
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Re: Why no crossover on an airboat?

Postby scorbin » Thu Jun 23, 2011 2:49 pm

I'm running an X-pipe on my SBC, sure cut down on the exhaust sound levels. From what I've read is that x-pipe/h-pipe can increase HP (not alot) and will flatten the torque curve.

Here's a link on mufflers/muffler law which has a few posts on cross over and X-pipe setups.

http://www.southernairboat.com/phpBB3/viewtopic.php?f=2&t=35448


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Last edited by scorbin on Thu Jun 23, 2011 2:53 pm, edited 1 time in total.

rost495
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Re: Why no crossover on an airboat?

Postby rost495 » Thu Jun 23, 2011 2:50 pm

appreciate the input.

Let the muffler do the crossover then is fine.

As to prop noise, well you get to it one step at a time. I"m not ready for the new reduction and prop yet, but have the new motor.... its just another 10K to get a new reduction, fuel injection and new prop.... while I can afford the muffler change at the moment....

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Wild Bill
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Re: Why no crossover on an airboat?

Postby Wild Bill » Sun Jun 26, 2011 11:21 am

I put a downspout on it since and it's really quiet. Just hear the Whump Whump of the prop at cruise! Just another way to do it...
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Wild Bill
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Re: Why no crossover on an airboat?

Postby Wild Bill » Thu Oct 20, 2011 8:57 pm

OK I said I would do a video so you can hear.





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Wild Bill
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Re: Why no crossover on an airboat?

Postby Wild Bill » Thu Oct 20, 2011 11:38 pm

gyrocopter582

Significant research and opinions went into what I did here, typically I go against public opinion. I even built tri y's for one of my small block projects however this decision was made with budget in mind and strictly noise levels. Inovative built the long tubes, the mufflers are cheap Thrush welded mufflers, 3" flex and pipe and a rounded diverter at the center of the rear pipe exiting into the 5" pipe. Those Thrush are a cheap 2 chamber design that copies (Chinese) Flowmaster and amazing how quiet it is. I was just going for the frequency doubling aspect of the single exhaust. I cant prove power gains or loss. Thanks for the positive reply!

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SLIDEJOB0520
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Re: Why no crossover on an airboat?

Postby SLIDEJOB0520 » Fri Oct 21, 2011 8:35 am

I AM A A/C MAN BUT I RACED SUPER LATE MODELS FOR A WHILE AND I CAN TELL YOU THAT A X -PIPE WAS WORTH 13-16 HP AT REAR WHEELS ON A CHASSI DNYO ALL DAY LONG.
WHEN IN DOUBT TACH IT OUT!!!!!!!!!

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Re: Why no crossover on an airboat?

Postby cntry141iq » Fri Oct 21, 2011 3:13 pm

I will second that number LOL but also remember an h pipe(balance pipe) is not the same as an x pipe ....
Don't waste your time ... it is the only thing you can't get more of
.. if it accidentally looks like I gave advice please ignore it .. and notify me immediately


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