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Jim Mantyla
 Post subject: Exhaust Systems
PostPosted: Sun Aug 14, 2011 6:27 pm 
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Dick,
You would be right if both cylinders were firing at the same time. Fortunately the pulses are releaased separately. hence the smaller pipe size.

Jim


Last edited by admin on Sun Aug 14, 2011 6:27 pm, edited 1 time in total.

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dickwolff
 Post subject: Exhaust Systems
PostPosted: Mon Aug 15, 2011 1:30 pm 
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OK... I'll buy that. (D'oh... I forgot to think.)

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In theory, theory and practice are the same. In practice, they are not.


Last edited by admin on Mon Aug 15, 2011 1:30 pm, edited 1 time in total.

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ljkrume
 Post subject: Exhaust Systems
PostPosted: Mon Aug 15, 2011 5:56 pm 
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I think the idea of using a cross-over is to separate the pulses as much as possible if you're using 2 tail pipes instead of 4. I.e., use one pipe for each pair of cylinders (front & back pairs). Otherwise, if only right cylinders were tied together and left cylinders were tied together, the pulse from the front would just reach the Y when the aft cylinder was trying to exhaust.

But for anything to work, what's not mentioned is the length of pipe for rpm or speed of the pulse, so you get it timed right and pulses don't interfere. Maybe if you do it right, the momentum of each can help pull the next one behind it too. That's what tuning is all about. A bit over my head but some people can do it.

Les.


Last edited by ljkrume on Mon Aug 15, 2011 5:56 pm, edited 1 time in total.

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jrevens
 Post subject: Exhaust Systems
PostPosted: Mon Aug 15, 2011 8:23 pm 
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Actually, the idea is not to separate the pulses a far as possible, but to design the system such that the leading pulse helps the one following it to exit more efficiently, leading to greater overall efficiency & power. Properly designed, the "pulses" work together.

John Evens N71JE
Arvada, CO

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T-18 N71JE
Kitfox 7 SS N27JE (building)


Last edited by admin on Mon Aug 15, 2011 8:23 pm, edited 1 time in total.

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jefferts
 Post subject: Exhaust Systems
PostPosted: Tue Aug 16, 2011 11:35 am 
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Actually a well designed exhaust system uses the rarefaction (vacuum) behind the adjacent exhaust pulse to scavenge the exhausting cylinder. You have to design the system so it resonates with the low pressure zone at the exhaust valve of the intended cylinder at the correct time. Its a bit of an art to design such a system, but over a reasonable range of RPM and power settings you can get a considerable increase in exhaust efficiency from a well designed system.
I've never designed such a system for an airplane, but back in a misspent youth a did quite a few for sports cars. I would guess that an airplane is a better choice, they run at pretty predictable RPM and power settings.


Last edited by admin on Tue Aug 16, 2011 11:35 am, edited 1 time in total.

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ljkrume
 Post subject: Re: Exhaust Systems
PostPosted: Mon Mar 12, 2012 2:25 pm 
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Hey Guys,

About exhaust systems, how important is it to have the sliding joint in the crossovers? I'm pretty satisfied with the one I built, but left that part out. Figure it's about 6E-6 in/in/F x dist x temp: from what I guess, the cold-to-hot difference might only be about 1/16th inch. I can also guess that's how much prying it takes just to install some systems. I can't tell if A/S shows those features in their catalog systems and see no mention of it. Seems that would be one more complication and another couple of sources to leak. On the other hand, I did use 'ball-joints' for the tail pipes, and posted a cheap source on the forum earlier.

Let me ask, do all of the cross-over systems have the sliding joints? Maybe I seriously need to add them.

Les.


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Rich Brazell
 Post subject: Re: Exhaust Systems
PostPosted: Mon Mar 12, 2012 3:12 pm 
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Bruce...go to the board indes and move down to Vendors/Builder's resources. Hit that baby and go to the second page and smash on exhaust systems. It should show Custom aircraft and a pic of the exhaust. Or...just goggle Custom Aircraft Products. They are in El Cajon, CA.
RB


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Rich Brazell
 Post subject: Re: Exhaust Systems
PostPosted: Mon Mar 12, 2012 3:15 pm 
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Sorry Bruce...that should be Custom Aircraft Parts.com :'(

RB


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fytrplt
 Post subject: Re: Exhaust Systems
PostPosted: Mon Mar 12, 2012 4:53 pm 
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Les,

You need the slip joints as it is the cylinders that grow, and they grow quite a lot! Any stress on the installed system, combined with engine vibration will surely yield a crack. The crack will most likely come where the two cylinders "Y" together. You could even crack the cylinder boss where studs are. Not pretty!

As one who thought I knew it all, I put "heavy duty" hold down bolts on a VW once. Turns out, the standard ones were designed to stretch with the cylinder growth. The heavy duty ones pulled out of the block!

Any good muffler shop has a tubing stretcher and can make the additional piece you need.

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Rich Brazell
 Post subject: Re: Exhaust Systems
PostPosted: Mon Mar 12, 2012 5:41 pm 
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That explains the HIGH temp copper anti seize ! O0 I thought it was just to make removing the pipes easier. :o BADA BING, BADA BOOM ! ;)

RB


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flychris
 Post subject: Re: Exhaust Systems
PostPosted: Mon Mar 12, 2012 10:42 pm 
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Ive got an ACS cross over for an 0360.... It's suppose to have 200 hrs on it looks new. Can take pictures bought it for my 360 but using a forward facing sump and wont work. Make me an offer


Chris
404-697-3069


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dickwolff
 Post subject: Re: Exhaust Systems
PostPosted: Tue Mar 13, 2012 6:50 am 
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PM sent, Chris. Thx.

d


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bfinney
 Post subject: Re: Exhaust Systems
PostPosted: Tue Mar 13, 2012 3:33 pm 
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So, if your pipes don't have any HIGH temp copper anti seize and the slip joints have seized, does anyone have an easy way of unseizing the pipes? actually I'll take any method that'll work.

Thanks,

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ljkrume
 Post subject: Re: Exhaust Systems
PostPosted: Wed Mar 14, 2012 1:23 pm 
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Ok Bob. I've got a pipe stretcher, guess I'll put it to use... Thanks, Les.


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Rich Brazell
 Post subject: Re: Exhaust Systems
PostPosted: Wed Mar 14, 2012 10:02 pm 
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Why not call Custom Aircraft Parts and ask them what they recommend ? In fact I need to go over by their shop this week and pick up my (2) Infinity Stick Grips at KSEE. I'll ask him what he recommends. This can not be the first time he has come across this problem. "Stay tuned, same time, same Bat Channel !" :o



RB


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