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  #1  
Old 11-08-2007, 10:59 AM
jbDC9 jbDC9 is offline
 
Join Date: Jan 2005
Location: Houston, TX
Posts: 868
Default 4 into 1 exhaust system; observations

So I recently hit the 200 hr mark on my QB RV-8 and thought I'd share my experiences with the 4 into 1 exhaust system installed, just in case anyone else is considering such a system...

The original reason I went with this system was noise; the usual Vetterman type exhaust is just too loud for me and has a sharp, barking kinda quality to it. I called up Aircraft Exhaust Technologies (since merged with AWI) and asked about their crossover system with mufflers. Chris steered me towards the 4 to 1 system instead, saying it performs like a Powerflow tuned pipe, flows lotsa air, and the sharp exhaust note is mellowed out from blending the 4 separate stacks into one collector pipe. "Great!" says I, ship it!

I have no gripes at all about the pipes themselves; they're good quality, very well made and are holding up fine so far. My main beef is how the system interacts with the RV-8 airframe. I suppose that from the outside the noise is mellowed out, but from inside it was pretty noisy and buzzy with quite a bit of vibration through the floor... but since I've never flown in another -8, I had no basis for comparison on the noise/vibration level; I figured that it was normal -8 behavior. The noise/buzziness was worse at high AOAs and low airspeed. Also, in the pattern on base and final with the power pulled back there was quite a bit of popping and backfiring from the stack.

My first hint of trouble from the noise/vibration came at the 140 hour mark with cracks appearing in the forward belly skin between the gear legs; ref my previous post here - http://www.vansairforce.com/communit...ad.php?t=18402. I patched the cracks and figured that'd be the end of it. But alas, it wasn't to be. A few weeks ago (200 hrs) I was under the belly again wiping it down and I found a two more cracks just forward of the original ones. Well now, that does it; this pipe has gotta go! But first, I called AWI to see what could be done; it was suggested to try a down turned pipe tip. I had it within a week and had a local muffler shop weld it on. The end result? Holy-freakin'-moly, it's like a whole different airplane. It's much quieter and smoother than before, even with high power and AOA with low speed; methinks this will end the vibration and skin cracking problems. And, as an added bonus, the popping and backfiring at low power settings appears to have been eliminated; after 5 or 6 trips around the patch I didn't hear one pop or fart from the stack. Yea! I wish I'd known about such a simple fix 180 hours ago.

I don't know if any other RVs with 4 into 1 systems have had similar problems, but in my case it's been a real pain in the neck. If you're considering this exhaust or are already running one and if the noise/vibration seem excessive, put on a down turned tip before the skin cracks get started.
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RV-8 QB sn 82030 - 1750 hrs
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  #2  
Old 11-08-2007, 05:01 PM
Adam Adam is offline
 
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Thanks John, This could not be more timely. I have just 4 hr on my RV-8 and Ive been telling others that my 4 into 1 feels like someone is knocking on the bottom skin. I was going to call them this week to find out what I could do but thought that I would put more hours on first, think I call them tomorrow.

Adam Silverstein
RV-8 4Hrs
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  #3  
Old 11-08-2007, 05:42 PM
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LifeofReiley LifeofReiley is offline
 
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I actually heard about your ordeal while I was in Houston a couple of weeks ago. The story I got was that you had considerable damage (cracks) to the fuselage and were not very happy. I'm glad you've worked things out.
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  #4  
Old 11-08-2007, 06:26 PM
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brenegan brenegan is offline
 
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Did they charge you for the tip or send it gratis? Do you have any pics of the cracks?
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  #5  
Old 11-08-2007, 10:23 PM
jbDC9 jbDC9 is offline
 
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Nope, no free lunch; the new tip was $65-70... but that's a small price to pay though when my alternative was to scrap or try to sell the original system and blow another $950 or so on a new crossover type.

Here are a coupla pics of the original cracks; they were along the floor ribs around the rivet holes.



And here's the ugly aftermath; yuck. I've wondered if I should replace that skin, but it'd be a big job... and the patches are uniform in size and shape, down on the belly... might not be quite as noticeable after a paint job. I'm talking myself into just living with it. Live and learn I guess.
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O-360-A1D/CS/Pmags
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Last edited by jbDC9 : 11-08-2007 at 10:27 PM. Reason: screwed up posting the pics
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  #6  
Old 11-08-2007, 10:32 PM
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brenegan brenegan is offline
 
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Thanks for sharing. I am thinking of going for the 4-in-1 when I get to that point, so i'll make a note to get the tip as well. Your patch job looks good.
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  #7  
Old 11-09-2007, 02:58 AM
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JordanGrant JordanGrant is offline
 
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Default Cleaner belly?

Hey, John. I have a standard Vetterman 4-into-2 crossover, but I was wondering about putting down-turned tips on mine for noise and for cleanliness. As you continue to fly with your new setup, I'd be curious to know if your belly stays cleaner now.
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  #8  
Old 11-09-2007, 05:52 AM
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Ironflight Ironflight is offline
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Quote:
Originally Posted by jbDC9 View Post
And here's the ugly aftermath; yuck. I've wondered if I should replace that skin, but it'd be a big job... and the patches are uniform in size and shape, down on the belly... might not be quite as noticeable after a paint job. I'm talking myself into just living with it. Live and learn I guess.
Oh, they're not so bad.....Take a look under a Grumman single sometime John....they have all sorts of "patches" that look just like that - reinforcement plates to keep installed stuff in the cockpit from pulling through the honeycomb. No one will ever notice them once it's painted - unless you go around pointing them out!!

Now "Get thee to a paint shop!!"

Paul
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  #9  
Old 11-09-2007, 05:53 AM
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Nuisance Nuisance is offline
 
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I went through some of this a few years ago.

linky

Recently, after changing to the ECI cold sump, I switched to the Vetterman 4 pipe exhaust. I don't believe I suffered any performance loss. Actually, I think the "tuned exhaust" is a bunch of hokey, unless you restrict your flying to one altitude.

look here in the middle of the page

I found the 4 pipe to be much quieter. It is also easier to fair in the bottom of the cowl for less drag. It is also cheaper. With the cold sump, I am going faster than before.

Have fun!
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  #10  
Old 11-09-2007, 06:29 AM
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AndyRV7 AndyRV7 is offline
 
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Reminds me of a 69 Chevelle I had a while back. I swapped the exhaust and could only get the pipes back to the rear axle (into the mufflers) the first day I worked on it. I went to an air show with my family that day and the sound inside the car was literally deafening. It wasn't so much loud as it was like a tremendous pressure in your ears. I guess that was just a lower frequency. Then, I got the pipes finished and out the back of the car. I couldn't believe how much noise (and potential hazard) it made just having the mufflers end under the floor boards. So your story of just pointing the flow away from the fuse is something I can fully appreciate.
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