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> Subaru Conversion Exhaust Design, Need advice/input
TonyAKAVW
post Jul 25 2006, 11:55 AM
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One of the last remaining things to figure out with my Subaru conversion is how to do the exhaust. I have a few restrictions that make the exhaust design more difficult than normal.

1. I want dual exhaust pipes to exit just on either side of the license plate (through the bumper)

2. I want the exhaust system components (mufflers, crossovers, etc.) to be mounted above the level of the axles. I'm putting a diffuser under the car eventually and need all the space I can get. So no mufflers or tubing below the transmission.

3. I have a set of primary tubes that I bought from Outback Motors that I really want to use as my 'headers.' They are good because they extend below the engine the same amount as my modified oil pan.

So thats pretty much the unusual requirements I have. The difficulty I see is geting any kind of crossover from each side of the engine. Seeing as how I have primary tubes that collect each exhaust port within about 6 inches, I'm wondering if I will gain much by having a crossover at all. Anyone have insight on this?

Also I'm looking for ideas on isolating heat from the rear trunk. With exhaust components mounted up high the heat will really radiate into the trunk. Some ideas I have come up with include: suspended metal heat shields below the trunk as in the OEM heat shield, wrapping the parts with insulation (since they will pretty much never see water this might work well), thermal insulation on the inside or underside of the trunk. Any interesting ideas would be appreciated here.

Finally I'm looking for muffler(s). from the 3 requirements I have I need something small. Reasonably loud is okay, but this will be a daily driver, so nothing that will overtly piss off the neighbors.


Any other ideas or suggestions on the design of this exhaust system would be welcome.


-Tony
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mrdezyne
post Jul 25 2006, 12:51 PM
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I'm going to try the same idea except I would like to try a center exhaust like a Boxster. Those outback headers are the way to go. Header wrap or a ceramic coating will certainly help for heat, maybe both. That plus a reflective heat shield under the trunk. Lots of stuff available out there.

For space savings are you planning on using one muffler instead of two? I haven't really had a chance to lay anything out yet so I'm just thinking out loud....
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cbenitah
post Jul 25 2006, 12:56 PM
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I'm glad you mentioned Boxster.. I would like to use a Boxster muffler for my car.. But I don't know anything about how to make it fit etc.. If someone out here could explain simple exhaust design (or whatever you cal it) I would really apreciate it...

So my question is, can a Boxster muffler work? Sorry Tony if I Hijacked it...
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Aaron Cox
post Jul 25 2006, 01:02 PM
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tony, go from outback stubby's, up and OVER the axles, and do a camaro style crossflow muffler behind the tranny

http://shop.ivalueinternet.com/bigexhaust/...series_flow.gif
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grasshopper
post Jul 25 2006, 01:03 PM
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I was going to use a boxter muffler on my car, but after I found out how much they weighed, I changed my mind, I think they weight around 50-60lbs. No kidding.
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Crazyhippy
post Jul 25 2006, 01:22 PM
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I came stright back off the turbo (IMG:style_emoticons/default/biggrin.gif)

It's over the axles too....

BJH
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TonyAKAVW
post Jul 25 2006, 01:26 PM
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Aaron: I will have to look, but I'm not sure there is room to put a dual in/dual out muffler there, without it being oriented vertically. I suppose once I get my engine and transmission in I can see what space I have. A related question is, what does having a crossover all the way back there do? Should the crossover be close? My intuition says that where the crossover goes for optimal performance is a matter of transmission line matching, and that the headers I have now probalby set things up such that it would be hard to match things properly. So maybe it doesn't matter (IMG:style_emoticons/default/smile.gif)

As far as the Boxster muffler goes (for me at least) its too heavy and big. I want this car to be under 1900 lbs, so I need lightweight everything.

-Tony
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Aaron Cox
post Jul 25 2006, 01:28 PM
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tony, yes, it would have to be vertical... thats how the 911/914 guys do it (go to pelican and search flowmaster. alot use the crossflow 80 series muffler)

dynomax has a slightly narrower one.., worse case you have a semi tight bend from the muffler to the exits.....
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mrdezyne
post Jul 25 2006, 01:31 PM
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I like this set up but the inlets and outlets need to be reversed.


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mrdezyne
post Jul 25 2006, 01:37 PM
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I found these a while back when searching for something to fit in a tight space. Might be worth a look...

http://www.spintechmufflers.com/spintech/spintechindex.asp

check out the "cruiser" series
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brant
post Jul 25 2006, 02:02 PM
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regarding the boxter muffler...
behind the axles on the back... absolutely the worst place you could add 60lbs if you car about how the car handles and is balanced.

brant
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banksyinoz
post Jul 26 2006, 01:33 AM
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tony do you need to use the catalytic converters on this exhaust as this may be an added part of the problem

given the size of the pipes a balance pipe (small) behind your engine bar may work, you havent given much option....

good luck
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mongrel-gs
post Jul 26 2006, 09:42 AM
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A boxster muffler will work with this conversion...
boxster muffler

It is heavy, but you could cut it and remove some internals to lighten it up. I left mine stock, mounted some rubber hangers, and welded up tubing from the outback stubs to the inlets. Easy peazy... there are two funny looking 'wire' hangers on the muffler that I cut off, and the threaded studs on top could be removed if desired.

Tony, I think flowmaster and others have dual in single outs that may work for you, look at crossflow mufflers for late 60 camaros and such. I started with a dual in dual out flowmaster that could have been positioned such that the bottom of the muffler was well above the bottom of the stock rear valence. It can be positioned horizontally, although it may be tight getting the tailpipe out the center. I futzed with trying to intall it at ~ 45 degree angle, still had plenty of clearance and with a few tubing bends I bet you could weave the tailpipe out the center. I ended up mounting it horizontal as I was running out of hands and jackstands. It was too loud for my taste though and weight wise did have a bit of heavy associated with it, although not near that of the boxster.

Scott Thacher fabbed a muffler out of some glasspacks, it sounded good and was simple. You could try a glasspack for each side into a central expansion chamber with a single outlet... just thinking...

Evan
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horizontally-opposed
post Jul 26 2006, 11:19 AM
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Boxster muffler is not 60 pounds, and is at the top in terms of quality.

http://www.914world.com/bbs2/index.php?show...c=47978&hl=

I found one for $35 on Craigslist for experimentation and might be willing make it available to someone else for the same price...

pete
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grasshopper
post Jul 26 2006, 11:45 AM
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Hey Pete, If you have a Boxter muffler, I am interested in it. That has been my plan the whole time. I read someones post on here no to long ago that said they weighed about that much..how much do they weigh?
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TonyAKAVW
post Jul 26 2006, 12:00 PM
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Okay, here's the engine with transmission for use in mocking up exhaust designs...

And then a few designs I'm looking at.


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Joe Ricard
post Jul 26 2006, 12:20 PM
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I don't know what would be wrong with a 4-2-1 header with equal length tubes. Split the tailpipe out to both sides as you desire from a muffler.
Looks good

single 2 1/2" outlet to a Dynomax Bullet would be More power and Bad Ass loud.
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neo914-6
post Jul 26 2006, 12:43 PM
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I'm going to run straight back borlas, I want to see the back of the Boxster transaxle. (IMG:style_emoticons/default/biggrin.gif)

Here's a Dynomax system:


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TonyAKAVW
post Jul 26 2006, 12:56 PM
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QUOTE
I don't know what would be wrong with a 4-2-1 header with equal length tubes. Split the tailpipe out to both sides as you desire from a muffler.


I already have these collectors, so making a set of equal length headers is not going to happen. thats probalby the best way to go, but for now I want to do something much more simple.

Felix: that is a wild looking exhaust system! That muffler is huge!

-Tony
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