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4" exhaust DIY

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cjridert1

15+ Year Contributor
403
6
Jul 4, 2007
Akron, Ohio
I was going back and forth about just doing a side exit exhaust and decided to put in some extra work and do a full turboback. I build this over the past few days and thought Id post some information on it. I pieced this together as cheap as I could and think its a great option for DIY dsmers.

SS piping was expensive to buy individual curves/straight sections, so I got a diesel downpipe from here that looked about right and cut/angled it a few times. Fits better than my 3" in the oilpan/Tcase channel. This was $106 shipped

I bought 16ga aluminum tubing from GlobalTech, total ended up being around $150 or something for 2 7" straights, 1 30°, and 3 90° angles (2 6"CTR and 1 10" CTR). I only ended up needing 1x 7', 1 90° 6"CTR and 1 30°. So I have a lot extra for other projects like a cold air intake and whatnot.

I wanted to muffler the thing to make it a little more reasonable on the street, so I got a diesel muffler off ebay for $70 shipped.

I put a flex section in for installation forgiveness and maybe some longevity. $35 shipped.

I needed to go from SS to aluminum back to SS for the muffler, so needed some V bands. I ended up V banding the flex section too because I was having a tough time getting the DP in and out of the car for fitment all as one piece.
3 x $28 (Steel) and 1 x $60 (aluminum).

So the thing ended up costing me $520 after and O2 bung and some fill rod with a bunch of extra aluminum to play with. Id think it would be easily less than $475 with ordering the right amount of aluminum, I just didnt want to end up short handed.

Heres some pics. Car is still a work in progress, so no idle/rev soundclips. Also didnt weigh it, but probably 1/2 of my megan 3" SS previous.
 

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As I was reading that post I was thinking to myself man idk how this is gonna look but then I scrolled down to the pics and that looks super sharp! Wish I had the patience haha
 
That thing looks really nice my man! Congrats!

I run a 4" aluminum exhaust and I cant say if the fact it is aluminum changes much in the tune (I am positive it does but not sure exactly how) but it sounds like the car the car is making a "HOOOOOOOOOOOOOOOOOOOOOOOOOOOM" sound. Hard to describe. The 4" definitely opens that bad boy up.

I think someone could market these. OP you should try your hand out it, I think a lot of people would be up for it.
 
In4soundclips.

For real, get some idle/rev clips. Maybe some drive-by as well? I would love to see how this sounds!
 
Thanks for the replies guys. Depending on what life gives me this weekend, I may have it up and running - if thats the case Ill get some clips posted up.
In regard to making a few to sell, I dont know if that is an option (unless just a catback style with a 3-4" backwards reducer or something). I just posted this up so if anyone was interested in duplicating and has the means, they have an approximate recipe for it.
 
I wonder what the real life benefits of this would be. I know less backpressure is better but to what extent.

Sent from my HP Touchpad using Tapatalk

I've heard that going from a 2.5" to a 3" on a 16g car is worth something like 25-50hp. Someone actually tested it a few years ago. So think what it would be like on a big turbo car!

AAAANNDDD, most v8 cars that make power generally run a pair of 2.5's or 3.0's. A pair of 2.5" is roughly = single 3.5", and a pair of 3" is roughly = a single 4.25"
 
I commend you on that exhaust. It looks very clean but if you're looking for a 4" v-band side mount exhaust I have one available. I cannot running it anymore after moving back to California.


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4" exhaust bellow 700whp is pointless..

Pointless only in a performence sense. Exhausts that are built to large for the application can have negative effects and actually lower your hp. A 3in is PLENTY for the applications that many of us are running. Half of us get boost creep on a 16g due to lack of back pressure as it is....
Not hating, just stating that you cant keep making your exhaust bigger for unlimited horsepower.
 
Pointless only in a performence sense. Exhausts that are built to large for the application can have negative effects and actually lower your hp. A 3in is PLENTY for the applications that many of us are running. Half of us get boost creep on a 16g due to lack of back pressure as it is....
Not hating, just stating that you cant keep making your exhaust bigger for unlimited horsepower.

couldnt agree more. it would be nice tho...:toobad:
 
Exhausts that are built to large for the application can have negative effects and actually lower your hp.

How?

The efficiency of an exhaust is mostly dependent on the exhaust manifold. If the builder of a manifold can build it in such a manner that the exhaust pulses create a negative pressure to help suck out the subsequent pulses (scavenging), he has built an efficient manifold. After that point, it's all about getting the exhaust OUT of the system. So if it's 3 inches or 10 inches, it doesn't matter, as long as it's big enough to get all the gasses out. Typically 3 inches is more than one would ever need that's why 4 inches is pointless under a certain power level. If the exhaust pipe is too small you create backpressure, and that is not what you want, especially since we already have a turbo in the line slowing the exhaust flow down.

Also, boost creep is NOT due to a lack of back pressure, it's the waste gate's inability to bypass enough exhaust gasses.
 
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4" exhaust bellow 700whp is pointless..

That's arguable.

Pointless only in a performence sense.
Your an idiot.

couldnt agree more. it would be nice tho...:toobad:
see above.
How?

The efficiency of an exhaust is mostly dependent on the exhaust manifold. If the builder of a manifold can build it in such a manner that the exhaust pulses create a negative pressure to help suck out the subsequent pulses (scavenging), he has built an efficient manifold. After that point, it's all about getting the exhaust OUT of the system. So if it's 3 inches or 10 inches, it doesn't matter, as long as it's big enough to get all the gasses out. Typically 3 inches is more than one would ever need that’s why 4 inches is pointless under a certain power level. If the exhaust pipe is too small you create backpressure, and that is not what you want, especially since we already have a turbo in the line slowing the exhaust flow down.

Also, boost creep is NOT due to a lack of back pressure, it's the waste gate's inability to bypass enough exhaust gasses.

Yaaaay you get a gold star for the day!
 

ROFL

And to believe this asshat was trolling me earlier. Nice catch 9awd.. Its definitely funnier within context.

At the end of the day however, I say just let people do what ever they want with their own cars I suppose-


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Stainless DP and flex section into full aluminum exhaust with multiple vband sections for easy removal including the muffler. Each piece will hang in place by itself without anything else attached to it. It has made a lot of little mini repair jobs a breeze because with the larger drive shaft I have now along with the 4" exhaust there is ZERO room to work...
I enjoyed mine and I'm in Cali too LOL. :p

To top it all off I'd say the whole thing weighs maybe 8lbs..

Once again though, props to the OP for his DP especially, that bad boy came out pretty slick and overall looks very professional.
 
I built a full 4" alumn exhaust a few years back. I'm considering selling it since I want to do a 4" side exit, but I was considering making the down pipe from aluminum.

I've seen many civics do it, seems to work for them, and I have the material.
 
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