Hey guys,

I am working on an exhaust system for my subaru conversion (2.5l n/a) and I was wondering if the engine prefers a single exhaust or a true dual exhaust. I know that the t4 works better with a single exhaust and I was wondering if the subaru is the same way because of the same layout. If it is a single exhaust, it would mean a little more plumbing and pipe bending... but would it be more beneficial? If not, the dual would much easier, 'cause I could just throw a muffler on each side and go two pipes out the middle.

let me know your thoughts.


-peter

I don't know the answer, but would like to as I want to do a suby na conversion as well. If you donkt find the answer here try the guys at NASIOC.com.
Peace,
Chuck

I have a dual exhaust setup on my 2.5L n/a conversion. I can't compare it to a single exhaust setup, but I suspect that would work better. Dual is loud...

The Suby engine doesn't need scavenging or backpressure, so you can go single or dual. It shouldn't affect the performance.

Do you have magnaflow? I think you mentioned it in a post a while ago, but I can't remember.

Loud is ok with me, but does it give a good tone? I was the thinking if I go dual, I might put a crossover pipe in to give a more uniform sound.

Ok, good to know. Thanks.

The nice thing about a merged collector and crossover tubes is the reduction in harmonics. There can be a loud droan from the exhaust going with duals. The length and diameter will effect performance and shift the harmonic sounds up or down in the rpm range.

An important aspect to also think of is how far from stock are you wanting to go. That stock ecu was tuned for a certain exhaust setup with a lot of engineering ranging from noise, efficiency, scavenging etc. etc. etc. The more you go from stock the worse it will run until the motor is warm and the o2 sensor starts making a change in how it runs. I did a ej22 swap and the obd1 computer isn't very tunable, so my car runs like shit till it warms up a little. The fuel correction maps for warmup wont be able to keep up if your exhaust is too different from the stock setup. Now if your megasquirting or unlocking your obd2 ecu and can street tune with a wideband setup and your brave / know what your doing the sky is the limit. Exhaust has a profound effect on performance... not as much as on a 2 stroke but it still has a large effect. Back when i dynoed bikes for a living crap exhaust could lose you more power than you would think. I saw a 999 that had "custom" super loud open pipes with no baffling and the bike lost 25+ hp over a bone stock one.

My .02 cents

I am running an EMS stinger. So i am far from stock. Im thinking dual with a crossover. I will see how that goes. If i go with a single can, I would have to do a lot of plumbing to get equal length pipes.

This is not a plug-n-play solution, but with a little bit of work you can use a production equal length header. I use the stainless obx el header. I know that obx is a bad word around here for type 4, but for the suby application it is very good quality. I was convinced after seeing dyno charts over on nasioc that it was worth the effort of getting an equal length header in there. As long as your engine is mounted relatively high, this can be a good solution. I use a resonator and a magnaflow muffler, the sound is fantastic.
If you want to see more details on how I did mine just let me know.

Click to view attachment

I'm going to dig up an old thread, as this one is the most recent and has the best info.

Has anyone looked at just running straight pipes on their Porscharu? I'll be putting an EJ20 out of an 04 in mine soon, and there seem to be a lot of videos on YouTube with people running nothing. On Ohio, my car is exempt from "E-Check" so I don't need a cat or a muffler at all if it's under 6-cyl. (At least that's the guy at the auto-parts store told me.)

Thoughts?

You'd sound like TWO too loud Harleys at once, imagine that. It would be sooo loooud I don't think you'd enjoy driving it, and around here you couldn't pass a single cop without getting a fixit ticket. In fact drive that past my house after midnight and I'd take a shot or two at you myself. Who knows, your experience might vary.... but I doubt it.

Excuse me, I don't understand this. Subaru engines don't "need" scavenging? I didn't know there was any multicylinder engine (or any gas pump) that wouldn't benefit from scavenging to improve flows. How are Subarus different in that regard?

look at the date of post.....

I doubt you'll get a reply

You're right of course, but I'm still intrigued, needed to ask.

By the way, Deans use of that OBX header is genial. The equal lengths remove the typical "subaru" exhaust note, and coming straight back like that means you can use the Smallcar front engine mounts. You can't do that using the stock exhaust, the Smallcar mounts block that space in the front, where the OEM exhaust goes across. He solved a couple of different issues by doing that.

every internal combustion engine will benefit from a properly designed exhaust.

his statement was uneducated.

even a single cylinder engine will benefit from scavenging, and yes the exhaust can be engineered to do so.

Yeah, I know, and there are even three or four different types, which is kind of why I was curious about what the answer would have been.

LOL thats funny, engine won't benefit for pulse scavenging. I think that comes from the aspect that some Subaru's use common exhaust ports making the issues of building a header a little bit of an issue. Like the EZ30 or the early 1.8, 2.2 series. Its an odd combination to make. BTW, OBX makes a header for the EZ30, if people need to save some time.

I think you should go with zoomies. 2 on each side of the car, just in front of the wheel...

From first hand experience , the subys run much better with longer primary's . The stock V is a joke. I had Stan's headers in auburn make a set for the vanagon. I think he was able to get 12 or16 inch primary's in a 4 into 2 into 1. It added a noticeable amount of tork low to mid. Top is junk cuz it's chocked by the stock vanagon cat.

Now on the 6 svx I'm not going to murge left and right. It has the same firing order as porsche so I'm going to copy them as far as possible.

And just to set the post straight you CAN hack the obd1 ecu and rewrite if needed.


Jcl. Ok done beating this horse.

Model Porsche for SVX build, okay, yet Porsche is a compromise just like all other car companies. And the head design is completely different on a 911 914/6 engine.

My plan right now is a (3/3)-2-1 on my SVX, yet I may end up with a 3/3 - 2 unit Im letting the guys at Burnsstainless figure that one out.

The intake on the SVX H33 is good for almost anything you toss at it. You need a better MAF, if your keeping the MAF. using the stock ECU, you'll need the MAF. And you will need larger injectors. The issues come from low levels of valve lift, and a very restrictive exhaust port design. The SVX is considered one of the better Subaru exhaust port designs. So you get the picture, its is not a Porsche 911. The 911 heads are about as clean as you can get. And even with them there is room for improvement. And lets face it the collectors on stock Porches are not a race grade collector.

The job here is easy if your using forced induction. They tend to be able to mask a slightly poor exhaust design. Though a great design will make more power across the board. Going to large or building a collector that expands to fast zaps power, and lets face it, I may play an engineer on TV, but I am not an expert in exhausts, just a well studied apprentice. Since I am wanting some big numbers out of my H33 i'll pass it onto the people who know. And pay a consulting fee to get it right.

CptTripps, the reason people run EJ20 with out mufflers is that little snail tends to knock down a lot of noise. Ran my TDI with 3" down-pipe all the way out, no cat, no resonators nothing, just the turbo. It could be very loud, and resonated like crazy. If you where in a tunnel with the windows down, it was not as cool as you would have hoped. I would at least stick a resonator onto the exhaust or a turned down tip. It will help. And keep you from drawing to much attention from Johnny Law, and a local noise ordnance.

And I may need to eat crow here, as when I drew out my design the only difference I got back was a 3 Stacked collector. The tubing runs look almost like all the 914-6 headers I see.

1-5/8" primaries, going into a 2" collector, 2" all the rest of the way, good for 300HP NA. Running a 3/3-2 tri-y design would mean the last collector would be a 3.75" pipe. Holy Ricer Bat Man.

Instead mine will be 2 2" pipes into a oval collector, 2x4" Dual mufflers on either side. Built out of 16ga Mild Steal, I don't feel like spending the money on 304 or 321 until I have proven the design.

dual drone - it is tolerable for a while but at some point you will want the drone to STOP.

"need more crossover pipe." will farrell

Sorry, I don't know the details of your build so this may be off-base or redundant, but when I was looking at putting a naturally aspirated EZ30R six into my car the plan was to use a two in-one out 911 sport muffler. With that I could come straight back on each side and I'd get the crossover and muffler built into one unit, could buy a cheap used one to experiment with, I knew it would fit, plus I'd get the 911 exhaust sound (less the cooling fan whine) as a bonus. Maybe an idea for what you're trying to do.

And by the way, the turbo does chop up the exhaust noise a bit, but not nearly enough to be able to get your wife or girlfriend into your car. Or to pass a cop without a ticket. Or to drive more than about 20 minutes without relief.

Exactly what in going for...911-ish sound. I'm going to see how close to that I can get.

So it looks like I'm doing a down-pipe, and joining for a single exhaust. Now to search for the right exhaust...