What kind of exhaust to build for the raceSVX

benebob · #1 01-06-2005, 06:24 PM

The exhaust is coming off hopefully tomorrow if I can get it up onto the ramps without any engine myself. My initial thought was to go with a single Y-pipe back pipe going to the pass. side with a glasspack on it but after some talk with my mechanic about his duel straight pipes on his EA-81 and the power it produced I was thinking about that as well. Problem is how do you fool the engine into thinking the O2 sensor is reporting proper info and think it would be worth the added weight? Don't wanna destroy the Y pipe for an experiment and not have it work. I do kind of like the thought of having flames shoot out when it shifts though.

#2 01-06-2005, 06:28 PM

mbtoloczko · #3 01-06-2005, 10:21 PM

Is this going to be a cat-back system or a manifold-back system?

huck369 · #4 01-07-2005, 05:23 AM

I say run duals with a cross-over pipe to even the pressure and for a location for the O2 sensor, through 2 glasspacks, and exit in front of each rear wheel......I mean it's a race car, that'd make it look and sound like one

Huck showing his muscle car roots.....

benebob · #5 01-07-2005, 06:18 AM

Just for simplicity sake I was gonna do pretty much that huck but just after the first gutted cat I was gonna take one pipe back and out in front of the pass side rear wheel. The cats aren't needed but I've heard stories about newer subies having issues with burning valves b/c of a lack of back pressure.

huck369 · #6 01-07-2005, 06:29 AM

As long as you have some type of muffler on it, I would think it should have enough back pressure to keep it from burning valves.

mbtoloczko · #7 01-07-2005, 08:56 AM

How does lack of back pressure cause burned valves?

benebob · #8 01-07-2005, 09:04 AM

Quote:

Originally posted by mbtoloczko
How does lack of back pressure cause burned valves?

Not a clue but from what I've heard it can and does in boxers. Of course this is something I would like to avoid. I do know that most post ea-81 subie engines I've had that have run catless have all had some noticable stumble issues without the back pressure.

huck369 · #9 01-07-2005, 09:58 AM

It's not a boxer style motor thing, it's a any motor thing...
I believe that between strokes with no back pressure, it can actually suck cold air back up the pipes which hits the red hot valves causing them to crack....this is my understanding of it anyway....

mbtoloczko · #10 01-07-2005, 10:18 AM

Quote:

Originally posted by huck369
It's not a boxer style motor thing, it's a any motor thing...
I believe that between strokes with no back pressure, it can actually suck cold air back up the pipes which hits the red hot valves causing them to crack....this is my understanding of it anyway....

ok. That's kinda what I was thinking. Couldn't see any other reason. I've been running catless and with straight thru mufflers for 6 months now with no probs. Probably just need to make sure that the tail pipe is sufficiently long.

huck369 · #11 01-07-2005, 10:24 AM

I've seen it happen before, but it's usually from a bad exhaust leak at the manifold, or from running open headers.....I figure if you have a good length of pipe on it it wouldn't be an issue. (Of course if you're running way oversized pipe, it would be worse than a pipe sized just right....)

wawazat?? · #12 01-07-2005, 11:25 AM

I've seen a number of tests on cars with shortened exhaust system, ie ahead of rear wheels, where torque is lost versus a full length exhaust system. This is typically on domestic V-8's.

I'm not sure what type of racing you're planning on and low-end torque may not be as beneficial as high end HP, but I wanted to bring it to you attention. Also, many racing venues are now testing dB ooutput and requiring muffled exhaust systems due to noise complaints.

Just my $0.02

Todd

#13 01-07-2005, 01:24 PM

On our race car we ran a 2 inch pipe about 1m from the stock manifolds and merged them into a 3inch pipe with 1 bola muffler woth a 3 inch out. It made the mean subaru noise, but was much more meaty than the 4 cyl ones you hear.
It was also well under 85dB

mbtoloczko · #14 01-07-2005, 02:33 PM

Not sure why you're worried about the O2 sensors. The ones used by the engine for closed loop are located a few inches past the exhaust manifolds. Unless you change tubing size at that point, you shouldn't have to touch the O2 sensors whether the exhaust system remains a 2-into-1 or is converted to a dual exhaust. If its an ODB-II car, the third O2 sensor that sits on the backside of the secondary cat has no bearing on engine performance, and there are plugs you can buy that will attach to that O2 sensor and send the "proper" signal to the ECU for that third O2 sensor.

Probably not much room under the car to run a tail pipe out the side. Since it can't be tucked out of the airflow, it might not be so great for aerodynamics either. I'd do like SVX files did and stick a megaphone straight out the back! If you do with true dual, you could have two megaphones, probably complete with flames shooting out the megaphones when you're off the throttle. :-)

benebob · #15 01-07-2005, 03:01 PM

Reason I'm thinking side is weight savings. There should be plenty of room for a 2 1/2 inch pipe I think. Will be putting on some sort of free flow muffler. Probably a cherry bomb style. Loud is somewhat acceptable as the car isn't streetable. Abnoxious is not as acceptable.

So the 02 sensors are actually in the Y pipe not the cat huh? Haven't looked under yet just assumed it be the same place as an EA-81 or EA-82.