Projects & Mods - 2.5" Tubular O2 housing

:. Projects/Mods .:. 2.5" O2 housing .:

Tools	Get From:
·O2 Sensor Socket	any hardware store (Sears, NAPA, etc
Materials:
·Tubular O2 housing	~$300 - Whatever vendor you like.
·[opt]Turbine-to-housing gasket	Mitsubishi
·[opt]housing-to-downpipe gasket	Mitsubishi

Introduction

The stock exhaust on our cars is a joke. It is absolutely tiny. For making 195hp, it does OK. For anything more, it has to go. One of the smallest and most restrictive parts of the stock exhaust is the oxygen sensor (O2) housing. You can make a bad situation better by busting out the die-grinder and porting the sucker out quite a bit, but in the end, you can only gain so much by this method.

So, folks have developed tubular alternatives to the cast stock pieces, and these flow much better. You usually find these in 2.5" and 3" flavors, with the wastegate either dumped to atmostphere or plumbed back in, made of stainless or mild steel, and configured for an internal or external wastegate. A third configuration is one with no wastegate allowance at all, for folks that have external wastegates mounted on the manifold.

2.5" housings are generally easier to live with, as the 3" housings can make oil changes difficult, since they can get in the way of the oil filter. As well, they require a completely new flange on your downpipe, since the stock flange doesn't have enough room for a 3" pipe to fit between, and still be able to thread on the nuts. For this reason, some folks like 122 Performance will put a partial downpipe on the housing, and you have to have your existing downpipe customized. Other vendors that make good pieces are Victory Performance, and Extreme.

Another fitment consideration to make is with your driver's side fan. Depending on the design, you may have to remove your fan entirely, or at least change to a "slimline" style fan. External wastegates make a lot of heat, so you'll want to have some clearance between that and plastic parts, so nothing melts.

Several other folks can make a good tubular O2 as , just ask around a bit, if you're so inclined. The mild steel versions tend to be cheaper, whereas housings configured for external wastegates, or of 3" size tend to be more expensive. Expect to spend around $300 +/-50 for a tubular O2 housing, for most configurations.

Installation Notes
Depending on if you've removed your O2 housing recently (i.e. since the car came from Normal, Ohio), this can be easy or hard. The first thing to do is to break the O2 sensor loose from the housing. The special O2 sensor socket has a small cutout in the side to allow the wire to pass through it while to loosen the sensor. DSM O2 sensors are particularly long, so you may have to put a socket on the back of the O2 socket, rather than plugging the rachet directly in. If you're lucky, it will break free. If not, run the car for a few minutes to get the housing warmed up - the expansion can sometimes loosen up a recalcitrant O2 sensor.

Next, unbolt the downpipe, since it has to come off anyway. Go anead and get the two 19mm nuts holding the downpipe (and the 17mm bolt holding the DP to the engine) disconnected. loosen up the nuts/bolts holding the O2 housing on the turbine housing of the turbo. Two of these are easily accessible from the front of the car. For the other two, you will have to get under the car and move/pull the downpipe.

Go ahead and remove all the attaching nuts and bolts, and then completely unscrew the O2 sensor from its housing. O2 sensors, despite the harsh environment they live in, are fragile, and many things can "kill" them. Avoid touching the sensor, and immediately put it in a plastic baggie so it won't get in contact with any oil, grease, or otherwise.

Installation should be the opposite of reverse. If you're installing a O2 mounted wastegate, then you'll have to pull your turbo to remove the flapper and port out the hole, but that's another VFAQ.

Two final notes - it is a bit easier to R&R the housings if you unbolt the dipstick from the block and pull it out. It's seated with an o-ring, so it just takes a bit of a tug. As well, unbolting the downpipe before loosening the O2 sensor housing bolts will keep there from being any weird pressures on the housing as you undo the bolts.

Before installing the new housing, I would *highly* recommend running a tap (10mmx1.25) through the threads on the turbine housing, since these bolts are second only to stock exhaust manifold studs in stripping and breaking.

You will notice from the pictures that this O2 housing resulted in the O2 sensor being placed right by the oil dipstick. So, I had to, ahem, relocate the oil dipstick a bit, and everything now fits as it should.

Testing and Results
As before, I did baseline runs with the ported 1g O2 that was on the car previously. Then, changing nothing else but the O2, I did some "after" runs. These were all with a first-gen g-tech "pro".

Constants:

same section of road, direction
small cool-down lap after each run, same each time
car weight entered into g-tech was 3100 (probably a bit low)
did not move gtech between experiments
short shifted 1st and took second to redline each time.
19psi with 2 gals 112, ~5gals 91
same amount of gas
"rich" autocross tune settings
reset ECU before each group of runs
ambient temp 58*F

Results:

Before:

Run 1: 278
Run 2: 278
Run 3: 277
Run 4: 278
Run 5: 279
AVG 2,3,5 = 278

After:

Run 1: 278
Run 2: 278
Run 3: 278
Run 4: 278
Run 5: 278
AVG 1,2,3: 278hp

Analysis
Strangely enough, there was absolutely no max horsepower gain with this part. Definitely not what I expected!

Impressions
Several things to be mentioned about this tubular O2 housing.

First, fitment was much better than I'd expected - the downpipe bolted right back up with no problem at all. I had to bend the oil dipstick tube quite a bit due to the different position of the oxygen sensor.

Seat of the pants improvement was difficult to say. I feel like the car pulled a bit harder at the top end, after the maximum HP reading had probably already been taken. Spool seemed to be largely unaffected, as was boost threshold RPM. Other than the noise when the WG opened, it was tough to tell if it was there.

The sound was not as loud as I had been led to believe, but it was still quite loud. It sounds almost staticky, which I did not expect. Perhaps making things even noisier is the fact that this particular O2 dumps onto the front crossmember. Even with only a few miles of driving, the crossmember was visibly soiled from the soot, about 6 inches in either direction. In my opinion, it's not a very pleasant sound.

Boost pressure in my car begins to drop off around 6000 RPM, and hits about ~15psi by redline. Part of this is the smallish turbo, aftermarket cams, and high altitude (turbos give up sooner). However, even when boost pressure fell below the MBC's setpoint at 19psi, the wastegate remained open, indicating exhaust backpressure was keeping the wastegate open. This is a fairly common phenomenon with 16g cars, but it was interesting to verify this first-hand.

So what's the verdict? Well, I got this piece for a song, even though I knew it wasn't exactly what I wanted. I think I'll sell it to finance some things I want more, and come back to the tubular O2 at a later time with a 3" External wastegate setup (won't have to worry about the premature-opening problem) plumbed back into the exhaust. I dislike the noise, I worry about the effect of the dump on underhood temperatures, and the general mess that it is clearly going to make down there.

Do I think this one made my car faster? Probably - I think the limitation was in the g-tech reading max HP's only. But, the seat-of-the-pants changes weren't enough for now. Coupled with being illegal for SM, and highly illegal for the street, the benefits aren't worth the negatives for me, at this point. Time for a race seat!

the housing

halfway done.

note interference w/ oil stick

oil stick moved out of way

Final Pricelist

Item	Cost	From
Custom 2.5" O2 Housing, Internal gate, external dump	$75 used	CoDSM member
Flange Surfacing	$0 (paid for by member)	AMS
TOTAL:	$75