CovertRussian's 05 LGT Build Thread

[covertrussian]

I started building a 3" exhaust for the legacy, while waiting for parts I figured I would test the current state of the stock cat-back. The most scientific approach is to use a back-pressure kit, that can be built for about $20.

 

Parts List:

• An old O2 sensor that I cut the back off and tapped a 1/8npt thread on (hole was already big enough).
  
• 1/8NPT male to male extender (I got a 3", should have gotten a 2", since it doesn't fit everywhere).
  
• 1/8NPT to 1/4" copper tube adapter
  
• 1/4" Copper Tube (need about 2 feet, so that it cools enough before it reaches your hose)
  
• 1/4" vacuum hose in various lengths
  
• Boost gauge (you should have one already!)
  

 

http://legacygt.com/forums/attachment.php?attachmentid=253900&stc=1&d=1502322202

 

My downpipe has an O2 sensor port right behind the turbo and right after the cat, which is perfect because it lets you test pre and post cat backpressure.

 

Screwed my contraption into the O2 sensor bung right behind the turbo and wired it into my boost gauge.

http://legacygt.com/forums/attachment.php?attachmentid=253901&stc=1&d=1502322202

 

Went for a test drive and was greeted with quite a bit of backpressure, about 7.5psi

http://legacygt.com/forums/attachment.php?attachmentid=253902&stc=1&d=1502322202

 

Next ran the line to be post cat

http://legacygt.com/forums/attachment.php?attachmentid=253903&stc=1&d=1502322202

 

This got me 4psi of backpressure post cat (with my crappy flow wall exhaust adapter too).

http://legacygt.com/forums/attachment.php?attachmentid=253904&stc=1&d=1502322202

 

 

What does this tell me? The bends in the downpipe and high flow cat accounts for about 3.5psi of back pressure, and the stock exhaust accounts for the other half at 4psi. Which means at best I can hope for 3.5-4psi with a new exhaust. Makes me wonder if the cat is clogged.

 

Another thing that I would love to test is pre-turbo backpressure.

 

UPDATE: Tested manifold backpressure here.

Edited January 21, 2018 by covertrussian

[Flinkly]

swap the front O2 to the bung after the turbo. should have no ill effects, as this is where the jdm sensor is located.

[covertrussian]

I'm thinking about doing it (since I think it will average all cylinders better on my EL header), but I would have to weld another bung for my wideband then, since I use the one behind the the turbo for my wideband.

[utc_pyro]

Another thing that I would love to test is pre-turbo backpressure.

 

Use the EGT sensor port in the uppipe. You have the Tomei ELH correct? It has the port, you just need to find an adapter from the metric threads to copper tubing.

 

I'm curious to try this myself... My CNT downpope with 110K is probably a bit clogged

[covertrussian]

Yup and even my Invidia Up Pipe had an EGT port, looks like M12x1.25, so I just need to find an adapter.

[rhino6303]

The wideband port is further down then on my previous downpipe, this should hopefully reduce the wear and tear on it.

http://legacygt.com/forums/attachment.php?attachmentid=253816&stc=1&d=1502161090

 

 

One thing you can try to help with sensors repeatedly dying is build a quick heatsink. Buy a short length of 1" copper pipe, cut it down its length and straighten it out. Once it is flat you can bend the sides up and drill a hole for the sensor.

 

I went through several sensors before doing this and it seems to have stopped the trend.

[covertrussian]

What's interesting is, my old downpipe had the sensor much closer and my UEGO didn't seem to mind at all.

 

But with that said, if I buy a new sensor, I'm gonna weld a bung further down the pipe, most widebands want 18" away from turbo usually. Just don't know if there is enough space to fit it and not hit the car body.

[covertrussian]

After the last set of backpressure testing, I wanted to see how much backpressure the engine was seeing before the turbo. I couldn't find an EGT port adapter, so used the O2 sensor instead.

 

http://legacygt.com/forums/attachment.php?attachmentid=254000&stc=1&d=1502495818

 

23psi by redline

http://legacygt.com/forums/attachment.php?attachmentid=254002&stc=1&d=1502495818

 

That's with the stock catback and the 3" to 2.4" adapter that sucks at airflow, you can see how bad it sucks with this exhaust ring on the gasket:

http://legacygt.com/forums/attachment.php?attachmentid=254001&stc=1&d=1502495818

 

Since I'm gonna be rebuilding the exhaust, pulled the stock catback off....

http://legacygt.com/forums/attachment.php?attachmentid=254303&stc=1&d=1503120834

 

Being a curious cat, I wanted to see what kind of backpressure the manifold would see with no exhaust at all (basically absolute best case scenario exhaust wise). To my surprise an open downpipe lowered the manifold backpressure by only 4psi, making it 19psi total.

http://legacygt.com/forums/attachment.php?attachmentid=254004&stc=1&d=1502495818

 

It started raining so I didn't bother testing before cat and after cat, plus riding around with no exhaust is a bit too obnoxious, so I will finish testing after I add at least one muffler.

Edited August 19, 2017 by covertrussian

[covertrussian]

Here's a little teaser of what I've been up all week....

http://legacygt.com/forums/attachment.php?attachmentid=254297&stc=1&d=1503120740

 

I still need to finish finer details of the muffler, etc. Will post up a full post, and some backpressure testing, once I'm done with that.

 

Meanwhile I noticed that this exhaust made me run REALLY Rich (dipping into mid 9's when tuned for 11.0:1), and it's mainly from much higher engine load grams/rev, even though the IAT's were 8*F warmer!

http://legacygt.com/forums/attachment.php?attachmentid=254259&stc=1&d=1503022801

 

What's with these cars, intakes make the ECU think your running less air then you really are, exhausts make the ECU think your running a lot more air?

 

Based on this, let me the first to say, you absolutely must get a retune for a catback. My AFR's are dipping into 9's, no wonder the car was hesitating.

Edited August 20, 2017 by covertrussian

[BarManBean]

Never ceases to amaze me as to what will make a difference in how these cars run. If you aren't tuning with every mod it's a total crap shoot. Kind of sad really.

[covertrussian]

Never ceases to amaze me as to what will make a difference in how these cars run. If you aren't tuning with every mod it's a total crap shoot. Kind of sad really.

 

I'm really trying to figure out why the ECU's are so sensitive, it's not because it's a MAF system (see below), I think it's code related.

 

For example, my MAFed Nissan, with an intake only saw leaner AFR's but not lower engine loads (which lead to running too much timing on Subaru's), so intake was a safe mod without a retune.

[utc_pyro]

Meanwhile I noticed that this exhaust made me run REALLY Rich (dipping into mid 9's when tuned for 11.0:1), and it's mainly from much higher engine load grams/rev, even though the IAT's were 8*F warmer!

http://legacygt.com/forums/attachment.php?attachmentid=254259&stc=1&d=1503022801

 

What's with these cars, intakes make the ECU think your running less air then you really are, exhausts make the ECU think your running a lot more air?

 

Based on this, let me the first to say, you absolutely must get a retune for a catback. My AFR's are dipping into 9's, no wonder the car was hesitating.

 

I think I've just given up on ever getting my car to run correctly.... How the heck does less EGBP change fueling?! Yes more flow and more load, but I presume your fueling map isnt going that rich.

Edited August 18, 2017 by utc_pyro

[covertrussian]

I think I've just given up on ever getting my car to run correctly.... How the heck does less EGBP change fueling?! Yes more flow and more load, but I presume your fueling map isnt going that rich.

 

Here is my fuel map... Stock Exhaust hit 2.40 g/rev column at highest. 3" Exhaust got to 2.70 g/rev, on a warmer day and warmer IAT's.

 

http://legacygt.com/forums/attachment.php?attachmentid=254260&stc=1&d=1503026572

 

Boost is exactly the same, so that's not the reason for much higher load. Now I'm not sure if it's inflated (like with intake, thus I need to adjust MAF scales back down), or if it's actually higher. I'll drive around and see what self learning sees in town, if it goes above 10% then I'll adjust MAF scales.

 

What's also interesting is, my first version of the exhaust used a modified stock LGT muffler (almost straight through). That was 4.5% richer then stock setup. Yesterday night I finished installing an 07 STI muffler (entry bored out to 3", but still with baffles, so much quiter), and now it is another 5.4% richer, which is just about 10% richer then with stock exhaust...

[utc_pyro]

Here is my fuel map... Stock Exhaust hit 2.40 g/rev column at highest. 3" Exhaust got to 2.70 g/rev, on a warmer day and warmer IAT's.

 

http://legacygt.com/forums/attachment.php?attachmentid=254260&stc=1&d=1503026572

 

Boost is exactly the same, so that's not the reason for much higher load. Now I'm not sure if it's inflated (like with intake, thus I need to adjust MAF scales back down), or if it's actually higher. I'll drive around and see what self learning sees in town, if it goes above 10% then I'll adjust MAF scales.

 

What's also interesting is, my first version of the exhaust used a modified stock LGT muffler (almost straight through). That was 4.5% richer then stock setup. Yesterday night I finished installing an 07 STI muffler (entry bored out to 3", but still with baffles, so much quiter), and now it is another 5.4% richer, which is just about 10% richer then with stock exhaust...

 

I still don't see how this is possible. If the maf and injectors are scaled properly, whatever happens post combustion shouldn't matter.

 

I want to see someone to flow bench the stock intake track and generate a "golden" maf scaling. We're all probably running around with our MAF and injectors scaled a little out of wack, or somehow missing some compensation tables that we keep adjusting everything else around. These sort of things just dont make sence otherwise.

[covertrussian]

I do have a theory, the catback reduced my exhaust backpressure by 3 psi (went from 4psi to 1psi post cat). With less backpressure the turbo is in a more efficient island zone now, which should translate to cooler air being pumped into the engine.

 

With that said, I'm only boosting 13psi on a TD05 Big 16G with 8cm housing, I just can't imagine being out of the efficiency islands on such low boost. Plus I understand how intake restrictions and pressure losses forces the turbo to overspin (good article here), but I'm not sure the same applies to exhaust back pressure.

[covertrussian]

Uploaded a 10% leaner fuel map and did a log this morning, 77F ambient (vs 86F & heatsoaked yesterday). Engine load (grams/rev) practically the same, MAF voltage is pretty much the same too.

 

This means that the way higher engine load was not a fluke. I'll continue driving on this tune for a little, to see how far off my base fueling is.

 

Does anyone know if there is an easy way to disable closed loop feedback control without pulling the O2 sensor?

[rhino6303]

Uploaded a 10% leaner fuel map and did a log this morning, 77F ambient (vs 86F & heatsoaked yesterday). Engine load (grams/rev) practically the same, MAF voltage is pretty much the same too.

 

This means that the way higher engine load was not a fluke. I'll continue driving on this tune for a little, to see how far off my base fueling is.

 

Does anyone know if there is an easy way to disable closed loop feedback control without pulling the O2 sensor?

http://www.romraider.com/forum/viewtopic.php?f=33&t=7897

[covertrussian]

I know the title is a bit of an oxymoron, a quiet free flowing exist? That's not possible right? It's been a week long progress for me to get it to that point...

 

First here is what the stock catback looks like. It's 2.4" OD at midpipe until the Y split, at which point it's 2.0" OD to the mufflers and out. This setup measured 23psi backpressure pre-turbo, 7.5psi right after turbo but before cat, and 4psi after cat.

http://legacygt.com/forums/attachment.php?attachmentid=254303&stc=1&d=1503120834

 

I had a bunch of 3" 304 stainless pipes laying around, decided to build a simple single muffler setup with it using my MIG.

http://legacygt.com/forums/attachment.php?attachmentid=254297&stc=1&d=1503120740

 

Key to keeping the exhaust quiet is using stock like mufflers, but they are usually fairly restrictive and small in diameter. I bored out the entry and exit pipes to be 3"

http://legacygt.com/forums/attachment.php?attachmentid=254304&stc=1&d=1503120834

 

Then afterwards I pulled out the two trumpets. This essentially make the muffler straight through, I could see day light from entrance, but there is that wall to break it up a little bit still.

http://legacygt.com/forums/attachment.php?attachmentid=254305&stc=1&d=1503120834

 

Everything welded and ready to be installed. I did my best to avoid any 90* bends since they restrict flow, so used all 45* bends. Later I found out that lack of the 90* bends is what contributed to the exhaust being louder then expected.

http://legacygt.com/forums/attachment.php?attachmentid=254298&stc=1&d=1503120740

 

New catback installed. This setup measured 1psi backpressure after the cat, and 20psi at the header (downpipe only measured 19psi at header). Which tells me that pre-turbo backpressure is linear and not exponential.

http://legacygt.com/forums/attachment.php?attachmentid=254299&stc=1&d=1503120834

 

Unfortunately the exhaust was still too loud, and very raspy (thanks to the equal length header). I stole a 5" Borla resonator from my G20 and welded into the straight portion right after the flex pipe. This reduced the raspyness majorly, but still was too loud for my taste and droned too much.

http://legacygt.com/forums/attachment.php?attachmentid=254300&stc=1&d=1503120834

 

Now I know why the muffler was loud, with it being almost straight through, the exhaust gasses didn't hit the walls couple times. If I inserted the entry and exit pipes past the center wall like stock does, I think it would be much more manageable. I started cutting my welded 3" pipes off, but that was starting to take too long, and I was worried it would still be loud. This is where I decided to scavenge an STI muffler from my wrecked Sentra (I've been using ~07 STI mufflers on my Nissans for a long time). Real downside to STI mufflers is they are bigger and longer, making for a much tighter fit on the legacy.

 

http://legacygt.com/forums/attachment.php?attachmentid=254306&stc=1&d=1503120834

 

This particular muffler I bored out to be 3" years ago, part of the process I pulled out the entry trumpet.

http://legacygt.com/forums/attachment.php?attachmentid=254307&stc=1&d=1503120834

 

From the large 3" entry you can now see the guts of the STI muffler. The right most pipe is the exit of the muffler, which is also a resonator (baffled). Now with this particular muffler, I bored out the next wall to be 3" years ago, then I stuck a 3" pipe in instead of the stock one that I pulled out in the previous picture.

http://legacygt.com/forums/attachment.php?attachmentid=254308&stc=1&d=1503120834

 

With the entry pipe going past the first wall, the exhaust gasses have to go to the front of the muffler, then to the back, then out the resonated exit. Well this time around I didn't have a long enough pipe and wanted to see if I can make the entry pipe stop right at the back of the muffler. This would allow some of the gasses to go straight out of the muffler (making it slightly louder and free-er flowing).

 

Here is a little diagram of the stock vs modified flow difference:

http://legacygt.com/forums/attachment.php?attachmentid=254309&stc=1&d=1503120875

 

Now that the muffler is done, I mocked it up and got it welded, along with new hangers.

http://legacygt.com/forums/attachment.php?attachmentid=254301&stc=1&d=1503120834

 

It installed a little lower then previous setup, that's mainly due to STI muffler being taller and needing to sit lower to avoid hitting the body. I think it should have plenty of ground clearance still.

http://legacygt.com/forums/attachment.php?attachmentid=254302&stc=1&d=1503120834

 

Next is the tip, it's way longer then it needs to be for the legacy, even with the shiny surround removed. Thus I had to cut the tip more, and while I was at it, repainted it to be black.

http://legacygt.com/forums/attachment.php?attachmentid=254310&stc=1&d=1503120875

 

Finally done! Here is what the final product looks like from the back.

http://legacygt.com/forums/attachment.php?attachmentid=254318&stc=1&d=1503122416

http://legacygt.com/forums/attachment.php?attachmentid=254319&stc=1&d=1503122416

 

This setup has a deep idling sound, but it's still very quiet. At partial throttle you can slightly hear the exhaust, but at full throttle it's dead silent from the cabin. This of course means it's super restrictive right? Well I was shocked to be greeted with 1psi backpressure post cat, and 20psi pre-turbo still!

http://legacygt.com/forums/attachment.php?attachmentid=254321&stc=1&d=1503122441

 

Now the next interesting thing is what I mentioned the other day, about engine loads and MAF voltages changing with exhausts. I pulled up logs from my previous setups, all from same road and very similar ambient temperatures, this got me a very interesting Engine load (g/rev) comparison...

http://legacygt.com/forums/attachment.php?attachmentid=254320&stc=1&d=1503122441

 

The first item is 2.5in downpipe and stock catback (Blue line) = Max load of 2.36 g/rev

Next is GS 3in Downpipe and stock catback (Green Line) = Max load of 2.46 g/rev

Next is GS 3in Downpipe, 3in Catback and bored Legacy Muffler (Yellow line) = Max load of 2.54 g/rev

Finally GS 3in Downpipe, 3in Catback and bored STI Muffler (Pink Line) = Max load of 2.58 g/rev

 

If Grams/s and grams/rev have any say in airflow then my STI muffler actually flows better then the Legacy one did!

 

As I mentioned earlier, my fuel was filthy rich at WOT with this exhaust, I had to increase it by 10%, but it seems fine around town (+/-3%), which means MAF scales are not too screwed up with this.

 

Power Gains

This one is a real bummer, at 82-84F ambient temps, there were no real power gains. Everything stayed pretty identical, I'll reserve my judgement until it cools down again, cause I think stock TMIC heatsoak is what's killing 80*F+ numbers.

 

I did do a bunch of back to back tuning to see if the exhaust wanted new timing ranges, subtracting 2* of timing made me loose a good bit of power and adding 2* made me not gain any power. What this means is, the engine is happy with this exact timing range, any more or less results in power loss or knock.

 

I'm a little surprised that the car didn't want any more timing or any less, I would have expected it to want a slightly different timing curve.

Edited August 19, 2017 by covertrussian

[JmP6889928]

I really enjoy reading your thread. You're doing a lot of cool work that no one else has really attempted. Keep at it. You'll find the perfect sweet spot and all of a sudden, everyone will be wanting you to build them stuff. Ask me how I know.

[Andy_Mac]

Much tidier than my attempt at it.

Mine barely showed any post turbo backpressure at all with the catless DP.

Pre turbo peaked at 26psi with boost at 16psi

Will see it start to skyrocket once you add more boost and run out of efficiency

 

Edited August 19, 2017 by Andy_Mac

[covertrussian]

I noticed that my cooper line cools real quickly so no need for extra spirals or anything, and it's not super fragile. I had to bend it in all directions installing it two of my cars.

 

26psi is pretty normal from what it seems, what turbo is this? Mine is on the lower end of the scale due to 8cm housing probably.

[covertrussian]

Gas mileage update from 3" turbo-back exhaust. I didn't test GS 3" alone, so this will be a 2.4" vs 3" turboback setups.

 

Was really curious to see what the new exhaust would do. Last time on stock intake I got 29.56mpg, new exhaust got me 29.72mpg. Basically no real improvement or loss. The car did have more power, and it did feel like it was in higher vacuum range more. I think with a timing map retune (read: less timing) the car should see some gains.

 

The reason why I think the exhaust will help is, my preturbo backpressure at highway RPM's and loads was at 3psi on stock exhaust, new exhaust had it be at 1.5psi. End goal is to get it down to 0psi while cruising.

[Andy_Mac]

I noticed that my cooper line cools real quickly so no need for extra spirals or anything, and it's not super fragile. I had to bend it in all directions installing it two of my cars.

 

26psi is pretty normal from what it seems, what turbo is this? Mine is on the lower end of the scale due to 8cm housing probably.

 

Heats never been an issue. Only had it coiled when brazing it on. Left two small loops for vibrations and stretched the rest out through the engine bay up to the pitchstop mount. Figured it'd have quicker response with capillary tube as opposed to 1/4 inch but doubt there'd be any noticeable difference.

Turbo's just an iddy biddy JDM VF45 TS but will have something real taking it's place in the foreseeable future.

[covertrussian]

Ran into an interesting issue with the exhaust. After about 1 hour of highway driving it got louder and felt like exhaust was vibrating against the car. A couple hours later I checked and all looked fine, no contacts. Drove again for an hour and it started again, got under the car and saw that the muffler was pushing against the back of the frame.

 

Next day looked under and there was about 1/4" space, so plenty not to contact. You can see where it was contacting the body though.

http://legacygt.com/forums/attachment.php?attachmentid=254445&stc=1&d=1503456719

 

Lowered the exhaust to cut off the old mounting flanges, you can see the contact points. I had a lot of fun with the grinder getting these off.

http://legacygt.com/forums/attachment.php?attachmentid=254446&stc=1&d=1503456719

 

Basically the exhaust would heat up and expand back. I think think the Flex pipe is responsible for all of this movement. I can't imagine stainless steel moving that much.

[rebourne]

What a PITA. But on another note, that's frickin awesome! geek side of me loves it.