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Small 16G at 24 psi. Safe? (Boost creep after porting)

Posted by 99OZDSM, Mar 25, 2020

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  1. 99OZDSM

    99OZDSM Proven Member

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    Let me preface this by saying I've been doing a lot of reading and I know this is a loaded question due to the amount of variables involved. Supporting mods in my profile should be up to date. Boost leak tested up to 25 psi (I was aiming to run 20 psi). Stock 7 bolt long block compression test: 180 175 180 175 (was performed yesterday), so the engine is healthy.

    After doing some mods this past winter and firing up the car to tune it, I have been getting the well documented issue of boost creep. I pulled the turbo, ported the 90 degree turn down, waste gate hole, wastegate exit, and entrance into my down pipe. Slapped the turbo back on the car and while it creeps less, I am still creeping up to 24 psi (24.4 psi max from my ECMLink log). In terms of knock, I am getting ~1 count of knock during a 3rd gear WOT pull, so that is not an issue. I also have not started tuning as I am trying to resolve my boost pressure first.

    Bottom line, I believe the stock 7 bolt on stock head studs should be able to handle 24 psi out of a small 16g. Should I tune around my creep? I know that the small 16g is out of its efficiency range at 24 psi, will the turbo fail on me?
     

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  2. Bock

    Bock Probationary Member

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    Not an expert but i ran 20 psi of my small 16g last summer. Was at 24psi as well before my clutch start to slip(few run, its not a daily driver).
    Im upgrading my clutch right now so i'll be back at 24 this summer. Im sure that running a turbo at 100% of its efficiency will wear it quickly but in my case, i have a backup turbo on the shelf.
    Im not daily driving the car so i cannot speak for longevity.
     

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  3. gofer

    gofer Moderator

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    It's not boost pressure that's going to lift the head, it's cylinder pressure so what you're looking at is airflow and remember the 7-bolt stock head bolts that are 11mm aren't as capable of holding up to as much cylinder pressure as the 6-bolts that are 12mm. I recommend upgrading to standard ARP head studs because they're cheap insurance that you won't lift the head, push coolant, and blow the HG even once you get your boost pressure in check. You can replace them without pulling the head too, just swapping one at a time in the proper torque sequence/order and you should have no issues.

    For what it's worth, I think I started pushing coolant/lifting the head on the stock 7-bolt 11mm head bolts when I was logging ~36lbs/m on my s16g but I was also using E85 and running pretty aggressive timing advance which also increases cylinder pressure.


    Moving onto boost control issues. To fix boost creep on your setup you either need to figure out a more efficient way to expel wastegate exhaust or induce a restriction on the exhaust of your car to keep it from creeping. These are your options to fix boost creep...
    - Install a external wastegate: Depending on where you live, your goals for the car, or your budget this might not be an option. Typically states that have strict emissions tests that do a visual check aren't okay with external wastegates and they definitely don't maintain the "stock" look under the hood either. As far as costs go, sometimes the o2 housing and the wastegate aren't enough because you could run into clearance issues with radiator fans, etc. which drives up the price even higher to fix your boost creep.
    - Install a external dumped o2 housing (keep the stock internal wastegate): This isn't a guarantee but in my experience, it works. The stock o2 housing recirculates the wastegate exhaust gases in a poor location and causes turbulence in the exhaust which creates back pressure. Exhaust gases will take the path of least resistance which is over the turbine wheel causing the turbo to build more boost than you want. https://www.punishment-racing.com/product/atmosphere-vented-o2-housing-for-eclipse-talon/
    - Reinstall the stock downpipe: Adding a restriction to the entire exhaust will allow you to keep boost pressure in check however, you'll be leaving some performance on the table. This was the option that I took to get boost under control until I could decide what path I wanted to take.​

    Personally, I like having the ability to run wastegate spring pressure on my setup because that means you have absolute control of boost. Then, if the logs/setup seem to allow for more boost then you can increase it to the desired amount. You didn't post a log but from going off what you said, 1* of knock really isn't much but letting a setup creep like isn't ideal.
     

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  4. 99OZDSM

    99OZDSM Proven Member

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    Really appreciate your response, I was hoping you would respond as I have come across many of your posts on this and the FP68hta. I also didn't mention, I don't really care if I blow up this turbo as I have been looking at the FP68hta V1 that is currently on sale. My small 16g is coming off the car next winter at the latest. But I definitely do not want to blow my engine up.

    Great point about airflow and cylinder pressure. I will have to check my log and see what I was getting.

    I have been constantly researching boost creep since I put my car back together and am aware of the options you listed. I guess I am looking for a near term/quick solution. I am honestly trying to minimize my garage time during this pandemic and trying to prioritize my family time but of course my car is in the back of my mind.

    -External Gate: I know this will basically eliminate boost creep and is the best route. However, this is something I was aiming to do next winter when I was planning on upgrading my turbo. I also would like to research more and make sure I know what I need. You made a good point about clearance issues with the radiator fans, I am on the stock fans with a Mishimoto radiator now and it is tight in there. I was looking into getting SPAL fans for next winter.

    -External 02 Dump: I would prefer a non obnoxious exhaust but I was considering this as it would not require much time to bolt on. I keep reading that this solution is hit or miss though but I follow your logic. In theory, there should be zero resistance to the wastegate flow. Another issue is my PR intercooler piping might be right in the way of the dump. With that said, I was looking at the recirculated pieces from vendors like STM but didn't think it would make enough of a difference. What is your opinion on these?

    -I do not have the stock exhaust anymore. I do, however, have a "high flow cat" to swap in place of a test pipe. I actually threw it on the other day and it dropped my peak psi to from 24 to 22 psi. This is when I decided to pull the turbo and port the turbine housing/wastegate path.

    Do you think the peepers mod/extending the wastegate flapper is worthwhile? I also keep reading conflicting opinions about the flapper mod and whether it actually increases the flow rate through the wastegate hole.

    I will definitely look into getting ARP head studs to install as soon as I can. I might as well grab a Kiggly HLA oil pressure regulator while I'm at it. These were always in the plan further down the road, was hoping to build the head and do it all at once.
     

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    1998 Mitsubishi Eclipse GSX
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  5. gofer

    gofer Moderator

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    I'd keep aiming for that goal then and not get rushed into such a big purchase, do your research on the parts that you want for the setup so you know what will work and what won't. I've rushed into purchasing things to fix unexpected problems and while I was still getting quality parts they might not have necessarily been the best choice for my setup. Live and learn.
    I don't personally know anyone who has an aftermarket recirculated o2 housing that still uses the internal wastegate so I can't speak to it. The JMF piece looks like it would be the most effective at reducing (may not completely eliminate) boost creep because of the location, angle, and size of the recirc. It looks like it places the outlet of the wastegate exhaust gas directly inline with the inlet of the downpipe and it uses a 1.75" recirc. Again though, you may have to do some more reading/research because that's something I've never done personally or know of anyone doing, that doesn't mean it can't work though!
    That's too bad you don't have the stock stuff, I was hoping to give you a cheap option. I'd keep the high flow cat on there and figure out your future wastegate setup options in the mean time, you can always turn up the boost to 24psi if you decide to later.
    The Peepers mod gives adjustability to the throw of the wastegate arm but doesn't do anything to increase the amount the internal wastegate flap can open. You can test the idea that the flapper isn't opening completely (which would tell you if the Peepers mod would work) by disconnecting the wastegate from the flapper and doing a WOT pull. Ideally you would build 0psi but if it's still creeping to 24psi then extending the wastegate arm won't do anything as the flapper just can't open anymore...

    http://www.curtbrownracing.com/mitsubishi-heads.html

    Curt Brown's the go-to with any port work and if you compare his head build prices to anyone else's on the market you won't believe it.
     

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    11.634 @ 126.050 · 2G DSM

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  6. 99OZDSM

    99OZDSM Proven Member

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    Agreed.

    This piece from JMF looks very tempting. It looks beautifully made and seems like it would reduce creep at least. I am going to look into this more. I am building this car for street/autox so the noise level may prevent me from buying it unfortunately.

    I was hoping to avoid this route but I'd rather be safe than sorry.

    I will look into this once I am ready to build my head! Thank you for your help.



    As of right now, what do you believe is necessary for me to buy? Just the ARP head studs? And obviously I will need to figure out a path forward on my boost control.
     

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    1998 Mitsubishi Eclipse GSX
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  7. gofer

    gofer Moderator

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    The first thing I'd do is pull your race pipe and install the high flow cat if you're seeing a 2psi decrease in boost. After that I'd pull the wastegate arm off of the flapper and do a WOT pull to see what my boost pressure is doing, post back with your results as I'd be curious what boost looks like then. This may show that extending the wastegate arm (Peeper's mod) will help...

    As far as spending money, if you want a short term solution that might help with boost creep while you figure out your external wastegate setup you can try that JMF piece that's pricey or (what I'd recommend) pickup a cheaper option (PR recirc o2) or try to find a stock 2g AWD downpipe to us as a temporary solution until you can get the o2/external gated setup you want. The cheapest and certain way to cure your boost control problems is finding a stock 2g AWD downpipe...

    You don't necessarily NEED ARP headstuds but if your plan is to get the most out of your current build then as I mentioned, they're cheap insurance that you won't lift the head.
     

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    11.634 @ 126.050 · 2G DSM

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  8. 99OZDSM

    99OZDSM Proven Member

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    For the near term, I'm going to say no to the stock downpipe just because I don't want to go through the hassle of getting my Wideband 02 bung welded into a stock downpipe.

    I think my immediate plan is to do a WOT pull without the actuator attached to the flapper. I assume it will creep. Then throw my high flow cat on (hurts me a little bit on the inside) and try the recirculated PR 02 you recommended. Hopefully I can then get my psi to 21 psi, ideally 20 psi.

    Assuming I can drop my psi to ~20 psi, I can start to tune. So I was thinking, once I start tuning and theoretically make more power, could my boost creep start to increase again?
     

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  9. 99OZDSM

    99OZDSM Proven Member

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    Ended up throwing the high flow cat on last night and disconnected my wastegate actuator to let my flapper open freely. Unfortunately, I hit a max of ~14 psi. I did not do a pull with the wastegate actuator on, I will try to do that today at some point and see what max boost I am hitting.

    I ordered the PR 02 recirc housing last night and will report back once that is on. Will be buying ARP head studs and Kiggly HLA before the end of the day most likely. Anything else you recommend I upgrade while I have the VC off?

    I was also looking at my last WOT pull (I bailed out around 5800 RPM) with the test pipe on. Log attached. I hit 320 gm/s max, which I believe is 42.33 lbs/min. Not sure how accurate that is or where the ECU gets this input? MAF?
    This is on basically the EVO 8 timing and fuel tables. Please ignore my WB, it has started giving me issues but I just updated the firmware (never done this since 2013 when I installed it) this morning. Hoping that resolves it. Before I started messing with boost control, I pretty much had my MAF Comp table dialed in, as well as idle/cruise fuel trims. Bear with me as I have just switched from ECUflash to ECMLink literally last month.
     

    Attached Files:

    Last edited: Mar 27, 2020

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  10. gofer

    gofer Moderator

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    That's awesome news hitting 14psi with the wastegate arm disconnected. You can cancel that o2 housing order, should have waited until you did the test. If you reconnect it and see 22-24psi again then the Peepers mod is likely to fix your problem because it would seem that the wastegate isn't opening the flapper entirely.

    I'm on my cell but when I get to a PC I'll check out the log.
     

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  11. 99OZDSM

    99OZDSM Proven Member

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    Thanks for all your help so far. I honestly don't have the ability to weld so peepers mod would be a challenge at the moment.

    Well the 02 is already on its way, haha. I put my wastegate arm back on the flapper and did some pulls. Seems like I am hitting about 22 psi. Seems decently consistent too. Log attached. First pull was in 3rd gear, second is in 2nd.

    I believe my MBC is set around 20 psi. Would making any adjustments to this help at all?
     

    Attached Files:

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  12. gofer

    gofer Moderator

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    Hey dude, I misspoke. I guess that's what I get for reading your message while I'm at work and not paying attention. You hitting 14psi with the wga disconnected from the flapper shows that you're creeping 14psi since you would have ideally hit 0 so you were think correctly. I'm interested to see the results after you get that o2 housing bolted up as you'll be the first to go to a recirc keeping the internal wastegate that I know. The Peepers mod would not benefit you... Sorry for the misinformation above, I struck it all out since it was wrong. :coy:

    As far as the WOT log goes that you attached (log.2020.03.22-06.elg) the airflow is inflated, a good indication of that is looking at your BoostEst and comparing it to your actual Boost value. If BoostEst > Boost then your airflow reading is inflated if BoostEst < Boost then your airflow reading is deflated. Not to get too far off topic but you were asking about the limits of the stock head bolts, there's a simple equation to calculating actual airflow though based on the two values, you always want to pick a point between 5.5k and 6k when your engine is at peak VE.

    So I picked the 5.5k point in your log and got these values...
    Boost: 24.4psi ---- BoostEst: 30.1psi ----- Logged Airflow: 41.1lb/m
    Then convert them to psia...
    Boost: 24.4psi+ 14.7=39.1psia ---- BoostEst: 30.1psi+14.7=44.8psia (the 14.7 is atmospheric pressure at sea level, at altitude in Denver it's only 12)​
    Then put it into the following equation...
    100 (Boost in psia / Boostest in psia) - 100

    100 (39.1 / 44.8) - 100
    100 (0.87) - 100
    87 - 100
    = -13%
    Then throw that info into this equation
    Airflow reading x %

    41.1 x -0.13
    = -5.3 lb/m​

    So your actual airflow #'s are closer to 41.1 - 5.3 = 35.8lbs/m
    I would completely remove your MBC or back the adjustment knob all the way out so you're for sure running wga spring pressure while you're troubleshooting boost creep, it's one less variable.

    Looking at (log.2020.03.27-02.elg) it looks like you got your wideband working at least. LOL You're right about running ~22psi and not seeing any knock (I ignore it below 2*) but you're also at -5* of timing so your car probably feels pretty slow too. On a stock 7-bolt LB running 91 you should be able to get away with ~5* timing advance at MBT and bring it back to at least 8* to 10* by redline.




    All and all, that's a pretty decent looking log besides the fact boost is all over the place. Once you get a handle on that and can control it with the MBC you'll be in business.
     

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  13. 99OZDSM

    99OZDSM Proven Member

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    No worries, man. I was trying to wrap my head around this. I'm hoping the recirc drops my boost another 1 or 2 psi. If that doesn't work, I am tempted to try an 02 dump next.

    Amazing! Thank you for going through this example. This is will be helpful to understand once I get to tuning.

    Thanks for your feedback. I am still fairly new to tuning and this is valuable feedback.
     

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  14. 99OZDSM

    99OZDSM Proven Member

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    I am happy to report back that the PR 02 housing you recommended fixed my boost creep! Log is attached (also started tuning). It seems like I am holding a pretty consistent 20 psi. After install, I was hitting about 22 consistently but a quarter turn back on my mbc brought it down to 20 psi. @gofer

    For future reference: Side by side comparisons of the tubular 02 vs. the stock cast piece makes it obvious that the aftermarket piece would flow better. This piece also relocated the 02 sensor to be only in the turbine exhaust path, so this may have helped waste gate flow some too. I spent a decent amount of time porting it though and filing the flanges flat. Definitely worth it for the price.
     

    Attached Files:

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  15. jed344

    jed344 Proven Member

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    Took a quick peak at your log. I have found when they start to knock they will continue to want you. I normally don't have timing drop then rise then drop again when under boost. Sometimes keeping it smoother with a degree or two less around peak tq allows you to run more timing on the big end. Aswell as sometimes running it richer on top end say 10.8 or so will aswell. What octane fuel is it on? I would expect to see few more degrees on the top end but small exhaust housing and low octane fuel can hold you back. Also your tps voltage is just a hair off should be seeing 5v at wide open. Sometimes big jump in timing 3deg+ will induce knock aswell.
     
    Last edited: Apr 4, 2020 at 7:37 PM

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  16. 99OZDSM

    99OZDSM Proven Member

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    Thanks for your feedback. I am running 93 octane and used the Evo 8 stock maps as a starting point. I've slowly been bumping up the timing in the general spool up and boost regions of my timing map. So under boost, I should keep my timing consistent? Also, would peak torque be when load maxes out? I know the "torque" data logged item is to be taken with a grain of salt. I know the TPS voltage is slightly off, I've been fighting that. I believe my throttle plate gets slightly stuck when fully closed.
     

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  17. gofer

    gofer Moderator

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    Good to hear man, we'll have to put that one in the back pocket for a solution to boost creep too.
    Before I get too deep into the weeds here, I'm no expert but this is how I understand ignition timing from reading/tuning over the years...
    "Peak torque" is a bit misconstrued because what is peak torque? Really you're focusing on achieve the right ignition timing for MBT at each RPM (which is a moving target) to get the optimum cylinder pressure that leads to MBT (maximum brake torque). If ignition timing is too advanced gas in the cylinder will ignite too soon and push down on the piston when it's coming up in the compression stroke which will reduce torque and more than likely cause detonation. Go the other way, starting ignition timing too late and peak cylinder pressure is decreased so you won't achieve MBT either so there is an optimal amount of ignition timing at each point in the RPM curve to achieve MBT.

    Hopefully that gives you a bit more understanding what ignition timing is actually doing in the CC. Since you're running 91oct you'll likely never see MBT because you're octane limited unless you throw meth inj into the equation. When you're tuning ignition timing and looking at knock what you're doing is advancing ignition timing (increasing cylinder pressure) until you see detonation and then pulling it back a degree to see if it cleans up.



    Watching that video, if fuel ignited at the speed of light you could set timing to TDC and achieve MBT but that's not the case.and you must take piston speed into account too. During spool up piston speed is slower so it requires more ignition timing as boost is building and cylinder pressures are fairly low, as boost increases so does cylinder pressure and rpm so you'll want to run less and less ignition timing to continue to achieve MBT until you hit peak boost (which is where you'll have the least amount of timing advance) and then as RPM (piston speed) continues to increase you start bringing timing back to reach MBT. Cylinder pressures plays a role in MBT too, which is why you can run more ignition timing with less boost, so timing tables show a increase in load means a decrease in timing advance. You can see that happening in your log with the factory Evo VIII stock maps, look how advance timing is during spool-up and then it dip when you hit full boost, then boost flat lines and timing begins to increase and once boost starts tapering off you hit lower load cells in the timing table and timing really starts to advance. That's because you can run more timing even with the same piston speed (RPM) because cylinder pressures decrease along with boost decreasing.

    Looking at your log I'd pull a degree of timing from the 2.2 down to 3.4 load rows @ 5k (since you saw knock there) and see if it cleans up during the next pull.

    Once you get those ARP headstuds installed you can turn up the boost. :thumb:
     

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  18. 99OZDSM

    99OZDSM Proven Member

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    For anyone reading this later on. I will caveat this by saying I ported my turbine housing (90 degree bend knocked down, waste gate hole widened under the stock flapper, ported housing to match 02 housing gasket from extremepsi), and also ported the stock 02 housing entrance and exit. I am no means an expert so some efficiencies probably could have been achieved but I doubt by a substantial amount. My mods are up to date in my profile but I was running a 2.5 catless exhaust and was creeping to 24 psi. Swapped my high flow cat on and it brought my creep down to 22 psi. From here, I bought the PR 02 housing and ported this as well. Once installed I saw 22 psi again, but was able to effectively turn my boost down to 20 psi with my mbc. I have yet to try putting my race pipe back on, which would be the ultimate test, but am putting that off for the time being.

    I have been doing a lot of reading over the years myself, I just never was in a financial situation where I had a "car budget" so to speak. So when I tuned on ecuflash before it was geared more towards a safe tune rather than pushing for power. So this is essentially my first time attempting to optimize my set up through ecu tuning (and I have a budget in case anything goes wrong). From my understanding, an ideal way to achieve MBT (or maybe the only way) is to tune on a dyno so you can see where MBT occurs correct? A dyno also offers you the ability to achieve steady state in almost every individual ignition timing cell. Without a dyno, we are left with tuning by the knock sensor.

    That video is amazing! I've seen many internal combustion videos but never one where it shows combustion through a window. Very cool to see one that is not animation. And thank you for your explanation of ignition timing in relation to cylinder pressures and how each variable can affect the overall pressure. I'm someone who wants to know why I'm doing something rather than just following directions. If you have intuition into a process, it improves your decision making. This helps me correlate the ignition timing curve in relation an increase in boost/rpm.

    I have the head studs and Kiggly HLA sitting on my work bench right now waiting to go in when I get the time!
     

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  19. 99OZDSM

    99OZDSM Proven Member

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    20200402_141939.jpg
    20200331_181147.jpg
    Some pictures I took.
    • As you can see, the wastegate path looks more efficient. Instead of turning immediately like the stock piece, the tubular piece has a short straight section then smoothly bends into a transition almost the entire way to the downpipe flange. Not to mention the diameter of this section looked larger. I'd imagine both flow velocity and increase in cross sectional area increased overall wastegate mass flow rate.
    • The transition from the waste gate path to the turbine path (not pictured) was without a doubt more efficient. The opening was much larger (after porting) compared to stock.
    • Also of note, the entire turbine path is larger than stock. It starts at 2.5 inch and ends at roughly 2.45 inches. At first I was suspicious that this might make boost creep worse but perhaps the overall increase in flow also helped waste gate flow.
    • The 02 sensor is relocated to only the turbine section, which also helps waste gate flow.
    • Oh, and this all fits under the stock heat shield so that was nice.
     

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