Flinkly's OBXT

[Flinkly]

Hey Flinkly, I came across your build thread via your posts on the Romraider forum. The custom arduino gauges look awesome. Like you, I'm not particularly happy with the PLX gauges and would like to build my own.

 

Can you share your arduino sketch?

 

Sorry if this seems like a lame first post!

 

the sketch is tailored to the OLED screens i got, but collecting and converting the data from the PLX sensors is pretty simple. the hardest part is dealing with less than perfect data packets. program needs to be smart enough to get past bad packets, which suprisingly Romraider isn't...

 

i'll see if i can find a sketch on my PC. really, the best thing to have is the PLX packet information, which i've got a PDF of around here somewhere...

 

EDIT: attached PDF is the information needed to collect the packets over serial using an arduino or other microcontroller.

PLXApp018.pdf

[Flinkly]

totally forgot to attach an arduino file...

 

 

BUT, what i really came here to say is that it seems as if my PLX AFR Gen 2/3 sensor is trying to give up the ghost. i've had a time or two over the years where it's just been wrong for a drive, but on power cycle comes up just fine. it's been installed just after the turbo since i bought it years ago, so used daily.

 

Yesterday on my way home it seemed dead. totally wrong values. again last night i headed out to the Depot to get some flooring, and was still dead. Which is fine since it was ~$150 and lasted like 4 years, and i've got a Gen 4 waiting to be installed.

 

Anyways, on the way home from getting the flooring, it worked fine again. and again on the way to work. i guess it's still got a few more days/months left...

 

 

EDIT: Bought the sensor module and gauge on 7/28/2011, so it lasted ~6 years! Hope the next does as well.

 

I actually can't believe I've had the car so long...

[vangloryous]

So what exactly did you do to get over 25 mpg cuz Im getting 22.8 max on my 5spd, 06 OBXT w/85000 miles on it, stock?

[Flinkly]

So what exactly did you do to get over 25 mpg cuz Im getting 22.8 max on my 5spd, 06 OBXT w/85000 miles on it, stock?

honestly, alot is probably driving style and my normal commute (speeds, traffic, hills, etc.).

 

the only things other than routine maintenance that help are probably my wheels (24lbs to 16lbs each) and maybe the bellmouth cobb dp (free-er flowing exhaust). my tune is far from optimum, so i wouldn't say that does me any benifit, and probably hurts me.

 

i do overinflate my tires 2psi, but i'm sure that does little to nothing.

[rebourne]

I get 18-19 vangloryous. My commute is considered a form of torture in some countries. 23 ain't bad.

[Flinkly]

Should also check out CovertRussian's threads on tuning for efficiency and his own car thread. he tends to look into the mods that help and hurt both power and efficiency and does as good of a job as you can without a dyno to check results.

 

Otherwise, as i stated before, the biggest factor by far is your route and how you drive. then maintenance, then you'll get into the gritty details of mods/tune and how they play off one another.

 

On the flipside, it's easy to willy-nilly get and install mods you think are great, that actually hurt efficiency and/or power.

[Flinkly]

dangit. made a post and f'd up and lost it. gah. well, second try...

 

so, no update per-se for the car. Just washes, oil changes, gas fillups and drives. It does have 2 car seats now, and the new one fits fine since i don't have a seat base for it. I only drive her like 2 miles on side roads, for anyone who feels like flipping out.

 

 

 

Now what i came here for is to link this turbo exhaust info. Super interesting read, and was posted by a Garret turbo engineer on an impreza forum (if you trust the interwebs...), so it should be well tailored to our cars.

 

Makes me think of modding a USDM downpipe first section to fit the TS system, lock the wastegate and add external wastegate dumped to atmosphere. or worst case, pumb the wastegate back into the second DP section, maybe a custom one, sans cat. the TS turbine flange already seperates the turbine exit from the internal wastegate, so i can essentially hook right up to the turbine exit all on it's own. will need to look at the gasket again to make sure it would work, or worst case make myself a copper gasket to use for turbine to DP.

 

projects... which i never do. but still a good read on exhaust ideas for turbo cars.

 

 

 

N/A cars: As most of you know, the design of turbo exhaust systems runs counter to exhaust design for n/a vehicles. N/A cars utilize exhaust velocity (not backpressure) in the collector to aid in scavenging other cylinders during the blowdown process. It just so happens that to get the appropriate velocity, you have to squeeze down the diameter of the discharge of the collector (aka the exhaust), which also induces backpressure. The backpressure is an undesirable byproduct of the desire to have a certain degree of exhaust velocity. Go too big, and you lose velocity and its associated beneficial scavenging effect. Too small and the backpressure skyrockets, more than offsetting any gain made by scavenging. There is a happy medium here.

 

For turbo cars, you throw all that out the window. You want the exhaust velocity to be high upstream of the turbine (i.e. in the header). You'll notice that primaries of turbo headers are smaller diameter than those of an n/a car of two-thirds the horsepower. The idea is to get the exhaust velocity up quickly, to get the turbo spooling as early as possible. Here, getting the boost up early is a much more effective way to torque than playing with tuned primary lengths and scavenging. The scavenging effects are small compared to what you'd get if you just got boost sooner instead. You have a turbo; you want boost. Just don't go so small on the header's primary diameter that you choke off the high end.

 

Downstream of the turbine (aka the turboback exhaust), you want the least backpressure possible. No ifs, ands, or buts. Stick a Hoover on the tailpipe if you can. The general rule of "larger is better" (to the point of diminishing returns) of turboback exhausts is valid. Here, the idea is to minimize the pressure downstream of the turbine in order to make the most effective use of the pressure that is being generated upstream of the turbine. Remember, a turbine operates via a pressure ratio. For a given turbine inlet pressure, you will get the highest pressure ratio across the turbine when you have the lowest possible discharge pressure. This means the turbine is able to do the most amount of work possible (i.e. drive the compressor and make boost) with the available inlet pressure.

 

Again, less pressure downstream of the turbine is goodness. This approach minimizes the time-to-boost (maximizes boost response) and will improve engine VE throughout the rev range.

 

As for 2.5" vs. 3.0", the "best" turboback exhaust depends on the amount of flow, or horsepower. At 250 hp, 2.5" is fine. Going to 3" at this power level won't get you much, if anything, other than a louder exhaust note. 300 hp and you're definitely suboptimal with 2.5". For 400-450 hp, even 3" is on the small side.”

 

"As for the geometry of the exhaust at the turbine discharge, the most optimal configuration would be a gradual increase in diameter from the turbine's exducer to the desired exhaust diameter-- via a straight conical diffuser of 7-12° included angle (to minimize flow separation and skin friction losses) mounted right at the turbine discharge. Many turbochargers found in diesels have this diffuser section cast right into the turbine housing. A hyperbolic increase in diameter (like a trumpet snorkus) is theoretically ideal but I've never seen one in use (and doubt it would be measurably superior to a straight diffuser). The wastegate flow would be via a completely divorced (separated from the main turbine discharge flow) dumptube. Due the realities of packaging, cost, and emissions compliance this config is rarely possible on street cars. You will, however, see this type of layout on dedicated race vehicles.

 

A large "bellmouth" config which combines the turbine discharge and wastegate flow (without a divider between the two) is certainly better than the compromised stock routing, but not as effective as the above.

 

If an integrated exhaust (non-divorced wastegate flow) is required, keep the wastegate flow separate from the main turbine discharge flow for ~12-18" before reintroducing it. This will minimize the impact on turbine efficiency-- the introduction of the wastegate flow disrupts the flow field of the main turbine discharge flow.

 

Necking the exhaust down to a suboptimal diameter is never a good idea, but if it is necessary, doing it further downstream is better than doing it close to the turbine discharge since it will minimize the exhaust's contribution to backpressure. Better yet: don't neck down the exhaust at all.

 

Also, the temperature of the exhaust coming out of a cat is higher than the inlet temperature, due to the exothermic oxidation of unburned hydrocarbons in the cat. So the total heat loss (and density increase) of the gases as it travels down the exhaust is not as prominent as it seems.

 

Another thing to keep in mind is that cylinder scavenging takes place where the flows from separate cylinders merge (i.e. in the collector). There is no such thing as cylinder scavenging downstream of the turbine, and hence, no reason to desire high exhaust velocity here. You will only introduce unwanted backpressure.

 

Other things you can do (in addition to choosing an appropriate diameter) to minimize exhaust backpressure in a turboback exhaust are: avoid crush-bent tubes (use mandrel bends); avoid tight-radius turns (keep it as straight as possible); avoid step changes in diameter; avoid "cheated" radii (cuts that are non-perpendicular); use a high flow cat; use a straight-thru perforated core muffler... etc.”

 

"Comparing the two bellmouth designs, I've never seen either one so I can only speculate. But based on your description, and assuming neither of them have a divider wall/tongue between the turbine discharge and wg dump, I'd venture that you'd be hard pressed to measure a difference between the two. The more gradual taper intuitively appears more desirable, but it's likely that it's beyond the point of diminishing returns. Either one sounds like it will improve the wastegate's discharge coefficient over the stock config, which will constitute the single biggest difference. This will allow more control over boost creep. Neither is as optimal as the divorced wastegate flow arrangement, however.

 

There's more to it, though-- if a larger bellmouth is excessively large right at the turbine discharge (a large step diameter increase), there will be an unrecoverable dump loss that will contribute to backpressure. This is why a gradual increase in diameter, like the conical diffuser mentioned earlier, is desirable at the turbine discharge.

 

As for primary lengths on turbo headers, it is advantageous to use equal-length primaries to time the arrival of the pulses at the turbine equally and to keep cylinder reversion balanced across all cylinders. This will improve boost response and the engine's VE. Equal-length is often difficult to achieve due to tight packaging, fabrication difficulty, and the desire to have runners of the shortest possible length.”

 

"Here's a worked example (simplified) of how larger exhausts help turbo cars:

 

Say you have a turbo operating at a turbine pressure ratio (aka expansion ratio) of 1.8:1. You have a small turboback exhaust that contributes, say, 10 psig backpressure at the turbine discharge at redline. The total backpressure seen by the engine (upstream of the turbine) in this case is:

 

(14.5 +10)*1.8 = 44.1 psia = 29.6 psig total backpressure

 

o here, the turbine contributed 19.6 psig of backpressure to the total.

 

Now you slap on a proper low-backpressure, big turboback exhaust. Same turbo, same boost, etc. You measure 3 psig backpressure at the turbine discharge. In this case the engine sees just 17 psig total backpressure! And the turbine's contribution to the total backpressure is reduced to 14 psig (note: this is 5.6 psig lower than its contribution in the "small turboback" case).

 

So in the end, the engine saw a reduction in backpressure of 12.6 psig when you swapped turbobacks in this example. This reduction in backpressure is where all the engine's VE gains come from.

 

This is why larger exhausts make such big gains on nearly all stock turbo cars-- the turbine compounds the downstream backpressure via its expansion ratio. This is also why bigger turbos make more power at a given boost level-- they improve engine VE by operating at lower turbine expansion ratios for a given boost level.

 

As you can see, the backpressure penalty of running a too-small exhaust (like 2.5" for 350 hp) will vary depending on the match. At a given power level, a smaller turbo will generally be operating at a higher turbine pressure ratio and so will actually make the engine more sensitive to the backpressure downstream of the turbine than a larger turbine/turbo would.

[Flinkly]

Ordered the bits i need for the OBXT to pull a trailer with brakes:

 

- Takonsha brake controller

- 50' of 12 awg TXL wire for the brake controller

- Rear 7 blade plug (with 4 pin plug too)

- another 4 pin plug to adapt the new plug to the subaru trailer wiring

 

 

While i was at it, i got other electrical bits:

 

- 25' of 6 awg wire for fuel pump +

- 20A inline fuse holder and fuse with 6 awg wiring

- 30A 5 pin relay

- 10' of 2 awg for:

 

alternator+ to battery+

battery- to body

battery+ to starter+

 

 

Will run all the wire along the drivers side in the sill. try to make it as nice and neat as i can. Will also be making a custom sheetmetal case to mount the 7 pin trailer connector to my Subaru hitch on the drivers side. i think i'll use some carriage bolts and such to clamp it to the bar on the drivers side, but time will tell (waiting for the plug to arrive before designing...).

[Rhitter]

When are you twin-scrolling?

[Flinkly]

When are you twin-scrolling?

 

Someday...

 

Honestly, I just want to make sure the engine is good for it (compression, and leakdown if necessary), then do some maintenance (will for sure have done, ~$1k at Surgeline), then install and tune (tune will probably be ~$350, install of "hard" parts - ?).

 

I've just never have got around to having the checkup done. It's ~$275 at Surgeline.

 

I also have a compression test kit as well, but no garage spot at the moment (tent trailer that my wife got us, that I'm refurbing for use this summer...). I am working to re-organize the garage to make it fit elsewhere, but it all takes time.

 

I do have ~$950 in paypal funds that I can use at will, and will be selling a few bits like my Cobb DP, once I make the change. This is all with respect to the cost to tune and other extra bits that still need to purchase and have installed.

 

 

I'm just out of spare time (<- my main excuse). I'm getting rid of an arcade I built myself since I just can't support all the hobbies I used to when I was single (and without kids). Getting rid of some scuba gear, should probably get rid of the "classic" car i have all over the garage...

 

bah.

 

 

Has anyone seen the TS kit for $550 in the classifieds? holy cow. cheap.

[utc_pyro]

 

Has anyone seen the TS kit for $550 in the classifieds? holy cow. cheap.

 

Yep, and it's super freken tempting. Just wish I had a garage available so I could install it.

[xt2005bonbon]

Has anyone seen the TS kit for $550 in the classifieds? holy cow. cheap.

 

Maybe I should get it. Then once I am done with it, I'll sell it to you.

[xt2005bonbon]

Just 'studied' this kit a bit more... Looks like you'd need to change the intercooler to an STI style intercooler, which means you'd have to change the intake manifold too?? Haven't looked at that part in details yet.

So even though it looks really good on paper, I may see why people are not jumping on that great deal: requires lots of work to get it installed and stuff.

[Flinkly]

Just 'studied' this kit a bit more... Looks like you'd need to change the intercooler to an STI style intercooler, which means you'd have to change the intake manifold too?? Haven't looked at that part in details yet.

So even though it looks really good on paper, I may see why people are not jumping on that great deal: requires lots of work to get it installed and stuff.

 

pfft.

 

the VF37 core (CHRA) is identical to the VF52. so as long as you've got a VF52 (or at the least a compressor cover), AND assuming it's a stock VF37, you can just swap the VF52 cover on and bob's your uncle.

 

so you can just swap the header/up/dp and turbo on (with the new stay bracket), and you're golden.

 

for the VF52 cover swap, you'll also want to swap one of the two coolant lines for a more seamless install.

 

 

or get a GS intercooler and use the STI coupler for the "in" and LGT coupler for the "out". They have those, right?

 

 

Also, to round out the thread, i'm working on a SS flange to adapt an OEM USDM dp to a TS turbo, with a separate wastegate dump (to wherever you want to dump it...)

[xt2005bonbon]

OK. I understand. I don't have a VF52 though.

 

The GS intercooler option is definitely nice though. But that's another $800-1k spending .

[Flinkly]

don't they make adapters for STI turbo's to connect to LGT/WRX TMIC and intakes? like a silicone bend and a flange to go on the "in" of the TMIC?

 

I've never looked, but feel like something may exist.

[xt2005bonbon]

Maybe they do. Don't know. Then again, not sure if I'd couple this nice set up with our 'meh' stock intercooler.

[magnusonsubie]

You can run an STi turbo with the GS intercooler. You just need to buy the $50 adapter silicone hose.

[WRX USA]

don't they make adapters for STI turbo's to connect to LGT/WRX TMIC and intakes? like a silicone bend and a flange to go on the "in" of the TMIC?

 

I've never looked, but feel like something may exist.

 

That’s what I’m running with the Dom1.5. Like Magnusonsubie said it’s an a silicone adapter hose (GrimmSpeed Intercooler Kit (090060) Turbo Outlet Hose). I paid just less than $90 through Infamous Performance.

[Rhitter]

don't they make adapters for STI turbo's to connect to LGT/WRX TMIC and intakes? like a silicone bend and a flange to go on the "in" of the TMIC?

 

I've never looked, but feel like something may exist.

 

No they don't the LGT intercooler would run into the turbo. You may be able to clock it on some random directories and make something custom m Process west and Grimmspeed are the only intercooler options so you don't have to replace the intake manifold.

[Flinkly]

OK. I understand. I don't have a VF52 though.

 

The GS intercooler option is definitely nice though. But that's another $800-1k spending .

 

there aren't any legit IHI compressor covers or dead turbo's for sale, but there are "knock-off" VF52 compressor covers on Ebay for ~$50 (who knows how good they are, but they do look like IHI covers without the IHI lettering...)

 

eBay VF52 knock-off compressor cover

 

There are also a few JDM OEM STI TS DP first sections for sale. just get some gaskets and hook up your USDM OEM second section to the end and it should mate up just fine. ~$200 (who knows how the CAT looks within...)

 

JDM OEM STI TS DP first section

[xt2005bonbon]

there aren't any legit IHI compressor covers or dead turbo's for sale, but there are "knock-off" VF52 compressor covers on Ebay for ~$50 (who knows how good they are, but they do look like IHI covers without the IHI lettering...)

 

eBay VF52 knock-off compressor cover

 

There are also a few JDM OEM STI TS DP first sections for sale. just get some gaskets and hook up your USDM OEM second section to the end and it should mate up just fine. ~$200 (who knows how the CAT looks within...)

 

JDM OEM STI TS DP first section

 

Interesting. I am currently using an Invidia catted DP but I do have in my (hoarder) pile my OEM USDM DP. Dude, you are really tempting me now...

side note: how can they sell that compressor cover for 50 shipped?? They're making 10$ out of it?

 

side note 2: reason I am also looking at changing turbo is for the simple reason that I am using a lot of oil and am beginning to blame it on the vf40. I hope that is it though. (see discussion here)