Turbo outlet pipe diameter and EA82T's ?

[discopotato03]

Been scratching head lately and wondering why this Garrett ball bearing turbo is lazy to come on boost .

Today it was pointed out to me that 2.25" tube is not exactly big on the back of a turbocharger supposedly rated at 170 - 270 Hp . I'm beginning to think the volume in the dump pipe may not be enough to prevent a slight pressure rise behind the turbine housing and if thats the case it could be part of my problem .

My exhaust system is 2.25 except for a 3" cat converter where an RX L normally has its first muffler . It had gradual reducers fitted either side of the cat to get back to the 2.25 tube size either side of it .

I guess I could have another dump pipe made up from 2.5 or 3" tube back as far as the cat , or in my case the 3" swivel joint in front of it .

I'm curious to know what other people have found with the front 1/3 of their EA82T's exhauste in 2.5 or 3" .

Cheers A .

[Gannon]

Well given that the factory dump pipe starts at about 2" at the flange and is 1.75" from the Cat back, id think that anything was an improvement.

How does your turbo compare to a normal TD04? Is it bigger?

A TD04 on an EA82 is a bit more laggy than the factory VF4. Although dont you have a BB turbo?

Have you got your boost gauge in yet? What rpm does the needle start showing positive pressure, and at what rpm to you hit 7psi?

For me, from memory, it was about 1700 and 2300 respectively with both the VF4 and the TF035.

One thing i did notice was that the TF035, the torque delivery was a little softer, whereas the VF4 sorta had nothing, then all of a sudden, heaps.

[discopotato03]

Turbosmart took forever with the boost gauge and guess who got sent away with work just before it arrived ?
Then the fella that took it home to show me left it there so no progress on that today .
Am thinking about mounting it , its cup mount , on the upper LHS column shroud where it can be seen without blocking access or view of anything significant .

Yes I do have a TD04 but never used it . Just on that its not diffucult to see why Subaru went with the three bolt triangular flange for flat fours , easier than four bolt .

It seems I went a little big on turbine style and trim , EA82T's are not big on exhaust energy for an 1800cc four banger . Ball bearings are hands down a better system but you still need to harness enough pulse energy to spin the compressor fast enough to do its job .

Anyway my outlet pipe is 2.25" which I think measured 2.13" ID on the very near caliper . The turbine wheel i used is ~ 54 x 47mm and a pretty open nine bladed thing in 84 trim . The base model version of this turbo uses a 53 x 42mm 11 bladed 62 trim turbine and I think that will help get it going earlier . I also managed to find out that there is an OE version of this turbo with smaller housings both sides and it uses a triangular three stud mount flange as well . 20 20 hindsight is a wonderful thing .

Gannon when the boost gauge goes on I get back on what boost this thing actually runs , I know if I wind it up the fuel cut still bites so must back the boost T off a few more clicks . Must get around to disconnecting whichever pressure sensor sets it off .

I am interested to know if a larger diameter dump pipe would do anything and will make more enquiries .

Cheers A .

[Gannon]

Here is my boost gauge


I just drilled a hole with a holesaw (i made sure there was nothing important behind it first) and placed the gauge in there. The factory green backlight for that switch panel even shone through the hole where an illumination globe normally fits.

I later painted the silver ring matte black, looked much better.

It seems I went a little big on turbine style and trim

Didnt i say that the TF035 was perfect for the EA82T (it made 130kw on the 2L Forester) Thats 174hp, which is more that what you are expecting on an EA82T

If your up-pipe is bigger than the factory drinking straw, but smaller than 2 inches, i dont think there is much more you can do in that department.

I cant see your 2.25 inch downpipe being a hindrance either unless you are planning on making 300hp. Turbo gasses are very hot and flow pretty easily.

If you have any progress pics, email them to me and i'll post them up.

[twilightprotege]

2.5" is way big enough for any amount of power you'd get with a ea82t, probably even 2.25" with a nice thin walls, mandrel bends and free flowing mufflers will be enough.

i wouldnt change what you've done

[steptoe]

I'd swear mine is 2 1/2 inch from the bottom of the factory cat back.Running factory turbo with the bigger orifice at the moment which gives more further up the revs than the smaller hole did.See 6500 rather too often whereas smaller did not like 6000rpm.

I used to associate with a workplace psychopath masquerading as an engineer that rebuilt turbos, he reckoned many people mistake exhaust flow drives turbos whereas he says it is the expansion of the exhaust gases that spins it. Are these pulses you talk of due to heat expansion?

[discopotato03]

Exhaust gas always moves because thermally driven expansion takes the path of least resistance . Burn gasses in an enclosed space and the increase in temperature pushes the pressure up .

You get a pulse effect because of the way poppet valves vent the cylinders in a piston engine . They open one at a time (exhaust valves in each cylinder) in the firing order of the engine - end of each four stroke cycle .

Most Subaru flat fours are dogs because they either have siamesed exhaust ports (EA81/82) , or join the exhausts together not far past the heads in the headers . Only the twin scroll type EJ turbo engines work like a properly designed four cylinder is supposed to . Cost/packaging/emissions would have have been the driving force behind this at the design phase .
Its the reason why you get lazy turbine response , too much pulse damping and potential energy lost that could do something for you .
My 2L FJ20 had its larger GT2860RS making positive pressure at 1600 revs . To quantify that turbo had the same turbine in the larger of the two available housing sizes with a larger diameter compressor and two families up in compressor housings . Those are an inline DOHC16v thing and out of the box the ports are big enough for a black man to put - well you get the picture . Big on exhaust energy and good for exciting turbos .

Because the EA82T is down on exhaust energy the only effective thing to do is step back to a slightly smaller turbine in a smaller trim with more blades , greater trapping efficiency at the expense of flow resistance . I've been meaning to get the inside calipers into a VF4's turbine housing to see where it is size wise , compressor is roughly 52.5 by 39mm . Mine is 54.3 by 42 . Both housings are tiny on the OE turbo and we now know why .

Anyhow family stuff and back to the boost gauge .

A .

Nope , still don't like TF034's , they were designed to be a diesel engine dryer and no I'm not removing the spark plugs !

[Gannon]

Nope , still don't like TF034's , they were designed to be a diesel engine dryer and no I'm not removing the spark plugs !

But it worked. I was running 10psi and it didnt have any trouble holding that boost till redline.
Yeah sure the turbine is a little small, but so is every other breathing part of the engine.

Have you looked at the secondary turbos that were fitted to the Subaru 2.0 Twin turbo?

They might be in your size range and there are plenty of them kicking around.

[discopotato03]

No I'm determined to make a GT25 ball bearing derivative work .

I went into Explosive's , quad bike peoples , workshop and removed the turbine housing off an OE VF2/VF4 to have a look at its turbine dimensions .
It was actually a little larger than I thought at ~ 53mm by 43mm 9 blades .

I think what I'm doing is not far wide of the mark its just that I'm a bit limited in what I can get housing size wise . There is a smaller ratio compressor housing that fits my turbo , the one from the Ssang Yong OE diesel GT2554R turbo . It also has the only 0.56 A/R GT25 turbine housing I've ever seen , most are 0.64 A/R but high performance versions like my GT2860RS have the 0.86 A/R one .
Only drama like I mentioned is that the 0.56 A/R turbine housing has different inlet and outlet so needs more fabrication to fit . Actually I need to measure the weird outlet those housings have to see what tube size they can take .

Also finally got that Turbosmart manifold pressure guage in early this evening . Works well but needs the wiring finished so it illuminates with the guage lights .
From what I can see it gets positive from a little over 2000 but only a couple of pounds till 3 and over in the lower gears . In higher gears it climbs from 2500 and up but not fast enough to give that "rising floating" feeling . I'd say the 76 trim GT28 turbine isn't getting enough exhaust energy to spin the compressor fast enough to make boost and torque lower down the engines rev range .
At least now I can see whats going on so changes can be noted .

Pics to Gannon when I get the chance , cheers A .


Cheers A .

[Gannon]

What about engine management. If your mechanical ignition advance is too retarded, that will mean bang and less powerful exhaust gas

[discopotato03]

Yep we'd thought about that too . The std system tries to retard reasonably early because its expecting to get boost reasonably early , by retard I mean the ported vacuum from the throttlebody reduces at any significant throttle opening so more a case of vacuum advance drops away .
This is where my car loses out because the timing goes backwards and theres almost no positive manifold pressure to make torque with .

If boost can be made early enough the std ignition system should work as it was designed to , lots of advance at part throttle and pull it back as the manifold pressure rises .
Where I hope to gain is better gas paths through this engine for greater volumetric efficiency . Its just hard when the base animal is such a sows ear and you have to cash in on as many inbuilt smarts as possible .

For the record this engine goes quite well for what it is considering its low CR (8.1) and lack of boost pressure . The increase in timing made it run a bit cooler and makes more low down torque .
I suspect the lack of EGR can make these engines run a bit warmer because of higher combustion temps and at times I wish it was working .

Cheers A .

[steptoe]

MY EA82T EGR works only between ~2 and 10 inHg. Watch how often you get in that mode. Won't asist heat under boost thats fer sure.

[discopotato03]

How do you know when its actually opening ?
It makes sense that it wouldn't open under boost because there'd be no vacuum to pull on the actuators diaphragm .

10 to 2 inches of mercury , on my gauge thats medium to high load off boost .

A .

[Gannon]

Cruising at 100km/h, most of the time the needle is somewhere between 10 and 2 inHg. EGR is supposed to reduce emissions while cruising.

[steptoe]

stuck me finger in it to feel as it opened and closed as I drove in many conditions and watched vacuum/boost gauge. you may recall i t pieced in a second unit to run in cabin to get the experience

[discopotato03]

Fair enough , I thought you were going to say you had a light inside rigged up to the vacuum solenoid !

Yep , egr is about lowering combustion temperatures because its high temps that allow the single atom of nitrogen and oxygen to bond forming NO or as they like to print NOx .
The lower combustion temps also allows you to run slightly advanced timing without the detonation issues . Pressure and temperature is what drives detonation .

I should add that lower combustion temps also means less thermal load on the engines cooling system so something every EA82 underdog should be aware of .

A .

[steptoe]

solenoid would not indicate when egr is open just when ecu lets it if it needs to...under boost or higher vacuum than 10 solenoid may still be powered up

[Gannon]

EGR also improves fuel economy. By letting it oxygen-less air after the air flow meter, you have to apply more throttle to remain at cruising speed. (stay with me)
But fresh air into the engine stays the same and so does fuel input.
The fuel saving comes from lower pumping losses because the throttle is open more.

Pretty neat hey?

[discopotato03]

I think you'll find that pumping losses are to do with exhaust gas out rather than induction air in . The loss is crank power used to force the gasses out with the rising piston if the exhaust is restrictive .

A wider open throttle can raise the dynamic or effective compression ratio , the cylinders fill a bit better because the throttle is a bit less of a restriction . The thing to remember is that the more completely you fill the cylinder on the induction stroke the more air there is to compress on the compression stroke .
On a petrol engine (without fly/die by wire throttling) you are purely controlling air into the engine and its up to the carburettor/s or injection system to add fuel as required .
Really partly filling the cylinders with a basically spent gas won't make power to drive you down the road . It is purely a control used to trim exhaust gas temp/pressure for NOx and knocking/detonation issues .

What manufacturers have been doing for some time is making engines with fairly high static compression ratios because this is what gives crisp throttle response and good part throttle fuel economy . Part throttle dynamic compression is higher with a high static CR than a low one , who said EA82T , BUT once the throttle is opened wide strategies are needed to limit NOx and knocking when the dynamic CR climbs up on the high static CR . Things like knock sensing systems can pull the timing back but that can increase combustion temps as well so they still have EGR up their sleeves .
Actually many later engines don't have an EGR solenoid and valve as such and do it with variable cam timing . With this you can have controlled exhaust pollution into the cylinders by keeping the exhaust valves open longer into the induction stroke when exhaust manifold pressure is higher than inlet air pressure .

With turbo engines often the intercooler was introduced so that the manufacturer could raise the static CR for good part throttle off boost performance/consumption and the charge cooling was there to help reduce the inlet air temperature which has a direct affect on combustion temperature . Turbo boost is next to useles if you have to retard the ignition timing a long way to fight detonation so intercoolers are there partly to help get the engine to run more like an NA one CR wise when not on boost .

Show me a real low (7.7-8.3) CR late model turbo petrol engine with even half effective intercooling .
Still a ways off yet but people are running NA CR's on turbo engines burning E85 and they pull like a locomotive . Imagine an STi Rex with 10 to 1 CR and little/no detonation .

Cheers A .

[Gannon]

The pumping losses i was referring to are caused by drawing air past an almost closed throttle.

Have a read of this Autospeed.com/EGR Comeback


So whats preventing you from fitting an intercooler and your aftermarked ECU?

Surely both of these will give you the result you are looking for