Borg Warner EFR Series Turbo's V 2.0

[Full-Race Geoff]

Air filter restriction on matchbot might come close in some instances at sea level but overall is inaccurate at simulating a Restriction orifice.  We went through this with a rally team and BW engineering a few years back and they concluded there weren't enough people asking for this support to warrant further development of the software with a restriction orifice input.  

@discopotato03my understanding agrees with yours, singlescroll small turbos with restrictors and antilag gets it done.  this got further compounded by the cracking of dividers in turbine housings compared to the convenience of a vband clamp.  IMHO - with the quality of today's investment castings I think the conclusion might be different.  

[Full-Race Geoff]

On 1/16/2024 at 10:21 PM, Lithium said:

the Xona/FP turbos are pretty expensive but they do work to unusually high pressure ratios. I think they have got a bit more common with "restrictor classes" in various forms of motorsport for that

 

this isnt the thread for this convo, but im becoming a believer of the xona turbos for high pressure ratios.  i started testing them on S58 high boost setup and very impressed so far - especially considering their packaging  

[Lithium]

59 minutes ago, Full-Race Geoff said:

this isnt the thread for this convo, but im becoming a believer of the xona turbos for high pressure ratios.  i started testing them on S58 high boost setup and very impressed so far - especially considering their packaging  

I like all this.   The thing that killed my ability to resist responding was the mention of modded S58s 💦   God they're good.

 

[Komdotkom]

I've got a bit more information from the owner about the turbo and it appears to be quite a strange hybrid. It was built to be similar to the GT2860R Rally which is a turbo which was designed specifically for rally cars on a 34mm restrictor.

This is great in theory but when you overlay the choke line on the compressor map all of a sudden things are looking less good. 36 lb/min for a 38mm restrictor I think is on the money.

 

I think my question now becomes do you tune the wastegate position to be keep it just below the choke point of the restrictor and taper shaft speed as rpm increases. I'm assuming that once the orifice chokes the flow gets ugly and we also see a vacuum in front of the compressor blades which is not great. Or do you just smash as much boost in there as possible and make it choke as soon as possible? My thinking is that the turbulent flow and vacuum in front of the compressor is NFG but I don't have any experience with this.

 

[Lithium]

So I have very little experience with restrictors so like always, just sharing my thoughts.   The only car I have tuned with a restrictor was years ago, and had a standard Mitsi TD05 in it and the owner was on a tight budget so the approach I took with tuning the whole thing was "to finish first you must first finish" and kept the boost curve "within" where the turbo seemed to be working safe... enough.

So before I get into the strategy I'd consider doing with such a thing ( @Full-Race Geoff / @GTSBoy / @discopotato03/ usualy suspects - I am not 100% confident on this stuff so welcoming input or corrections here) is the way I understand things a compressor map is a CORRECTED airflow chart.   It assumes ambient temperature and pressure at the compressor inlet is "standard" near sea level, mild day kind of stuff.   As you get closer to the max flow of an orifice the down stream pressure drops, which means the "actual" air density upstream of the compressor is miles off standard and I think that if I'm right there then it's very important to not overlook the effects of this, especially if you aren't logging turbine speed etc.

If you are running say 5psi BELOW ambient pressure at the compressor inlet then the air density will be much lower than what the compressor map states and the *actual* airmass moved will not be what you see on the compressor map.  You may need to exist at a point >50lb/min "corrected" flow in order to achieve ~36lb/min *actual* mass flow.   I'd think of it that a compressor map really is a volumetric flow map that as an afterthought is converted to mass flow assuming that your turbo is feeding on sealevel air pressure at ~20c or thereabouts.  

I'm not saying that going for  50-60lb/min turbo will fix this issue as the more "actual" mass flow you try and move the higher the depression after the restrictor and the whole situation will just keep getting worse, but I think it's very important to bare this in mind if you are turbo matching as well - imho if you want to map a turbo that is going to be able to achieve near 36lb/min *actual* mass flow then you should probably size it for more like 50lb/min or more if you CAN if you want to run it without overspeeding the hell out of it.

Regardless of how you go about sizing it, if you are able to measure the depression after the restrictor - or wheel speed, then you can at least make smart decisions about how to do your boost curve.  I would target the boost curve to stay comfortably under where it's going to start spiralling out of control as realistically when the "depression" starts really kicking into effect what will happen is the harder you push the turbo the worse the depression will get, the EASIER (weird, right?) it may become to spin the turbine faster and the sooner you're likely to explode a turbo.

If the engine etc are strong enough I would 100% send it as hard and safely as possible through the middle, you get the added advantage there that mechnical loss is less at lower rpm so more power for the same mass flow.  *HARD* on the engine, but if you have a narrow power curve then that's the way.   I'd definitely bleed it back at the higher rpm "in anticipation" of the pre-compressor depression ramping up.  If you had a way of getting a gauge on that I'd be tempted to decide what you think is acceptable and tuning it to not exceed that.

 

Just my 2c.

Edited January 18 by Lithium

[GTSBoy]

^^ Yes. Essentially. With respect to what happens to compressor maps.

Even without a restrictor, the choke limit on any compressor inlet is the sonic velocity. Obviously you can't and don't exceed ~300m/s in the inlet. Importantly, even without a restrictor, air going that fast is already at significantly reduced static pressure (this is because you gain dynamic pressure at the expense of static pressure - they have to add up to the presure you started with, which is only 101.325 kPa at sea level on an ISO standard day). The dynamic pressure associated with the velocity is many tens of kPa, and you only have ~100 kPa available at atmospheric pressure. So the air density goes down. I think that standard compressor maps effectively take this inlet velocity static P drop into consideration anyway. After all, they are tested in an actual compressor housing, with an actual inlet throat.

With a restrictor, you will choke** the flow in the restrictor and then the air expands back into the volume between the restrictor throat and the impeller inlet face, leading to the reduced static pressure that you would expect. This reduction in static pressure and density is on top of the existing drop in static pressure resulting from the high air velocity. Shit starts to get weird and you have to keep your wits about you when talking about this stuff, because now the "vacuum" caused by the restrictor means the air is at a lower density, which means its sonic velocity is higher than it was at normal/standard density and the amount of dynamic pressure associated with velocity is on a different slope than it used to be. All very complicated, and I'm not going to try to straighten it out in my head sufficiently to make sense of it.

Anyway, what it means is that you actually a dedicated compressor map for the inlet pressure condition that you have to run at. You can't easily use the standard comp map and just look to higher pressure ratios (to account for the vacuum in the inlet). This is because the relationship between mass flow and pressure ratio will also be changing, so where the choke line is, where the speed lines and efficiency lines are, will all move around. You'd need to do the work that generated the standard comp map again, with a restrictor in place, to create a map that you can trust.

 

** The reduction in static pressure caused by the restrictor occurs even without reaching the choke point. A restrictor is just that, a restrictor. It causes a pressure drop, and some of that pressure drop is permanent and unrecoverable. That's how they work.

[burn4005]

Confirmed. I work in LNG and when we are assessing mechanical designs from vendors for compressors we are supplied compressor maps (also radial/centrifugal due to pressure ratios required, but shaft powers of around 10MW) for a range of design inlet pressures and they are markedly different. unforunately i can't share them to illustrate my point.

 

A restricted inlet effectively puts an upper limit on the mass flow to the engine. you can suck harder at lower pressures but this eventually crosses over into not being worth it as your velocity vs density isnt worth it any more and a turbo can't do anything an NA engine can do in that respect.

Edited January 19 by burn4005

[Komdotkom]

Thanks gents, your input is very much appreciated

Clearly I'm not smart enough to work this out, who do you engage as a consultant to spec a turbo for something like this? I wouldn't know where to start looking for the right kind of boffin for this.

[GTSBoy]

1 hour ago, Komdotkom said:

Clearly I'm not smart enough to work this out, who do you engage as a consultant to spec a turbo for something like this? I wouldn't know where to start looking for the right kind of boffin for this.

I strongly suspect that unless you have the ear of the engineers at Garrett, or equivalent - ie you're running an important race team in an important race series - then you're probably not "designing" these things from first principles. You're probably running on trial and error. It's still a time-tested approach to exploring new ground, even if the ground is not completely new. If someone else owns all the maps and won't share, you have to make your own!

I'm sure there are people who are sufficiently clever in a few orthogonal directions who could start with what's known, and via good gut engineering, or small step trial and error, or throwing a lot of random shit at the wall to see what sticks, or big bold concepts, could get to the answer(s) as to what works.

As such, I'd suggest you'd be looking to see if you could leach information from any rally race teams that had to run under some old restrictor rules where they bought or learnt the lessons, and could pass on much of it because it's no longer relevant to their competition. There might be some of those in Oz. Maybe also in NZ.

[discopotato03]

One of my mentors speciality was rallying early Datsuns .

There came a time when turbocharging was the thing to boost the performance of Rally and Circuit race cars - call it the Group A era .

Traction was always the issue on the dirt and AWD was the answer for this .

Manufacturers did all things fair and foul so the regulators had to find a way to level the performance playing field . Inlet air restrictors was their solution . Simple and effective - you can have as much air as this gadget can flow and no more .

So , the first thing they found was that conventional performance turbos didn't work . They'd get to the flow limit of the restrictor and fall flat on their face . So the next step was to downsize their turbos so that most of its effective range fell within the flow limits of the restrictor . Some of you may remember that the TME spec Evo 6 4G63s had a TD05 turbo with a smaller compressor than the std or GSR spec Evo 6 . They came on boost earlier and made rated boost (from memory) at something like 2800-3000 revs . 

We can do a lot of guessing about choke flows  , my theory go like this 

Just about everything on planet earth air wise is pressurised by our basic 1 Bar at sea level . 1 Bar being approx 14.7 Psi/100kpa/1000Mb .

Many people have a hard time believing that their is no such thing as "suck" , death and tax man aside . When an engine draws air in it's actually being pushed in by atmospheric pressure . The roads to high airflow with only 1 bar pushing is a lot of area . With turbos again you won't get any more air in than the atmosphere can push through a given orifice . 

When the compressor flow starts to out run the restrictor the pressure starts to drop ahead of it to the point where its so low that the atmosphere can't push any more in - it literally chokes .

So you are left with a situation where you have to make best use of the air volume available and have the engine in a state of tune to work effectively with this flow ceiling . 

What the Rally teams ended up with was something more like a petrol fired diesel performance wise . Lots of torque at low to medium revs and forget about much over 5000 .

If you look at pics of Grp A rally turbos they're nothing like anything else  . Compressors look smallish with small trims in materials like magnesium . Turbines are made of very high temp spec alloys and possibly a little larger in diameter with medium trim sizes . As I said initially they gave up on twin scroll for the reasons Geoff mentioned and had ALS to virtually have them up to speed from a high idle .

With Garrett I can't say but I know Mitsubishi put a lot of effort into Grp A homologation special turbos and these turned up on production cars . Evos 1 and 2 used a TD05H 16G - I think the "small" 16G 60 odd mm compressor . Evo 3 got the same TD05L turbine but with a unique compressor wheel of similar dimensions to the "big" 68mm 16G diesel wheel . Everyone calls this Evo 3 16G compressor , the difference aside from aero geewizzadry  was that the wheels hub and front boss were reduced in area and mass so less weight and more blade area for a given inducer/exducer size . As we know Evos 4-9 went twin scroll and reverse rotation possibly with the same wheels aero . Twin scroll gave them the ability to wake up quickly and interestingly Mitsy turbine housing sizes increased from around 9cm to 9.8 and 10.5cm from Evo 6 . There were a few TD05Hr variations in the Evo 6 era - aimed at spinning up earlier and being able to cope with the restrictor in Rally trim . The TMEs turbine was TiAL to make it lighter and the compressor was reduced in size to make it live within a lower total air flow rate .

Beyond Grp A but there were also a couple of special TD05s for the Evo 9 RS . They were a limited option of the TiAL turbine but with a light weight magnesium compressor wheel as well . There was two versions of these , first the flat back compressor which cracked and second the tulip backed one that didn't . I have one of those buried somewhere . Also a third version that had the reduced sized compressor wheel . Interestingly all Evo 9 turbos have the larger compressor housing with I think increased diffuser diameter .

Any way , If it were me trying to spec a turbo with a restrictor I'd be finding out the restrictors max flow and working the compressor and housing numbers around that and the engines capacity .  If anything I'd start with smallish compressors in relation to turbine size which is basically how early generation diesel turbos are . 

 

My 5c spent .  

    

[r32-25t]

TLDR

[Shyboy]

On 7/3/2018 at 12:10 PM, Shyboy said:

Here is my results 

EFR 8374 1.05 rear 

Nitto 2.7

heavily ported head

4” dump in to 3 1/2 “ exhaust 

FullRace Manifold  twin 38 mm tail gates

e85 and all supporting mods

The car feel and dives awesome 

graph is showing old -5’s 

 

Here’s result for 8474. 1.05 rear

4” exhaust 

bigger cooler and manifold 

that’s done on RWKW 

[GTSBoy]

It's not really doing 9500rpm is it?

[Shyboy]

Not sure , this engine set up loves revving 

The turbo hooked up to speed meter  hope doesn’t over spin

[Lithium]

5 minutes ago, Shyboy said:

Not sure , this engine set up loves revving 

The turbo hooked up to speed meter  hope doesn’t over spin

So long as there are no leaks etc it should be fine, 480kw @ hubs on 25psi should be a walk in the park for an 8474.  Any reason it didn't get taken further?

Edited April 16 by Lithium

[Shyboy]

Unfortunately not much info 

was saying something about back pressure?? 4” exhaust 

[Lithium]

4 minutes ago, Shyboy said:

Unfortunately not much info 

was saying something about back pressure?? 4” exhaust 

Interesting, I know folks who have taken these turbos with that housing over 600kw @ hubs before back pressure started becoming a thing - do you have an EMAP sensor?   4" should be heaps

Epic setup regardless, 480kw even is no joke.

 

[Shyboy]

He said their dyno always reads low 🤷🏻

really wasn’t looking for high reading 

haven’t had a chance to drive it in anger 

did a bit of driving early January car was on RWD and went off the road on to curb 😂

 

Motec is monitoring everything 

 

[Mick_o]

1 hour ago, Shyboy said:

Here’s result for 8474. 1.05 rear

4” exhaust 

bigger cooler and manifold 

that’s done on RWKW 

About time mate lol! solid curve!

Hows my exhaust sound? 🤣 definitely no restrictions in that!

[Shyboy]

Lol

3years 

sounds great bit quieter than old set up and deeper 👍