Unlocking the hidden power and flow of your OEM turbo

[08Legacy-GT]

Is it true that also a quality blow off valve that can be adjusted (spring rise etc.) can be a simple modification that will help hold boost ontop of the electronic boost controller??

 

This would be true only if the by-pass valve currently is leaking under high boost pressure. Which even OEM's seem to hold pretty high pressure well. I have seen more issues with after market valves.

 

I think its good up to 22lbs

[joeleodee]

If you guys want to learn more about how boost pressure influences power output and charge temps, I suggest you play with Borg Warners Match Bot online tool.

 

 

 

As you can see, I have compared a variety of boost pressures all at the same rpm and conditions. I have even input accurate compressor efficiency data which indicates reducing as pressure rises (15psi is 66% eff. & 20 psi is 62% eff.) Turbo outlet temps range from 265f to 324f, and post intercooler temps range from 94f to 100f) So yes it is hotter with more boost.

 

Yet power calculations don't lie.

15 psi = 329 hp

16 psi = 339 hp

17 psi = 349 hp

18 psi = 359 hp

19 psi = 370 hp

20 psi = 380 hp

 

 

I would like a little more information on this tool. This looks like a spectacularly useful program to use when tuning for different turbos.

 

Anyway, back on topic, this is a good discussion. It's calling to question the accepted belief that the stock vf40/46 can't efficiently run high boost to redline. Unfortunately, I never pushed my stock turbo to find out. However, in my saga, I learned that I was running my turbo beneath it's optimal efficiency range. I was boosting at 20psi tapering to about 17psi and it just wasn't making good power. 330whp VD graphs on E85. It wasn't until I was over 20psi at redline and the VD graphs are comfortably over 400whp. If I didn't have a stock long block, I'd push this turbo to its limit to find out where it was. Manufacturer claims it's good to 30psi.

[Tuning Alliance]

I would like a little more information on this tool. This looks like a spectacularly useful program to use when tuning for different turbos.

 

Anyway, back on topic, this is a good discussion. It's calling to question the accepted belief that the stock vf40/46 can't efficiently run high boost to redline. Unfortunately, I never pushed my stock turbo to find out. However, in my saga, I learned that I was running my turbo beneath it's optimal efficiency range. I was boosting at 20psi tapering to about 17psi and it just wasn't making good power. 330whp VD graphs on E85. It wasn't until I was over 20psi at redline and the VD graphs are comfortably over 400whp. If I didn't have a stock long block, I'd push this turbo to its limit to find out where it was. Manufacturer claims it's good to 30psi.

 

Which turbo are you running?

 

Here is the online app.

http://www.turbos.bwauto.com/aftermarket/matchbot.aspx

[Max Capacity]

Just thinking out loud here, I'm not expert, but I do know Dave is at 5000ft above sea level, and Mike is here in CT about 300ft or so, would that cause Dave to see different things ?

[luchadorjose]

Just thinking out loud here, I'm not expert, but I do know Dave is at 5000ft above sea level, and Mike is here in CT about 300ft or so, would that cause Dave to see different things ?

 

If you think of engines and turbos as glorified air pumps, I think it could definitely cause a difference. At sea level, the turbo would be at a much different speed to move the same gram weight of air, and it would generate a different pressure. Perhaps with the "thinner" air, the turbo is spinning much faster, and being exposed to more heat as well as generating more heat on its own

[Tuning Alliance]

Correct at higher altitude the pressure ratio is higher due to less air. However, Dave stated he has seen this at various altitudes.

 

http://www.turbobygarrett.com/turbobygarrett/sites/default/files/turboTech/turboTechExpert/formula15.jpg

 

Where:

= Pressure Ratio

P2c = Compressor Discharge Pressure

P1c = Compressor Inlet Pressure

 

 

http://www.turbobygarrett.com/turbobygarrett/pressure_ratio

[Tuning Alliance]

Dave at ESP has offered up his 09 LGT (and dyno), which has a Stock TMIC and stock VF46 for testing. This isn't ideal because I will probably need to stay under ~18psi peak, but certainly I can clarify the results of high rpm boost increase.

 

So I am going to target 18psi peak tapering to 15 psi, by around 6000-6500rpm. Also we can test if it can hold anything above that, and if knock becomes an issue. I'm doubtful it can hold much more than 15 psi up there but we shall see.

 

In doing some back pressure calculations, and modeling I do expect to need a significant spring rate. As the turbine size gets smaller, back pressure goes up for a given boost. Since the VF40/46 has a very small turbine it makes significant pressure.

 

For example:

3000 rpm (15 psi of Boost) = Back pressure 13.1 psi

4000 rpm (15 psi of Boost) = Back pressure 16.3 psi

5000 rpm (15 psi of Boost) = Back pressure 19.3 psi

6000 rpm (15 psi of Boost) = Back pressure 24.5 psi

 

This indicates regardless of boost control, we will need lots of waste gate spring and pre-load to achieve 15 psi at 6000rpm, purely based on a model. However, on the road testing we were near 14 psi by 6000. The model is not including the waste gate port flow rate and flow rate change of a different spring rate. As flow rate is reduced essentially boost creep occurs and drives the overall boost back up.

[joeleodee]

Which turbo are you running?

 

Here is the online app.

http://www.turbos.bwauto.com/aftermarket/matchbot.aspx

 

I'm running an old AVO 450 turbo. Basically a stock location GT30 ball bearing turbo. It's been ported and polished. I don't know if that affects the VE characteristics of the turbo. I don't want to take this off topic, though.

 

As for the different elevations Dave is accustomed to and how it might affect his outlook, I don't want to speak for him, but from what I've seen, he has experience tuning at all different elevations.

 

Nevertheless, I am interested in seeing the results of your test. Will you be posting logs, graphs, etc?

[fahr_side]

Here is a quick example. Now mind you this is not a VF40 map, but the 52 and 40 have a very similar design, trim, etc.

http://i463.photobucket.com/albums/qq357/tuningalliance/IHI%20comp%20map%20Compare.jpg

 

First off I'd like to say thanks to these pro tuners for taking the time to get into this. Every tuner has a slightly different approach based on their own unique experience and customer expectations, and we should respect that whether we agree or not. The 'best' approach is the one that works best for you and your customers.

 

Some good info above but I wonder if some of it isn't leading us astray.

I think we can all agree that compressor efficiency drops rapidly with size, which is entirely reasonable when you consider the hub dimensions don't grow much even as inducer dimensions grow by 10 or even 20mm. Much less of the inducer area is open blade vs. hub as the wheel gets smaller.

IHI rarely leak maps and I think you'll find these RHF55 compressor maps all relate to the same wheel that's used in many turbos like VF-34, 36, 43, 48 and 52. Considering the VF-40 / 46 wheel is much closer in it's dimensions to the TD04L-13T, I'd look there for clues as to what's going on rather than at the larger ones.

We also need to remember that the pressure drops across the intercooler and intake system have to be added to our boost pressure to understand the final pressure ratio the turbo is running at. This can affect the final efficiency calculation a great deal.

As mentioned by others, the tiny turbine on the VF-40, smaller than even a TD04L, coupled with the not exactly massive 7.5cm2 P18 exhaust housing, is going to reach it's choke point quite early. That is the point where even you further increase turbine speed, it cannot flow anymore gas. This occurs when drive pressure has reached probably double the boost pressure, if not more, which is very bad for volumetric efficiency. At this point I usually find it more beneficial to let more gas flow through the wastegate, lowering EGT (allows leaner AFR), lowering boost (and therefore intake temperature) and improving VE.

 

I have a lot more experience on TD04s than VF-40s but being very similar in size I'd expect to see the same trends. Beyond a certain point, raising boost at higher revs raises intake temps so much that density falls significantly and MAF then barely increases. At this point timing has to be lowered and /or AFR has to be set richer to avoid knock, which cancels out the gains from raising boost. FWIW I find the highest useful boost pressure at redline to be around 9psi on the TD04s and 15psi on VF-43 / 48 units (2.5 liter platform), given ambient conditions where I am. Given the size of the VF-40 I'd expect best results to come at a boost pressure closer to that on the TD04 than the VF-48.

The point where the turbo is maxed out like this will be modified somewhat by ambient temperatures and altitude, so again any enthusiastic and curious tuner would be well served by trying both approaches to see what gives them the best results.

 

 

Sent from a device using some software.

[Tuning Alliance]

The Info I have says the VF40 Turbine is 52.5/40mm, while the TD04L is 47.2/41.1mm (Not sure if accurate). So not really smaller, but a definitely smaller outlet. 5mm bigger Inducer on the VF40 and 1.1 smaller exducer.

[fahr_side]

Yes, those are the same numbers I have. Actually, looking at my data, the VF-40 compressor seems much closer to the MHI 15G wheel in dimensions and trim, and for which we are lucky enough to have a compressor map

 

 

Bear in mind the widely-held belief that the IHI wheels are more efficient at lower flow rates where the MHI designs favor efficiency at higher flow in exchange for a shorter 'sweet-spot', or less efficiency at higher PRs in the middle flow range. Internet 'common knowledge', take it for what it's worth.

[Tuning Alliance]

Interesting, looks to me like your not getting near the flow limit unless above 2:1 PR. =)

[fahr_side]

Yes, but the flow limit, if you're looking at the edge of the efficiency plot, is at 60%. Do a quick calculation to see what the outlet temperature is likely to be!

[Tuning Alliance]

Yes, but the flow limit, if you're looking at the edge of the efficiency plot, is at 60%. Do a quick calculation to see what the outlet temperature is likely to be!

 

You will be in that 60% band not matter what, in the high rpm's. Just a matter of where.

 

I have a 17.6 psi actuator on the way, and so I will have dyno data to share in the not to distant future.

 

 

Assumptions 60% compressor efficiency, all at 6000rpm.

 

13 psi, 259f compressed air temp, intercooled air temp 89.8f, 373.5 HP

 

15 psi, 282f compressed air temp, intercooled air temp 93.6f, 392.1 HP

 

17 psi, 304f compressed air temp, intercooled air temp 97.9f, 402.4 HP

 

So as I was targeting 15 psi, this seems like a great spot, gaining some 19 hp, while another 2 psi seems to only gain 10 hp.

[fahr_side]

Have you remembered to add a couple of psi for intercooler and intake system pressure drop?

 

 

Sent from a device using some software.

[Tuning Alliance]

Have you remembered to add a couple of psi for intercooler and intake system pressure drop?

 

 

Sent from a device using some software.

 

 

Yes increasing pressure drop, increasing intake restriction, decreasing turbine and compressor efficiency. I think 15 psi at 6k is about all she will flow, but we shall see.

[Tuning Alliance]

So here is the improvement on an otherwise stock 09 Legacy GT. Pretty good gains on a stage 1, definitely restricted by the stock downpipe.

http://i463.photobucket.com/albums/qq357/tuningalliance/817ecfec-4a89-4a1c-b636-405f3282768d.png

[robburns201]

Bumping this very informative thread and can't wait for TA to start my tune...

 

Sent from my 0PJA2 using Tapatalk

[wbrawley]

Old thread, but I have a question about the last graph. The stock OEM looks to provide boost lower on and the KG looks smoother but starts past 3k rpm.

 

Would OEM be better for highway cruising power or KG better for MPG since no boost at cruising rpms?

[Max Capacity]

PM or contact Mike from his web site at the email address. He's a busy guy.

 

FWIW, he tuned both my cars. The stock turbo on the Spec B will get over 30mpg as long as I drive like a sane person on the highway.

 

You need to weight the cost against the increase in mpg when changing things.

[wbrawley]

PM or contact Mike from his web site at the email address. He's a busy guy.

 

FWIW, he tuned both my cars. The stock turbo on the Spec B will get over 30mpg as long as I drive like a sane person on the highway.

 

You need to weight the cost against the increase in mpg when changing things.

I don't wanna bother him for that since he's busy, just a "what if" question. Maybe somebody else can chime in that has changed to the KG and has seen better highway MPG.

[Flinkly]

Old thread, but I have a question about the last graph. The stock OEM looks to provide boost lower on and the KG looks smoother but starts past 3k rpm.

 

Would OEM be better for highway cruising power or KG better for MPG since no boost at cruising rpms?

 

honestly, the turbo is essentially a moot point for cruising MPG. Turbo's only come into play in high load demand situations, like acceleration.

 

Also, to Max's point, even if you somehow gained 5 or 10 mpg with a new, aftermarket turbo, the savings will mean nothing as you'll need to drive the car for like 25 years to break even, let alone actually save anything.

[Max Capacity]

I find my wagon get's the best mpg when I do all highway driving and keep it at 65mph or slower.

 

I do find even at 70mph its not bad, but once I begin to keep the turbo spooled, it get's that 23-24mph range.

 

Now my Spec B stock turbo and Mikes stage 2 tune, it normally gets driven once a week on Saturday night total 30 miles or so, 11 miles is highway each way. It's dash reads 22.8mpg most of the time. I keep the gas tank a 1/4 full or less so the gas doesn't get to old. When it does go on trips, it will get close to 30mpg on the highway.