Technical Understanding of the IHI (Why does my Power FALL off?)

[Dybz]

seems like you may have to update this based on the info that's cropping up in the other thread.

 

[grambles423]

seems like you may have to update this based on the info that's cropping up in the other thread.

Yup....I'll remove the "VTR501" and keep it away pending the investigation

 

[gkamenov]

Hello everybody!

I have Tiguan 2.0TSI (CAWA) with Revo Stage 1. I just registered here, because the engine is (as I think) the same as in MK6 and because the forum is nice!

Today I did some logging and here are the results. Is this, what happens after 5080 RPM the referred "IHI inefficiency at high rpm"? I thought it is due to air intake inefficiency (mostly due to the stock air filter). Or even could be the exhaust restriction..? I plan to do a run without air filter, just to see the results.

Here are the curves:

Everything is stock, except Revo Stage 1 software

 

[grambles423]

No intake will help you with the low compressor efficiency of the IHI. It'll help, but not overcome it. You're seeing almost a 7psi drop from 5000RPMs to 6200RPMs. That's CRAZY!

 

[A_Bowers]

No intake will help you with the low compressor efficiency of the IHI. It'll help, but not overcome it. You're seeing almost a 7psi drop from 5000RPMs to 6200RPMs. That's CRAZY!

Yes it is. It makes me sad to watch the boost fall off as rpms climb.

Needs k04

 

[grambles423]

Needs k04

Agreed. :thumbsup:

 

[Deaks2]

Bigger turbo is always the solution.

 

[gkamenov]

It is sad. I did another run with different air filter. The results are exactly the same.
Here is another view, showing the actual lack of pressure. It is 4 not 7 psi,
but anyway it is sad. Seems that VW have put the smallest available turbo...
It is just ok for the stock power.

Definitely K04 is the way.

 

[grambles423]

Yep, You can bounce on over to my build thread where all of this information has already been collaborated.

 

[Peteriroc]

It is sad. I did another run with different air filter. The results are exactly the same.
Here is another view, showing the actual lack of pressure. It is 4 not 7 psi,
but anyway it is sad. Seems that VW have put the smallest available turbo...
It is just ok for the stock power.

Definitely K04 is the way.

IHI turbo it´s not bad for the 2.0 TSI. has good pike (23 psi), in middle range.....beyond 4k rpm the lower compression ratio 9.6:1 EA888 has.....compensates the lack of boost, with higher timing (36º in my case with the STG 2).

It´s cristal clear k04 is a better turbo for the TSI but the I enjoyed a lot the IHI :thumbsup: has great torque in middle range!!!!

Cheers :thumbsup:

 

[zonzonalg]

Lets have some technical discussion. Sticky if you want, I feel its good to have an understanding of these matters. It helps better diagnose problems, and frankly, its just plain cool. You can never go beyond the realms of phyics, thats why when you explain the theory behind it and get a better understanding of it, you can solve problems easier.

I wont go into exactly HOW to read compressor maps should be read, but this link will do a fantastic job in explaining what you're looking at. It also goes into more about the different type of turbos and is EVERYTHING you need to understand your turbocharged engine better:

http://www.turbobygarrett.com/turbobygarrett/sites/default/files/PDF/Turbo Tech 103.pdf

Basically its a mathematical means to determine turbo efficiency and how well you can hold boost without:
1. Surging your turbo (Having too much pressure to counter spin the turbine wheel)
2. Running out of breath. (Too much flow and too little pressure)

Here is the compressor map for the KKK K03 turbo which was used in the FSI engine....very very similar to the IHI Compressor:

The Y-Axis is pressure ratio relative to atmospheric pressure. The X-axis is volumetric flow rate through the turbo compressor.

As you can see (Well....sort of), when you have low boost (stock 10-12psi), and go further up the RPM range, it'll hit the "Choke Line". The choke line is exactly what it sounds like, the point at which the turbo cannot hold the pressure and enevidtably loses boost with increasing flow rates.

So why does stage 1 do it so drastically?
16psi is roughly a 2.0 pressure ratio. Its requested sort of in a reverse parabolic shape across the RPM range:

Taken from KaJ's logs

Notice the upper left graph. At the end of the RPM the requesting boost is ACTUALLY at 8psi (1.5 ratio). Again, go back to the compressor map. This is the turbocharger choking itself and falling out of its efficiency range. But theres another reason why. What can it be?

I'll tell you what it is! Guess what else starts to choke the turbo? Thats right...the downpipe. Especially the stock downpipe. Its designed to keep emissions low and sacrifices some of that nice free flow to meet the standard. Now you can see why stage 2 with a free flowing downpipe is a nice touch to your tuning needs. I wont neccessarily go into the whole 2.5" vs. 3" debate (maily because different tuners tune for different things) but both are considered "free flowing" exhausts. They allow for better flow and less choking.

With that being known, you can refer back to the compressor map and see that with the right boost and the right flow rate, you can hit the optimal edge of the map and create some nice high RPM power, which is exactly what stage 2 tunes do.

What about bigger turbos?
Well...plain and simple. The only thing that changes for a bigger turbo is where the map is on the scale. It essentially moves up the flow range and can allow for more boost. Hence why you see more lag per more volume with bigger turbo systems. However, most tuners know that people love their low range torque. That is why you tune as close to the surge line as you comfortable with in the lower flow ranges.

Here is an example of what I'm talking about (K04 Content)

That line is the "performance line" plotted across an RPM range. This line is close to the surge line but within the turbo limits. Right around the higer rev range you can see where this turbo shines. But now you have a decision, you can tune for boost, or you can tune for flow. Thats where almost every tuning company is different. Theres a trade off between high boost and surging the turbo and destroying it and running low boost and have less power. Its all about what the end user wants. If you can find your happy medium, then more power to you!

You can see, however, if you tune for boost and basically follow the surge line up, it'll choke out up top and start running around the speed limits of the turbo. Not only will you DROP OFF power drastically, but you can risk grenading your turbo. Linearity is quite common and normal tuners will tune for the wastgate cycle to allow the compressor line to run RIGHT THROUGH the middle of the map (The most efficient point)

Also, notice the difference between the IHI and the K04. Look at the MASSIVE difference in Flow rates the turbos can handle. (X-Axis) What does this all mean? In the most simple terms....

IHI Compressor is too small and inefficient to hold pressure at upper RPMs

I'll update this later. I just had to brain dump most of the content to get an idea of where I was at in the conversation. If you have any questions, comments or concern or even things I should add, I'll be happy to do so.

Keep it technical and on topic.

Thanks for the usefull information Just se great

 

[XGC75]

Hey everyone I've got an interesting tidbit to share regarding boosting pressure with APR/Revo/Uni/Giac/etc:

You can actually increase power a little by making an engine slightly bigger or running it a little faster with a bigger cam, but the serious potential for increasing power (say, 50 percent more torque, everywhere!) lies in boosting the average cylinder pressure during the power stroke. Happily, not only is this completely feasible with turbo-supercharging[1] - which can easily generate 3 or 4 atmospheres of boost pressure with a single centrifugal compressor, or more with two-stage turbocharging - but boosting the power this way is easier on the engine than you might think. In fact, peak cylinder pressure and rod stress in a powerplant turbocharged to 2 atmospheres is only moderately higher (perhaps 25 percent) than a normal-charged engine, since less than a quarter of the charge mixture will have burned at the time of peak pressure.[2]
The continuing combustion following peak cylinder pressure is precisely why average cylinder pressure is considerably higher in a forced-induction powerplant. Midway through the power stroke with the piston at 90 degrees after top dead center, supercharged cylinder pressure can easily be three to four times that of a normal-charged engine, with torque over twice as high. True, turbocharging does load the rods and pistons more, and for a longer time, but the loading from higher cylinder pressure is dwarfed by the much higher stress from high engine speeds having nothing to do with the horsepower, the most critical being stretch to the rod and rod bolts when the crankshaft is yanking a piston downward from top dead center at high acceleration during the early part of the intake stroke.​

Jeff Hartman. "Turbocharging Performance Handbook" MBI Publishing Company. 2007
​

1) Turbo-supercharging is just turbocharging. The supercharging suffix refers to the supercharged air going into the cylinder. The compressor is turbine driven. The reason belt-driven superchargers got their more direct name is simply because they were popularized first.
2) This is explained earlier when the author describes top-dead-center pressures and post TDC combustion. Peak pressure occurs "in the 14 to 18 degree range after top dead center"

What he's saying is that peak cylinder pressure is not radically increased with increased boost, due to the relatively slow rate of combustion of the gasses in the cylinder. If one were to draw a graph of cylinder pressure:

Courtesy http://performancetrends.com/Definitions/Cylinder-Pressure.htm​

Supercharged air would only increase the peak a small amount, but the slope after peak pressure would be considerably less, so average pressure on the piston throughout the compression stroke would be considerably higher.

By the way, I would highly recommend this book so far. Very informative. It's not insulting to my intelligence as an engineer but it is direct enough that anyone could pick it up and expand their understanding of what turbocharging really is.

Feel free to add this anecdote to the OP

 

[Italianangry]

I agree with you..i have very low boost pressure around 5500 rpm...only 0,9 bar (but i live at 500 m over the sea level)

 

[grambles423]

Just confirmed our turbos are IHI RHF5 with custom Compressor and Turbine castings

 

[A_Bowers]

When you say "our" you mean regular GTI folks