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Old 05-04-2011, 09:41 AM   #1
grambles423
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Technical Understanding of the IHI (Why does my Power FALL off?)

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/turbob...Tech%20103.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 RHF5 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.
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Old 05-04-2011, 10:46 AM   #2
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Yes! Sticky! How about a K04 map?
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Old 05-04-2011, 10:59 AM   #3
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I understand the concept clearly enough, but the map itself is still chinese to me. I have no idea what is what on there lmao.
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Old 05-04-2011, 11:11 AM   #4
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Quote:
Originally Posted by davesxx01 View Post
Yes! Sticky! How about a K04 map?

The BT compressor map that I showed IS a K04 unit. KKK-K04-64 to be exact. It is VERY similar to the GT28 one right here:

GT28


Quote:
Originally Posted by BeauG View Post
I understand the concept clearly enough, but the map itself is still chinese to me. I have no idea what is what on there lmao.
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Old 05-05-2011, 08:26 AM   #5
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Old 05-05-2011, 08:58 AM   #6
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good info...
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Old 05-05-2011, 10:54 AM   #7
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Awesome

Always welcome to see objective analysis - science even - amidst a sea of subjective commentary (and half of the latter third-hand at that).

Very nice...and thanks,

Bob

PS Pic is from my daughter's Science Fair.


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Old 05-05-2011, 11:08 AM   #8
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i cant give you the answer in vernacular: "ITS TOO SMALL" haha

nice little write up, people should find this quite insightful
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Old 05-05-2011, 11:11 AM   #9
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Quote:
Originally Posted by DRedman45 View Post
i cant give you the answer in vernacular: "ITS TOO SMALL" haha

nice little write up, people should find this quite insightful
lol I'll edit the OP
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Old 05-05-2011, 11:34 AM   #10
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Nice!
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Old 05-10-2011, 10:23 AM   #11
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Yes! Your last two sentences!
Same hardware all around? If I start with a 3" DP do or should I keep it 3" all the way back or as some manufacturers do, or start with 3 and slowly taper to say 2.5 or 2.25 due to the temp loss/less volume of the exhaust gas?

Thank you for your time in this!

So I take it in a nut shell,

K03= Too Small!
K04= Just right if mapped close to surge line on the low end and is just right for most people. (ME!)
GT28RS= OK low and mid range and fun on top.
GT30 and up= Keep the RPM's above 3500 for serious fun! (If you have supporting engine and fuel mods)
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Old 05-10-2011, 10:39 AM   #12
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Quote:
Originally Posted by davesxx01 View Post
Yes! Your last two sentences!
Same hardware all around? If I start with a 3" DP do or should I keep it 3" all the way back or as some manufacturers do, or start with 3 and slowly taper to say 2.5 or 2.25 due to the temp loss/less volume of the exhaust gas?

Thank you for your time in this!

So I take it in a nut shell,

K03= Too Small!
K04= Just right if mapped close to surge line on the low end and is just right for most people. (ME!)
GT28RS= OK low and mid range and fun on top.
GT30 and up= Keep the RPM's above 3500 for serious fun! (If you have supporting engine and fuel mods)
If you do a 3" Downpipe, its really up to you if you want the catback. The diameter is only going to affect the area around the turbine exit. The catback is just more for sound control. I'll be going 3" all the way if that helps.

Your nutshell analysis is dead on!
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Old 05-10-2011, 01:02 PM   #13
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grambles,

Great idea for a post! Thanks for taking the time to put it together. I think the forum readers will enjoy a good technical thread.

The compressor map of a K04-64 (OE turbo from the S3 2.0T, in case anyone was wondering) is similar to a GT28R, but it's even closer to a GT2860RS. Here is the GT2860RS Compressor Map:



Garrett Turbo rates the 2860RS up to 360hp. Our TSI K04 Kit produces 370hp on race fuel.

Peak potential flow for the K04 is 0.24 m^3/s or about 38lb/mn which is similar to the GT2860RS.

As you can see, the 2.0T K04 is not like the old school 1.8T K04 turbos. Back then, a K04 was larger than a K03, but was still a pretty small turbo. The K04-64 is one of the largest K04 chassis turbos that BorgWarner has ever made and it can flow a lot of air, comparable to units used in some companies’ stage 3 kits.

Also, in the interest of sharing information here is a compressor map for the FSI K03. The TSI one will look similar.



Cheers!

Last edited by Alex/AWE; 05-10-2011 at 02:36 PM.
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Old 05-10-2011, 01:29 PM   #14
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Good deal Alex. Thanks!
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