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-   -   Technical Understanding of the IHI (Why does my Power FALL off?) (http://www.golfmk6.com/forums/showthread.php?t=18432)

grambles423 05-04-2011 09:41 AM

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:
http://s4wiki.com/images/7/75/K03-1870_EXA.png

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
http://www.golfmk6.com/forums/attach...9&d=1298508547

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)
http://i55.tinypic.com/2mccdg6.jpg

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.

davesxx01 05-04-2011 10:46 AM

Yes! Sticky! How about a K04 map?

BeauG 05-04-2011 10:59 AM

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.

grambles423 05-04-2011 11:11 AM

Quote:

Originally Posted by davesxx01 (Post 260194)
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
http://www.turbobygarrett.com/turbob...60-7comp_e.jpg

Quote:

Originally Posted by BeauG (Post 260205)
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.

http://www.turbobygarrett.com/turbob...3_enlarges.gif

grambles423 05-05-2011 08:26 AM

Updated

Heretic 05-05-2011 08:58 AM

good info...

untangle 05-05-2011 10:54 AM

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.


http://dl.dropbox.com/u/38233/-%20We...%20science.jpg

DRedman45 05-05-2011 11:08 AM

i cant give you the answer in vernacular: "ITS TOO SMALL" haha

nice little write up, people should find this quite insightful

grambles423 05-05-2011 11:11 AM

Quote:

Originally Posted by DRedman45 (Post 261073)
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

Arin@APR 05-05-2011 11:34 AM

Nice!

Bender 05-10-2011 08:28 AM

Quote:

Originally Posted by grambles423 (Post 264910)
Anyone else? Maybe It came off too classroom oriented lol

I will bite. So where does upstream and downstream airflow fit into all of this?

grambles423 05-10-2011 09:03 AM

Quote:

Originally Posted by Bender (Post 264914)
I will bite. So where does upstream and downstream airflow fit into all of this?

Upstream is really controlled by what is flowing through the compressor. Depending on your boosted volume, there really will not be much difference in flow entering the engine then the turbine which controls the speed of the turbo.

Now thats considering perfect round pipe. Pankcake pipes can hinder flow in upgraded situations. You can actually surge the turbo quicker if you pump too much boost in because the flow will not be quick enough to move the air mass through. That will eventually backpedal the turbo and blow it to hell. However, in our case (now that I've freaked everyone out), the pipe is plastic and has some bend to it. In a perfect world, we can upgrade it, but with the power levels it can take, it would actually deform a little to help the flow. But this is on a MICRO level. Its all a wash in the end. My professional opinion? I would leave it alone.

Downstream flow is a bit different because this graph really only shows flow through the compressor side of the turbo. However, turbine speed is dependent upon airflow through the engine which is dependent on airflow through the compressor. So there IS a relationship.

Whats downstream of a turbo? A downpipe. In as BASIC as I can put it, the smaller diameter you go, the harder it is for the flow to escape the turbine. The bigger you go, the more free volume you have to allow the turbine to spin. The question is.....how much difference is there really in 2.5" and 3"? In all professional honesty, nothing. Maybe 1-2 HP and maybe some area under the curve at higher speeds. The geometry between the molded exit of the and the wheel is almost engineered enough to allow for this free flow. The biggest issue is the blockage from the factory cat. And THAT is what tuners aim for when they design their downpipe.

All tuning companies (Mainly AWE and APR) tune for different things. Its also a HUGE cost deal. 2.5" is cheaper so most of the times people can get away with more expensive things such as an HJS cell and stainless steel, etc, etc. And sometimes is easier to manufacture. BUT 3" is more widely used. But there is NO right or wrong part. Just make sure to run the same hardware all around.

Questions?

davesxx01 05-10-2011 10:23 AM

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)

grambles423 05-10-2011 10:39 AM

Quote:

Originally Posted by davesxx01 (Post 264976)
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! :thumbsup:


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