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Quote:
Originally Posted by copbait73 View Post
Dave, you are correct, but more to the point. High compressor efficiency, high CAC efficiency equate to lower intake manifold temperature. All things being equal lower intake manifold temperature gives you denser charge at a fixed firing pressure therefore more knock margin. Firing pressure and knock margin for available octane makes these critical considerations. This is a point I don’t hear discussed often enough.

One engine can have a modern Garrett and another KKK with large compressor wheel. Each can deliver the same boost pressure at equal temperatures. Both engines make the same power, right? Wrong. The Garrett will do so with a turbine of higher stage efficiency that also has a correct power balance match with the compressor wheel. This turbo will require less backpressure to drive the turbine. Net, the engine makes more power.

In the world of ultimate HP, the best turbocharger match has the highest positive differential of intake pressure to exhaust backpressure - at a fixed boost level. In this situation my money would be on a Garrett.

On the street, a good turbo match is more appropriately described as the best compromise to fit the expectations and needs of the owner; performance, installation and cost. Here Garrett, KKK production or KKK hybrid show strengths and weaknesses. I listen to everyone on this site and see no two are exactly alike in their assessment - and that is very natural.
Excellent!

Last edited by 911st; 01-04-2010 at 06:37 PM..
Old 01-04-2010, 06:35 PM
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Originally Posted by RarlyL8 View Post
My muffler and waste gate dump are good for 12whp on a stock 300HP Euro 930 engine. The baseline engine I tested used the stock early Euro muffler. I also tested late USA 930s with CAT and found similar results. It is interesting to note that 0.75bar was maintained in both situations. I assumed boost may increase a little due to lack of back pressure on the waste gate but that did not occur on these stock cars. Any extra boost would of course scew the power number.
That is only a tiny part of the story. The engine revs quicker, more freely, and boost comes a few hundred rpm sooner. You also get all those great turbo sounds that the stock system hides. The driving experience is transformed.
A straight through non-restrictive and non-baffled muffler is a must-do before looking at performance enhancements. The turbo must not have back pressure.
Brian

Thanks for the inputs.

I am not sure I well explained the things. I am sure to understand your exact meaning either.... ah don't blame me ... my poor english !

Actually, I have a cat by pass on the turbo output + sport muffler. So on this exhaust output, I share completely your opinion !!! less restriction = more power and more spools at earlier RPM

My meaning concerns the behaviour on the Wastegate muffler only. Actually on C2T the small stock wastegate exhaust include the catalyst which provide an high restriction. Most of people thinks that a free flow wastegate exhaust doesn't bring any improvment... Personnaly, I start to think this wastegate exhaust restriction also reduce the total exhaust flow efficiency. Thus, I think this restriction is also increasing the back pressure.


Do you share this opinion ?
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Old 01-05-2010, 09:33 AM
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Thinking out loud.

Pressure in the heat exchangers is around 25-30 lbs on boost. Even with a muffler on the WG the WG will open as much as it can or has to, to maintain the desired boost pressure up to the point where the WG becomes a restriction. If that happens the motor will probably then experience boost crepe and raise boost above goal.

Not totally sure if this is the case.

Reducing back-pressure after the turbo is a different story as it allows gasses to pass through the turbine wheel faster and easyer to the lower pressure area created if there is no or less muffler (back pressure).

With less turbo back pressure more energy can be transferred to the turbine because of the greater differential pressures. Thus more energy can be compressor wheel and maintain boost longer. It also lowers pressure in the heat exchanger and more exhaust can exit the cylinders.

Thus more power at the same boost due to an increased in VE and more power as the turbo can maintain boost further up the rpm range.
Old 01-05-2010, 01:22 PM
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You mean pressure in the headers/manifold, not "heat exchangers", the heat exchangers are the boxes around the headers purely there for transferring heat to the cabin. I know you know this but your post will be confusing to those that don't
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Old 01-05-2010, 05:50 PM
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Yes, sorry I was being common.

Pressure in the headers.

Thx
Old 01-05-2010, 06:06 PM
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As we are speaking about it ,

Here is a picture comparison between a K27-7200 and a GT35.

So far, the hot side seems to have nearly the same overall dimensions while the cold side is definitively much larger on GT35.

Hot side here :



We must consider turbine efficiency it self.... but from the size of body, I think the handled exhaust flow speed are not such different.



Cold side here :



So far, the GT35 has a much bigger cold side than the K27-7200.

From these picture and from some reported experience, I strongly believe that the GT35 need also an increased wastegate flow in order in order to reach the same boost level.
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Old 01-10-2010, 05:22 AM
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The GT35 is a larger turbo than the 7200 11/11 pictured. The GT30 is smaller than a 7200 ...
A 46mm wastegate will handle either turbo on most applications. Attention should be paid to the waste gate plumbing as the signal origin needs to exit the headers without compromising flow. The standard elephant nose headers exit below the turbo at a very sever angle which may choke the signal as flow increases leading to overboost in high output engines.
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Old 01-10-2010, 07:51 AM
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Quote:
Originally Posted by RarlyL8 View Post
The GT35 is a larger turbo than the 7200 11/11 pictured. The GT30 is smaller than a 7200 ...
A 46mm wastegate will handle either turbo on most applications. Attention should be paid to the waste gate plumbing as the signal origin needs to exit the headers without compromising flow. The standard elephant nose headers exit below the turbo at a very sever angle which may choke the signal as flow increases leading to overboost in high output engines.
No doubt about the fact the TIAL 46mm can handle this flow. Especially if the wastegate output is linked to a free flow muffler. ( no cata inside wastegate exhaust ).

Did you get same kind of reported problem with peoples who bought K27HFS ?
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Old 01-10-2010, 08:33 AM
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The issue is not waste gate related but rather plumbing related. It is also not a problem with medium output engines. High output engines require more precise waste gate control as they are running on the edge of detonation AND pumping more air at higher boost. If the waste gate feed flow is compromised the wastegate may overboost as it is not seeing the pressure/flow that it should.
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Old 01-10-2010, 12:06 PM
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Anyone have the inducer and exducer wheel measurements for the GT 35 and K27-7200 they can post?

Thank you in advance if you can help.


I do like the transition out of the GT if it is up to a 3" tube size for a clean exit.

The id of the 7200 is an odd size from what I recall and most muffler builds just through a 3" tube on it creating a step that might create turbulence right were we probably do not want it.

Probably not a big deal but a lot of little details can add up.
Old 01-10-2010, 12:33 PM
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Quote:
Originally Posted by 911st View Post

I do like the transition out of the GT if it is up to a 3" tube size for a clean exit.

The id of the 7200 is an odd size from what I recall and most muffler builds just through a 3" tube on it creating a step that might create turbulence right were we probably do not want it.

Probably not a big deal but a lot of little details can add up.
Yes that's true there is a step between the turbo output and the tube....

Not sure it could change a huge part of the equation. But for marketing purpose it should have been done ....
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Old 01-10-2010, 12:59 PM
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Quote:
Originally Posted by JFairman View Post
"

If you don't mind a long distance call the best turbo rebuilder in the USA is Durabilt
You don't have to believe me though so call or email the top USA race teams and ask them who they use... Over here it's Durabilt, http://www.durabilt-turbo.com/
.
I did have discussion with DURABILT. At begining Mr Bob was very kind and answer to my email and question.

From his side he suggested to take a brand new K27-7200 core and to put a K29 wheel on the cold side. ( They don't change the cold side casting... they just machine it to fit the wheel).

Pretty interesting solution.........................I was ok to buy it but he said there is no available brand new core. And now this guy doesn't reply to my email !!!!
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Last edited by Thierry25; 02-16-2010 at 05:54 AM..
Old 02-16-2010, 05:50 AM
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I am starting to wonder if BW/Porsche was extreamly effective in how they disigned the K27-7200.

This is just a gut feel on my part. I am thinking the compressor wheels and turbine are nearly perfictly sized for a CIS 930 of modest tune.

And that both the turbine and compressor sides were just big enought and both stall at the same time.

The 7006 has bassicaly the same size compressor wheel but with its larger hot side makes more HP.

With the HF's and K29 quick spools -- a larger compressor wheel is added. This allows more air flow to be passed before the hot side starts to stall again.

Part of the reason a good wast gate circut is needed with these turbos or boost creep 'may' become an issue.

Years ago I bumped in to a pretty good turbo guy that was working on development a more efficient turbine wheel for the 7200. He believed there was opportunity to make more HP with the 7200 and keep the early spool with a more modern wheel. Thus, he seemed to think the compressor wheel was pretty good and the issue was more on the hot side.

Just a thought.

I know this is not the answer as the compressor map for the 7200 is limited.

Last edited by 911st; 02-16-2010 at 07:09 AM..
Old 02-16-2010, 06:55 AM
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Quote:
Originally Posted by 911st View Post
I am starting to wonder if BW/Porsche was extreamly effective in how they disigned the K27-7200.

This is just a gut feel on my part. I am thinking the compressor wheels and turbine are nearly perfictly sized for a CIS 930 of modest tune.

And that both the turbine and compressor sides were just big enought and both stall at the same time.

The 7006 has bassicaly the same size compressor wheel but with its larger hot side makes more HP.

With the HF's and K29 quick spools -- a larger compressor wheel is added. This allows more air flow to be passed before the hot side starts to stall again.

Part of the reason a good wast gate circut is needed with these turbos or boost creep 'may' become an issue.

Years ago I bumped in to a pretty good turbo guy that was working on development a more efficient turbine wheel for the 7200. He believed there was opportunity to make more HP with the 7200 and keep the early spool with a more modern wheel. Thus, he seemed to think the compressor wheel was pretty good and the issue was more on the hot side.

Just a thought.

I know this is not the answer as the compressor map for the 7200 is limited.
Oh very glad, I just got an answer from BOB. The compact K29 is now available

Actually the discussion with Bob was very interesting. According to this expert, the main limitation ( the wall) is the section (11 sqcm) of the hot side input. In fact, beyound a certain exhaust flow volume, the turbine wheel can not accept the flow speed and can be damaged ( turbine chock).

So whatever you use on the cold side, the hot side is limited be the exhaust flow speed...... thus it can not be over a given flow rate. From what I understood , this is is the ultimate limit of the turbo. From this fact, it seems impossible to expect more than 440-460 CV from a stock (11sqcm) K27-7200 hot side body . It seems possible to get some benefit by using a K27-7006 hot side.... but as the hot side input section is very similar to the K27-7200, the rule of the flow speed is the same. So yes it can be a good choice to use the K27-7006 hot side but it won't be a night & day difference.

Now, having said that, The K27-7200 in it standard version doesn't reach this exhaust flow limit first. In fact, there is some room to play on the cold side. So it is possible to increase (a little bit) the compressor side capability in order to get a bit more intake flow without to bring the turbine side in danger.


Is there anyone here who have a correct K27-7006 core for rebuild to sell ????
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Old 02-16-2010, 08:24 AM
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Thierry,

That confirms my thoughts.

With this then, a larger compressor wheel will slow down the hot side and allow more air to be pushed through the cold side.

With this approach the WG circuit must be part of the equation we can count on.

I had a 7006 K29 and a 7006 based HF. They both hit full boost at about 3600rpm. The HF was an early version but in my case, even with the larger hot side I could not keep from getting exhaust creep with my B&B WG design. It took a Tial .7 bar WG w a EBC set at 1 bar to keep it from going over 1 bar. On just the .7 bar spring I would hit 1.1 bar.

One contributor on this board that seemed very knowledgeable noted that the K27/T3 based turbos are mostly going to be a restriction for big HP on a 930 and that a T4 was the way to go.

The K27/T3 is about 5.5 sq inc and the T4 is about 5.5 sq in if I measured right.

However, the GT 35 seems evidence that a small turbine w a larger compressor wheel can work very well. Either its small hot side can pass more or our wast-gate circuit just needs to be there to take up the slack.

Last edited by 911st; 02-16-2010 at 12:21 PM..
Old 02-16-2010, 12:09 PM
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Thierry,

That confirms my thoughts.

With this then, a larger compressor wheel will slow down the hot side and allow more air to be pushed through the cold side.

With this approach the WG circuit must be part of the equation we can count on.

I had a 7006 K29 and a 7006 based HF. They both hit full boost at about 3600rpm. The HF was an early version but in my case, even with the larger hot side I could not keep from getting exhaust creep with my B&B WG design. It took a Tial .7 bar WG w a EBC set at 1 bar to keep it from going over 1 bar. On just the .7 bar spring I would hit 1.1 bar.


However, the GT 35 seems evidence that a small turbine w a larger compressor wheel can work very well. Either its small hot side can pass more or our wast-gate circuit just needs to be there to take up the slack.
Keith

Yes, you are correct about WG circuit. If the compressor side is bigger, this circuit must be adjusted accordingly.

As, my intake ports and plenum have stock diameter and as I play with boost pressure with my EBC , I believe that a 7006 hot side with the suggested K29 compressor wheel+ machined stock casting could be a nice combo for my application & target.

In fact I am not looking for a turbo which could spool earlier than my stock K27-7200. I am looking for a turbo which could start to spool at the same RPM than the stock, which could come stronger and suddenly ( I like this "old" generation behaviour) and which have a better effiency until 6000 rpm ( not like the 7200 which start to lose wind above 5500 beyond 0.9 bar of boost) .


Now havind said that, if I want to do that I must find a nice 7006 core for rebuilt....... so once again if someone has a correct one... feel free to send me a PM
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Old 02-19-2010, 03:19 PM
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T,

So is our conclusion that part of the advantage of the 7006 with its bit larger hot side is it dose not choke off as early as the 7200.

As both have basically the same size compressor's, the 7006 can spin at a little faster and deliver a bit more CFM?

This is on top of possibly creating less back pressure in the exhaust.
Old 02-20-2010, 07:53 AM
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The stock 7006 compressor wheel is 2mm smaller vs the 7200.

If you were to CC the 7200 and 7006 turbine housings you will find that they are very close. The 7006 is only slightly larger. However, it is the massive turbine wheel (7006) that "lowers" the exhaust pressure. This turbine wheel will typically shift the RPM curve 600 to 750 RPM's up the curve.

A 7006 will run out of "boost" similar to a 7200 within 150 to 200 RPM's of each other. This is due to the "smaller" compressor wheel. Years ago I took the 7006, but mated the 7200's compressor wheel. The results were "okay" Boost came on within 100 RPM's and was sustained longer.

Please note that whenever one installs a larger compressor wheel on any shaft, the net result is a lower shaft speeds. The compressor stage in more efficient, the turbocharger will meet the target boost setpoint at a lower speed, one direct benifit is being able to sustain boost longer in the engine RPM. If one increases the turbine wheel size we will shift the "output" up the RPM range. Porsche has done this over and over with it's various engines. You can look at the two 951 turbochargers, Both had turbine wheel changes and turbine wheel changes, again they did that with the 993TT/996TT similar K16 and K24's. A larger turbine wheel and A/R change occured. With the 951, 993/996TT the compressor wheels were changed. However, with the 930, the turbine wheels increased, but the A/R's stayed the same.

12 years ago I asked a KKK engineer why the compressor to turbine wheel ratio was so small on the 7006, his reply was that Porsche wanted to limit the boost/torque output. The smaller compressor wheel will run out of air at a certain RPM> call it a governor.

For most people that drive the 930 on the streets, they want a faster spooling turbo. Most stock engine with cams do very well with the 7200 based turbocharger. For that matter there are alot of 3.6 ltr 965's running 7200 based hybrids..
Old 02-22-2010, 06:35 PM
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Quote:
Originally Posted by Zeroclearance View Post
........................edit for space...............

12 years ago I asked a KKK engineer why the compressor to turbine wheel ratio was so small on the 7006, his reply was that Porsche wanted to limit the boost/torque output. The smaller compressor wheel will run out of air at a certain RPM> call it a governor.

........................................
"Governor" that pretty much hits the nail on the head in describing the 7006 compressor.
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Old 02-23-2010, 05:42 AM
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ZeroClearance,

Welcome! Excellent info!!!

Points of interest.

7200, and to a bit lesser degree the 7006 choke's or governs the turbos speed.

A larger compressor wheel slows the turbos acceleration (boost becomes more progressive).

A larger compressor wheel on a 7200/7006 will operate more efficiently (less heat more HP).

Can I add:

A larger compressor wheel can push more air at the same turbo shaft speed.

It takes higher exhaust pressure to equal or extend the shaft rpm over the 7200/7006.

Question:

Is the T3/K27 flange also a limitation? Or can a larger turbine with the right turbo extend your HP levels substantially?

At one bar boost what might we expect the pressure in the headers to be with a stock K27-7200 v a turbo with a larger compressor?

What is this effect?
Old 02-23-2010, 07:19 AM
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