Greddy Turbo owners thread
01-07-2011, 06:15 PM
#201
not that I really understand what MM and brettus are arguing about, but I thought this calculator may shed some light on the issue since it has waste gate calculations pity it doesn't have a rotary flow cycle or garret turbo's.
01-07-2011, 10:05 PM
#204
If you could explain to me what the WG arm is doing differently in each scenario I think I would be just about ready to conceede the argument .
This is the thing I struggle with in trying to accept what you are saying .
How can you get say , 10psi , with two different ways of holding the WG arm and the arm be in a different position for each scenario ?
01-08-2011, 07:27 PM
#206
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http://autospeed.com/A_111348/cms/article.html
This guy builds a fully adjustable boost controller and goes into why each aspect of the controller is important. There is a second part aswell...
Anyway, it may give you a better understanding-- that, or I've completely missed the point of the whole debate.
Chris
This guy builds a fully adjustable boost controller and goes into why each aspect of the controller is important. There is a second part aswell...
Anyway, it may give you a better understanding-- that, or I've completely missed the point of the whole debate.
Chris
01-09-2011, 01:01 PM
#210
IMG_20110108_140430.jpg?t=1294599489
IMG_20110108_140537.jpg?t=1294599526
01-09-2011, 02:38 PM
#215
so your saying that your wastegate can never fully open due to a restricted range of motion, just so you can spool up a little faster?
01-09-2011, 04:11 PM
#216
No . The reason for doing it , is that backpressure forces the wastegate open at higher rpm .This limits the boost/whp you can achieve at the business end of the rpm band .
01-09-2011, 05:54 PM
#217
yes , but also saying that for a given boost setting this is effectively what happens when you have a larger actuator anway .
No . The reason for doing it , is that backpressure forces the wastegate open at higher rpm .This limits the boost/whp you can achieve at the business end of the rpm band .
No . The reason for doing it , is that backpressure forces the wastegate open at higher rpm .This limits the boost/whp you can achieve at the business end of the rpm band .
have a play with that calculator I linked and see how much air needs to be bypassed at high rpm. the waste gate needs to be open.
I'm guessing the greddy turbine is a small a/r and the wastegate is choked already however by restricting it further you make it worse.
i think MM eluded to this in a previous post
Wrong!
What you did was make the actual wastegate port smaller so that it acted as a constant restriction.
By actually opening and closing the gate via normal boost control, a significant amount of heat and pressure is not forced to accumulate or overspin the turbo to get the desired result.
Pulsing the WG open and closed is not the same thing as simply making the port smaller.
What you did was make the actual wastegate port smaller so that it acted as a constant restriction.
By actually opening and closing the gate via normal boost control, a significant amount of heat and pressure is not forced to accumulate or overspin the turbo to get the desired result.
Pulsing the WG open and closed is not the same thing as simply making the port smaller.
my guess is by restricting the wastegate you are effectively running without one. it is the undersized compressor and the flow through the turbine that's controlling your boost pressure. you might as well weld it shut and run without the wastegate.
01-09-2011, 06:51 PM
#218
I don't have a good understanding of the actual theory however I'm now in agreement with MM.
have a play with that calculator I linked and see how much air needs to be bypassed at high rpm. the waste gate needs to be open.
I'm guessing the greddy turbine is a small a/r and the wastegate is choked already however by restricting it further you make it worse.
i think MM eluded to this in a previous post
have a look at wikki
my guess is by restricting the wastegate you are effectively running without one. it is the undersized compressor and the flow through the turbine that's controlling your boost pressure. you might as well weld it shut and run without the wastegate.
have a play with that calculator I linked and see how much air needs to be bypassed at high rpm. the waste gate needs to be open.
I'm guessing the greddy turbine is a small a/r and the wastegate is choked already however by restricting it further you make it worse.
i think MM eluded to this in a previous post
have a look at wikki
my guess is by restricting the wastegate you are effectively running without one. it is the undersized compressor and the flow through the turbine that's controlling your boost pressure. you might as well weld it shut and run without the wastegate.
Do you understand that most of the exhaust gases run through the turbine at ALL times ? A wastegate is really just a regulated exhaust leak - that is all it is.
Let me try explain what is happening in various scenarios with a Greddy on our engines :
Cruise : all exhaust gas passes through the turbine - none goes through the wastegate
Wastegate is completly closed in either case.
Boost generated - 0-1psi .This boost is before the throttle plate , after the plate is still in vacuum.
WOT low rpm : most of gases pass through turbine but if it all was allowed to pass through boost would build to very high level ( perhaps 20psi plus ) .
So the wastegate cracks open a little ,allowing a proportion of the gas to bleed off, and prevent this .The WG only needs to crack open a tiny amount to get to the desired level as flow is still very low .
WOT mid range : Still most of gas goes through turbine and some has to be bled off to prevent excessive boost . There is more flow now so the WG needs to crack open just a little more .
WOT high rpm : Still most of the gas goes through the turbine . Cracking the wastgate open a little more again will regulate your boost to the desired level.
This is the point where , if your actuator is small , the backpressure in the Ex manifold will blow you wastegate open and you wont be able to make high boost.
As you can see the wastegate is opening more and more as the rpms climb to achieve the desired boost at the manifold.
Now the crux of all this is that to make more boost in any load situation you have to close off the wastegate more and more in order to get more flow through the turbine. There is no majic to this - a certain wastegate position will leak a certain amout of gas allowing a certain flow through the turbine which in turn will allow the compressor to make a certain amount of boost .
My argument is that : how you hold that wastegate closed does not matter one bit . If you run high boost you are taking a risk but that risk is unrelated to how you did it .
All of this is pretty much irrelevant to stock Greddy owners because the turbo runs off its efficiency island even with a small actuator . Where the fun begins is when people upgrade the compressor and try closing off the wastegate via the undersized actuator . At high rpm it just wont do it .............................. hence the whole reason for this argument/discussion .
That's fine with me . The only people that will agree with me on this are those (with an upgraded compressor) that go through all the same BS I did trying different things before they actually try this suggestion .
Last edited by Brettus; 01-09-2011 at 08:53 PM.
01-09-2011, 07:29 PM
#219
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How are you getting on with your turbo Flash ?
01-09-2011, 07:37 PM
#220
Things are good! I've ran into this issue with regards to a serious loss of boost pressure from the wastegate. I'm planning on pursuing a fix with a combination of a larger actuator and a boost controller. Low to mid-range boost levels have been from 8 to 10 psi and falling to as little as 3 psi at peak RPM.
3 PSI ! Tat is low - most people seem to manage 5-6 even with the stock actuator ?
As a rough guide : if you are making somewhere between 160whp @ 4500 and 8psi , and 190whp @4500rpm and 10psi ............ all is well . If it is significantly less than this you may have another issue (other than boost control).
Sounds like it is running well otherwise - welcome to the club
Last edited by Brettus; 01-09-2011 at 09:21 PM.
