lol thanks I couldn't remember where the hell I read that! If anyone else was interested it starts on the end of page 7.

 

Wearing out the turbo is the least of your problems in this scenario.

 

Luckily for my DD application it may be something I never know. Rarely am I in high rpm, high boost, wot conditions for more than a few minutes, and by the time I feel my car will be track worthy I am hoping that somebody will have a readily available larger ball bearing turbo upgrade for the GReddy kit, much like MM's GT3071R upgrade of old.






I have to admit that my train of thought on this subject is very much like Brettus' and trying to grasp MM's explaination is taking longer to skink in for me.

Am I correct in this statement: "the GReddy turbine is getting closer to a state of choked flow with the WG arm shortened causing EGT's, and CHRA temps to be driven upwards allowing for pre-mature wear to the journal bearing and center iron exhaust port area?"

 

EXACTLY !

For the track I would have to agree with MM that this is not ideal and could result in premature failure of either turbo or engine or both.

For the street , where the punishing conditions of the track are practically impossible to recreate . I say this is a perfectly acceptable way to get more power from your setup.

Couple of things I would like to point out from my perspective :

1/As far as i know my turbo holds the record for the longest lasting Greddy turbo on this board at 38000 miles , almost all of those with this mod in place.

2/I have had absolutely NIL issues from doing this apart from possessing ,for the last two years, the most powerful (Greddy based) turboed engine on these boards by a big margin. And what a pain that has been ..... NOT !

 

When compressor is driven into choked flow, any additional rotational speed is just lowering efficiency, increasing IATs (which gives false observation of "boost") but mainly demands even more HP from turbine - turbine has to work at higher expansion ratio - simply said with higher backpressure. So holding wastegate "shut" in this condition not only increases exhaust pressure on its own, but also non ideal compressor conditions are feeded back to turbine, creating even bigger restriction.

This lowers VE% of whole system and again its another reason why boost holds.

Having WG functioning properly, you can maintain compressor operation within some norm and through this also turbine operation. Just put some numbers into turbo calculator and you will see how much exhaust gas is redirected through WG. Certainly it hasn´t just leak magnitude

 

Except I wasn't talking about the compressor being choked.... I still saw an increase of 40+ grams per second through the compressor with a mere 3psi increase.

What I was refering too was the wastegate being choked.

Just an FYI I'm not trying to argue the facts that this is harder on your turbo/engine and that negative consequences have been experienced and documented but I am just trying to get my head around the thermo/fluid dynamics of this.

 

Nah, you didn't. Not at exactly the same Ve/RPM, anyway.
Even with absolutely NO adiabatic heating, 3 PSI is about 44 g/sec.

 

Well stated. Thanks.

 

Good stuff guys.

 

You guys talk as though this mod shuts the wastegate completely . Sure it stretches the legs of the turbo and if you take it too far you will reach the point of diminishing returns as 999 pointed out .

BUT - most people that run the upgraded Greddy don't ever get close to that point and they leave so much power on the table it's a joke . Especially the ones who upgrade and can't make much more power than a stock Greddy .

As an aside ...... I seem to remember MM actually strongly advocating over-spinning his 3071 turbo to make 400whp and cooling the charge air down via water/meth .

 

I think I covered this pretty well.

Its not boost control strategy. In the top end, compressor is driven into choke with this approach, it gives you false observation of boost and some marginal increase in flow, but you can do it much more effectively with lower turbine inlet pressure, EGTs, IATs and slightly better VE, maybe slightly better BSFC when wastegate works correctly, and turbo isn´t overspeeding.

Just look at boost control strategy of modern piston engines with smallish turbochargers. They wind it up in midrange and intentionally let "boost" fall of in top end. Compressor operation remains in norm and so does turbine operation. You can achive same flow with lower turbine expansion ratio...

 

Dude. You are hired!
Where have you been the last 3 years when I needed you?

 

I have so much to learn.

 

oh wow... someone Jeff likes

 

Not necessarily - there is a point that this will happen if you go too far . Below that there there is plenty of power to be gained without overspinning the turbo. Basically the stock Greddy WG actuator is marginally too weak for a stock Greddy compressor and WAY too weak for any of the upgrades. For upgraded turbos this mod is just doing what you would do with a larger actuator anyway.

Point taken , but like i keep saying , this varies by degrees . I can state with a high degree of confidence that I have found this choke point you speak of and for the last two yrs have run my turbo just below this point to eek out the most power I safely/efficiently can .

 

Nah, I´m just internet nobody who likes to argue on interwebz forums

Seriously, I just enjoy gaining technical knowledge and actual understanding how things work
Turbocharging is one of very interesting topics, usually vastly misunderstood by masses
Not many people understand that everything from air filter to muffler tip is system and each part influences other.

In the end of the day, its just another internet forum based on opinions. Facts of few knowledgeable guys will disappear under layers of opinions. And people doesn´t like to think for themselves

 

Been awhile but I finally got around to taking a picture of my recirculated BOV setup. I ended up going with the 1" synchronic recirc fitting and, after some crafty googling, found a nice matching blue pipe.

Had KDR weld the bung on the intake. Have been very happy with the results.

 

I am all for learning, I have to agree finding the correct answers is tough.

 

Again I am not trying to argue, but my boost profile still falls off at high RPMs and I have a hard time believing that my compressor is experienceing Choked flow at 300g/s.

What I am having a hard time understanding.... And I think Brettus is on the same mindset; is how can a small actuator opening the wastegate 45deg cause choked flow when a larger actuator opening the WG 45deg will not.

 

Nothing MM or 999 has said has convinced me this is a bad idea so long as you don't go too far with the adjustment . They have made it obvious to me ,however, that it is irresponsible to suggest people do this without knowing how to make the adjustment such that the speed /flow from the turbo falls below the choke line.

This is where the discussion should be going IMO .

So this is how i did it :
Place one boost gauge at the turbo exit and another in the uim ( a BC is a handy 2nd boost gauge). Monitor both gauges as you wind the arm in one turn at a time .
You should find that the two boost levels will be within 2-3PSI of eachother at high rpm.

If the arm is wound in too far you reach a point where (at rpm past 6500) the turbo boost will rise suddenly and become way greater than the manifold boost .
EG 9psi at UIM vs 14psi at turbo in my case .
This is the point where you know you have gone too far so back off the arm till it stabilises.

There is probably a better way than this - if someone can make a suggestion I'm all ears .

 

Found this on the Garrett website which I think is relevant to what we are discussing here . What they are basically saying here is that for a good streetable turbo you want to operate it closer to the choke line at peak power as this allows it to operate in the middle of the map at lower rpm - which is where you are going to be most of the time .

For the track this wouldn't be ideal as you would want the turbo to be operating in the middle of the map at peak power for best efficiency .

 

Well, its not that tough. Only problem is that most people can´t or doesn´t want to accept it and comprehend it as fact.

 

How can you know? Without compressor map and exact parameters of given situation? You have to understand that for given flow at certain PR and efficiency you need certain amount of power from turbine. Any more turbine power (read holding WG closed) will be overspeeding compressor and making less efficient setup.

Because they will be opened differently?
As above, you need only so much power for given flow at given PR and Eff%. Excess is wategated. Well, in proper setup

 

differently huh ?

Please explain .

 

Latest dyno along with a Log taken at the same time :







Few of points of interest :

IATs : Ambient was 18deg C and steady state cruise IAT temp was 25 C . After the run the IATs continued to climb for a few seconds from 28C up to 32C .

MAF : Noticed on pre dyno logs that MAF was a little higher than at the dyno (350g/s vs 340 g/s) Had similar thing happen with the mid mount turbo dynoed just before mine.

AFR : Dyno runs look to be about a point higher than the OEM sensor - same was found with midmount car. Dyno sensor was mounted in tailpipe.

EGT : Top temp of 960ish Degrees C a little lower than in the past probably due to richer AFRs.