JKav,

thank you very much for your contribution.



I have a large fmic and 2,5" pipes from compressor to tb.



My 3071r .63 comp housing is a T04S, 4" inlet, 4" pipe to the air filter:
single A'pex Power Intake dry filter... could it be restrictive ?


1. I'll check for leaks
2. as I told, is a T04S, with anti-surge porting



Sorry, I can't understand this passage... or the relation with a waste gate issue...


Thank you...

 

There is one issue that has not yet been mentioned here, but is a factor in this discussion. The tuner who previously addressed Italian EVO's car has him running ~29psi of boost on pump fuel (93-94 octane equivalent). Italian EVO has noted extremely high exhaust gas temps and rich AFR, which appear to be the result of retarded ignition timing in an (ill-fated) attempt to accomodate the excessively high boost pressures. Obviously retarding the timing significantly creates a condition whereby combustion persists into the exhaust cycle, and the rich AFR is only exacerbating the condition.

According to gas law, significantly elevating temperature likewise increases the pressure of the system, which seems to explain (at least partly) the high exhaust pressure. This is why I suggested in an earlier post to re-run the pressure test after his car is retuned for the lower (23 psi) boost level that I recommended. I believe he has a retuning session scheduled, so it will be interested to denote the difference. My estimation is this will go a long way toward reducing (if not eliminating) both his high EGT problem as well as the excessive exhaust pressures.

 

Exactly Ted,

you already told me about this possibility...

As soon as I'll get my car remapped, I'll make a new engine delta P test.

Bye !

 

ItalianEvo, 2.5" sounds good but it still wouldn't hurt to check because some ICs, while large, can still have high pressure drop. It's not a likely culprit, but possible. Not sure about the filter but 4" inlet is plenty.

Who made the T04S housing for your GT3071R? Or rather where did you buy the turbo.

Also are you running an aftermarket exh manifold? Check for exh leaks at the head, at the turbine inlet, and where the w/g attaches. Any leaks upstream of the turbine will make backpressure go up.

What does your exhaust look like?

 

Would ideal gas law apply to an open system such as this though?

 

It seems logical that so long as the system is capable of retaining any degree of elevated pressure between head and turbine, increasing EGT can only drive pressure upward.

 

www.pagparts.com ( USA )

Turbine is a T31 .63, turbine exhaust is 2.5" OD.



HKS tubular 4 in 1


Ok...
it seems to me that I have not any leak... I'll check again...

btw I'm really not able to understand how a leak upstream of the turbine could increase the backpressure... i'm feeling an idiot...



FUll 3" no cat.
Wastegate is HKS, wg exhaust is 1.75" and it goes back into the DP 27" far from the turbine.

Thank you.

 

Neither do I. I've experienced a leak upstream of the turbine, and exhaust pressure between the head and turbine housing was reduced, not increased.

 

A small leak upstream of the turbine acts just like a wastegate. It bleeds off mass flow, and to maintain turbine power the turbine expansion ratio (or pressure ratio) increases. Provided it is a reasonably small leak, turbine power (and boost) will be maintained, but at a higher exh manifold pressure.

This is also why higher-flowing turbines (or a larger a/r) typically make more power at a given boost than an otherwise equivalent lower-flowing turbine. The higher-flowing turbine wastegates less flow, and is thus able to run at a lower expansion ratio, reducing exh man pressure (and improving VE and generating more power assuming the valve events are appropriate to take advantage of the improved engine delta p).

Larger leaks will bleed too much flow and render the turbine essentially useless, and the exh man pressure will fall off. And boost will too.

Accordingly, if you plot exh man pressure and boost pressure vs rpm you can see precisely where the wastegate opens (right at the inflection point in the slope of the exh man pressure curve!)... if you have enough data points of course

 

ItalianEvo, one thing to be aware of is that someone other than Garrett themselves machined the turbine and compressor housing for your turbo. The only true Garrett turbine housings for the 60mm GT30R are the Ni-Resist 711679 family. The T31 housing was recontoured by someone at some point and adapted to fit your GT3071R. That's not to say that they didn't do a good job, but there is no guarantee that appropriate wheel clearances were maintained. As a very general rule, there is less risk associated with genuine Garrett parts than non-genuine parts.

Also, the GT3071R is available with a T04B or T04E housing from Garrett. The T04S housing you have is, again, something created downstream of Garrett themselves and is subject to the same caveat as your turbine housing. Depending on who did it and how well they did their homework... kind of a crapshoot.

 

That makes sense, however if any WG activity is required to maintain the desired level of boost and a small leak goes unnoticed, the user would simply alter WG solenoid duty to compensate, and the end result should be roughly the same.


FWIW, I once lost one side of a gasket between turbine housing and exhaust manifold, and that leak was large enough to seriously compromise turbo performance. The leak was plainly audible as well.

 

higher temperature always results in more pressure (all other things equal) for subsonic flow systems.

 

i don't agree with (or see) the reason for larger turbines making more power at a given boost. the wasting of flow work is there to maintain the said amount of compressor power for said amount of boost.

the larger turbine operates at a lower expansion ratio because it's larger. also you don't get anything for nothing. while it operates on less ratio it still operates on the same or more fluid mass, fluid momentum.

the improved engine delta is the reason for making more power as the increased ve of the entire system makes power.

somehow i feel i might be saying the same thing as you, since it wastes less flow then it's because it's larger and maybe uses more fluid momentum to get the same compressor power but that's really unrigorous and bothers me.

basically i don't see what wasting less flow does for anything.

 

It's going to take XXX amount of energy to drive the compressor wheel. If you try to drive the wheel using half as much gas, that gas will have to carry twice as much energy when it hits the turbine wheel. Since all the gas in the manifold will carry the same energy, though the gas going through the turbine will have twice as much energy, so too will the gas you are wasting out the wastegate. That means the engine has to work twice as hard to get the same wheel speed.

Another problem is choke flow. At some point the turbine cannot flow any additional volume of air, so the air must be compressed further to fit through the same volume. When that happens, backpressure and EGT skyrocket as the exhaust gas must be compressed more and more to breathe through the turbine nozzle and that compression causes heat. And, since the turbine is taking more and more energy to run as the massflow through the compressor rises, the exhaust cannot be bled off through the wastegate without losing power to the compressor wheel.

Unfortunately, sizing a hotside so that ALL of the exhaust gas passes through it generally means extremely slow spool up on a gasoline engine. You end up with a compromise: quick spool-up with low efficiency, or slow spool up with high efficiency?

The quintessential dillema of turbine sizing, only partly solved by VNT/VGT at the cost of your wallet.

-Adrian

 

for the first point... i don't understand why wasting comes into the picture because once you're wasting you've reached desired boost level in which case it no longer matters.... or so i was believing.

does it matter once you hit target boost?