Fourdoor

iTrader: (11)

All of the stock based turbos (stock, TME, WR, and 20G) surge under these conditions. Go out and try it with a stage 4 car that is still on the stock turbo and you will see what I mean. Not sure if a "stock" car would do it, but I know a stage 4 car on the stock turbo does.

Keith

jbfoco

iTrader: (13)

David, do you have any dyno sheets or numbers at higher 24-27 psi mabey with meth.... spool up number?

I am a dyno sheet away from ordering

thank you!!!

MalibuJack

iTrader: (5)

No doubt.. the choice of DV/BOV has a big effect on how part throttle surging is handled.. something that holds tightly for maximum boost would very easily cause surging.. the 1G DSM seems to give me the least surging in these circumstances, but the other ones seem to hold better at very high boost levels.

David Buschur

iTrader: (53)

My car is sitting here, since the shootout, waiting on a new transfer case. The one in it is extremely noisey, so I have not moved it since August 14th. When I get it up and driving again I will put it on the dyno and dial in more boost with the 20G.

On the topic of the BOV, could very well be the BOV as my Tial has the heaviest spring in it I could get.

David Buschur
www.buschurracing.com

Creamo3

iTrader: (48)

Dave,
I am anxiously awaiting the arrival of my turbo, quick question. Will I have to make any adjustments to the wastegate actuator or will it be dialed in to hold the higher boost levels?

Supernaut

Hey dave I remeber you stating in a thread recently that you picked up 90 WHP simply by changing the old Mitsu internally gated housing to a T3 housing, you think that this is the hurdle that any bolton turbo faces and why the ER hasn't been as impressive as once believed?

ruzs

iTrader: (5)

David,

thank you very much for the explanation. I appreciate your feedback and am now perfectly clear as to the performance of your turbo. As soon as my finances look better, I will buy one from you. Thanks,

Sigfrid

machron1

iTrader: (1)

Any time you increase the compressor wheel size without increasing the turbine size, you give leverage to the charge air side and increase the likelyhood of compressor surge. That said, I would imagine about 90% of the blame for compressor surge falls on the BOV setup. You normally don't need an extremely strong spring for a BOV since the pressure from the intake manifold signal hose is at the same pressure as is the pressure below the valve when the throttle body butterfly is open. If you are running crazy high boost it's a little different story but I don't think a 20g warrants ultra-stiff BOV springs (Of course I could be wrong I've never run one). I would try to go with that lightest spring possible that doesn't give you any significant boost pressure loss and see how that does. If you are always just at the cusp of the BOV leaking, it doesn't take much vaccum to open it which means a smoother transition between positive and negative boost.

If you don't know, compressor surge is when there is pressure in the intake tract, then the butterfly of the throttle body is closed (by lifting off the throttle of course) so there is nowhere for the pressurized air to go. If it can't escape via the BOV, it finds the path of least resistance, which is back through the turbocharger, causing the turbo to abruptly stop or even spin backwards. So, the turbine wheel basically stops which causes a bottleneck in your exhaust manifold, and your engine chokes because of the added backpressure. Obviously this is not a good thing.

djh

The air may be flowing the wrong way but the compressor wheel does not stop or spin backwards in surge. During surge the instability in mass flow is orders of magnitude greater than changes in shaft speed. But severe surge can destroy a turbo.

Dave

Precision Dyno

iTrader: (5)

The pressure in the inlet track does not seek a path of least resistance. It hits a brick wall. A wall of pressure that it cannot overcome once the throttle has been closed. That is the reason we use BOV's or the like.
To allow that pressure to escape or be diverted away from the discharge of the turbo/IC setup. It allows the turbo to continue spooling, spinning (whatever you want to call it) until the pressure can build again in the manifold.
Trust me if the compressor wheel were to stop as you state every time there was an ounce of surge the shaft would snap like a twig. Its like down shifting really hard and then trying to put the car in reverse. I can almost also guarantee you that the turbine will not spin backwards. At least not one that has been sized for the 2.0l engine we are used to.
I do get your point though that compressor surge is bad.

machron1

iTrader: (1)

I've never personally done studies but it's a widely held belief that when off-throttle and there is no relief from a BOV, the pressure in the piping leading to the intake manifold overcomes the force of the compressor wheel, and in many cases (of course not every time) stops or reverses the rotation of the turbine/shaft/compressor assembly as well. I could be wrong, but I'm fairly certain if you had 30psi on the compressor side of a turbo and ~5psi from a choking motor on the turbine side, the wheels would slow down and/or stop and/or reverse in a hurry. By definition, a BOV is there to relieve pressure in the intake tract when the throttle plate is closed and to keep the turbo spinning freely.

Regardless, my main point was obviously that it's not good and can normally be avoided with the right-sized spring on the BOV, not the specific RPM of the turbine. Even if the wheels don't spin backwards, the compressed air certainly is flowing backwards, wreaking havoc on your bearings. And, it's at least forced to slow down enough to make your engine buck as if someone shoved a banana in your tailpipe.

machron1

iTrader: (1)

Pressure always seeks the path of least resistance, it's the law!
If you find any pressure not doing it's job it should be promptly arrested.

It does seek the path of least resistance, which is back through the turbo where it came from.

You made my point by saying "the bov allows the turbo to keep spooling, spinning (whatever you want to call it)". So, without a BOV or with one having too large of a spring, it will do the opposite, which is not to keep spooling or spinning or whatever lol.

machron1

iTrader: (1)

I think you are confusing the surge point of a turbo at the limits of its efficiency range where it begins to cavitate, and the surge during throttle-off operation without the benefit of pressure-relief w/ the BOV. Of course at the surge point of the turbo's compressor map nothing will spin backwards because it is obviously under enough turbine load to get it there in the first place. When off-throttle there is significantly less pressure on the turbine. Two different issues here.

Precision Dyno

iTrader: (5)

Machron,
Pressure will NOT find a path of least resistance. It will find balance. Or its goal is to find an area of lower pressure and gravitate toward it.
That is the theory behind Naturally aspirated combustion engines as well.
Plus, the air in the inlet tract will NOT flow backwards. It will cram into every section it can. If the system cannot evacuate or capacitate all of the airflow under pressure it will find a "relief" section. That section will be thru the opening left by the blades inducing the incomming air. The compressor will try to continue doing its job. At the point of initial surge the pressure stays built up in the system until the engine is not producing enough energy to spin the turbine. At that point the relief is over and the air "pressure" has equalized in the system. It has been bled off thru the inductive part of the compressor. The inducer side of the housing.
At that point only Pressure can be seen on the other side of the inductive tract.
For the most part we are trying to say the same thing. Anyway your point is well taken.

Precision Dyno

iTrader: (5)

LOL Are you confusing electrical theory with laminar flow?
JK I understand your point.