PTS Flowbench Forum

Forced_Firebird wrote:

SSR wrote:

Forced_Firebird wrote:
I what would happen if we applied our vacuum source in blow configuration into the plenum, rather than drawing it through the port if it would closer mimic a positive pressure situation? One would probably have to set the manifolds, and throttle to the equation to be accurate, but then also would have to mimic the positive pressure and any cam overlap to the mix since the exhaust pressure is so great in a turbo system.

Until we experiment, we are just going with what we know works in my little world.

-John

I'm not too sure what you are saying there ^^.

**If you suck through an average shaped port then the air will favour the short side, if you blow through it will favour the long side**

Do you think this is true? If so then does it have any complications, or would it change the way we shape a turbo port or measure it with our benches?

I think maybe it depends on your overall boost pressure, you may see +14.7psi in the plenum, but will you still be seeing that in the inlet port? Here you still might be seeing vacuum until (throws a number in) say, 28psi.

For sure inlet plenums must be designed with some 'equal port share' in mind, but I think they too are to be questioned and could work differently at different boost pressures. The low boost OE style ones don't seem to have anything which guides the air into the ports, so I'm guessing that at a certain boost pressure or air speed we need to be thinking of doing something about this.

It's very difficult to find some empirical evidence on this subject so I am either;

Wrong

People are keeping it to themselves

It's too advanced (hardly likely!)

I'm just theorizing, but...

We all know that airflow is what's sought after.

I agree about the SSR (love the handle BTW).

But here's the catch. It's NOT really about the boost pressure, but rather the airflow - I generally use pressure numbers for 2 reasons: 1. Place the compressor map to desired power levels 2. To map the fueling. Let's use a simple example of twin vs single turbo. At the same boost levels using identical turbos, do you think the single turbo will flow as much as the twins?

Another case in point. A local is talking about his 21psi setup where I know the turbo is past it's efficiency and he wonders why he's not making any more power. Why? Not because of the amount of boost, but rather the ability for the compressor wheel to move the volume needed to make more. Boost levels go up but power output becomes stagnant only increasing inlet temps.

My thought is if you are using a turbo that can outflow the engine (positive pressure), you would think that the air IS actually being "blown" into the engine, the only way any vacuum would be seen is if the piston was already on it's way down before the valve was opened.

Am I in left field with this thinking?

Artigas,

There is a fine line when deciding on the application of a specific turbo between being "too big". You have to remember, the closer you are to 1:1 ratio on exhaust to intake manifold pressure, the better. The same reason that causes the compressor to be too small as I mentioned above, the turbine can become a restriction giving you the same outcome (high EGT's, choke points). This causes undesirable intake/exhaust pressure ratios.

As far as spooling time, there are many ways to correct it that are rather simple for someone who builds turbo systems. One is a ball bearing journal. You can have on in your hand a literally blow into it and watch the wheels move. Truly amazing, but is also very expensive.

Divided pulse manifold/turbine housing. This is also great. I have recently worked on 2 different cars. A BMW inline six and a Honda 4cyl. Both using the same turbo from a Deisel truck (Holset HX35), both have divided turbines/manifolds. The BMW sees full boost at about 3500rpm under light load, the Honda sees it at 4000 under light load. The BMW redlines at 6800RPM the Honda at 7200RPM. You would think that because of the two different sizes/styles of engines there would be a big difference in the spool time, but it's not the case in real life. This same turbo runs a large diesel engine to 30psi.

Finally the quick spooling device. This allows you to have a large turbine, large compressor and not choke and not lag, either. You feed all cylinders to one half of the twin scroll turbine until a desired pressure level is reached, then open the other half to prevent choke.

Well, enough rambling. Got to get back to welding these headers. Sorry to get off topic.

-John