GFB

It is possible due to the poor breathing of these engines? This only happens with the ottomind (tapped wire) and XZT+ on, sometimes with only the ottomind, but not with only the XZT+. The ottomind doesn't fuel until it sees boost, but with these injectors it really fuels hard and spools really fast. If I let off the accelerator quickly between shifts, sometimes during only mild spirited driving, 20-30psi, I will get a surge. Turbo is stock HX with banks turbine housing, which I am told is a 14cm.

qzilla

I cannot answer your question 100% but, there are a couple of things that come to mind.

First, and the thing that everyone is going to tell you is that you are killing that little turbo. This may or may not be the issue but, that will be the first thing you here and it is a likely suspect.

Second, is that it is really, really difficult to make these trucks really smooth. The VP44 pump is just not that refined and the control is not that great. It takes a lot of electronic horsepower to make it smooth. When you are tapping the wire if you do not have a lot of resolution and a large map based on many factors then you are going to get a surge somewhere.

This has always been a complaint with almost every product ever released for these pumps. Any of them that make a lot of power typically have some drivability issues.

That is why I decided to get into this market.

I think I am safe to say that every single product on the market is using an 8bit processor and most of them are pretty slow. We are using a 32bit processor at 60 mhz which is wicked in terms of processing power. The only thing this allows us to do is have more resolution and look at more parameters to make decisions. WE look at load, rpm, tps, boost and a couple of other variables that I won't name. When you take all of those into the fueling decision you can make a better choice of what to do.

Most are limited to looking at boost or boost and RPM at the most.


Now, the other thing that it could be is a fuel supply problem but, it does not really sound like it. Is the surge at WOT or when you are rolling in it or with a load or something? I don't think it is WOT because you should see well over 25-30psi with that setup. heck you should see 30 psi or better with just the XZT+.

GFB

It is not a pump surge, but rather a compressor surge or "turbo bark". Fueling is plenty and I keep the boost in check (35 or below usually).

qzilla

Is it at a steady throttle or when you back off the throttle or as you accelerate? You might be running over the top of the turbo?

GFB

It's when I back out of the throttle quickly. If I easy off slowly it won't do it.

qzilla

That is easy then.

You are barking the turbo. If you keep doing this you will snap the shaft. I promise.

When you are fueling these turbos with much more than stock fueling you need to make sure you roll back out of the throttle.

What happens is that you have a certain amount of drive pressure on the exhaust side of the turbo. When you are accelerating you are driving the turbo to suck air. When you just stop that drive the turbo has to react. With stock fueling you can never drive it all that hard. When you start having some fuel behind it you are really accelerating the shaft speed and when it stops the intake side basically cavitates and causes pressure going the other direction on the shaft.

You can see where this is really hard on them.

Now, what you are hearing is the intake side cavitating. That is bad, really bad.

So stop it and your problem is solved.