Boost 'sag'?

[DrZiplok]

See the boost plot at:

http://www.dsmtuners.com/gallery/showphoto.php?photo=11906&papass=&sort=1

Note how, after the spike, it tapers from 16psi at 4000rpm down to about 14psi at redline.

The tap for this plot was taken from the front port on the throttlebody; I have my boost gauge tapped at the FPR port and I don't seem to see the same results there (though I must admit I don't stare at my boost gauge while driving).

Is the 'sag' just an artifact of the tap point? If not, what sort of problems would cause this? It doesn't seem to behave like a boost leak...

Any ideas?

 

[blackawdturbo]

Originally posted by DrZiplok

Is the 'sag' just an artifact of the tap point?

Not sure

If not, what sort of problems would cause this? It doesn't seem to behave like a boost leak...

Any ideas?

Any kind of exhaust leak before the turbo would cause boost drop off like this.

 

[Enigma_Man]

It could be a matter of where you tapped it. The throttle body is somewhat of a restriction, and you might see lower pressures there? I don't have any real experience with that, but just a thought.

What might cause that if it's not just a matter of where you tapped it is a worn out turbo. I see you have a 16G, how old is it? Seen hard times, or always taken care of? Crap... I just closed your car info, and I can't seem to get back into looking at it.

But a restrictive exhaust or intake could cause it (I think I remember seeing a fairly extensive amount of mods, so prolly not that)

I guess there is the possibility that you're somehow flowing more than the 16G can put out, like the problem the 2g guys have with the T25. Other than that, I can't think of anything.

-Jesse

 

[InferiorWang]

we just learned this in physics. when air has to flow thru a smaller area it has to go faster and there is less pressure in that area. so if the tb is a restriction, then air is flowing faster and there is less pressure at that spot in ur intake. When ur getting to the higher rpm's even tho ur at the same boost level, more air is going thru the tb in a second. It's like an airplane wing. When air has to go faster over the top of the wing there is less pressure psushing on top than on the bottom creating lift.

I never thought that I'd actually use something from my physics class.

 

[DrZiplok]

Unfortunately for the physics class, there's nowhere that the charge air is moving faster than at the point where the MBC is tapped, so that's not it.

I guess it's possible that the stock intake snorkel is just too restrictive, so the turbo is working against a partial vaccum.

Rats. I'm not quite prepared for the conversion to a 2G MAF yet, and I don't really want to buy two intake snorkel replacements.

 

[InferiorWang]

have u seen that someone is working on a conversion so we can use an ls1 or lt1 mas? u can get the 3, 3.5, or 4 inch pipe. the thing is going to compensate for larger injectors too.