All you people running about 9 psi of boost: at what rpm are you getting 9 psi and what pulley size are you using?

The reason I ask is if you look at a compressor map for the V2 S-trim blower, you'll see that the V2 should be putting out 9 psi (pr=1.61)with an impeller speed of 35000 rpm.

v2 compressor map

I have been under the impression, though, that you guys are getting 9 or 10 psi at redline with the 3.25" pully. But that would give you an impeller speed of more like 47000 rpm. The compressor map says you should be making a pr of 2.1 at that impeller speed, or over 16 psi of boost.

There's a disconnect here, and I'm wondering what it is.

 

Boost at the head is prolly right, you get boost loss in the intake manifold from all the turns and the pipe.

 

I was wondering if that was the case. So the boost on a Maxima is losing about 6-7 psi by the time it gets to the intake manifold? That seems like a lot.

 

I may be wrong, but that rating is "dead head" blowing into a cap. The volume of air the motor use's, CFM, has an effect on peak pressure. A 2.0L motor will show more boost than a 4.0L motor from the same CFM.

Sorta maybe kinda what may be the deal...

 

I'm pretty new to reading compressor maps, so maybe I've got it all wrong. But if you look at the map I referenced above, you see lines for impeller speeds that show a pressure ratio at a particular flowrate, so I don't think the pressure ratio given is the deadheaded pressure.

For every impeller speed, there is a maximum PR at a certain flowrate. If you impede the flowrate sufficiently (for instance by putting a big blower on a small engine) you operate to the left of the peak efficiency, near the surge line.

At the other extreme if your engine wants more air than the blower can deliver, your PR drops drastically, especially for the high impeller speeds.

Operating near the surge line or too far to the right results in loss of adiabatic efficieny, i.e. you heat up the air more than if you were operating at the center of the efficiency islands.

The limited investigation I have done indicates that the V2 and V1 blowers are slightly too large for the Maxima engine, because they result in operating points pretty close to the surge line, rather than in the center of the efficiency islands. The situation becomes worse when going to smaller pulleys.

But I'm not sure I completely understand how to read the maps and how to apply them to our engines, so I may be totally off base.

 

Well all I know is when I went from a 3.125" pulley getting ~9.5psi to a 2.62" pulley at 13.5 psi my dyno looked like this...



So I wasnt too worried about the chart

 

Can't argue with them numbers!