The BRP thread is most likely the best place to get you questions answered about PD blower all though some of the info you are requesting could help me make my Boost profile graph more accurate.



Here is the way I understand PD blowers.

If the blower is designed to produce on average 6.5psi at WOT for the given engine if you are at 1k RPM and you go un throttled (WOT) the blower would very quickly start pumping out the design CFM/ rev of the blower and very quickly fill the throttle volume thus creating positive pressure in the manifold.

With the AFAC12 (my desired setup) the compressor has internal compression so the mass of air coming out of the blower at say 1kRPM and WOT would instantly be at 4psig (increasing linearly 1psig/1kRPM ideal) (before regulation) and would more quickly fill up the throttle volume. At least that

 

I'm following both threads, and was asking questions to get some more clarification on the Boost profile graphs.

Is there any way to plot charge density?

 

Eaton does have graphs of flow rates some where out there but that is an ideal number (AKA on a flow bench)

The number you are actually looking for are the flow rates post blower/compressor once it is bolted on the Engine which can vary depending on the other modifications that have taken place (camshafts, ported manifold, high flow exhaust systems...ect)

Using flow rate numbers on one particular engine with each of the blowers/compressors installed is the only way I know of to get a true comparisons of the actual system flow rates.


I think the simplest way to get the answer you are looking for is to install a Mass Flow meter in line and install each of the systems one at a time on the same engine and graph those numbers VS RPM and HP/TQ.

But you question is at the heart of FI!!!!!!!!!!

It increased Mass flow rate of O2 we are trying to get ;
A higher pressure is just the most effective method to get that increase. Other than NOS

Here is an example of what I am talking about

Say you have a compressor that is only capable of putting out 8psi under any condition.

If you have an engine that breaths better( cams, ported manifold, high flow exhaust..ect) it will have a lower manifold pressure but will have higher mass flow rate (AKA more HP/TQ) than a engine on the same compressor that had a higher manifold pressure.

As you can see here higher manifold pressure does not always mean more power. That

 

[QUOTE=deppenma,Mar 21 2006, 05:00 PM]But you question is at the heart of FI!!!!!!!!!!

It increased Mass flow rate of O2 we are trying to get ;
A higher pressure is just the most effective method to get that increase. Other than NOS

Here is an example of what I am talking about

Say you have a compressor that is only capable of putting out 8psi under any condition.

If you have an engine that breaths better( cams, ported manifold, high flow exhaust..ect) it will have a lower manifold pressure but will have higher mass flow rate (AKA more HP/TQ) than a engine on the same compressor that had a higher manifold pressure.

As you can see here higher manifold pressure does not always mean more power.

 

Boy do I feel stupid. I've been watching this thread since day one, and some of this is only just now becoming clear. I just realized that throttling the input of the axial flow supercharger gives us the same flexibility we have with an electronically controlled waste gate. I know you guys have been discussing it, but I only just now fully realized the implications. It seems that between varying the number of stages and throttling the input we can boost the motor to within an inch of its life at pretty much any engine speed we choose. Am I reading too much into all this?

 

deppeme, in your last post you are basically saying that 8psi of boost is not always the same. the CFMs (amount of air flow) is more important. alot of people dont realize this. good to point that out. i really wanna see the afsc and BRP chargers finalized.

 

Throttled superchargers why we do it that way.

With the vortech style centrifugal superchargers do not require throttling because they are not creating any significant amount of boost pressure when at cruising speeds and partial throttle positions and any boost that is created while minimal can be vented by way of a dump valve that is usually located on the Aftercooler.

The reason that a positive displacement supercharger (pump) is throttled is the fact it will always pump the same amount of air pre rev if it is un-throttled.
With the TB in the factory location the supercharger would be continually be pumping enough air to create 6.5psi in the manifold if the TB was at WOT. Now since we are at cruising speeds and the TB is partially closed and the PD blower is un-throttled it would produce pressures in the tubing and air to air intercooler greater than the 6.5psi it would produce if the TB was at WOT.
The pressure that see as a result of a PD blower is a ratio between the amount of CFM the blower puts out vs the amount of CFM the engine takes in at WOT.
The main problems with having a un throttled PD blower is
1)the substantial amount of engine power it takes to run a PD Blower if it is un-throttled which would cause a constant drag on the engine
2) there would be substantial heat in the air stream going to the Air to air which would most likely exceed the capacity of the intercooler
3) when you do open the TB (stock location) with a un-throttled PD blower setup you would have a very large boost spike greater than the 6.5psi that you are expecting.

On the AFSC (draw through system)
Having the Throttle body before the compressor drops the engine drag to near 0hp. The AFSC is unable to compress the incoming air mass if it is below a specific intake pressure thus it becomes nearly transparent in the air stream at partial throttle positions up to a point what the throttle angle allows enough incoming mass flow/pressure to give the compressor something to compress.

If you were to install the AFSC (throttled) and did not install the belt the compressor would free spin in the incoming air mass (AKA true draw through system)
With a un-throttled AFSC we would have some of the same problems as the PD blower but not all of them.
1) we would not have a boost spike that would go above the actual amount the AFSC can put out since it has internal compression and I sonly able to put out as much as it

 

If the system is designed properly (which I am sure it will after talking to RP and picking his brain a bit) you should never be able to generate so much boost out of the AFSC to get to close the point where engine damage can occur.

Looking it from A Failure Modes and Effects analysis stand point.
And using the standard AFSC 8psi max setup and a turbo setup (8psi)

There are more thing that are going against you in a turbo setup.
You have a wastegate that if it failed closed you would very quickly destroy your engine due to a large boost spike (high pressure with high intake temperature and higher combustion temperatures). Or if any of the boost controllers that you have programmed to control that wastegate are programmed wrong and/or also fail you would still have a problem with boost spikes. And don

 

[QUOTE=deppenma,Mar 21 2006, 03:06 PM] The PD blowers must fill up the Throttle volume before +pressure occurs thus you don

 

I agree with you 100% slimjim8201.

I main reason I showed the lower range having a lower pressure was the fact as the pump starts to build pressure in the throttle volume the rpm jump so quickly that it gives a misleading representation of the actual boost profile is lower in the low rpm range.