Pressure vs. Flow - Let's do this!!!!
02-06-2010, 04:59 PM
#51
Are you talking random engines only or do want to apply that to comparing the unmodified Renesis with a 40ish lb/min compressor ? Beacuse i strongly believe the answer is different in each case as mentioned earlier .
02-06-2010, 09:28 PM
#62
Registered
I will chime in here:
With 10 to 1 rotors I made 12 to 13 PSI at 4-8.5K rpm, with about 330- 350 on the MAF.
With 9 to 1 rotors I make 10 PSI at 3.5 -7K rpm, with about 350-380 on the MAF
I have less "boost" with the same pulley, but (it feels like) more power (more flow?).
With 10 to 1 rotors I made 12 to 13 PSI at 4-8.5K rpm, with about 330- 350 on the MAF.
With 9 to 1 rotors I make 10 PSI at 3.5 -7K rpm, with about 350-380 on the MAF
I have less "boost" with the same pulley, but (it feels like) more power (more flow?).
02-06-2010, 10:21 PM
#64
I will chime in here:
With 10 to 1 rotors I made 12 to 13 PSI at 4-8.5K rpm, with about 330- 350 on the MAF.
With 9 to 1 rotors I make 10 PSI at 3.5 -7K rpm, with about 350-380 on the MAF
I have less "boost" with the same pulley, but (it feels like) more power (more flow?).
With 10 to 1 rotors I made 12 to 13 PSI at 4-8.5K rpm, with about 330- 350 on the MAF.
With 9 to 1 rotors I make 10 PSI at 3.5 -7K rpm, with about 350-380 on the MAF
I have less "boost" with the same pulley, but (it feels like) more power (more flow?).
More flow but , have you changed the efficiency of the engine and therefore made less whp even though you have more flow ?
You really need to dyno ..............
02-07-2010, 12:03 AM
#66
Up a hill under partial throttle for example you can be under 6psi or more boost before the throttle plate and 0 pressure in the uim .It feels like WOT and 0 in an NA car but you are only at 1/4 throttle .
Last edited by Brettus; 02-07-2010 at 12:13 AM.
02-08-2010, 02:56 AM
#70
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you have an area of high pressure(post compressor). then a rotor turns a few degrees and the intake ports open up to the combustion chamber. instant low pressure area, add to that that for a time the low pressure area is expanding. physics tells you that is what moves the mass of air from point A to B. Now add to that momentum, possibly thinking of it in the same terms that ppl think of scavenging effect in the exhaust(although it would only be partially correct in that sense). momentum matters because as you reduce restrictions, you allow this mass/volume/whatever of air to attempt to reach pressure equilibrium more efficiently - meaning more powa!
there are a LOT of things over my head, but what physics i know comes easily to me. maybe its not an easy topic to grasp, or just not an approach for everyone, but i still dont get what the fuss is all about
(FWIW i know the both of you fully understand this stuff, likely better than i.)
02-08-2010, 08:13 AM
#72
Hey Kane, I happened to take a look at the "Aux Ports Closed" thread and saw where you mentioned "3 days of discussion and some people still can't seem to get their head wrapped around it". I thought I did? 
Anyway, in reading that thread, there was discussion about altering the timing of the various intake ports and the effect of volumetric efficiency (what we commonly measure as engine torque). Of course, to have a complete understanding of volumetric efficiency we must also examine the fuel consumption (BSFC) but that is not imprtant right now.
One thing I have been wanting to do, but haven't had the opportunity, is to close all the ports but the primary and do a dyno pull from idle to redline while recording the RPM at which manifold vacuum starts to become evident. My guess? Somewhere near 3,750. Then, repeat the process with the SSV opening up at whatever RPM is chosen and see where manifold vacuum again becomes present. My guess on that one? Somewhere around 6,200 RPMs.
There is only one problem here; separate vacuum taps would need to be installed in EACH port runner, as close to the engine as possible, in order to determine the RPM at which each port becomes an impediment to airflow. I guess I will have to wait until I get another engine so I can tap the manifold and cap them up when I am done.
Anyway, in reading that thread, there was discussion about altering the timing of the various intake ports and the effect of volumetric efficiency (what we commonly measure as engine torque). Of course, to have a complete understanding of volumetric efficiency we must also examine the fuel consumption (BSFC) but that is not imprtant right now.
One thing I have been wanting to do, but haven't had the opportunity, is to close all the ports but the primary and do a dyno pull from idle to redline while recording the RPM at which manifold vacuum starts to become evident. My guess? Somewhere near 3,750. Then, repeat the process with the SSV opening up at whatever RPM is chosen and see where manifold vacuum again becomes present. My guess on that one? Somewhere around 6,200 RPMs.
There is only one problem here; separate vacuum taps would need to be installed in EACH port runner, as close to the engine as possible, in order to determine the RPM at which each port becomes an impediment to airflow. I guess I will have to wait until I get another engine so I can tap the manifold and cap them up when I am done.
That is a really good idea....I'd like to do the same on an FI engine.... it would be cool to see what port timing is better for the higher VE%.
I need more $$$ for dyno time! HAHA
Actually what I need is for it to freakin stop snowing so I can drive to the mother f-ing dyno.
It sounds like most of use are on the same page mostly about the pressure vs flow thing. I'd just like to see a few folks map it like I did so you can really see how compressor selection does matter.
PS - Now I see why you are bringing vacuum into play...intake vacuum is a sign of lower VE% than optimal (assuming WOT and all).
02-08-2010, 08:45 AM
#74
Well ultimately (and this is wicked OT), but I want to test each port opening and get them to open just in time before the power drops off due to small intake volume... same as the OEM concept but custom for my FI application. I have done it once on a Turbo-ed VTEC, and it is a PITA and took me forever.
02-08-2010, 09:09 AM
#75
I'll go back and read this when I have an hour to kill, but I can see a LOT of rough edges here.
A couple of posts stuck out as particularly disturbing in their "red is green" assertions, but I don't think any of Kane's stuff is far off.
There are some simple ways to convey the meat of this subject, but there is a fundamental level of "3D" thinking that has to be present for any of this to make sense and many, many people (perfectly normal, nice people) are simply not capable of this.
A couple of posts stuck out as particularly disturbing in their "red is green" assertions, but I don't think any of Kane's stuff is far off.
There are some simple ways to convey the meat of this subject, but there is a fundamental level of "3D" thinking that has to be present for any of this to make sense and many, many people (perfectly normal, nice people) are simply not capable of this.