BC

Here are some I found:

<a href="http://www.vortechsuperchargers.com/tech/s-trim_map.html" target="_blank">S -Trim</a>

<a href="http://www.vortechsuperchargers.com/tech/ys-trim_map.html" target="_blank">YS -Trim</a>

<a href="http://www.vortechsuperchargers.com/tech/s-trim_v2_map.html" target="_blank">V2</a>

Now if I am reading these things correctly, then the V2 and S trim compressors are not going be very efficient at the boost levels I wish to attain (starting at 8 and eventually going to 15 with a redone bottom bend and cams).

Do we have a total CFM number for the 5.0 S4 engine? I have Graham Bell's book in the other room, but if there is a theorum for that, then put it here.

I wanted the SQ stuff from vortech, but I am concerned that the voume needed will not be available with those Trim options.

Lagavulin

</font><blockquote><font size="1" face="Verdana,Tahoma,Helvetica">quote:</font><hr /><font size="2" face="Verdana,Tahoma,Helvetica"> Do we have a total CFM number for the 5.0 S4 engine?</font><hr /></blockquote><font size="2" face="Verdana,Tahoma,Helvetica">CFM = (cid x rpm x 0.5 x Vol Eff)

Brendan, if you go to this thread and find the post on the pulley sizes and the boost they make, you’ll find the calcs so you can calculate your CFM for a given amount of boost.

<a href="http://forums.rennlist.com/forums/ultimatebb.php?ubb=get_topic;f=14;t=006105" target="_blank">http://forums.rennlist.com/forums/ultimatebb.php?ubb=get_topic;f=14;t=006105</a>

In the meantime, here are numbers for an S4 at 6,200 rpm and 88% VE:

00 psi = 476.77 CFM
04 psi = 606.50 CFM
08 psi = 736.23 CFM
10 psi = 801.10 CFM
12 psi = 865.97 CFM
14 psi = 930.83 CFM
15 psi = 963.27 CFM

</font><blockquote><font size="1" face="Verdana,Tahoma,Helvetica">quote:</font><hr /><font size="2" face="Verdana,Tahoma,Helvetica"> ..with a redone bottom bend and cams..</font><hr /></blockquote><font size="2" face="Verdana,Tahoma,Helvetica">Since you’re reading the A. Graham Bell book, look at page 236 and you’ll see the section on ‘Cam Selection’. You’ll find that the stock cam will work very well and is really the best all-around choice if it's going to be street driven.

BC

Thanks.

Even at 10pis, we are talking about being on the RIGHT side of the efficiency island on a V1 or V2.

This is what concerns me.

I will look at that page. Thanks again.

GoRideSno

This should help confuse things

Marc of Devek "the ve is different for each rpm step....each cam.....each cam timing...each a/f ratio, etc.!
The highest I have found is 127% back calculated from a dyno pull at 3700 rpm, give or take a few, plus or minus 10% on both and you will be ok."

Here is the <a href="http://forums.rennlist.com/cgi-bin/rennforums/ultimatebb.cgi?" target="_blank">link to the thread. If it dosen't work search "cfm flow of the S4 engine"</a>

Lagavulin,
This is part of the reason why the boost wiht a roots blower is not as steady as should be imagined.
HTH
Andy K

BC

And now, How do I convert CFM to lbs/minute?

I have a converter, but it gives ounces per hour, and then it went to "powers" and I didn't like that class.

Lagavulin

Keep in mind that you should be looking at the values where peak torque occurs, not peak horsepower. It should be noted too that a street car will hit it’s torque peak more often than it’s peak horsepower.

The torque peak is the RPM where the engine achieves it's max chamber filling ability, and the trick is to match the compressor’s peak efficiency at this point.

Since we are shooting for peak torque RPM and not peak horsepower RPM, we will end up with a redline airflow point somewhat to the right of the island, exactly what is desired; however, Corky recommends not letting it go below 65%.

For a street car, the rule of thumb is take the torque peak RPM and add 25%. If we use 4,500 RPM as the torque peak, then the RPM we are shooting for is 5,625 RPM.

Using 5,625 RPM as the torque peak and 10 psi (..1.68 PR), then the resulting target is 726.81 CFM.

For 10 psi, find the compressor whose max efficiency occurs at 727 CFM and 1.68 PR.

BC

This makes the math all seem much more clear - Thanks Lag.

I am also shooting, however, for a motor that will hit good power at 3k, and carry the power up like a locomotive past 7k. Any changes to your math with this notion?

Thanks,

Lagavulin

</font><blockquote><font size="1" face="Verdana,Tahoma,Helvetica">quote:</font><hr /><font size="2" face="Verdana,Tahoma,Helvetica">I am also shooting, however, for a motor that will hit good power at 3k, and carry the power up like a locomotive past 7k. Any changes to your math with this notion?</font><hr /></blockquote><font size="2" face="Verdana,Tahoma,Helvetica">All I can say is look at Tim's dyno chart as there is lots of power everywhere, including down low.

As a point of reference, I rode in a supercharged 87 928 that was at the time putting out 100 less horsepower as he's running 7.5:1 cr and 9.5 psi (..for the time being).

Anyway, it is no exaggeration to say that I stopped breathing out of fear as the car mashed me back in the seat as the road kept getting narrower and narrower the faster we went. And the faster we went, it kept pulling like you cannot imagine, unless you go for a ride yourself.

By the way, when we hit 60, the auto shifted to second and did not chirp the tires. Instead, it burned them for at least 1/2 to 3/4 of a second.

Just as impressive was when he slammed on the brakes. If I didn't have a seat belt on, my head would have been lodged in the windshield. He installed 'Cool Kevlar' brake pads (..or something like that); with that kind of horsepower, it is imperative to have brakes which match.

My point is, that is crazy horsepower and you'll be more than satisfied, I promise.

As you may already know, Tim is running the V-1 Trim whose max airflow is 1,200 CFM. I will be going with the V-2 SQ Trim whose max is 1,000 CFM as I will not be running as much boost as Tim. You should be happy with either unit.

Carlos

Guys this is simple. Call Vortec. Trust me, there are any number of people there that have the necessary technical skills to help you select a blower for a 5 liter engine turning X rpms and producing X hp. The choice is to become an expert yourself or use the skills of someone else who alredy has.

tveltman

I was trying to find the CFM of the 5L stock engine, and I came across this page. After looking around the internet a bit, I discovered that this formula is in error, and should read:

(cid x rpm x 0.5 x Vol Eff)/1728

Ahh, what the hell, I'll just steal this from some other site (http://www.moddedmustangs.com/forums...ze-r-trim.html)

( 14.7 + psi ) / 14.7 = P.R. (press. ratio)

P.R x CFM = boosted CFM

boosted CFM / 13 = lbs/min

ptuomov

Guys, when doing forced induction math, always start with SCFMs.

One cubic foot of air at standard temperature and pressure assuming average composition weighs approximately 0.0807 lbs. So 100 SCFM = 8.07 lb/min = 484.2 lb/h.

The brake specific fuel consumption of a typical supercharged gasoline engine is about 0.6 lb/(HP*h) and the typical mass air-fuel ratio is about 12.5. Therefore, for each 100 SCFM you burn fuel at the rate 38.736 lb/h. With BSFC of 0.6, this mean 64.56 hp per 100 SCFM of air.

1 cubic foot is 1728 cubic inches and a 300 ci engine is thus 0.17361 cubic feet engine. If a four stroke engine spins at 6000 rpm and has 100% volumetric efficiency (defined in ACF units), then it pushes thru 520.83 ACFM. Under the above assumptions and assuming that the intake manifold conditions are close to the standard conditions, the engine will then produce 336.25 hp.

Now you can pressurize the air. Then you have to measure the conditions in the intake manifold and do a conversion between ACF and SCF. This will get you to the predicted hp. Calculator for conversion at http://www.engineeringtoolbox.com/sc...fm-d_1012.html


---

SCFM - Standard Cubic Feet per Minute

It is common to rate the compressed air consumption in Standard Cubic Feet per Minute - SCFM.

The SCFM - Standard Cubic Feet per Minute - determines the weight of air to fixed or "Standard" conditions. There are several definitions of SCFM. The most common used in the United States is with "sea-level" properties:

14.696 Pounds per Square Inch (psia)
60 Degrees Fahrenheit (oF) (520oR)
0% Relative Humidity (RH)

ACFM - Actual Cubic Feet per Minute

Unfortunately, real life "actual conditions" are seldom "standard conditions". When pressure is applied a volume of air - it gets smaller vacuum is applied to a volume of air - it expands. Actual air volume flow is often termed ACFM - Actual Cubic Feet per Minute. Actual Cubic Feet per Minute - ACFM, depends on the pressure, temperature, humidity of the actual air.

The conversion from SCFM to ACFM can be expressed as

ACFM = SCFM [Pstd / (Pact - Psat Φ)](Tact / Tstd)

where

ACFM = Actual Cubic Feet per Minute
SCFM = Standard Cubic Feet per Minute
Pstd = Standard absolute air pressure (psia)
Pact = absolute pressure at the actual level (psia)
Psat = Saturation pressure at the actual temperature (psi)
Φ = Actual relative humidity
Tact = Actual ambient air temperature (oR)
Tstd = Standard temperature (oR)

Calculator at http://www.engineeringtoolbox.com/sc...fm-d_1012.html

tveltman

http://www.homemadeturbo.com/forum/f...t-control.html

Not saying it would necessarily be useful on a 928, but it wins major duct-tape points, so I thought I'd pass it along...

123quattro

Brendan, I would do this. Go look at supercharger kits for whatever car with a similar sized engine. Compressors are generally known to support a certain hp amount on a certain engine. You can pretty easily come up with that info from the internet and message boards. Say you want to make 700 hp. Buy a compressor capable of that. I wouldn't fool with trying to match compressor efficiencies to engine rpm at a calculated boost. You are trying too hard. That, or call the manufacturer and they can tell you in two minutes which model would be for you.

People do this all the time with turbos as well trying to match one to an engine. They basically all just support a power level. Decide how much power you want, and then buy that sized turbo. I wanted 500 hp on my Audi. I bought a GT3076R for it. I want 600 hp for my 928. I'm going to use a GT3582R. I don't care that Garrett says it's too small for a 4.7L engine. It will work.

BC

Thanks John. I wrote this thread back in 2003, so quite a bit has changed. I finally have my supercharger assembly! And it will be BIG boost.

123quattro

Ah, should have checked the original date. Sorry.