Yes i do appreciate that, do you have any thoughts on the dip at arounf 300cfm or 6000rpm? depending on which way you want to look at it.......As i stated in the other thread, there are many air restrictions in the air path, throttle body being one, now the more you try gain in boost requires more air, so the effects of poor air path become more amplified, I feel the graphs your showing, are probably correct and that the dip at 300cfm is due to air restriction, because up to that the 17% is pulling more air, after it almost the same, i do not know where you are measuring the air flow from to speculate which of the air restrictions that i have found could be causing this.. what is your impression of the dip?

 

Also i would rule out you volumetric effecientcy, i agree many of assumptions could be made here....

 

I just got the Supercharged! book by corky bell, thanks to your other thread, i will be running some numbers through the formulas they have and see what they come up with, on cfm requirments and such....... give me a few............

 

There are two MAP sensors in the MINI - one just before the supercharger inlet (upstream pressure). The other is in the intake manifold (downstream pressure). The downstream pressure sensor also has the IAT sensor built into it. Ambient temperature was measured by the MINI's sensor clipped to the front grille.

One of the many fudge factors is the temperature inside the air filter. Obehave did some testing showing the temps inside the Alta airbox compared to ambient that showed somewhere in the 5-8 F range. I guesstimated the temp as 10 C. Cheese is only an hour or so of fast driving from me, so I ASSumed we have the same weather conditions today. 2 C and 1005 mbar absolute pressure.

 

Sounds, good im still working the formulas in this book, do you have it by any chance, it is very nice good formulas, im kinda getting lost(not confused) like a kid in a candy store.....several formulas ive been looking for.....

 

Here's the formula I used for airflow (plucked from "Supercharged!&quot:

airflow = cid x rpm x 0.5 * Ev /1728

 

thats a normal aspirated motor though.......

 

Correct. Check out my spreadsheet. Column R is Corrected Pressure Ratio. Basically:

(manifold pressure - ambient pressure) / (manifold iat - ambient temp)

Absolute numbers for all of them.

 

page 58 theres an error 384*1.87 does not equal 384......

 

97.6cid*7500*.5*.8/1728=169.4444

boost ratio on a 19% using your 17.5psi

17.5+14.7=32.2 absolut pressure

32.2/14.7=2.19

so.....

169.444*2.19=371.15 cfm

 

What did you do for temperature? I'd be curious to see a 2nd gear 1500 rpm to redline pull in your car. Logging RPM, MAP, and IAT is all that's needed.

What do you think of the Volumetric Efficiency estimates? I copied them from semi-accepted figures for the VW 1.8T.

 

im playing with that now, i have to go to the store to get batteries for my calc it died, ill be back..... this is fun, instead of argueing..... lets do the math together

 

just for numbers at 19psi the cfm goes to 388.5
20=400cfm
25=457.6cfm

 

I'm not sold on the VE numbers but I dont have any proof. Just thinking outloud but the M45 displaces .45L per rev whether you need it or not, raising the (volumetric) efficiency over 100%.

--
Cheese

 

>>dgszweda1 wrote:
>>>>
>>What are you basing that on? Both my data and that of Cheese, have 27-28 datapoints between 2k and 7k rpm. :???:
>>
>>Absolute temperatures vary based on driving conditions leading up to the runs. I'll post up a spreadsheet with the raw data and a CFM calculation.


Andy,

That was why I was asking. You plot looks like a lot of "steps", while Chees's is much smoother. Typically in graphs this means there are less data points. This is not always the case, that was why I was asking.

 

>>
>>Andy,
>>
>>That was why I was asking. You plot looks like a lot of "steps", while Chees's is much smoother. Typically in graphs this means there are less data points. This is not always the case, that was why I was asking.

The reason for the steps is the resolution of the IAT sensor... its only whole numbers.


--
Cheese

 

ok for the heat made by the supercharger......
(PR^.28-1)*Tabs

PR is pressure ratio, Tabs is total absolute temperature

for a 19% using you 17.5Psi we get a ratio of 2.19

so.....

(2.19^.28-1)*550=134.99 Absolute temperature gain

now....

Thermal efficiencies of a roots blower is .55%

so our actual temps is 134.99/.55=245.44 degrees but remeber this is befor the intercooler.....and why i recommend upgradeing it with a 19%

 

Also that formula is base on a 90d Normal day...

 

But now you put the intercooler, i will use an approximate for the stock of 85% effecientcy because that is very easily attained....

Actual Temp rise of 245d*.85=208.25 degrees removed by intercooler....
leaving a intake temp of...37 degrees temp rise, meaning on a 90d you should seee intake temps of 127d after the intercooler(stock) not all that bad, not great either mind you...

now on a larger air to air or water to air inter cooler you should be able to get 95-98% effecientcy so.....

245*.95=232.75=12.25 degree rise =90d day +12.25 =102.25 intake temp
245*.98=240.1=5degree rise =90+5=95 degree intake temp.....

SO now that ive shown that, like i said before i dont think temperature due to the extra boost is that big of a problem to be worring about.....but i would consider upgrading the intercooler with a 19%....

Also dont forget these are temps at full boost, when do you stay at full boost for any legnth of time, and dont forget also that if you ever do let off the gas, the vacumn cause a refridgerating effect, also tehse formulas dont calculate in heat loss through the supercharger, and plumbing, and head, heat loss due to vaporising fuel, etc, etc, so we can only use these formulas to approximate temps.....

there is another formula we need to use with this though, we need to calulate, the compression temp(in the cylinder) and add that in, which cannot be cooled......

so remaing in a 90d "standard day"....

CR^.28*550=absolute compression temp ....

8.3^.28*550=994.7 absolute Temperature due to compresstion @ 90d

so lets try with our temps.....
(stock intercooler)
8.3^.28*(550+127)=1224.45 cylinder chamber temp at ignition(whew thats hot...but mind you there are the other cooling factors we havent added in as i already mentioned, evaporating fuel by itself can easily bring this under the 1075d limit....like i said before though its getting real close, and probably would work but i still stand by my recommending a higher effecient intercooler with 19% pulley, even as simple as a water spray on stock intercooler(at maximum boost) will suffise but i do not know how to calculate that as far as increase of effenientcy, cryo and nitro spray on intercooler would definatly work as long as you dont run out...)

now more effecient intercoolers.....
(95% effecient)
8.3^.28*(550+12.25)=1016.8333d (thats under by itself)
(98% effecient)
8.3^.28*(550+5)=1003.77d..nothing needed to be said.....

 

Hey Mancheese, i would have to disagree on you comment on .45l per revolution, keeping the volumectric efficientcy above 100%....if im not mistaken it never reaches 100%.....

, remeber ther is losses in there to on the cfm side so we would actully have to spin a little faster...)

Also dont forget any flow restrictions to or form the supercharger effects these numbers.....

 

now Andy i need to qute you from one of you earlier posts on out technical merits thread...

"The supercharger is a Roots-type blower, manufactured by Eaton to BMW's specifications (notably, the water pump is driven off the back of the charger). It turns 2.06 times engine speed, which works out to 14317 rpm at the 6950 rpm rev limiter."

now with this at 14317rpms we should be able to get boost levels to meet our 17 PSI number, but we dont.....

as well, lets see the 17,200 rpm supercharger limit(courtsy of magnuson product, http://www.magnusonsproducts.com)

17200*.026=447cfm.....

hmmm....

24PSI+14.7PSI=38.7Absolut PSI

38.7Psi/14.7Psi=2.6 Pressure ratio

2.6*169.44=446.07cfm.... shows its possible, but actually a 19% goes a hair past 17,200....

2.4(pulley ratio,19%)*7500(redline raised due to aftermarket ECU's)=18,000rpm(i know its past 17,200, but i dont run at redline....except on emergencys)

now 18,000rpm*.026=468cfm

now 39.7(25PSI) Absolute PSi/14.7=2.7006

2.7*169.44=457.6cfm( :evil: .......

 

Caddman,

I haven't had a chance to go over your numbers. But, I'd REALLY like to see a 2nd gear pull from your car, logging RPM, IAT, and MAP.

 

Also Andy<
iwas trying to find those numbers for you, apparently i havent done a dyno run with my new data logger, or i lost the results?, I thought i have done it, but i cant find em....Anyways ill try and make it to the dyno next week and see what i can come up with, hopefully its not booked up!!!

 

lol, we posted at the same time....

 

>>i am a new soon-to-be owner of a 04MCS (just placed my order last week).

Congrats on your order. Be aware the pulley upgrade voids your supercharger warranty.

>>two questions i have about the pulley change:
>>1) just wondering about the gas economy tradeoffs in going to any of the pulley reduction schemes.

Some owners have reported with the 15% reduction pulley upgrade that their gas mileage improved a little, maybe 2 mpg or so. It all depends how you drive. I would expect similar results from the 17% or 19% pulley upgrades as long as driving habits are unchanged.

>>2) i have seen threads about changing the ECU chip.
>>any serious downside to not making the change?

The pulley upgrade can be a stand alone modification and there really isn't a serious problem using the stock ECU which runs rich. An ECU upgrade specifically for the pulley upgrade would be helpful (adds HP and torque and improves air/fuel ratio) but not required. Some ECU upgrades have different versions for the various size pulleys- see GIAC. Right now the EvoTech and PowerChip ECU upgrades are tuned for the 15% pulley.