Re: Of Long Posts and Superchargers...
I have glanced on the compressor map and can not determine the rpm scale, they dont seem to be marked, lines.
At a boost level of 20 psig I am figuring that we are at a pressure ratio of 20 / 14.7 or 1.36??? Some one wanna whoop up on my head ann edkate me. If it is 1.3+ thats low on the map. The atmosphere is 0.0 PSIG (14.7 PSIA = absolute)
On this curve which MAY be similar to ours stock speed is about two times the crank speed which is 1.6 L X 2 = 3.2 liters which is twice the amount of air going into the motor with no boost 0.0PSIG at the manifold.. We have 4 cycle engines that inhale every other rev, which is a intake of 1.6 liters (at 100% volumemetric efficiency). That would IDEALLY DOUBLE the pressure to 29.7 PSIA ABSOLUTE or 14.7 PSIG boost stock.. That seems to fit our stock conditions.
Questioning the church again, is our pressure ratio 1.3+ or is it higher ( like 2.36 ????????) I hate to get teckki but these things interrupt my string of whiskey sours / errr thoughts -with lots of cherries, fruit is good for you.
If I am at 1.36 : 1 then Iam really low on the map. If its 2.36 I am way off the high end of the map. I suspect that I dont know my ASP (A 178 joke ) from my Head ( cylinder) when it comes to this chart. Do I get any arguments or do I have concensus for once???????
If I say OK 20 PSIG is 34.7 PSIA then the ratio is 34.7 / 14.7 or 2.36 : 1 which is off the high end and relates to my red Herring ( red get it) guess above. Trying to extrapolating to 2.36 on the chart would again ASSUMING 15,000 s/c rpm correlate to the word "volume in the line Built in volume ratio =...." high up off the chart. 185's get 20 PSIG on other cars and at 6000RPM turn the pulley at 15,000 RPM on the s/c.
THis in WOODY speak would relate to a temperature of about 150 C which in my head is about 30 x 9 or 270 + 32 = 302 F degrees and above the desired range for Teflon. Forget the innercooler, it can handle the higher temps, think bigger delta T water to air inlet...
Yeah 302 is NOT THAT HOT but there are lots of centrifugal forces at 15,000 RPM that have to be considered. We will have a few learned people on here that can assist us with this chart and TEFLON cold flow properties. Were also pushing 50+ horsepower into the blower to do this which is about 150,000 BTU's of heat energy. Here the efficiency falls into play. THis heat is in addition to the heating of compression Adiabatic heating and raises the s/c temps ........in a word WOOOOaaagh thats a lot. I also get 56% efficiency on the chart.
At peak efficiency island on the chart the power in is About 17 HP, 110C or 212 degrees F OUT, I ASSUME and a pressure ration of 1.8 which works out ot be 26.46 PSIA or almost 12 PSIG boost. We are taxing this unit a lot and excluding the input pulley speed, were pushing the Dog doo out of this s/c. Over three times the HP load indicated at the charts SWEET spot.
SO many of us are going for 20 PSIG that well soon find out how much safety margin is built into this blower. AGAIN this is why is good to increase the inlet air density ( lower intake restriction, lower air temps both in and out, and lower restriction manifolds ) Better flow and air density will reduce the pressure at the outlet of the s/c needed, to achieve a given manifold pressure, more boost out with less HP needed and lower compression ratio = lower temps.
Work over , weekend, time to start date night #1.
Enjoy, Woody
EDIT: BTW 15 Meters cubic is less than 580 CFM, FYI
Last edited by waldig; Jan 23, 2009 at 02:59 PM.