The BB DET T-25 compressor will flow about 27 lbs/min at a 2:1 pressure ratio (about 1 bar boost). That is about 390 CFM.Chris Colburn said:I know that the Eclipse's T25 cfm rating is 265. I want to know what the SR20DET T25 cfm rating is. Or the GT-iR T28 CFM rating.
Nope. CFM measures Cubic Feet per Minute. Cubic feet is a measure of volume. CFM is a volumetric flow rate.Chris Colburn said:I always thought that cfm and lb/min where measuring the same thing but in different units. Like miles to kilometers, they both measure distance but with a different unit of length. The conversion I always used for cfm to lb/min was 14.5 cfm to 1 lb/min.
Well, then maybe those who are concerned about the spec can explain to me what the hell it means. I saw the spec under the other thread, and it really doesn't mean s**t to me.SERprise In WV said:
Now then...let's relate all that to the proposed intercooler we're trying to do a group buy on. According to Forge Motorsports, it flows 253 cfm
cooling air flow 1200 ft / min. Some have expressed concern over the cfm rating being low (compared to other units).
Well, for reasonably incompressible flow (you can assume air is incompressible as long as it as at a flow Mach number of less than 0.3 or so--this is useful for doing stuff like pipe flow analysis, but not for analyzing compressor wheels), pressure drop is proportional to density time volumetric flow rate squared. The volumetric flow rate is important because it is an idicator of velocity (for a fixed are and mass flow rate). Note the density term, though.However...if I read your above dissertation correctly, the cfm rating isn't too terribly important, as our engines are 'fixed' at 238cfm, turbo or no turbo. As far as I can deduce, it's the mass of flow and not the volume of flow that is important in terms of intercooler performance, turbo performance, etc.
Agreed.Even if I have difficult to read english,your text is very clear to me!!SERprise In WV said:Rob--
Wow. That appears to be an entire year of Physics and Engineering classes, all balled up into your one post. Wonderful information, and written in a way that even I --who graduated from the Holley Double-Pumper School of Air Flow in the 1980s-- can understand.
In your world, Rob, it's simple stuff. However, you've managed to explain things clearly, and for that I am thankful.This just comes from Bernoulli's equation. Basic stuff.
SERprise In WV said:
I would imagine that, just on cooling surface area alone, it is safe to say that the Forge unit has to be more efficient than, say, a stock Bluebird or even GTi-R intercooler. More efficient cooling, yes. But more efficient at moving air quickly? That appears to be the $450 question here.
Bigger pipes won't have any influence on the effectiveness of the core. They may have a small influence on pressure drop, but most of the pressure drop is in the core. Look at all those fins the flow has to pass through!I would also imagine that having Forge build the same intercooler, but with 2.5" inlet/outlet would only make it more efficient. If for no other reason than doing away with a smaller restriction on both ends.
Inches of mercury is a measure of pressure. 28.4 inches of mercury is about 13.95 psi. This is Garrett's standard compressor inlet pressure. It is lower than ambient to account for inlet restriction from an air filter, etc. Rankin is a measure of absolute temperature. 0 Rankin is known as 'absolute zero', the coldest temperature you could theoretically have. Absolute zero is theoretically impossible to achieve. To go from Faranheight to Rankin, and 459.67 to the temperature. So, 545 R is about 85 F.Chris Colburn said:
You did loss me on the "at 28.4 inches of mercury barometric pressure and 545 Rankin absolute temperature"
I assumed a 14.2 psi inlet manifold pressure for a naturally aspirated car (instead of 14.7) because I assumed there would be about .5 psi of pressure drop from the piping and the filter.I don't get where you get 14.2 (atmoshpere 14.7?)
Intake manifold density is calculated from the ideal gas law:and how you figured out the intake density (lbs/cubic foot). I mean I understand how to take mass and divide it by volume but how do you know the volume of the intake manifold?