Calculators for HP/Airflow accurate?

R

Rods

Turbo Crasher
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Apr 23, 2006
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http://www.rbracing-rsr.com/turbotech.html

I was playing with that calculator and punching in CFM and LBS per min doesnt seem to match adds and other items I'v seen that say they flow such a CFM and will support the HP given,,, example I saw an I/C flows 800 CFM supports 1000 hp well the calculator says different
 
I don't think that calculator is correct. Here's how I figured:
PHP: 
n(lbs/min)= P(psia) x V(cu.ft./min) x 29
            ----------------------------
                 (10.73 x T(deg R))

P = 74.3 psia (14.3 psi baro + 61psig)
V = 405.627 CFM (3900 engine rpm x 363 engine cid) / (1728 x 2)
T = 560 (100F ambient air temp, lotsa spray)

That makes the lbs/min of airflow to be 147.4118344 lb/min. By my other calculation that equals roughly 764.6008403 HP, not the 1217.8 as displayed in the calculator. My head hurts.


bnraond.
 
That calculator is for gas engines which have a WAYYYY different air to fuel ratio then the diesels.

Gas vs. Diesel
idle - 8:1 vs. 50-100:1
cruise - 14.7:1 vs. 25-32:1
WOT - 3-6:1 vs. 12-15:1.

Most of this has too do with the chemical compositions of the fuel (Diesel requires more air due too having more carbon and hydrogen atoms), The other contributor is the different techniques of ignition. This is why joe farmer got 760 hp vs. the calculators 1200 hp.
 
joefarmer said:
I don't think that calculator is correct. Here's how I figured:
PHP: 
n(lbs/min)= P(psia) x V(cu.ft./min) x 29
            ----------------------------
                 (10.73 x T(deg R))

P = 74.3 psia (14.3 psi baro + 61psig)
V = 405.627 CFM (3900 engine rpm x 363 engine cid) / (1728 x 2)
T = 560 (100F ambient air temp, lotsa spray)

That makes the lbs/min of airflow to be 147.4118344 lb/min. By my other calculation that equals roughly 764.6008403 HP, not the 1217.8 as displayed in the calculator. My head hurts.


bnraond.
Click to expand...

brandon why are you such a genius?! :Cheer:
 
feelmecummin said:
brandon why are you such a genius?! :Cheer:
Click to expand...
I ain't, I can promise you that! I just wondered one night how many CFM I would need in an air filter at STP and decided to figure it out.

brandon.
 
I didn't realize that no one published their air filter flow data until after I'd figured how much I needed. I guess they figured busty girls in magazines would sell more filters than a table with flow data. :doh:

brnaodn.
 
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