DIY_EFI Digest V4 #388

[Gary Derian]

I was reading my own post when I realized that exhaust is not air, DUH, so
this quick analysis needs some more work.  Also the fuel burned is now
gaseous form.  Lets see... 12.5 O2 + C8H18 = 8 CO2 + 9 H2O.  Air is 20% O2
so I have to add 50 N2 to each side, so 62 moles of air makes 67 moles of
exhaust so we have to add 8% to the exhaust flow.  That means 600 cfm is 167
hp at 800 deg F.

Gary Derian <gderian at oh.verio.com>
>
> It takes 140 cfm of intake to make 100 hp.  Since exhaust is hotter, there
> is more.  Lets assume 1100 deg F for exhaust and 70 deg F for intake.
> (1100+460)/(70+460) = 2.93.  Therefore every 100 hp has (140*2.93) = 412
cfm
> of exhaust.  600 cfm would be only 145 hp.  If the exhaust cools to 800
deg
> F by the time it gets to the muffler, 600 cfm would be 180 hp.  The engine
> could easily stand 1 or 2 psi backpressure so that muffler is good for
more
> than the above hp levels.  If you knew the backpressure at 1000 cfm, you
> would better know the flow characteristics of the muffler.
>
> Gary Derian <gderian at oh.verio.com>