boost presser and power gain

[Robert Gallant]

> What interdependence is between boost presser  and power gain?
> If not turbo engine is 100 hp, what power growth will obtain by 2 bar
> (absolute) boost? And how march reduction of compression ratio will
> needed?
> 
> If anyone has these formulas,  please let me know!


Here's the equations from the old book Street Supercharging.


Pr = (Pa + Pb) / Pa
Y = (Pr^.283) - 1
dTi = Y(T + 460)   Note:  adding 460 changes temp to deg Rankine.
dTa = dTi / Ea
Td = dTa + T
Dr = Pr(T + 460)/(Td + 460)


dTa = Actual temp increase
dTi = Ideal temp increase due to increasing pressure
Dr  = Density ratio
Ea  = Adiabatic efficiency
Pa  = Atmospheric Pressure (14.7 psia)
Pb  = Boost Pressure (psig)
Pr  = Pressure Ratio
T   = Intake air temp in deg F
Td  = Discharge temp

Here are some numbers as a check:

Adiabatic effic = .68
Atmos Pressure = 14.7 psia
Temperature = 80 F
Boost Pressure = 8 psig

Td = 183.9 F
Dr = 1.295

Multiply unboosted HP by DR to get a rough guesstimate of boosted HP.

Remember this is only a guesstimate!!  It doesn't account for the HP
required to turn the supercharger (-), the superchargers ability to
overcome intake inefficiencies (+), ...

If you want to see the effect of an intercooler just modify Td for the
temp drop across the intercooler and Dr for the pressure drop across the
intercooler.

I don't have any advice about compression.  I'm running a supercharged
'86 Rx7 (roots type supercharger) with stock compression 9.4:1 at 11 psi
of boost on 94 octane fuel, and 15 deg of timing retard.

BTW:  If anyone is interested, I put the equations into a MatLAB script.

-- 
Rob
MailTo:gallant at oasys.dt.navy.mil