BSFC and injector sizing

[Firechaser]

We had a car last week on the Dyno that Hartline was live tuning hit 94% DC on 120/lb injectors....he threw down right around 600 at the wheels at around 28lbs on a 67 turbo. A little tidbit of real world info

 

[krom]

Did a dyno today with 2 walbro pumps, stock lines, fuel pressure at 60 with both pumps always on. At 21 lbs of boost had a duty cycle of 58% with 120 lb injectors, 510 hp at 5600 rpm. Was not trying for hp numbers just to see if the tune was safe and if the pumps and injectors were adequate.

 

[BEATAV8]

Can someone explain why a turbo engine requires more fuel pr hp than a NA engine........that would mean a turbo engine is less efficient than a NA engine?? Here is some data from a dyno manufacturer.

http://www.land-and-sea.com/dyno-tech-talk/using_bsfc.htm

.........................................................................................Engine @ 1,000 @ Peak TQ@ Peak HP
Type RPM Torque Hp 4-stroke (low compression, carburetor) .........0.62 0.47 0.52
4-stroke (high compression, carburetor) ..........................................0.60 0.42 0.47
4-stroke (high compression, closed loop) ........................................0.52 0.35 0.42
4-stroke (supercharged, carburetor)............................................... 0.75 0.50 0.55
4-stroke (turbocharged, closed loop).............................................. 0.57 0.45 0.50
2-stroke (low compression, carburetor) ..........................................0.85 0.55 0.60
2-stroke (high compression, carburetor) 0.80 0.50 0.55
Diesel 4-stroke 0.35 0.25 0.30
Diesel 2-stroke 0.40 0.29 0.34

Seems logical, turbo engine of equivalent displacement has increased cylinder pressures and cylinder temperatures requiring richer mixtures and less spark advance. True for full load operation where the turbo engine can make considerably more power than the N/A counterpart.

At part load operation the turbo engine will win the efficiency comparison though. Thermodynamically the turbo engine is recovering energy from the exhaust so it will win.