# [V8] V8 fuel pressure, injectors and such.....

DasWolfen at aol.com DasWolfen at aol.com
Sun Mar 7 03:58:33 EST 2004

``` The Hp figures were computed from weight vs trap speed and corrected for
altitude and temp.

The 370 results for John J's 93 had me scratching my head for a while but I
think I found the answers. One is the fuel pressure the other in the formula
used to calculate required fuel.

Standard injector ratings are based on flow at 3 bar or 43.5 psi above
manifold air pressure. PT and ABH V8's run a fuel pressure of 60psi or 4.08 bar
above manifold air pressure. The result is an increased flow of roughly 18% above
rated capacity.

The formula for required fuel is: Brake Specific Fuel Consumption x
Horsepower = lbs/hr of fuel. BSFC is usually plugged in as .45 for a street engine. I
submit that PT and ABH's are not the average street engine. V8 Audis have
higher compression, better cylinder head flow, and vastly better exhaust flow than
the norm. Without spending big money for dyno testing its impossible to prove
but my observations lead me to beleive the BSFC for John's cammed, ported,
and Scorpion equipped 93 is closer to .42

The car is running Bosch injector 150 424, 173cc

Starting with fuel flow capacity: 173 x 1.18 = 204.14cc or 19.44 lbs/hr

Moving to required fuel.....

.42 x 370 = 155.4 / 8 = 19.42 lbs/hr required

19.42 required 19.44 available

As you can see 370 hp is attainable (barely) with a stock injector if my
guestimate for BSFC is correct. Admittedly thats running right at saturation and
probably explains why trap speeds fall off after 2 runs. Adding a few lbs of
fuel pressure would help but the car is a daily commuter and rarely ever sees
full throttle for more than a second or two. But.....

There's a heavily modded 91 5 spd sitting in front of the shop.... with a
4.2 bolted in tight... just waiting on a set of cams to appear...... >=0)

```