[V8] Re: V8 fuel pressure, injectors and such.....

[J örgen Karlsson]

Hi,

I think that we are getting somewhere. The 3.6 electronics does not seem to panic over the 'off the charts' flow it see when used to control a 4.2 litre. This is very good information. It does not seem to panic because of the larger injectors either, which is even better.

By porting the mass air sensor section of the intake manifold a bit (10-15% larger bypass area should be safe) and fitting 20-25% larger injectors (or increasing the fuel pressure a bit) the engine management should be able to support well over 400hp.

I think that your BSFC estimates can be correct but I think that top end power will be much stronger with a richer mixture.

I disassembled and examined a PT manifold today, I wish that the ABZ manifold was built with the same tolerances and attention to the surface finish:( The PT mainifold is a work of art. If the intake gaskets weren't so damned expensive I would have tried it on the ABZ.

Jörgen Karlsson
Audi80 4.2Q



-----Original Message-----
From: DasWolfen at aol.com
To: jorgen.m.karlsson at home.se, CoultL at aol.com
Date: Sun, 7 Mar 2004 03:58:27 EST
Subject: V8 fuel pressure, injectors and such.....

 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)