This is topic suggested fuel pressure setting in forum Tech Talk at Northern California Ford Owners  .


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Posted by hidnn.o.s. (Member # 1219) on :
 
I've heard 39-40psi from some friends. Just wanted to see what everyone else suggests or has had experience with?

My setup is a 306, cobra manifold, stock nicely ported heads, crane 2030 cam, 24 pound injectors and all the little boltons like pulleys/maf, etc.

Car is an aod with 410 gears.
 
Posted by shade- (Member # 298) on :
 
sounds a wee bit high for stock heads and 24's, that's the factory setting for 19'ers (with vac-removed of course). probably a good place to start though. richer is always safer.
 
Posted by Black94 5.0 (Member # 655) on :
 
You don't want to go too low with 24#'s and stock heads...Atomization should become a problem at around 32psi fuel pressure...

What's your timming at?....I'd probably run 39-40 with 14* of timming...Every car is different, you just have to "test n tune"... [burnout]
 
Posted by mtbaughs (Member # 4052) on :
 
40 psi is fine with ported heads and a cam
 
Posted by Fostang (Member # 3752) on :
 
Are 24 lb injectors even required for his set up?

What would be the recomended for 19lb injectors then? 44?
 
Posted by hidnn.o.s. (Member # 1219) on :
 
The heads are ported nicely. Flow far better than stock and my timing is at 12-13 degrees.
 
Posted by 9lbpony (Member # 3510) on :
 
assuming the MAF or computer is set up for 24# injectors, running anything other then "stock" fuel pressure is probably a bad idea. The injector slopes are based on the behavior of those injectors at stock pressure. If you lower the pressure you'll only lean out the WOT curve at loads the car has never seen in closed loop.

i.e. if it's lean at cruise, the car will add fuel (pulsewidth) to get the A/F ratio back to 14.7:1. Let's say this is occuring at 4ms of pulsewidth and that it had to add 10%. Anytime the car is at 4ms pulsewidth (open or closed loop) the car will add 10% more fuel (long term fuel trim). Now when you hit a higher load, say 8ms of pulsewidth and the car has no closed loop data at 8ms of pulsewidth because it never hit that high a load in closed loop, it won't have any data to apply to the behavior so the car would likely be lean if you were running a lower fuel pressure. The MAF would report the airflow, the computer would calculate the pulsewidth based on injector behavior (which would be based on stock pressure) and the injector would deliver less fuel then the computer thought it would due to the lower pressure. The computer wouldn't "learn around" this behavior because the car would be at open loop (WOT)

So the short answer is that unless you are computer tuning the car, you are going to get better drivability results at the stock fuel pressure. While the injector size may or may not be "big" for your combo, my car runs just fine (and burns damn clean) at low loads with 42# injectors at the stock 39psi.

Man, that was a longer answer then I orignially intended.

[ April 19, 2004, 03:12 PM: Message edited by: 9lbpony ]
 
Posted by Black94 5.0 (Member # 655) on :
 
9lbpony~The computer still thinks it has stock flow rated heads and 10 degrees timming, not to mention that the fuel curves and load tables are probably tricked by a recalibrated maf that the computer still thinks is calibrated for the stock 19# injectors...

I understand what you mean, but I think a fuel pressure regualtor can come in handy if you know what your doing and don't go too lean....

Basically, unless you have a custom chip, turning the distributor and bumping up the timming and adjusting the AFPR and adding a few pounds of fuel pressure will help especially when you increase the air flow, like ported heads and or an intake manifold... [patriot]
 
Posted by hidnn.o.s. (Member # 1219) on :
 
the mass air was obviously calibrated for the injectors. It is a 75mm Pro M bullet.

Too much injector for the setup? STOCK 93 cobras' have pretty much the same setup and have 24 pounders [Confused]

So you guys suggest sticking with 40psi as well [Confused]

Thanks for all the input [patriot]
 
Posted by Fostang (Member # 3752) on :
 
Basicly what I was trying to ask is if it was required to upgrade to 24's or could you manage with 19's.
 
Posted by five-0 (Member # 3513) on :
 
what do you guys know about a speed density system? What should my timing be? How many PSI should my regulater be at? And spark plug gap? I have an 87 5.0 with no mass air. Some mods: performer RPM intake, 70mm throttle body, bbk shortie headers, no cats, and flows, MSD 6AL, pullys, 255 fuel pump, 4:10 gears, 100 shot, stock heads cam and injectors, fuel pressure regulater [Confused] [Confused] [Confused] [Confused] [Confused] [Confused] [Confused] [Confused]
 




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