H0SS302

The hardest part is breaking the motor down enough to be able to work. If you degree the cams(which you should) AND put in new valve springs(which you also should do) the complexity goes from removing and tightening bolt to a little more in depth processes. This is nothing a shade tree mechanic can not do though. All you need is a solid how to and a free weekend.

PDowdy1

okay sounds like a plan its gonna take a day or two

boduke0220

well **** you guys!!!


lol so around 300 hp our stock injectors start getting maxed out?

H0SS302

Pretty much yea. As you add more air into the motor the injectors need to keep up to keep your desired a/f ratio. The pulsewidth of the injectors(the length of time the injector stays open during a cycle) increases to the point at which they are constantly spraying fuel. The pulsewidth is a value used to calculate duty cycle: Duty cycle= Pulsewidth/time between ignition events

You really dont want your duty cycle to be higher than about 80%. You can run em higher, but its asking a lot of them. At 300hp with stock 19lb/h injectors, your at that point if not pushing it.

...kind of went off on a tangent there.. but I got a new book and I had to use my newfound knowledge somehow.

Hangwire

Something that should be cleared up is....If you have a 99-04 GT then you have 21lb injectors, not 19. This may not be true for the early 99-04s but I know this for an absolute fact for the 03+s because mine has 21lb injectors)

As a rule, your PCM will run your injectors until 90% duty and then it wont push them anymore. Given this once you pass 263 HP your 19 pound injectors will be maxed out.

Fuel Injection Duty Cycle

MAX HP=[19*.964] * .9/.5 * 8 = 263.7504

19=lb/h of injectors

.964=40 is .964% of 43 (Since this formula is based on an assumed 43 PSI and Ford uses 40 PSI of fuel pressure, we have to simply take .964 % of what ford claims our injectors can flow. This essentially means that though Ford calls these 19 pound injectors, they are officially 18.316 pound injectors outside of the Ford world)

.9=duty cycle in % (We are calculating what the 19 pound injectors can handle at 90% duty cycle so we use .9. If we wanted 80% we would use .8 and so on)

.5=Brake Specific Fuel Consumption ((This gets into technicalities I dont quite fully understand but as a general rule this goes as the following: (.5=N/A) (.6=5-8 PSI) (.62-.65=8-10 PSI) (.7=10-12 PSI) ))

8=Number of cylinders on your engine

So for example....if we wanted to know what 36lb injectors would support at 80% cycle on an N/A V8 we would do the following:
[36 * .964] * .8/.5 * 8= 444 HP

Lets say we wanted to know what 42lb injectors would support at 70% duty cycle on a 5-8 PSI V8:
[42 * .964] * .7/.6 * 8= 378 HP

Clearly there are many many variables in real life so this is a general guideline. Hope this helps, I can clear things up more if its too confusing.

H0SS302

LOL do you have Greg Banish's book also? I was going to write down all the formulas for calculating all the fuel system stuff but stopped at duty cycle. LOL

and yea its true, 03+ come with 21lb/h. my 01 has 19lb/hr, so I used my car as an example. To be honest I didnt even look at his yr model, probobly should have.

Hangwire

Nope, learned this from Cliffyk and wrote it down

Butttt I am interested in this book now....how much does it cost? Sounds like it provides useful information as opposed to Haynes.

H0SS302

ROFL Cliff got it from the book I think too!

Advanced Engine tuning-Greg Banish

its like 20 buck off amazon

PDowdy1

yeah ive got an 03 so i have he 21lb injectors.
thanks alot everyone it have been a great help.
Any recommendations on the 4.68 ratio gears?
thats what im looking at gettin and i was wondering if anyone had the reviews

Hangwire

Ok even for a car that sits overnight on the strip and never physically leaves the strip 4.68's are excessive. 4.30 at most or i'll cry.