The bigger injector, less fuel psi theory?

[Coupe50h]

Well we had a discussion on this, sort of, in another thread, jeff chambers I believe said "if the maf is calibrated to the injector, run 40 psi vac off" (but who would run a maf that wasnt calibrated?)

Well like many of other stangers have done, I went to the track to test this out, I did find out my car ran it's best time at 39 psi, weather was humid as he11, I only let my car cool off about 10 minutes between each run no ice.
I ran 3 times:
1st pass: fuel 40 psi, I bogged it not expecting the track to hook like it did, made a 12.96 106.33 the 60 ft was sad, but i was looking at mph.

2nd pass: I thought id raise the fuel up to 42 psi, I ran a 12.80 at 105.?? I was dissapointed since i usually go 107+

3rd pass: i went down to 39 psi, 60 ft'd in the mid 1.7 and went 12.75 @ 106.71 (damn humidity kept my mph down, but i was happier with that.

my conclusion, I think i could have went faster with a little less fuel, but jeff was right, I found anything over 40 psi hurt me, it actually made my car hesitate on the topend, think i was detonating on the 2nd run.

Take it easy.

[lx mike]

When i did my heads and cam swap i also got a set of 24 lb injectors and had the tube for the maf to calibrate it. we got it running and set the fp at a tad over 40 psi

When i went to the dyno it was way rich (11.5) and it ended up being that 38-39 psi is where it got the a/f to around 12.8-13 range.

[Dark_5.0]

My car runs great with the fuel pressure @38psi with my 24# injectors.

I tried 36# injectors @ 38psi since I wanted to eventually boost it and the injectors were a great deal. I ordered the sample tube for my mass air sensor and it was extremely rich. So back to the 24#ers I went.

[88workcar]

Rules to live by.

1. The boss is always right
2. If the boss is wrong, refer back to rule #1.

In my eyes, Jeff is the "BOSS"

I just went mass air, I had to try also. Jeff was right. But it is no use to me anymore, the turbo will blow through a carb. So all the fuelie stuff will be sold.

[fiveohpatrol]

another reason your car was running worse with more fuel pressure was the weather. When it is humid out the oxygen in the air is less dense and throwing the same amount (or in your case, more) fuel at it will not be able to burn as efficiently as it would in better conditions. In those conditions I bet you could have picked up some more mph by dropping the pressure another 1-2 psi.

good luck

[Coupe50h]

Yea, I actually had a guy tell me to drop the pressure that night, he said not to run "fat" fuel pressure in the humidity.....

[Scrapla]

What can you do to a stock fpr is anything to adjust fuel pressure. I have a stock fuel system on my 347 except for my 24#ers and mass air calibrated for them.

[fiveohpatrol]

spend the money on a afpr and bigger pump. might wanna up the injectors too if you have a decent HCI setup on there too

[~The Jester~]

Just a thought, whenever I do any "testing" at the track like that I always use the "A-B-B-A" method, and only change ONE thing at a time.

In your case it'd go something like this:
1st pass, "A" setup. 40 psi fuel pressure.
2nd pass, "B" setup. 42 psi fuel pressure.
3rd pass, "B" setup. 43 psi fuel pressure.
4th pass, "A" setup. go back to your original settings, 40 psi.

Sounds like a lot of work, but you'll end up with more accurate data to work with. The more or less eliminates the bad hook/good hook type stuff. "Was that pass better because of the 42 psi, or did I just get ahold of the track better?"

MOST of the time at the track, this is not feezable, time doesn't permit. But when/if you can, this is the way to go for testing.

Just my $.02!

And yes, Jeff and Andy are the BOSS! LOL

[~The Jester~]

On a side note, being a professional firefighter, I know a thing or two about hydraulics.

So, YES! Given a "standard" pump pressure, the bigger the nozzle, the less pressure at the nozzle. It's all physics bro.

PSI and VOLUME are completely different things. I can give you 197,002 PSI fuel pressure in a 1/8" line, is the VOLUME going to be there? Helllz no. Conversely, I can also give you (literally) 6,000 GPM in a 5" line. Pressure? NONE. Prolly 5 or 6 PSI at best. Your injectors depend on the "pressure" to correctly atomize the fuel, but your motor depends on the VOLUME to make the ponies.

"Brake Specific Fuel Consumption". Live it, Learn it, Love it! Remember that, look it up when you get a chance. Basically it takes "X" amount of fuel to produce "Y" amount of horsepower. PERIOD. It's all about Kinetic energy, or "STORED" energy. That one gallon of fuel can physically only make "X" horespower, no matter WHAT engine you run it throuh. You can have the best of the best heads, intake, cam, etc etc. But if the FUEL isn't there, it's not gonna make the numbers. Bottom line.

At first it's confusing, but after you get into it, it all sorta falls in line and makes sense.

What we're shooting for here is "X" GPM at "Y" PSI. The X is what our motor NEEEEEDS to make the ponies, the "Y" is what the fuel system has to deliver to make our injectors and such work properly. It's a combination of the 2 that makes the whole darn thing work.

Daaaaam! I just read that, and confused myself! LOL I'm not 100% sure on alot of things, but this I AM. Ask Jeff, Andy, etc etc, they'll agree with me here. Or, at least I hope they do!

[Dark_5.0]

Originally Posted by ~The Jester~

On a side note, being a professional firefighter, I know a thing or two about hydraulics.

So, YES! Given a "standard" pump pressure, the bigger the nozzle, the less pressure at the nozzle. It's all physics bro.

PSI and VOLUME are completely different things. I can give you 197,002 PSI fuel pressure in a 1/8" line, is the VOLUME going to be there? Helllz no. Conversely, I can also give you (literally) 6,000 GPM in a 5" line. Pressure? NONE. Prolly 5 or 6 PSI at best. Your injectors depend on the "pressure" to correctly atomize the fuel, but your motor depends on the VOLUME to make the ponies.

"Brake Specific Fuel Consumption". Live it, Learn it, Love it! Remember that, look it up when you get a chance. Basically it takes "X" amount of fuel to produce "Y" amount of horsepower. PERIOD. You can have the best of the best heads, intake, cam, etc etc. But if the FUEL isn't there, it's not gonna make the numbers. Bottom line.

At first it's confusing, but after you get into it, it all sorta falls in line and makes sense.

What we're shooting for here is "X" GPM at "Y" PSI. The X is what our motor NEEEEEDS to make the ponies, the "Y" is what the fuel system has to deliver to make our injectors and such work properly. It's a combination of the 2 that makes the whole darn thing work.

Daaaaam! I just read that, and confused myself! LOL I'm not 100% sure on alot of things, but this I AM. Ask Jeff, Andy, etc etc, they'll agree with me here. Or, at least I hope they do!

Pressure and volume are one thing but we are not talking about a steady stream here. The eu has the ability to adjust the pulse width as well.

[~The Jester~]

Originally Posted by Dark_5.0

Pressure and volume are one thing but we are not talking about a steady stream here. The eu has the ability to adjust the pulse width as well.

Yep! You're right! I'll be the first to admit that I know Jack about fuel injection, but fluid dynamics, I DO know about.

Given the stated fact that the ECU can adjust pulse width ie "duration" of the fuel pulse, if the pressure and/or voume isn't there, then we're not living up to our potential. Right?

Picture it this way, I have 1 bazillion PSI flowing though a 1/32" line, and my ECU tells that injector to hold open for so-and-so milliseconds. Seeing as how that there is no VOLUME behind that 1 bazillion PSI, the fuel pulse will "fizzle", or die out. I understand we're talking milli-seconds here, but with that in mind, wouldn't it be better to have a full "fuel signal" throughout the injector pulse? Think about it bro!

A constant AMPLE fuel supply is where it's at. Carb or fuel injected, doesn't matter. A CONSTANT AMPLE fuel supply! Return, return, return. Send TOO much up front, let the motor take what it wants, and send the rest back to the tank. Trick here is to let the motor have "priority".

Volume DOES NOT equal pressure! But BOTH are needed for a properly operating fuel system. I know what you're saying, and it makes sense. But THINK about it for a few minutes.

[Coupe50h]

Originally Posted by ~The Jester~

"Was that pass better because of the 42 psi, or did I just get ahold of the track better?"

MOST of the time at the track, this is not feezable, time doesn't permit. But when/if you can, this is the way to go for testing.

Just my $.02!

And yes, Jeff and Andy are the BOSS! LOL

Thats why I said "I was looking at mph", the 60' really doesnt affect mph unless you really bogg or spin halfway down the track.

The "x" amount of fuel to make "Y" amount of power can be a good way too look at it, volume that is.
But pressure seems to be a different story, Look at it this way, A 700 hp turbo stang would need some serious fuel volume right? would a 700 hp naturally aspirated bigblock need the same volume, even though it is not forced inducted?
This thread has alot of usefull replies......so thanx alot.....

[~The Jester~]

Originally Posted by Coupe50h

The "x" amount of fuel to make "Y" amount of power can be a good way too look at it, volume that is.
But pressure seems to be a different story, Look at it this way, A 700 hp turbo stang would need some serious fuel volume right? would a 700 hp naturally aspirated bigblock need the same volume, even though it is not forced inducted?
This thread has alot of usefull replies......so thanx alot.....

YEP! It sure would! There is only "so much" kinetic energy stored in that one gallon of fuel. So in order to realize the 700 horse, be it N/A, or blown, turboed, blown AND turboed, Nitroused/Turboed/Blown whatever. To make 700 Horse, you need "X" amount of fuel, and it doesn't matter what pressure it's at. But you have to give the engine what it NEEDS. At this point it's all about the volume. Where fuel PRESSURE comes into play is the injectors, carb floats, friction loss in the fuel line, friction loss in the pump, restriction in the filter(s) etc etc. It's all physics.

I don't mean to go off on a rant, but it's looks like I'm gonna! LMAO

There was a guy at a local car show last summer that had a Dodge Dakota with TWO blowers on it. Looked really nice, and he made it a point to drive past us every few hours to show off his "horsepower". He had a sign in front of his "pit" spot stating that the truck made 1,300 HP. So, being the vindictive person I am, took it upon myself and got a collection of ching ($$$) from other participants to put this truck on the portable dyno that also happened to be at the show.

I walked over to this guys pit, and flat out told him that there was NOOOO way in hell that little Mopar was making 1300 Horse. Conversation went something like this:

"Nice Truck!"
"Thanks!"
"1300 Horse is a little high though, don't you think?"
"Nope, engine builder said so."
"There's a dyno right over there, I have $100 in my pocket to pay for the dyno runs that says you won't make the number. And another $100 for YOU if you prove me wrong."
"You seem pretty sure of yourself, but I'm not gonna beat on my truck to prove you wrong."
"Brake specific fuel consumption."
"What the hell does that mean?"
"That means that you can't feed FOUR 450 CFM carbs with a -6 fuel line, and expect to make 1,300 horsepower. Guys I know ditch the -6 line when they get above 450 ponies."
"You obviously don't know what you're talking about."
"The dyno is right over there, I'M paying for it. Prove me wrong."
"I'm not gonna beat on my truck to prove YOU wrong."
"OK, no prob. I understand that your chicken, and in your mind your pretty sure it won't make the numbers. No prob at all, but quit "piping" us every hour, cuz we CAN make the numbers, and we're not afraid to prove it."
"What the hell do you drive?"
"580 horse Mustang."
"That's less than HALF of the horses I make!"
"Yes sir, it is. ACCORDING TO YOU. I want to see your truck on the dyno, I have a dyno sheet that PROVES my car made 580 horse, all you have is a sign."

BLAH BLAH BLAH, you get the idea. Bottom line is that there is no way in hell you can make 1,300 horsepower with a -6AN line. THIS is about volume, that's what I'm trying to teach you guys. One gallon of fuel will make "X" horsepower in a "perfect world". PERIOD. The laws of physics say so.

[~The Jester~]

Just some links for yinz guys to read when ya get a minute.

http://www.answers.com/topic/brake-s...el-consumption

http://www.carcraft.com/techarticles/986/

THIS is the one!
http://productengr.com/

Absolutely NOT trying to be a bonehead here, just passin along what I've learned.

[fiveohpatrol]

there's no such thing as stored kinetic energy. KE is the energy of a body in motion

[~The Jester~]

Originally Posted by fiveohpatrol

there's no such thing as stored kinetic energy. KE is the energy of a body in motion

You are 100% right, energy in motion is Kinetic Energy. "Stored" Energey is "Potential Energy". My bad.