Fuel Pressure
 

I was getting crappy times with my fuel pressure set at 48psi.

Can you guys take a look at my sig. and tell me what it should be set at...

I have now set it to 38psi.

Thanks...

Not sure why you have 24# injectors. 38 psi is probably fine. You are the only one who can tell. Make adjustments until it runs it's best, and leave it there.

Take care,
~Chris

Do you think the 24# injectors are too small or do you think the stock 19#r's would would have been just fine???

You would still be well within the 19 # injectors range, but the 24 # injectors are a good choice for you set up. @48psi you were running way rich at WOT.......38psi sounds about right to me.

With all the money you have in your ride you would greatly benifit from a dyno tune. Thats my advice.

Later,

19# injectors are plenty for up to 350 hp in a N/A engine, and from your sig, you don't have 350 hp.

Take care,
~Chris

Thanks for the advice...

I blew a tire out the other day and will be replacing it today...

I can't wait to see if setting the pressure at 38 makes a big difference.

You know about the Dyno tuning, I agree 100% but I'm so lame, the closest Dyno is about 75 miles away and I'm too lazy to make an appointment to get it done but I'm gonna try soon or at least before I go back to the track.

Thanks again...

For you information, i have edelbrock perf RPM head
with E303 cam and the weak cobra intake. My fuel
pressure is at 38 PSI with #30 injectors. I did the fastest
quarter mile at that pressure.

When i had the # 24 injector the car was faster when
the FPR was at its maximum (65-70 PSI).

I think the optimum gas pressure vary a lot from car to
car. The difference could come from different mass air,
computer, compression etc I m just guessing correct me if
i am wrong.

SC

I think you're right... It probably does vary from car to car.

I know that in the past when I had set my pressure to 42, the car seemed slower but I don't if it was just my mind messing with me.

From the info I've gathered from other cars with the somewhat the same mods as mine, I'm hoping that around 38psi will help my sorry ets dramatically.

thanks...

My ET went from 13.30 @ 102 to 12.43 @ 108
when i raised up my fuel pressure from 38 psi to 67
psi with 2 psi increment each time. (# 24 injectors)

When it was at 38 psi i could heard a lot of small "pop"
coming out of the pipes as i was slowing down at the
end of the track. The car was also very inconsistent and
ran better when the engine was hot. I lost 2 thenth at
night compare to what the car did during the day. I think
that it was few symptoms telling me that my car was hungry.

Hope this help,

SC

It does help Thanks...

My idle is kinda ruff with the cam I have and when I set the psi to 38, it sounded alot smoother...

I don't know if that tells you anything or not...

I'll start playing with it tonight as you did by increasing it by two until it feels right starting at 38psi.

I am guessing again, but when the fuel pressure is
varying suddently when adjusting it, the idle could
be a little more rough until the computer recalculate
its A/F ratio table. You should ask this to someone
that has more experience but i could be right.

The idle has nothing to do with the perfomance at
WOT. I would go to the track to adjust everything
or have a dyno session.

SC

Tried to put my $.02 in earlier but my computer crashed. Our setups are very similar. I'm running 21# accel injectors @ 37.5#. I could've got by with 19# but since I was buying new I figured I'd allow the extra margin for improvements. What condition are your injectors? new, used, leaking by? Planning on a dyno run in October with wideband O2. If you want, I could let you know how it turns out with my A/F ratio.

Saw a supercharged 91 on a chassis dyno last week gain 31 ftlb & 17 hp (AT the wheels) just by reducing fuel flow. He didn't have an adjustable regulator and he could only do so much with his FMU. 1st run his A/F ratio went off the scale low (super rich) as soon as they put the pedal down. 2nd run his A/F ratio held where it should for an extra 1200rpm then it slammed off the scale low. 3rd run...I didn't hang around to see since he couldn't make any other adjustments. If you don't have a dyno, then you just have to play the test & tune game.

Check out Accel's site at www.mrgasket.com , they've got some pretty technical info on their injectors. Maybe it'll help you figure out which direction to go.

Cool thanks for the info...

Yeah if you could let me know how your session goes, that would be helpful. I will have hopefully figured it out by then...

I'm gonna try to get some dyno runs in by then too.

Thanks

Sorry dude but either you fuel pressure gauge is messed up. Or you are making 500 HP. with just heads and a cam.

24# injectors @65-70 psi would be way in the HELL too much fuel.

This goes further than this being my opinion. Logicaly, realisticly or any other way you want to look at it there is no way.

DARK_5.0

The car is faster at that pressure. It is anormally
high but i have no way to see what are the signals of the
Sensors and what the computer does with it. I know it
looks like the cars has 500 HP when looking at the pressure
and injectors, however with the computer s reading and
treatment it could only shoot for 350 hp-400hp of gas.

I know an other 5.0 which has a similar pressure and his set
up looks like mine. I think the mass air or the higher compression
could be the problem. Anyway, i have never seen any black smoke
at the pipe (maybe a little smoke when i shift it) and the car is
very consistent at the track.

If anyone could help me with this or tell me what could be the problem
feel free to leave your comments.

_______________________________________________

BEST 0-60 FEET 1.633 sec
BEST 1/8 MILE 7.820 sec
BEST MPH 88.41 MPH
BEST 1/4 MILE 12.283 sec
BEST MPH 108.95 MPH

I cant argue with your results:) ........

Nice times,

This is an interesting thread. The topic has been covered quite a bit in the past, but it is one that seems to elude everyone.
I too am running 19lb injectors, with heads/cam/intake car. The analyzer says i too should have FP at 67psi, currently and dynoed with 38psi (roughly 300rwhp) untuned and with no adj on the dyno.
I am going to the track this weekend and will post results at 67psi.
Best to date is 13.45@110mph with 2.1 60'.
Any logic to such high fuel pressure????? Any damage??
thanks

When the pressure was at 38 psi (# 24 injectors) the
car was very slow. When i was flooring at 2000 RPM
i could notice a kind of flute noise in the pipes like if
the explosion has never occur in a cylinder.

Also, as i said, i could easely notice a lot of "pop"
when releasing the gas pedal at the end of the 1/4 mile.

Now the car is running fine with 38 psi and #30 injectors.
The spark plugs are fine, no black smoke, never broke, good ET,
no strange noise only strange fuel set up.

Is there someone who can explain that?

SC

By the way,Hyper92GT i still have my #24 injector and vortech
MAF tube......... interested? HEHEHE :D :D :D :D

Did you really pick up 6mph with just a FP change,
nothing, absolutely nothing else. Let me know.

I am S/C the car over the winter, so if you have 36lbs I'll buy those :)

Again anyone explain.

What kind of tires were you running for that pass?? With that 60' & MPH, I'm guessing you had daily driver street tires. Please prove me right.

Thanks.

I'm currently n/a (gonna be blown or juiced in about 6 months)running 30# injectors w/ Edelbrock Performer heads, TFS track heat intake, 190 # intank pump, etc. I'm adding a AFPR in a few weeks ad want to know what fuel pressure I should put the car at prior to dyno tuning it (just a reasonable # until it gets tuned).....so I can get to the shop. :D

Yes about 6 more mph in the same day at the track...
i did over 12 run to adjust it. I was adjusting it
even during the elimination (bad idea)

SC

I was thinking the same thing the 110 mph trap speed is good for low 12's:confused.

Even if he was on street tires hit ET should have been better with a 2.1 60ft.

Very odd.

If 38 doesn't work for me, I'm gonna try and raise it up to 60 and see what happens...

I know when I lowered it from 48 to 42, it seemed much slower.

Please let us know the results from the track...

Yes those runs were on street tires BFG KD's very stiff sidewall and the track prep sucked.

60' 2.09
1/8 8.86
mph 80.80
1/4 13.45
mph 110.37mph

I will post my results on Sat. Going Friday night (weather permitting). I expect mph to be down 1-2 due to weight of roll-cage, but et up with new rear suspension (control arms, adj shocks).

Mike

Hyper - going from 80 mph in the 1/8 to 110 in the 1/4 is very impressive. You must be making some serious power. I'm curious, what mods do you have?

With my old 302 heads/cam/intake combo, I would usually go 83 or so in the 1/8 and then 105 or so in the 1/4 - or 22 mph increase. You've got a 30 mph increase!

E

That looks like the timeslip of someone spraying at the end.

Picking up 30 mph from the 1/8th to the end is unheard of on a car that is only trapping 110.

This whole damn thread is weird:D

Eric
I wish I could explain it , the car just hauls in 3rd and 4th.
Ususally i trap 83-85mph depending on traction and run 108-110mph consistantly.

I think my car needs more fuel here are some details:
306 sqr. decked block
TRW forged pistions 9:1
Crane cam 270/276 .533/.544
TFS heads, fully ported, manley values hardened rods, dual spring valve
Crane rollers 1:60
70MM T/B
Edlebrock port matched upper/lower
75mm mass air pro-M
pullies/MARCH Ram Air kit
BBK long tubes 1 5/8 with Flowmasters
3;73 gears suspension, cage etc.
MSD 6A, MSD Blaster, 9MM wires etc.
AFPR, 190L/hr pump
Sure some other stuff but you get the idea.

i get only 20.5 mph on the last 1/8 mile...
because of my gear (3.55). Typical mph
gain is around 22 to 24 for a mustang with
3.73 / 4.10 gear (head/intake/cam combo)

If you get 30 mph, well that means your on
street tire, spending more time accelerating
on the last 1/8 because of a lack of traction
on the first 1/8 mile.

SC

I'm running a 3.55 gear and got ~22 mph increase on the big end with my old combo.

I agree with this to a point. But, I don't think that if I switched to street tires I would see 8 mph increase. I understand the whole slingshot theory on street tires, but it has its limits.

E

Okay guys...

I finally was able to drive my car with the pressure set at 38psi and it ran like crap. When I would rev the engine in neutral, it would backfire every so often. There was no power at WOT. Then when I did what (eatsgmcar) did and set it at 60psi, it ran great. There seemed to be much more power at WOT to the point that when power shifting, the car would get a little squirly when shifting from 1st to 2nd. My car has an aode and usually at the most before, the tires would just chirp but not at 60psi!!!

Talk about weird... I'm gonna have to reverify this by going to the track some time soon...

Thanks,

60# sure seems high. But I guess I'll be giving it a try if I ever get my car back from Moroso.

I'm new to the power shifting game. Never wanted to do it cause of the rebuild cost. But since I started rebuilding my own, I practice the power shift every chance I get. I'm on my 3rd set of 2nd & 3rd synchros in as many months, but they only cost $12 each. Then figure 3-4 hrs putting them in. Much cheaper than any tranny shop I've ever seen.

Anyway, my question was: How do you power shift an automatic? I thought you could hold your foot to the floor and let the tranny do the rest. I'm not very familiar with ATs. Actually, I don't know anything about ATs other than they give you a lot more consistency than a MT.

Thanks.

I'm not sure if it's really called power shifting but it seems to give me faster times at the track...

I manually shift my aode from with o/d off at around 5800 from 1st-2nd-d. I have a Transgo shift kit in the tranny but it doesn't always shift fast enough on its own...

Some other guys with aods told me that shifting manually would give me faster times...

Now my times aren't that fast but I've never really had my car running in top condition yet...

Moponys: I run the same heads and cam but with the Cobra intake. My best setting was at 18 degrees timing /45 psi. I initially set the car up at 14 degrees/39 psi but it was sluggish. The additonal timing and fuel pressure was worth 3 tenths and 3 mph at the drag strip with the same 60 ft and density altitude.


Pkrwud: Your incorrect about the horsepower assumption. Actually the combo is worth more than 350 considering he has the TFS street intake which is better than the Cobra. I could trap 108 mph in my 3500 pound conv. with this set up.

If you say so. I'm not seeing it. Got a dyno sheet?