Speed density fuel pressure

M

mustang50920

New Member

Mar 22, 2010

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Mar 22, 2010

#1

• Mar 22, 2010

• #1

Hey all new to sight my first technical post. I have and 87 that is still speed density. My modifictions are gt-40 upper and lower 65mm throttle body cold air some cheap msd ignition coil and cap ford racing wires long tube headers bbk high flow cats flowmasters, 24lb injectors i belive a 155 fuel pump not sure was on car when i bought it umm smog and a/c delete and the timing set about 14/15. i just ordered a bbk fuel pressure regulator and was wondering what the ideal fuel pressure would be?

 

Kdubslugga

Active Member

Jun 7, 2003

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Akron, OH

Mar 22, 2010

#2

• Mar 22, 2010

• #2

Every car will be different, the only benefit an AFPR will have is if you have it tuned on the dyno. I wouldnt want to go below 42 psi until you have it dynoed

 

M

mustang50920

New Member

Mar 22, 2010

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Mar 22, 2010

#3

• Mar 22, 2010

• #3

idk if this is true but i have heard that with speed density that the computer does not adjust fuel pressure to modifications as a mass air car would do so i ordered this and was curious to get the right mixture since my car is running lean as of now

 

Mustang5L5

That is…until I whipped out my Bissell

Mod Dude

Feb 18, 2001

43,179

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224

Massachusetts

Mar 22, 2010

#4

• Mar 22, 2010

• #4

Might want to take the 24's off a speed density car and put the 19's back on. Having those on there without any sort of tune or chip can cause headaches. With your mod level, you don't need them anyway.


You are correct though. 24's, adjustable FPR and larger flowing fuel pump could potentially cause tuning issues with speed density. The car can compensate slightly by the O2's, but over 3500RPM you'll more than likely run a little rich.

Convert to MA, otherwise, take the 24's off. As for what FP to use...base is 39 psi with the vac line off. Use that for a baseline but without a dyno, you have no idea if raising or lowering it is giving you a better Aif/fuel ratio.

 

M

mustang50920

New Member

Mar 22, 2010

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Mar 22, 2010

#5

• Mar 22, 2010

• #5

i had 19's on it but they went bad and i had the 24s laying around with a mass air meter and a9l computer. unfortuntly my a9l got flooded out when my garage flooded one night so i am still speed density until i find a new computer. Is running the 24's going to cause that much of an issue?? what kind of issues?

 

Mustang5L5

That is…until I whipped out my Bissell

Mod Dude

Feb 18, 2001

43,179

17,884

224

Massachusetts

Mar 22, 2010

#6

• Mar 22, 2010

• #6

potentiall running rich above 3500RPM. Do you notice black smoke behind you when you go WOT?

If the car is running fine, don't worry about it until you convert to MA.

But to answer your question, set the fuel pressure to 39 psi with the vac line off and capped.

 

liljoe07

5 Year Member

Feb 18, 2009

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Cartersville,Ga

Mar 22, 2010

#7

• Mar 22, 2010

• #7

It will cause it to run rich, as the ECM is now operating the 24's as it would the 19's. The O2 readings will pick this up and try to correct the pulse width, but it may be out of the ECMs capability to trim back the fuel that much.

 

S

slow87GT

Founding Member

Jun 5, 2000

162

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Tonawanda NY

Mar 22, 2010

#8

• Mar 22, 2010

• #8

24's are fine with SD

with your combo I would back the fuel psi down to 35 or 36