Stock Fuel pressure

TMASTER · 06-16-2003, 10:18 PM

What is the stock fuel pressure sopposed to read on the guage with the vaccum line off ? mines says 45psi with vac line off with the stock regulator. 38 with vac on. ??? Seeing if my guage reading wrong.

Mountain Main · 06-16-2003, 11:30 PM

What I learned from Jimberg is that you can ground the STO. With the KOEO and the fuel pump will prime it's self. The STO is self test connector that you hook up for diagonostics. If you put the connectors clips to the bottom. The connection is all the way to the left. I perfer this method. Your gauge should read with a stock regulator at 39 to 40 PSI.

TMASTER · 06-16-2003, 11:38 PM

I was told mine should be set at 41psi with the vaccum line off. With all the modifcations I have done.
I have a adjustable regulator now, and thats not a problem, but why would i want less pressure than the stock pressure?
I have a 190lph pump, 19lb injectors, Timming at 15 degrees. Did the fuel pump make the pressure higher?

jimberg · 06-17-2003, 12:26 AM

You really don't want less pressure than stock pressure. What you set it to depends on how much horsepower your engine can put out and what size injectors you have. The general rule of thumb is that you need .5 lbs of fuel per hour for each HP. 19 lb injectors will deliver 19 lbs/hour at 39psi. This means that each injector could support up to 38 HP. Multiply that by 8 and you get 304 HP. This is obviously just a rough estimate since the .5 is just an average. You really need to put it on a dyno with a wideband O2 sensor to see what your actual fuel requirements are.

If you want to calculate the rating of your fuel injector at a higher fuel pressure, you use this formula:

Sqrt( New Fuel Pressure/ 39 ) * injector rating

If you want to figure out what fuel pressure to run to meet a specific rating, you use this formula:

(39 * target injector size ^ 2) / injector rating ^ 2

Injector rating would be 19 in your case.

TMASTER · 06-17-2003, 12:59 AM

hmm complicated

so in theory the stock regulator and injectors should be good for 304 hp at the flywheel. Ill have to take it into the dyno, thats the best way to make it set right. Thanks

06-16-2003, 10:18 PM	#1
TMASTER Registered Member Join Date: Sep 2002 Location: TEXAS Posts: 161	Stock Fuel pressure What is the stock fuel pressure sopposed to read on the guage with the vaccum line off ? mines says 45psi with vac line off with the stock regulator. 38 with vac on. ??? Seeing if my guage reading wrong.

06-16-2003, 11:30 PM	#2
Mountain Main Registered Member Join Date: Feb 2003 Location: Minturn, CO 81645 Posts: 109	The best way to find fuel pressure What I learned from Jimberg is that you can ground the STO. With the KOEO and the fuel pump will prime it's self. The STO is self test connector that you hook up for diagonostics. If you put the connectors clips to the bottom. The connection is all the way to the left. I perfer this method. Your gauge should read with a stock regulator at 39 to 40 PSI.

06-16-2003, 11:38 PM	#3
TMASTER Registered Member Join Date: Sep 2002 Location: TEXAS Posts: 161	hmmm I was told mine should be set at 41psi with the vaccum line off. With all the modifcations I have done. I have a adjustable regulator now, and thats not a problem, but why would i want less pressure than the stock pressure? I have a 190lph pump, 19lb injectors, Timming at 15 degrees. Did the fuel pump make the pressure higher?

06-17-2003, 12:26 AM	#4
jimberg Registered Member Join Date: Oct 1998 Location: Rogers, MN Posts: 2,089	You really don't want less pressure than stock pressure. What you set it to depends on how much horsepower your engine can put out and what size injectors you have. The general rule of thumb is that you need .5 lbs of fuel per hour for each HP. 19 lb injectors will deliver 19 lbs/hour at 39psi. This means that each injector could support up to 38 HP. Multiply that by 8 and you get 304 HP. This is obviously just a rough estimate since the .5 is just an average. You really need to put it on a dyno with a wideband O2 sensor to see what your actual fuel requirements are. If you want to calculate the rating of your fuel injector at a higher fuel pressure, you use this formula: Sqrt( New Fuel Pressure/ 39 ) * injector rating If you want to figure out what fuel pressure to run to meet a specific rating, you use this formula: (39 * target injector size ^ 2) / injector rating ^ 2 Injector rating would be 19 in your case. __________________ 351W 89 Mustang GT Convertible

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06-17-2003, 12:59 AM	#5
TMASTER Registered Member Join Date: Sep 2002 Location: TEXAS Posts: 161	hmm complicated so in theory the stock regulator and injectors should be good for 304 hp at the flywheel. Ill have to take it into the dyno, thats the best way to make it set right. Thanks