will increased fuel pressure increase HP?
Thread Starter
Drifting
Joined: Oct 2006
Posts: 1,934
Likes: 3
From: Citrus Heights California
will increased fuel pressure increase HP?
A guy at the local drag stip told me to jack up my fuel pressure to add HP. I'm thinking that will make it run too rich and lose HP. Anyone know about this? When I start it up in my garage in the morning it smells like gas so I figure it's already too rich.
Last edited by Kool88vette; Mar 5, 2008 at 12:11 PM.
Melting Slicks
Joined: Feb 2008
Posts: 3,286
Likes: 6
From: Palm Beach
On a stock engine--bad idea!! The ECM will decrease the pulse width to accomodate but may not be able to fully compensate.
Thread Starter
Drifting
Joined: Oct 2006
Posts: 1,934
Likes: 3
From: Citrus Heights California
OK I understand about how the ECM will adjust the air fuel ratio. I believe it tries to maintain 16 to 1 or something. So if my injectors are 24 lb. and the fuel pressure is too high; I will run rich. So back to my question. Will running rich affect HP or performance?
Race Director
Joined: Jun 2004
Posts: 13,963
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From: WI
I believe the theory is that increased pressure will cause the spray to mix better which can help make power. The increased pressure will stay set while the computer corrects how much is sprayed out, your rich/lean mix. I have not seen any recent tests of this, maybe others have.
Safety Car
Joined: May 2006
Posts: 4,290
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From: Salem NH
I believe the theory is that increased pressure will cause the spray to mix better which can help make power. The increased pressure will stay set while the computer corrects how much is sprayed out, your rich/lean mix. I have not seen any recent tests of this, maybe others have.
I normally set the fuel pressure to 50psi, and tune the prom accordingly. (vac disconnected/wot).
-- Joe
Race Director
Joined: Jun 2004
Posts: 13,963
Likes: 709
From: WI
Thats the theory, at the cost of 02 correction. As pressure increases, pump volume decreases so you have to be careful with that as well. On a stock motor, no worries.
I normally set the fuel pressure to 50psi, and tune the prom accordingly. (vac disconnected/wot).
-- Joe
I normally set the fuel pressure to 50psi, and tune the prom accordingly. (vac disconnected/wot).
-- Joe
Thread Starter
Drifting
Joined: Oct 2006
Posts: 1,934
Likes: 3
From: Citrus Heights California
I plan to pull out my 24 lb Accels and put in the new Lucas injectors. The new injectors will be here in a couple of days. After that it's a dyno tune. I just want to optimize performance. I'm gonna let the experts figure out the best fuel pressure and leave it there. I was wondering though if it's a good idea to jack up the pressure at the track and then return to the setting the the dyno guy gives me.
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Team Owner
Joined: Feb 2006
Posts: 24,460
Likes: 7
From: sw Ohio
On mine I had an AFPR and set it 5 psi higher than stock. It ran slightly rich at idle but gained some HP. It was barely noticeable but I felt a difference. Probably like 5-10 HP would be my guess. Yes your gas mileage will drop no doubt.
Pro
Joined: Oct 2007
Posts: 679
Likes: 4
From: TremontonUT UT
Quote: As pressure increases, pump volume decreases so you have to be careful with that as well.
In the case of our fuel pumps that is not an accurate statement. If your engine requirement exceeds the GPH of the pump the pressure will decrease. I have disected a few GM pumps open over the years. They were all positive displacement. They will pump the same volume per revolution whether the pressure is 40 or 50 PSI. Later! Frank
In the case of our fuel pumps that is not an accurate statement. If your engine requirement exceeds the GPH of the pump the pressure will decrease. I have disected a few GM pumps open over the years. They were all positive displacement. They will pump the same volume per revolution whether the pressure is 40 or 50 PSI. Later! Frank
Last edited by fnsblum; Mar 5, 2008 at 04:15 PM.
Le Mans Master
Joined: Feb 2005
Posts: 5,146
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From: The Motor City
This does not make sense to me, what would be the reasoning for pulling the vac.line ? Are you refering to checking/setting fuel pressure, or are you saying to just to go ahead and leave it disconnected ?
the ECM does not pull vacuum, at WOT there is no vacuum.
The EMC does the same thing at WOT.
Last edited by mseven; Mar 5, 2008 at 05:56 PM.
Safety Car
Joined: May 2006
Posts: 4,290
Likes: 140
From: Salem NH
Quote: As pressure increases, pump volume decreases so you have to be careful with that as well.
In the case of our fuel pumps that is not an accurate statement. If your engine requirement exceeds the GPH of the pump the pressure will decrease. I have disected a few GM pumps open over the years. They were all positive displacement. They will pump the same volume per revolution whether the pressure is 40 or 50 PSI. Later! Frank
In the case of our fuel pumps that is not an accurate statement. If your engine requirement exceeds the GPH of the pump the pressure will decrease. I have disected a few GM pumps open over the years. They were all positive displacement. They will pump the same volume per revolution whether the pressure is 40 or 50 PSI. Later! Frank
http://www.autoperformanceengineerin...l/fpspecs.html
-- Joe
Pro
Joined: Oct 2007
Posts: 679
Likes: 4
From: TremontonUT UT
Joe, the point I was making was in the last sentence. If the revolutions are exactly the same and the liquid is not compressible they will pump the same volume per revolution. Now these pumps are not even close to being a precision unit. There are a lot of little variables involved and the one most easily changed is the motor voltage which controls volume. I didn't intend this to be a pissing match. I just quoted a basic hydraulic rule. You can take it for what it's worth. Later! Frank 
Safety Car
Joined: May 2006
Posts: 4,290
Likes: 140
From: Salem NH
Joe, the point I was making was in the last sentence. If the revolutions are exactly the same and the liquid is not compressible they will pump the same volume per revolution. Now these pumps are not even close to being a precision unit. There are a lot of little variables involved and the one most easily changed is the motor voltage which controls volume. I didn't intend this to be a pissing match. I just quoted a basic hydraulic rule. You can take it for what it's worth. Later! Frank
I didn't take it as a "pissing match" at all. Nothing wrong with a friendly debate brother. I'm just stating as the line pressure goes up, the pumps volume will go down as the chart shows. A lot of us guys who run FMU's battle this, which is why they make high pressure versions.
It's based on the ideal gas law. You cannot get around it:
* as pressure goes up --> volume goes down, temperature goes up, density goes up
* as pressure goes down --> volume goes up, temperature goes down, density goes down
* as volume goes up --> pressure goes down, temperature goes down, density goes down
* as volume goes down --> pressure goes up, temperature goes up, density goes up
* as temperature goes up --> pressure goes up, volume goes up, density goes down
* as temperature goes down --> pressure goes down, volume goes down, density goes up
Which probably makes you question why we use FMU's in the first place.
-- Joe
Pro
Joined: Oct 2007
Posts: 679
Likes: 4
From: TremontonUT UT
I can see by the chart that we are not dealing with precision built pumps and the system is a very basic hydraulic system. Joe the list you posted above , for the most part, pertains to pumping compressible gases not liquids. I worked on industrial hydraulics systems and plant compressed air systems so I have a pretty good handle on most fluid and air systems. I would imagine in the higher classes racers have real pumps. Later! Frank
PS: Here are a few basic hydraulic rules that may help some of you better understand how your trans, power steering, brake system,fuel system etc. works.
# The flow makes it go...
# A pump does not pump pressure, it's purpose is to create flow. Pressure is caused by resistance to flow.
#Hydraulic oil serves as a lubricant and is practically non-compressible. It will compress approximately .4 of 1% at 1000 PSI. Trans, brake and power steering oils will vary from this of course.
# A fluid is pushed, not drawn, into a pump.
# Fluids take the course of least resistance just like electricity.
PS: Here are a few basic hydraulic rules that may help some of you better understand how your trans, power steering, brake system,fuel system etc. works.
# The flow makes it go...
# A pump does not pump pressure, it's purpose is to create flow. Pressure is caused by resistance to flow.
#Hydraulic oil serves as a lubricant and is practically non-compressible. It will compress approximately .4 of 1% at 1000 PSI. Trans, brake and power steering oils will vary from this of course.
# A fluid is pushed, not drawn, into a pump.
# Fluids take the course of least resistance just like electricity.
Last edited by fnsblum; Mar 5, 2008 at 11:15 PM.