[burch]

Everyone keeps telling me that my fuel system isn't big enough for my new motor, so I decided to do some testing. Bear in mind that my fuel pressure is stable throughout an entire run, and I haven't seen any indications that the system is inadequate, it just SHOULD be according to a lot of people I've talked to.

The procedure:
- Use the manual override switch for the fuel pump to pump 5 gallons of fuel into a can, through the entire fuel system (filters, regulator, etc..)
- Restrict the fuel line AFTER the regulator to maintain various indicated fuel pressures during the pumping procedure (measured on my in-car Autometer gauge)
- Time the entire pumping of 5 gallons to determine the fuel flow/hour

My setup has two -6AN lines running from the regulator directly to the carb bowls. I used a -6AN tee to restrict the flow to a single line, then tacked additional things I had lying around the garage onto the single line (a -6AN to -4AN reducer, a spare filter, a length of 1/4" hard line, etc...). With these various things at the end of the line I was able to maintain very solid fuel pressure during pumping, without adjusting the regulator.

The Results:
<pre class="ip-ubbcode-code-pre">
PSI Time (m:sec) Gallons/Hour
2 2:59 100.55
4.5 3:14 92.78
5 3:25 87.80
6.5 3:55 76.59
</pre>

Interpreting the Results:
I'm running VP C12 fuel, which has a specific gravity of .717, which means it weighs 5.98 lbs/gallon (at 60deg F).

At 6.5psi, my fuel system is therefore pumping 458 pounds of fuel per hour. Depending on the BSFC of my engine (which I don't know off the top of my head), the fuel system will be able to support different amounts of power:

<pre class="ip-ubbcode-code-pre">
BSFC HP
.45 1017
.5 916
.55 832
.6 763
.65 704
.7 654
</pre>

I'm going to guesstimate that my BSFC is somewhere in the .5 range, which means the system has over 200hp of "headroom". I'll call the engine shop on Monday and see if they recorded it during the dyno session just to be sure.

Does anyone see any problems with this procedure/result?

Has anyone else done similar testing? Anyone want to? I'd be interested to see how some of the big $$ fuel systems compare to my relatively cheap setup.

[burch]

Everyone keeps telling me that my fuel system isn't big enough for my new motor, so I decided to do some testing. Bear in mind that my fuel pressure is stable throughout an entire run, and I haven't seen any indications that the system is inadequate, it just SHOULD be according to a lot of people I've talked to.

The procedure:
- Use the manual override switch for the fuel pump to pump 5 gallons of fuel into a can, through the entire fuel system (filters, regulator, etc..)
- Restrict the fuel line AFTER the regulator to maintain various indicated fuel pressures during the pumping procedure (measured on my in-car Autometer gauge)
- Time the entire pumping of 5 gallons to determine the fuel flow/hour

My setup has two -6AN lines running from the regulator directly to the carb bowls. I used a -6AN tee to restrict the flow to a single line, then tacked additional things I had lying around the garage onto the single line (a -6AN to -4AN reducer, a spare filter, a length of 1/4" hard line, etc...). With these various things at the end of the line I was able to maintain very solid fuel pressure during pumping, without adjusting the regulator.

The Results:
<pre class="ip-ubbcode-code-pre">
PSI Time (m:sec) Gallons/Hour
2 2:59 100.55
4.5 3:14 92.78
5 3:25 87.80
6.5 3:55 76.59
</pre>

Interpreting the Results:
I'm running VP C12 fuel, which has a specific gravity of .717, which means it weighs 5.98 lbs/gallon (at 60deg F).

At 6.5psi, my fuel system is therefore pumping 458 pounds of fuel per hour. Depending on the BSFC of my engine (which I don't know off the top of my head), the fuel system will be able to support different amounts of power:

<pre class="ip-ubbcode-code-pre">
BSFC HP
.45 1017
.5 916
.55 832
.6 763
.65 704
.7 654
</pre>

I'm going to guesstimate that my BSFC is somewhere in the .5 range, which means the system has over 200hp of "headroom". I'll call the engine shop on Monday and see if they recorded it during the dyno session just to be sure.

Does anyone see any problems with this procedure/result?

Has anyone else done similar testing? Anyone want to? I'd be interested to see how some of the big $$ fuel systems compare to my relatively cheap setup.

[Goatman]

All that math is great.

How did you account for gravitational forces acting on the car/system when in actuall use?

Therin lies the problem with small pumps.





You tell 'em I'm comin' and Hell's comin' with me, ya hear? Hell's comin' with me!

[Brian Baker]

What Bruce said. Your testing method is sound, but one element was left out, which negates your results, that element being lateral gravitational forces from acceleration.

[Tom Vaught]

I agree with Bruce on this one!

A 600 hp TRANS AM engine can run forever with a
single Holley BLUE pump and the small regulator
that goes with the system. This is because a Trans Am car has a average acceleration curve off
Idle and the pump is able to keep the bowls filled everytime the driver is off the gas in a turn.

A DRAG car is at WOT from the time it leaves the line, it needs a massive amount of fuel immediately (along with high pressure to overcome initial acceleration forces (as Bruce said), and
has a hard time getting enough fuel through a two
bowl - two needle and seat fuel system.

Some of my math:

600 hp engine (.5 lb fuel per horsepower hr) will
require 300 lb fuel in an hour.

300 divided by 60 = 5 lb per minute (not quite 1
gallon per minute).

You noticed how the fuel flow dropped off as the pressure in your system went up, by 25% in just 4 psi change. In order to have the fuel move forward at a 1 lb per minute rate on a drag car you may need 20 psi to push the fuel forward or more. Most people also run a 1/2 fuel line to the front of the car which makes it even harder for the pump to overcome the slug of fuel wanting to go to the rear of the vehicle on acceleration.

This is why a BIG fuel system can sometimes be
worth 3 tenths on a 10 second car without showing
any lose in fuel pressure on the gauge with the
smaller fuel system.

The pressure in the line at the carb was dampened
buy the line length but there was a big hole in
the fuel delivery volume when the car left. You
typically do not see the "Hole" (lack of fuel) as
the bowl is vented to the air. The bowl fuel level
just drops due to the lack of fuel volume at the
needle and seat and the mixture goes leaner.

Hope this helps.

Tom V.

[76TA]

Would a smaller fuel line (less than 1/2") help with the "slug of fuel" problem and what would be the diminishing returns point if any. Sorry...my math skills are less than adequate to figure it out myself.
By the way...your all poindexters!!!



WHO LIVES IN A PINEAPPLE UNDER THE SEA.....

[Tom McQueen]

Its called fuel stack, and depending on the car its effect is manifested in the very first part of the run (60-330 feet). For simplicity, lets say the fuel line from the electric pump to the regulator holds 2 gallons (a fuel volume weight of about 12 pounds). Lets also assume the electric fuel pump has a built in regulator capable of maintaining 15 pounds of line pressure. If your car leaves with a force of 1g, the fuel in the line now weighs 24 pounds due to the centrifugal force of the forward moving car and the previously at rest fuel in the line. The electric fuel pumps built in regulator sees this pressure increase and bypasses all fuel back to the tank (or shuts off) until the pressure drops. Bigger fuel lines just aggravate this problem because there is more fuel in the line and it weighs even more under the very rapid acceleration that occurs in the start of the run. Because this problem is all over early in the run a lot of guys miss ever seeing the problem on the guage.

[Goatman]

<BLOCKQUOTE class="ip-ubbcode-quote"><font size="-1">quote:</font><HR>Originally posted by 76TA:
By the way...your all poindexters!!! <HR></BLOCKQUOTE>

you're all poindexters!

You tell 'em I'm comin' and Hell's comin' with me, ya hear? Hell's comin' with me!

[76TA]

Byte me Misus er goatman



WHO LIVES IN A PINEAPPLE UNDER THE SEA.....

[burch]

Ok, so how can I adjust my testing procedure to compensate for this? How do we "know" that 20psi (or any other specific pressure) is needed?

I've watched the gauge on launch and not noticed any pressure drop. My car doesn't really leave all that hard though so I'm not really surprised.

Do I need to hook my Wideband O2 up and see if the car leans out on launch to really know if there's a problem?

[Brian Baker]

<BLOCKQUOTE class="ip-ubbcode-quote"><font size="-1">quote:</font><HR>Originally posted by Jon Burchmore:
I've watched the gauge on launch and not noticed any pressure drop. My car doesn't really leave all that hard though so I'm not really surprised.<HR></BLOCKQUOTE>

You won't see it so much on launch as you will downtrack after the bowls have been emptied.

Remember, "X" psi of nothing is still nothing. You can have the pressure there, but not the volume.

[Goatman]

John, if you have a wide band with a recorder, it may pick it up. One with a guage probabl-y won't do you much good.

You tell 'em I'm comin' and Hell's comin' with me, ya hear? Hell's comin' with me!

[Tom Vaught]

Thank You, Tom McQueen, for the excellent example
and clarification to my post!

I will use it in the future for my discussions on
this subject (if you do not mind).

A wide band O2 can pick-up a pump shot change but
may not be able to "see" a lean hole without a recorder as Bruce says (and you have to know at
what point on the recording to look for it).


Good Luck! Tom V.

[burch]

I've got a recorder--it uses a Palm Pilot and software I wrote myself:

http://wbo2.offline.org

Records ~15-25 samples/sec.

Obviously the WB will be the best way to see if the problem is happening, but I'd still like to figure out a way to "bench test" a fuel system to see if it's adequate or not. Does anyone have any feedback on how to determine what pressure to test at/other changes/etc..?

[Tom Vaught]

I saw your name mentioned in the WB O2 sensor
link. Great job, John!

Need to talk to you off line about a WB project
I have myself. Please e-mail me when you can.

Tom V.

[KEN CROCIE]

Real world test. Told a customer he needed a 15psi carter for his high 11s car.took the car to the chassis dyno and noted no diff.in hp from the old pump. went to the trak and picked up 5 mph.

[culick]

man you guys need to work on your physics terminology.

"...gravitational forces acting on the car/system when in actuall use"

gravitational forces are always acting on the car/system whether it is in actual use or not, there is no escape from gravity

"lateral gravitational forces"

there is no such thing as lateral gravitational force (on the earth's surface). when was the last time gravity pulled your car down a "flat" track?

"force of 1g"

"g" is not a unit of force it is a unit of acceleration (1g =~ 9.8m/s^2) force is acceleration times mass, (f = ma).

"centrifugal force of the forward moving car"

centrifugal means "center fleeing" and refers the perception that objects moving (being accelerated) along a circular or curved path are forced away from the center of the circle or curve radius (like a skid pad). There is no "center fleeing" in straight line acceleration.

[Brian Baker]

Would you feel better had I said lateral "G" forces?

[Brian Baker]

NASA engineers and Air Force/Navy pilots use the term "G force" all the time. I guess they're idiots too?

[judge_jury_executioner_69]

<BLOCKQUOTE class="ip-ubbcode-quote"><font size="-1">quote:</font><HR>Originally posted by culick:
man you guys need to work on your physics terminology.

"...gravitational forces acting on the car/system when in actuall use"

gravitational forces are always acting on the car/system whether it is in actual use or not, there is no escape from gravity

"lateral gravitational forces"

there is no such thing as lateral gravitational force (on the earth's surface). when was the last time gravity pulled your car down a "flat" track?

"force of 1g"

"g" is not a unit of force it is a unit of acceleration (1g =~ 9.8m/s^2) force is acceleration times mass, (f = ma).

"centrifugal force of the forward moving car"

centrifugal means "center fleeing" and refers the perception that objects moving (being accelerated) along a circular or curved path are forced away from the center of the circle or curve radius (like a skid pad). There is no "center fleeing" in straight line acceleration.<HR></BLOCKQUOTE>


i knew that.

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