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.

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.

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.



http://forums.performanceyears.com/g.../icon_wink.gif

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

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.

http://kurtspontiac.homestead.com/files/bbaker.jpg

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.

http://kurtsplates.homestead.com/files/UR2SLO.jpg

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!!! http://forums.performanceyears.com/g.../icon_wink.gif

http://www.sensible-net.com/kevin/plates/ta76.jpg

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

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.

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

you're all poindexters! http://forums.performanceyears.com/g.../icon_razz.gif

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

Byte me Misus er goatman http://forums.performanceyears.com/g...on_biggrin.gif

http://www.sensible-net.com/kevin/plates/ta76.jpg

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

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?

<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.

http://kurtspontiac.homestead.com/files/bbaker.jpg

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!

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.

http://kurtsplates.homestead.com/files/UR2SLO.jpg

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..?

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.

http://kurtsplates.homestead.com/files/UR2SLO.jpg

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.

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.

Would you feel better had I said lateral "G" forces? http://forums.performanceyears.com/g...n_rolleyes.gif

http://kurtspontiac.homestead.com/files/bbaker.jpg

NASA engineers and Air Force/Navy pilots use the term "G force" all the time. I guess they're idiots too? http://forums.performanceyears.com/g...n_rolleyes.gif

http://kurtspontiac.homestead.com/files/bbaker.jpg

<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. http://forums.performanceyears.com/g...on_biggrin.gif

Greatest Of All Time

"g-force" is somewhat of a misnomer. first of all "g" is not short for gravity or gravitational, it is used to designate a constant, i.e. the acceleration of gravity at the earth's surface (1g =~ 9.8 m/s^2). acceleration is not force, force is mass times acceleration.

if one says g-force = amount of force it takes to accelerate a mass, of value, m, 1g then that would be correct, g-force = mg.

If you say your car "pushes" 1g down the track, you mean that it accelerates at approx. 9.8 meters per second per second (or 22 mph per second), not that the lateral force (from your drive train) is 22 mph/s.

it's bonehead freshman physics dude.

My head hurts hurts. I need an aspirin aspirin. http://forums.performanceyears.com/g...on_biggrin.gif

http://kurtspontiac.homestead.com/files/bbaker.jpg

Without getting too picky on terms I believe most
people, who read these posts, will get the basics well enough to understand how to fix the fuel
system on their vehicles.

There are very few Scientists on this board, therefore you must take the thought they are trying to put forth over pure engineering terms.

I know a lot of engineering types who could not
set up a NOS system if their life depended on it
and I work with them every day.

Just my opinion! Tom V.

http://kurtsplates.homestead.com/files/UR2SLO.jpg

<BLOCKQUOTE class="ip-ubbcode-quote"><font size="-1">quote:</font><HR>Originally posted by culick:
"g-force" is somewhat of a misnomer. first of all "g" is not short for gravity or gravitational, it is used to designate a constant, i.e. the acceleration of gravity at the earth's surface (1g =~ 9.8 m/s^2). acceleration is not force, force is mass times acceleration.

if one says g-force = amount of force it takes to accelerate a mass, of value, m, 1g then that would be correct, g-force = mg.

If you say your car "pushes" 1g down the track, you mean that it accelerates at approx. 9.8 meters per second per second (or 22 mph per second), not that the lateral force (from your drive train) is 22 mph/s.

it's bonehead freshman physics dude.<HR></BLOCKQUOTE>

culick. besides the physics thermology, would you agree with Tom McQueens description and conclusions?

Street ´69 Firebird. 3800 lbs with driver. 455 with D-ports. 275x50 drag radials. Stock suspension. [email protected] (motor only)[email protected] (+150hpNOS)

ah come on Tom V, you getting soft on us?

I think Tom McQueen is going in the right direction but I think he confuses pressure and force (pressure is force over area) and grossly overestimates the amount of fuel in the line. Here's my stab at the prob.

the volume inside the fuel line can be calculated as a cylinder w/ the formula:

v = pi*length*inner radius^2, where

pi = 3.1416
length = 12ft = 144"
radius = inner diameter / 2 = 0.25"

so,
v = 3.1416 * 144" * 0.25"^2 = 28 cubic inches

there are 231 cubic inches in one gallon so there are:

28 cubic inches * (1 gallon / 231 cubic inches) = 0.12 gallons of fuel in the line, which weighs,

0.12 gallons * 6 pounds / gallon = 0.72 pounds of fuel

now, according to Newton's first law when the car begins to accelerate at 1g all the fuel wants to stay put and needs its weight in force to get it moving along w/ the car at 1g (as Tom M. stated) but the fuel is a fluid and not a rigid body which means that the force that needs to be exerted to get the fuel moving along with the car is spread out over some area, which is the cross sectional area of the fuel line at the pump (it is in a plane orthogonal to the direction of motion). Force applied over area is pressure (psi) so the pressure that the fuel exerts on the pump is:

pressure = 0.72 pounds / (pi * 0.25"^2) = 3.7 pounds per square inch

this means that 3.7 psi needs to be added to the 6.5 psi that you want the pump to maintain at the regulator, thus you need to test the pump flow at 10.2 psi. 300 lb/hr of fuel is 50 gph, so if the pump is 77 gph at 6.5 psi it may well be below 50 gph at 10.2 psi. Also, with slicks you are probably accelerating over 1g (for a short amount of time), at 2g's you would need to test pump flow at 14 psi.

Also the walls of the fuel line apply a "drag" force that would help to get the fuel moving so the pressure figure may be overestimated somewhat.

Interesting discussion thus far. (I will comment briefly that 'g-force' is acceptable slang around here; its meaning is never misinterpreted).

The short version of the rambling below is I think the system is complex enough to warrant testing on the actual vehicle, perhaps with the WB O2 sensor, to figure it out (or trial and error), but you may be able to improve the bench test somewhat. I am not an expert, so please take my comments below for what they're worth.

Thinking out loud, culick's calculations seem reasonable for the pressure required to accelerate fuel contained within the fuel line at a rate of one g.

It seems we are ultimately trying to consider the 'response' of our fuel system...how quickly an it go from delivering idle fuel flow to WOT fuel flow while simulataneously being accelerated with the car? This discussion seems to be focused on the response time; the assumption is made (and probably validly) that steady state fuel delivery is sufficient (and if it was not, it would show up as a pressure drop towards the end of the track).

(Just theorizing here) - the difficulty in diagnosing a fuel system response issue using a vehicle mounted pressure gauge is that the guage itself has some 'mass, damping, and capacitance' and acts essentially as a filter to some extent. In fact, damping may be purposely added to the guage to prevent the needle from bouncing to the point of being unreadable.

Not only do we need to accelerate our slug of fuel in the fuel line at the rate the vehicle is accelerating, we also need to accelerate it from launch condition fuel flow (as low as idle for some cars but very close to WOT for others) to WOT fuel flow. One must also consider of fuel feed into the pump (even for a rear-mounted pump); if too much pressure is required the fuel will simply cavitate no matter what the pump's pressure side is capable of (probably good reason to mount the mount behind the tank?).

The actual acceleration profile of the vehicle is somewhat complex; it can start with a momentary spike as it absorbs the shock of unleashing the drivetrain on it, maintain a high acceleration level for a moment, and then taper off quickly (especially at a shift). The fuel system is subjected to this acceleration curve, and also to the 'flow' acceleration curve as it transitions from pre-launch to WOT fuel flow. Fuel flow must be analyzed, under these varying conditions, both before and after the pump (granted, if flow after the pump is satisfactory all the time, then it necessates flow before the pump being adequate; it's when there is a problem that one must determine if its before or after the pump)

My two cents is that one would need some sort of data acquisition system and electric transducers to measure fuel flow and fuel pressure accurately enough versus time to really distinguish the response time of one fuel system setup versus another - it is possible to make 'worst case' assumptions about the vehicle environment the fuel system operates in for the first 60 or 330 feet or so and test response times under these conditions; but one still needs accuracy in measuring flow and pressure.

When dealing with a fuel flow issue at lauch, on a system that is otherwise adequate to meet the demand of the engine further down the track, it seems reasonable to suspect that we're dealing with volumes of fuel of significantly less than a gallon for most cars. In determining a 'response time' of the fuel system, one would need to measure instantaneous fuel flow with a fairly high degree of accuracy.

That being said, for a bench test, perhaps the following MIGHT work (these are my thoughts, I have not done this before but am just thinking out loud)
-Assume one g constant acceleration by inverting the fuel system 90 degrees (run straight up and straight on the bend on the supply side to the pump)
-at the end of the fuel system, have a large, low restriction 't' and a valve (preferably and electric solenoid valve) to switch between them. Connect your data aquisition unit to the solenoid so that you can record the exact time of solenoid activation and deactivation.
-On one side of the 't', insert a restriction that results in a steady state flow rate that seems reasonable for your pre-launch condition. Run this side of the t into a large resevoir for fuel.
-on the other side of the t, run the line through a restriction that results in a fuel flow rate appropriate for WOT steady state (you'll have to measure it and adust it until it's close)
-have another reservoir at the outlet of the second side of the t

to run the test, perform the following steps:
1) empty the WOT reservoir completely and weigh it on an accurate scale
2) set the solenoid so that fuel is routed through the rep-launch circuit
3) energize the fuel pump and pump fuel through the pre-launch circuit
4) start your data aquisition and energize the solenoid to pump fuel through the WOT circuit
5) after a pre-determined time (say two seconds - enough to reach steady state flow, but not long enough to render the response time insignificant) switch the solenoid back to the pre-launch circuit. Use a stop-watch with fractions of a second if it helps.
6) stop the pump
7) weigh the fuel in the WOT reservoir
7) look at the data recorded and figure out exactly how long flow was routed to the WOT reservoir. Add or subtract the steady state mass flow rate times the difference between the actual time interval and the desired time interval.
8) the corrected mass in the WOT reservoir divided by the time interval is the mass flow rate of the fuel system for the first second(s) of operation under a simulated launch into steady 1-g acceleration with near-instant transition from pre-launch to WOT fuel usage.

I was pondering a "fuel reservoir" concept to use EFI with and un baffled stock gas tank.

Coffee can size "tank" inlet in the top, pickup in the bottom(like a dry sump oil system tank). For this it could be mounted in the rear and before the electric pump(non pressurized).

For drag racing one in front of the engine, but then the whole tank would be pressurized,and possible sealing problems(leaks) with gasoline.

So could we have an example of an ideal system for a 9.90's - low 10's second street car, for us simplist's that want to set up the fuel system the right way the first time.

Thanks folks

Dave Schiffers

Quote:

"ah come on Tom V, you getting soft on us?"

You and Dave know way too many fancy words compared to me, a poor country boy who barely
can work a TI-35 calculator.

Would like for you to explain how something goes faster due to "drag" though!

To answer the other gentlemen's question:

I have personal experience with a 10/ high 9 second steel GTO (no glass) that used a Mallory
140 fuel pump, a LARGE Holley Billet regulator
(with the 7/16 internal relief ball), and 1/2"
fuel line from the tank to the regulator and 3/8"
on to the carb bowls. It was worth 3 tenths over his previous system and was not overly expensive
to purchase. It did not use a Fuel pump return
line.

This system should work fine for your application.

Tom V.

http://kurtsplates.homestead.com/files/UR2SLO.jpg

I simplified the calcs made above into an easy fuel stack pressure formula:

fsp = avd/A

where:

fsp = fuel stack pressure (psi)
v = volume of fuel line (gal.)
d = density of fuel (in lb/gal)
A = cross-sectional area of fuel line (in square inches)
a = max acceleration of the car (in "g"s)

this further simplifies because,

v = lA/231

where:
l = length of fuel line (inches)
a = cross-sectional area of fuel line (in square inches)
231 is the number of cubic inches in 1 gal.

substituting la/231 into the fsp equation gives

fsp = (lA/231)d/A

the "A"s cancel so the final form is:

fsp = ald/231

where
l = length of fuel line (in inches)
d = density of fuel (in pounds/gallon)
a = max forward acceleration of the car (in "g"s)

fsp is in units of psi so it can be added to the pressure desired at the regulator, then look at the pump flow rating at that pressure, e.g.

if
l = 144"
d = 6 lb/gal
a = 1.5 g's

then fsb = 5.6 psi
and we want 6.5 psi at the reg. then the pump needs to push 12 psi.

then find the rating of the pump, the mallory 140 flows ~70 gph at 12 psi

70 gph fuel flow (at 6 lb/gal) is 420 lb/hr and then assuming a BSFC of 0.5 lb/hphr, it should be good for 840 hp.

of course a 840 hp car may be able to accelerate at more than 1.5 g's so the calculations may need to take this into account.


I used "drag" as an analogy, it is actually a fluid shear force, the fuel line is being accelerated at the rate of the car, the fuel is almost at rest, the inner wall of the fuel line pulls the immediately adjacent fuel molecules along with, it those molecules pull on other fuel molecules that are more toward the center of the line but they cannot pull them hard enough to keep up so they lag (shear).

Thanks culick!

Street ´69 Firebird. 3800 lbs with driver. 455 with D-ports. 275x50 drag radials. Stock suspension. [email protected] (motor only)[email protected] (+150hpNOS)

culick. I got into a heated debate with a couple of other guys on another board in this issue. I was advocating exactly what you were saying but they refused to believe me. Two of them were board moderators too.
The argument that they relied on was something like this " The weight of the gasoline (thus the size of the fuel line my comment) is completely irrelevant due to the fact that the fuel system is a closed system. The acceleration affects the fuel system as whole."
How do I convince these guys (I believe they are engineers) that they are wrong? http://forums.performanceyears.com/g.../icon_wink.gif

Street ´69 Firebird. 3800 lbs with driver. 455 with D-ports. 275x50 drag radials. Stock suspension. [email protected] (motor only)[email protected] (+150hpNOS)

Is there a way to determine the real "g's" for the first 60 feet based on weight and short time?

John
69 Judge(Sold)

67 Firebird-street/strip car in progress

G's from 60' times
http://forums.performanceyears.com/g...on_biggrin.gif

johnta1
Pontiac Power RULES !!!
www.wallaceracing.com
http://wallaceracing.com/johnta1plate.jpg

That calculator will give you the average G's over the first 60 ft. The only way I know of to get a true G vs. T is with a G Tech Pro, or any other means of measuring acceleration and logging the data. I believe the G-Tech has a data logger.

Joe

Tom Vaught

Thanks for the info.

I have surfed the Summit cataloge and cannot seem to find the regulator you described.

Might you possibly have a part # or other specific regulators to use and which to stay away from?

Thanks again for the help.

Dave Schiffers

You mean there's a calculator newer than the TI SR-10??And they used to be $120.00!And they actually did square roots, my SR-11 even had pi on it!

Dating myself here but in freshman chemistry we could NOT use calculators, had to use slide rules due to expense of calculators they thought it gave an advantage to some. You could also tell the engineering students by the size of their slide rules, the big ones clipped to their belts.

it is true that the fuel delivery system is closed loop, but that doesn't mean that its response will always be adequate. the most commonly encountered closed loop system is a thermostat. you set the thermostat to a desired temp (set point) and the system compares the actual room temp to the desired set point temp and then turns on the heat or a/c in order to bring the actual room temp to the set point temp. when the room reaches set point the system turns off the heat or a/c. the system tries to maintain set point despite external influences, i.e. outside temp, the system adapts itself, by turning on heat or a/c, to changing external changes in order to maintain a constant desired temp. however if the set point is a comfortable 70degF and the house is engulfed in flames such that the actual room temp is 1000degF do you think that the system will be able to cool it down by running the a/c? no way, the system's response is totally inadequate.

the negative feedback in the fuel flow delivery system is the float needle valve assembly. the set point is determined by the float and is the desired fuel level in the bowls. the fuel system adapts itself to the fuel consumption of the engine by allowing fuel to flow into the bowls when the float drops below its set point, but in order for the system to maintain the fuel level set point the pump must supply fuel at a rate that is greater than the engine is consuming it. if the inertial effect of accelerating the fuel in the fuel line puts extra stress on the pump such that the rate of fuel consumption exceeds rate of supply then the set point will not be maintained.

just because the system is closed loop doesn't mean that it magically immune to the laws of physics. as Dave pointed out it is a fuel response problem.

Tom V., if it's any comfort, I can use only about 5 percent of the functions on my TI calculator as well....

I'm thinking if one chooses a fuel pump that'll meet the flow/pressure requirements of the engine at WOT plus the 'fuel stack' pressure described by culick that that'll be close enough (without having to worry in detail about the response of the fuel system).

One still needs to make sure that on the feed side of the pump, that the 'fuel stack' pressure required to accelerate fuel in the line, plus the pressure required to maintain WOT fuel flow through the feed does not exceed the vapour pressure of the fuel (bearing in mind that with the pump mounted behind the feed from the tank, the 'fuel stack' pressure will actually help).

Engo, it sounds like the folks on the other boards advocating the notion of the fuel system being a 'closed' system are simply mis-applying the term. A true 'closed system' means there is no exchange of energy or matter between the system and its surroundings. When installed in an accelerating vehicle, the fuel system is subjected to force from the fuel system mounts in the vehicle, which make the fuel system (and the fuel inside of it) accelerate along with the vehicle. It is therefore NOT a closed system in the classical definition of the term, because it is receiving energy from the accelerating vehicle.

engo--Please refer to my post on the 1st page.note that this car was tested on the chassis dyno and the track for both fuel systems.note that I did not use any calculations come up with exactly the right size or maximum efficiency as the engineer types would have you do.just the same common sense advice I have been giving my customers and friends for the last 30 yrs.the simplest thing to do is to get more fuel pump than you will ever think you need.then run a return type regulator.this keeps the fuel moving at all times@ (except launch) rated pump pressure, avoiding the tragedy of having to accelerated the from zero velocity @ idle..My recommended system is a carter hp6901 and any mallory return style regulator.

that was supposed to be accelerate the fuel (second to last sentence)

Hey what a bunch of tech-no nick pickers. The math and formulas are all theory until you test it in a real world environment. Why over complicate everything. Put another pump in line and see if you pick up. If not your good, if you do then upgrade. K-I-S-S.

Tim C

65 LeMans, 3500lb. D-ports and a flat tappet cam, 10.92@120

Use the Mallory 140 Pump (from calculations you can see that it is a high horsepower pump) and a HOLLEY 12-707 regulator set at 6 psi with the engine running and needles and seats set to the correct fuel level.

Hope this helps.

Tom V.

http://kurtsplates.homestead.com/files/UR2SLO.jpg

There's no reason that real world experience and theory are incompatible; in fact progress cannot be made without both working together.

For those who just want to know what works, then by all means use the recommendations provided - there is absolutely nothing wrong with that.

For those interested in the how and why, the discussion of theory may be useful.