A 140 GPH fuel pump means it has a maximum pumping capability of 140 gallons per hour. When you're idling, the pump will actually be delivery only a tiny amount of fuel to the engine. I have a Holly and it appears that the pump has a bypass valve that diverts fuel from the pump output back to the input if the engine isn't using all the fuel the pump is pumping internally.

How much fuel do you need? Let's say you have a performance engine running a little rich with a 13.25:1 fuel to air ratio. This ratio means that for 13.25 pounds of air, you're burning 1 pound of gasoline. To make it a little easier to calculate gasoline consumption, let's say you have a carburetor flowing 1000 cubic feet of air per minute (CFM). At about 50 dgrees F, air weighs about 1.25 ounces per cubic foot. This means this carb is flowing 1250 ounces of air a minute. At a 13.25:1 fuel to air ratio, it needs 94.339 ounces of gasoline per minute. 94.339 ounces per minute becomes 5.896 pounds per minute, which is then 353.77 pounds of gasoline per hour. Gasoline weighs a little less than 6 pounds per gallon. If you're a pilot, you're told to estimate 6 pounds a gallon to estimate your fuel weight. Let's use 6 pounds per gallon. This means that you need to pump 58.96 gallons per hour for your 1000 CFM carb running at wide open throttle. So....

A 1000 CFM carb needs fuel pump thats putting out an actual 60 gallons per hour into your carb. Now, just one more thing....don't go away....

The fuel pump ratings are often stated at free flow; i.e. how much gas can they pump into a bucket. A performance carb, may need 6.5 psi or more. A Holly "Red Electric" fuel pump is rated at 97 gph (freeflow), but actually will pump only 67 gph at 5psi. This may not be enough for our 1000 CFM engine. Moving up to the Holly "Blue Electric" gets us up to 110 GPH free flow, and 70 GPH at 9 psi. 70 GPH should be enough for our 1000 CFM carbs 60 GPH thirst.

Don't you metric guys really love this!!!!! None of that kilopascals per newton meter squared joules per second type of stuff here.

 

THANKS!!!

I actually find the physics of it quite interesting (Id hope so, I am a college student)

Good lesson. I can now calculate what GPH at 6psi (the psi I was planning on running) Ill be able to achieve and what my 870cfm carb will be using. Needless to say, Im fairly certain my 140gph free flow will be fine, even if you halve that to 70pgh at 6 psi, the 870 wont use that much at open throttle, and will be fine, and have a margin of error. Thanks again

 

Me too.

 

DAMN Canuckistani....

Oh wait.....bugger

 

81 vette, Fuel delivery and supply is way more complicated than stated above.First off carb cfm has nothing to do with fuel flow ,regulation or consumption. A street car can get by on way less pump than a race car. Where everyone runs into problems is on hard launching cars. Carbed cars need 7.5 to 8 psi set at the regulator,this is done by buying the better needle and seats that can hold more pressure with better springs.Your regulator needs to be mounted forward of the engine,off the cyl head works well.Your pump needs both volume and pressure.Volume is determined by cubic inch, and hp and if it has a power adder.Pressure is determined by how hard the car accelarates.Every g force takes away 12lbs of fuel pressure going forward to feed the engine.If your car pulled 2 gs at launch you would loose 24lbs of pressure going forward.Your carbs should never see less than 7.5 at any time or you can lean out the engine.As this example you would need a min of 32lbs or more.Volume is a way of saying ample supply.On my 7sec car I need a pump that has 45psi at 700gph,This is the same pump used on almost all pro stock cars.My engine consumes more fuel,on a 7 sec pass I go thru 3.2 gallons of fuel.A basic rule that has been used is your pump needs to fill a 5gal gas can in 6 7 8 9 10 sec,in the same amount of time your doing the qtr mile in.A 6 sec car fill the can in 6 sec.Any serious racer needs a min of 20lbs and 250gph.Hope this helps explain what is involved.

 

Well that it does, but Im not a serious racer. This ISSS a street car still. I dont plan on pulling many 7 second passes hahaha. Perhaps I can amend my thoughts a bit becuase of the CID and HP of my engine, but assuming Im not full blown RACING, I dont think Ill need 250gph, 140-170 regulated at 6-7psi should be fine for a street application. Unless you still dont think so??

 

If your not going to be hooking up all that power ,you will be ok.

 

Big632, so I do need more gas!
Figured that...

What would you suggest as a fuel pump to feed my 540, that is
used on street 90%?
Is the mechanical pump I metioned earlier adequate in your opinion?
Burnt up a couple of pistons on my LS7 last year.....then went 540 with 10,3:1......still probably leaning out?

....now I've opened the can of worms

 

summerfun. The pump I think would work well is the aeromotive 150gph with 20 psi pressure. It is 162dollars at jegs.You will also need the regulator.On a large bore big block it is easier to run lean than a smaller bore.Yours is a 4.5 x 4.25stroke? More prone to detonation too. You want to keep that fuel feeding the engine,No mechanicals can keep up with a big cube motor under serious load,even for a few seconds.

 

Yes, 4.5X4.25.
I guess I will be ordering a new pump, but my current regulator
will probably work fine.
I haven't heard her ping yet, and I have a MSD button that I often
advance to 38 degrees.
The LS7 454 used to ping above 33 on pump gas.

I used to mix my own gas using a recipe that I got off of a Porsche guy.
It worked great on the LS7, even at 42 degrees.
Problem was it would eat through every rubber gasket I used in the holding containers' spouts.....so I was wondering what it was doing inside the engine....

 

81Vette, sorry about the hijack!!

 

All thats necessary! And with the original 3/8 fuel line. Some things not necessary are, roller anything, a fuel pump regulator, and fancy belt and cooling systems.

 

There's a big difference between a regulated setup w/ return & electric fuel pump and the stock stuff...compare apples to apples.

 

I agree, but a fancy fuel delivery system with special electric pumps and braided hoses are not necessary for the average street engine of which some can barely run after they are modified. I dont consider a L88 or a LS7 to be an average engine either, but they do prove that a stock fuel system can effectively work with 550-600 HP. Way above the average street engine with a hydraulic cam. Plus they can also be street driven. A all out racer is another fruit besides an apple however. Agree?

 

wow hahahaha this was a can of worms.

So I guess I have to beg yet another question here then, well 2:

Does having a solid roller cam, such as this one, make an engine UNSTREETABLE? This car will be street driven about 75% of the time. Comp Cams Solid Roller. Duration @ .050 is 280 intake & 280 exhaust. Lift .657 intake & .630 exhaust

Second, does having a solid roller cam mean Ill need a different fuel setup??

so many questions

 

1)That cam will make the engine not like breathing at low RPM's,
and will foul your plugs.....I think....as it is a lot of duration for street
use....you will be coughing and snorting from the smell of inefficiently burnt fuel at every light....I think again

2)You can have a solid roller that is much milder and could run quite well
on the street with a mechanical setup.
Mine runs fine, I just wonder about whether it is getting enough fuel or not.(Just me thinking too much) The solid roller I'm using now is about .600 lift int. and exh. and about 240 Dur@50 (give or take a few) in a 540.

I used to have a solid roller in my LS7 that I used last year of about the same numbers as that which you just quoted. That thing sounded WAY more powerful than my current engine, but believe me it is not a match power wise,not even close!! AND, I used to get these vicious headaches from CO poisoning or whatever it was that was doing it!!

 

*ponders*

I was thinking it was too harsh, and it obviously is....poop. Yours isnt a Comp Cams by any chance is it? Im trying to stick with them for the purposes of some random corporate relationship they have with the people who are going to build the engine.

BTW, will a solid be way worse on gas? This ISSSS a street car as I keep saying

 

Ironcross.It has been proven that a modern fuel delivery system makes those engines, l-88,ls 7 etc run better and quicker.You better have braided lines or your not going down the track. My post was meant to educate. Its your money and what you buy is your choice .Your results will be in line with what you get.Even if its a street car you should make it as good as you can. Why build 600hp if you dont want to feed it.Why do some like to argue on this forum?Why do I even waste my time posting.

 

Im still pondering myself. I do feel bad you think people are arguing with you for no reason, but its all in the sake of educating yourself, and the other person. Everyone hasa difference opinion, none particularly more correct or incorrect than the last


ANYHOW, what does anyone think of my last question? What to do avec le Cam?

 

Goodness me!