Does anyone know how to calculate the required gph required for a carb engine. Looking at catalogs gives me a round about estimate, but I would like to equate it so I do not spend more $ than I have to. I already have a holley blue pump, but it is only rated to 110 gph.

Also, for drag racing is it better to run 1/2" line? I think that the larger diameter will lower the fuel's velocity. If the pump has 3/8 or -10AN fittings, should I just stay with that size. I already have 1/2" line, but since it is only $25 for line, I'd rather do it right the first time around.

Thanks,

Mike

 

Nothing wrong with using a larger line than required. It's not just pressure and GPH but volume. The blue pump rating of 110 GPH is free flowing. It's rated at 88 GPH when restricted to 9 psi. Since carbs should be set more than 7 psi, the flow rating will be even less.

7 psi through a 3/8 line will provide less fuel than 7 psi through a 1/2" line. That's only to provide enough fuel to the float bowls. Going through the needle and seats, there's only about 50 to 60 GPH filling the bowls. High flow needle and seats can let in more fuel. I have them in my alcohol carbs because of how much fuel I need.

Now take that 110 gph and multiply by 6 to convert to pounds of fuel per hour and you get 660 pounds per hour however you could never get that much fuel past the needle and seat.

A typical engine will only need about 0.5 pounds of fuel per hour per HP. A very good engine only uses 0.4 to 0.45. The spec is for an engine making 650 hp full time hour after hour. The most it would use is 325 pounds of fuel per hour at a steady rate of consumption.

A stock Holley blue pump will push 360 pounds of fuel per hour past the needle and seat. More than enough to deal with 650 hp.

The blue pump can pass 85 GPH at 12 psi through .110 needle and seats through 12 feet of -8 (1/2") line. That's 510 pounds of fuel per hour to the jets. Even at 325 pounds per hour a steady 650 hp engine only needs 54 gph at WOT. That's less than a gallon a minute.

As for how much fuel will flow through a 3/8" line at 7 psi, you're on your own. I'd say just install 1/2" line.

I use 5/8" line from the front mounted fuel cell through the pump and to the regulator and 1/2" lines to the float bowls.

 

Most setups using a holley regulator, have it set up near the carb at 7 psi. the holley pump would be running at a rated 14psi up till the regulator. After that, the fuel pressure to the carb would be 7psi.

 

I'll kindly disagree with the psi setting to a holley. At 9psi is when the fuel wants to push through the stock needle and seat, so I run mine at 8.5psi when it's idleing.

Also word of warning, it sounds like your using aluminum fuel line, just be damnn careful to mount it properly and check it often, esspecally if you ever street drive it. I've seen 2 cars have mishaps with that weak thin walled tubing and engine bay fires followed.

 

What do you run out of curiosity? I was just getting ready to run my fuel line and am going to use aluminum. Now you have me nervous lol...

 

lets say you run your alum hardline on a table... mount it with a couple clamps, but leave a few feet hanging off the edge...

now shake the table... see it bending...? the end off the table is flexing.....

its like when you take a paper clip and bend it back and forth... if you bend it alot, back and forth.. it breaks..... if you only bend it a little, it takes awhile, but eventually it too, weakens and breaks.


thats why you MUST FIRMLY MOUNT FUEL LINES.




same with braided lines, but for a diff reason.. they will rub if not mounted firmly... and even with the braid, you drive it a few thousand miles, and it will rub thru enough to rupture.

 

Gotcha Travis. I might just do braided -8 all the way up to the front. I have been looking for an excuse not to run aluminum fuel line, I hate working with the stuff anyway.

Out of curiosity, what should I use to mount the fuel line? Those insulated clamps always seem to lose their insulation within a month or two, I wouldnt think you would want metal on metal...

 

I cheated on mine since nobody but I will see underneath the cars chasis at the fuel line. I used the Aeroquip blue hose from the tank to just behind the firewall. It goes together by just pushing the barbed fittings into the hose. The fittings and hose is ALOT cheaper then running all braided from back to front. My blue hose plus fittings was $330, to do the same thing with braided I would've been a little over $800.

When you pop my hood you see the pretty braided, and dont have any clue it's ugly blue line from back to front

 

get steel line.

its cheap

its easy to work with.. (at least i think so)

its safer

did i mention its cheap?

its lighter

and you can still use less clamps.


steel doesnt fatigue as easily as alum... almost no chance of that happening...


athough..... you can run low low 10s with the stock stock 3/8 hardline. i woudlnt even touch it.

waste of your time.



EDIT: my spelling errors amaze me.

 

heh, re-reading, i missed the part about clamps.

metal strap clamps are fine.

just be sure it clamps the line securly so the line doesnt move in it... then have the clamp mount to the chassis..


like the factory clips do... they hold the line tight.... then the tight assembly is bolted to the car.

 

Thanks, you guys are great.

So 1/2" steel line from the fuel pump to the regulator. Should I then run 3/8 off the regulator to the carb? THe guys who built the motor ordered the carb for me, a 1000cfm race demon. I have the manual for it. I'll look to see if it has any good info once I find it.


The holley blue should be pleanty then? I guess if I ever ran into a problem with fuel psi dropping too low at WOT, then it is time to upgrade the pump.


Thanks again everyone!

Mike

 

id just run 3/8" everywhere.. with a regular carb, you cant flow more fluid then what thats capable of supplying.
i believe someone even said that above.

 

Head this advise on running lines from reg to carb...MAKE THE LINES FLEXIBLE!!! This will aid in bowl removal when playing with jets. I had one buddy who is a hard head and I warned against him running 3/8" steel lines to his bowl, but like the hard head he is, he did it. Yes it looked alright, but actually more cheesy than anything else. Then when he went out to tune, he would have to unbolt his regulator, then undo both fittings (one going to carb and the other coming out of the regulator) so he could pull the bowls off to change jets. Was'nt too long before he started getting leaks, which he would temporarily fix by snugging up tighter, then the day came when he stripped out his regualtor.

So do yourself a favor, if your running hard line, stop it at the regulator input and go from there with flexible of somesort, wheather it be 2 -6 lines to the carb bowls or a log.

 

Out of curiosity, what rpm are you shifting your car at?

 

The Barry Grant site has some good info on fuel flow requirements here.

http://www.barrygrant.com/bgfuel/def...age=81#FUELCAN

 

When racing I shift it out at 6K, I've tired 6500-7000 and only picked up .04, so for sake of the motor living (main reason I shift so low) and keeping power in the bag if I cut a bad light or spin, it's nice knowing I have the extra umph if I need it.

For what it's worth, we did the BG fuel test when I got my new fuel system hooked up and it filled the gallon jug in 11.89 seconds, good enough for a 7 sec car so waay overkill for me. When that first pump died i had to install a Holley Red pump to get me through since nobody in town carried anything but than junk Red pump. Same fuel lines, etc...did the fuel test and it took 38 seconds to fill that same 1 gallon jug. When making passes with the red pump soon as I launched the fpg would drop to 3psi and it would start popping/banging through the gears since ti was starving for fuel, I lost .3 and cant remember mph. Install a Holley Black spring into the Red pump and then pressure stayed at 7.5psi the whole pass and it lost the lean popping/banging.

 

one thing to remember when considering fuel requirements....

not so much for a race car, but for a street strip car

when you say xxxhp....requires xxx gallons/hr of fuel flow.....its important to remember that number is only a guidline.

and it ONLY takes into account the amount of fuel that would be required to run the engine at the RPM at which it makes peak HP for 1 hour.

no engine runs like that, unless it had a CVT and was burried to the floor for an hours straight at peak HP.

so generally you need a little less than the formula or popular race car guy convention says you do.

 

First you need to pick a pump that will handle the type of HP your engine is rated for. That you should be able to get from your engine builder. Next you'll need to find a pump that can handle the HP requirements, and usage ie. drag race only, street use, autocross etc. Once you've determined what pump/regulator you're going to use, then plumb it according to how the system is engineered to work. Using the wrong size lines can, and will affect the way it performs.