I don't think my mostly-stock fuel delivery setup is efficient for my motor. I have replaced most of the rubber lines with similar size rubber line, and replaced the metal line at from the pump to the carb with larger diameter rubber, and swapped in a mechanical Edelbrock pump. All the stock metal lines from the tank to the pump are still there. Sometimes, my clear fuel filter (located just before the carb) is only 1/2 or less full, even though I can see the fuel rushing through it toward the carb. This is at idle or just revving it in the garage during timing adjustments. I would like to see that full all the time. I feel that if it is half full, then the carb may be half full also, ie. not getting optimum fuel delivery. I was thinking a second electric pump back by the tank, and replace all line with larger, possibly braided stainless line. What would be a good starting line size, pump configuration, and changes in line sizes throughout the system. I am currently under or near 300HP? (probably way under, just estimating for hypothetical purposes) and have Edel 600cfm. I would like a system that would be good for up to 500HP, just for a little overkill and efficiency. The extra efficiency will help push the fuel forward during launches at the track. What are some efficient setups that you guys have? This is an economical racer/driver, not a top-dollar racer, so economical parts, and not high-end parts, are needed. I could easily construct this with all JEGS purchased high dollar parts, but that would really be overkill (and overpriced). I just need efficient and economical, middle-priced stuff.
Use the fuel can test. 1/4 mile ET Time to fill 1-Gallon Gas Can *Use line into carb 7sec under 12 seconds 8 sec 15 seconds 9 sec 20 seconds 10 sec 25 seconds 11 sec 30 seconds 12 sec 35 seconds You get the drift. I was running -8 line and have now switched to -6 line from the tank to the carb. I use a holly RED pump at the tank in-line with a canister filter. I have eliminated the small clear plastic one in the engine bay. Barry Grant (love em or hate em) has amazing fuel delivery info on his site.
That is kinda cool...I am pretty sure mine wont fill a can that quickly. Is that at idle or revving, or does it make a difference (mechanical pump)? The -6 seems to work well? And that is an electric pump at the tank, with something else at the other end, or just the one pump? I was thinking I would need one pump near the tank to push gas toward the front, then another to push it up and into the carb.
I had a guy tell me it was 1 gph for every 7 horse power. So a pump that was 110 gph would take care of 770 pony car. JF
Respectfuuly, your trying to way over engineer the fuel system. A good mechanical pump on the engine will provide all the fuel your motor can use. The filter you can see into is causing you to think all this before you really find you have a problem on the present engine. You can't use anymore than about 7 psi pressure in almost any event. It's the volume that counts. 5/16" hard line is plenty for your present setup. If you still want to replace the system with a better one, consider a two pipe system with a adjustable regulator and pressure gauge. This will give you complete control and no air issues. We have both this type system on a 300 hp+ 302 carbed Cobra and a front driven two pipe system on the Sprint car at over 500 hp on alky.
110 gph is good, but not if it was running through too constricted a system, like I assume our cheesy stock metal lines are. My edelbrock is rated at 110gph but I can idle it and watch the fuel in the filter get lower, so the carb is sucking it faster than the pump can get it there. I assume because I am using too small a fuel line, constricting flow to, or away from the pump.
Blue, 5/15" hard line, is that what came stock on the mav? That is what the outer diameter looks like. And I agree, I am assuming poor fuel flow because I can see it. Much of the time, the filter is full with just a few small bubbles, then sometimes it is empty, or pretty close to empty. There are also a couple of other times when I stall, or lose power, such as after a long burnout, which a recent thread said may NOT be due to the fuel flow. But also stalling and/or serious power loss for a few seconds after hard accelleration in town after 2nd or 3rd gear kicks in. These two items are what got me thinking that I should see the filter full all the time. I will go ahead and pull out a 1-gallon bucket and see how long it takes to fill it. I will report back in a few...
Ooops! one small problem...the car will probably not continue to run for the minute or so that I will need after I take off the fuel line to the carb... Should I just let it run until it stops, then calculate how long it WOULD have taken to fill the gallon?
I run just one pump at the tank and nothong up front but the regulator set at 7# (Demon calls for 6-7.5#) As foir the test, your fuel bowls should allow for a 35 second run.
I was reading another thread about venting the gas tank. Mine is not vented at all. Stock cap, and all venting tubes and canisters removed, vent line at the top of the tank is clogged all up, so I just capped it. Never heard a "whoosh" when opening my gas cap, though, so I assumed that it was venting through the cap, being 35 years old with poor seals...? I will try the run with the line off and get back.
I was able to get 3 qts in approx 65 seconds before it died. That comes out to about 85 seconds for a gallon, which is WAY less than what I need for a 12-second car, according to the earlier chart. This was at idle, should I do it again at rev or will it make a difference...?
for what you are doing now, an aftermarket mechanical with 3/8 line would do you fine for a while. for that matter, a 110-140 gph electric with 3/8 line would be great, too. the only way to keep track of fuel delivery problems is to put a fuel pressure gauge that you can see thru the traps on it. not a 1 1/2 gauge either. put a connector in the fuel line just before it splits at the carb, with an 1/8 npt hole in it. get an earls type 1/8 -3 male fitting. get a gauge that has an 1/8 npt for another 1/8 -3 male fitting on the back of it with a mounting cup for it . mount it to an angled piece of 1/8 aluminum that can be slipped between the hood and cowl and bolt it to the front of the cowl. might have to notch the edge of the hood for the -3 line to go thru between the hood & cowl. get an appropriate length of -3 premade teflon braided line and connect the gauge to the carb connector. when you dont want it exposed to the elements or prying hands, unscrew the mounting bolt and screw the whole mount to maybe the tower brace. when you go to the track, mount it up top where you can see it as you go down the track. glance at it all the way down the track. especially at the top of each gear. if you think about it, the greatest demand on fuel is sometimes at the top of first gear. the motor is accelerating its rpm fastest then. my glass gauge is fairly empty at idle, too. i'm running a carter hi perf mechanical pump. as you rev the engine, the mech pump will, of course, pump more fuel. checking flow at idle wont tell you much unless you idle down the track.
Why did I think you wouldn't agree? The modern FI car uses a line not much different in size. The 5L fuel line is no larger and fuel pump 88 L/Hr enough to feed nearly 300 hp at 40 psi. Take care.
When the wife gets home, i will run the fuel can test again (with help), but with about 2000-2500 RPM rev. It HAS to pump faster with rpms. Besides, my idle is only a lopy 500, which is nothing like what I am doing on the track. Thanks for all the help so far.
