Correct fuel psi for carbed 350

[Kazuya1274]

I have a Carter 5 psi 72 gph electric fuel pump on my ZX, running the stock inlet line. The car runs down the road good but starts to buck slightly in 5th gear after driving for a while. When I floor it, the car accelerates to a point then flattens out. I've got a nice setup on the engine, and it should be screaming. Fuel pressure drops down to about 1 or 2 psi when I open the throttle at idle. Have yet to tape the gauge to the windshield and go driving though. I am just wondering if my fuel pump should be putting out more psi. My friend found some specs in his Chilton manual for the pickups, and the 350 models required 7 psi I think, and the 454 required 9 psi. With my engine putting out (on paper) 350 to 400 HP, does my fuel pump seem adequate for the job? If not, what kind of pump should I be looking at?

[280zwitha383]

Just a suggestion but you could run a mechanical fuel pump on the ZX depending on how far you have it set back. That would give you an idea what it should run like or you could just leave it that way. A stock mech. fuel pump for an SBC is about $12 as apposed to $50-$100 for an electric one. I would think 7-8 psi is good. 5 seems pretty low to me.

[Kazuya1274]

I'd try that except that the engine is shoved back too far to clear a mechanical fuel pump. Otherwise I'd switch right over. You are right, 5 psi is probably too little though. I think I got an electric fuel pump for a carbureted 6 cylinder

[280zwitha383]

Well, you should do a search then. I saw a post where the guy said his Edelbrock requires 6.5. Look at the documentation for you Demon carb if you have any, otherwise do a search.

[patzky1]

I had a stock Q-jet and was running about 7 psi just fine with an e pump. Then I got an Edelbrock 1405 (600 cfm, AFB style) carb and it wanted to leak past the float needle seats until I got a regulator and put it down to 6. Your carb may be different, but Edelbrocks aren't supposed to like more than 6 psi. Point is, don't rush to get a higher pressure pump until you know your carb can handle it.

 

You may have a semi-clogged filter or line somewhere. I had a similar experience to yours before and it was due to a slightly (not very) dirty fuel filter in the line just before the carb. Once I changed it out the car came back alive on the freeway after merging, etc. instread of falling right on its face.

 

Pat

[Corzette]

My 650DP Demon and all Holleys Ive had 750DP need about 7 PSI...8 to 9 will spill em over and make ur plugs wet or foul them in time. Watch where your lines run too cuz vapor lock is a real issue with these cars sometimes due to the underhood temps. My 240 has issues in the summer at the track with the hood on, hence I run without it. I have braided lines too but still have issues if its too hot. This will make your Fuel pressure start declining quick. You will experience serious powerloss when the engine starts starving...been there done that. On the 280 the fuel lines are ran thru the fender into the front of the car so I have no issues with it. I guess its time to reroute the Corzette lines in the future. Holley red pump is 7 PSI I think and could be run without a regulator. The blue is 14PSI without regulator....they sure are noisy though lol. Be careful with that carbureted pump as side drafts and maybe SUs only like 3 to 5 pSI if memory serves me correctly. I remember gas pouring out onto my headers from the Mikunis I had with the fuel pressure too high.....scary. The fuel gauge is a good tool...

 

Terry

[Guest zfan]

5.5 is plenty for a Edelbrock carb. I have run the 600 and 750 on my 350's before going to 383. I always used a regulator as I guess I am picky. 5.5 worked just fine. My guess is you have a pinched line or clogged filter.

 

Mike

[Guest Aaron]

Is the stock fuel pump still in place? If so, your pump will be able to get enought gas through it to make the car run, but under acceleration it won't be able to suck enough through.

[dr_hunt]

Electric pumps don't suck very well, they push. Sounds like your stock fuel lines may be the problem, not the pump, or maybe a combination of the two. Everybody is right about fuel pressure, hoever pressure doesn't cut it, it's the flow that makes HP and it sounds like your not getting enough flow at anything more than part throttle. The pressure will drop when the flow starts (ie. WOT), which is why alot of pumps put out high pressure at low flow numbers. What size is the stock line? I'd suggest running braided hose -6 or -8 or run the summit 1/2" aluminum line. Also position the electric pump below the fuel tank level or at least halfway between the bottom and top of the tank. If you don't do that then the pump is trying to lift the fuel 1 foot or so and the Vaporization point of gas doesn't allow for alot of lift. For instance you can suck water up about 20 feet at sea level before it vaporizes.

 

Food for thought; In my car I run the aeromotive A2000 pump which pumps some ungodly volume cause I run alcohol and it is positioned even with the bottom of my fuel cell. Fills a 5 gallon fuel jug in 20 seconds through the regulator using one -8 line that usually goes to the back bowl of the carb. If I turn the pump on and run one of the -8 lines into a fuel jug, the pressure gauge at outlet of the regulator reads 3 psi and the one on the pump outlet reads 6 psi, so, in my -10 braided hose from the pump at the back of the car to the front of the car I have 3psi pressure drop at that flow with only one of the -8 lines off and that is with a -10 line from the pump to the regulator folks. So with that puny little stock fuel line, at WOT I'd bet you have too much pressure drop and no flow to the carb. But, that's my guess, so take it for what it's worth. Today I'll take 5 bucks for my opinion, you can send it paypal if you want or just donate it to hybrid z. JK but it is a Good idea, donate it.