gt-titan Posted September 2, 2013 Report Share Posted September 2, 2013 i am switching my 305 tbi motor to carb...the motor is in my s10 that had a 4.3 in it before swap.....my problem is with how to control the fuel pressure....i have been told i dont have enough pressure to worry about having a pressure regulator with a fuel return line witch the tbi system has...but i also was told i will need a fuel pressure regulator with a return line ... i have looked up on line how much the stock fuel pump for the 4.3 puts out.. and it is very low pressure.... i have looked on a few diff forums before i asked on here... but i havnt had any real help.... Quote Link to comment Share on other sites More sharing options...
PsychoticGaming Posted September 2, 2013 Report Share Posted September 2, 2013 You could just drop the tank, pull the pump, put in a pick up tube and just run a mechanical fuel pump off of the block. Don't quote me but I believe there is a 12-15 psi difference between mechanical pump (carb) and tbi unregulated pressure (which would be higher). This way you don't need a return line nor an FPR. Quote Link to comment Share on other sites More sharing options...
gt-titan Posted September 2, 2013 Author Report Share Posted September 2, 2013 You could just drop the tank, pull the pump, put in a pick up tube and just run a mechanical fuel pump off of the block. Don't quote me but I believe there is a 12-15 psi difference between mechanical pump (carb) and tbi unregulated pressure (which would be higher). This way you don't need a return line nor an FPR. yeah i thought about that one also...im making that my last choice...lol Quote Link to comment Share on other sites More sharing options...
Nickey4271647545519 Posted September 2, 2013 Report Share Posted September 2, 2013 A TBI fuel system runs at 15psi iirc. For a holley you'll need 7-7.5psi and edelbrock will want 5psi. Here's a FPR that's designed for a return style system for a decent price. http://www.summitracing.com/parts/qft-30-899/overview/ Quote Link to comment Share on other sites More sharing options...
gt-titan Posted September 2, 2013 Author Report Share Posted September 2, 2013 A TBI fuel system runs at 15psi iirc. For a holley you'll need 7-7.5psi and edelbrock will want 5psi. Here's a FPR that's designed for a return style system for a decent price. http://www.summitracing.com/parts/qft-30-899/overview/ it is a holley 750 and ....so if it needs 7 to 7.5 can i run a fpr without a return Quote Link to comment Share on other sites More sharing options...
Richard Cranium Posted September 2, 2013 Report Share Posted September 2, 2013 it is a holley 750 and ....so if it needs 7 to 7.5 can i run a fpr without a return Not that I know anything about carburetors. But wouldn't that be hard on the pump? An electric pump is giving full flow at all times regardless of throttle. A mechanical pump on the block would slow down and pump fuel slower at idle and speed up with throttle providing more fuel to fill the float bowl. I would think that at idle when the motor is using the least amount of fuel your electric pump would burn up while it spins, but very little fuel passes through to cool it. Also, as the engine idles and burns less fuel you might see a spike in the fuel pressure since the pump is still running, but has nowhere to go. I could be completely off base, I don't have any experience with this. If it was me, I would put a regulator with a return in the line and run the system they way it was designed to run. I wouldn't be comfortable running it as a non return system. Quote Link to comment Share on other sites More sharing options...
Nickey4271647545519 Posted September 2, 2013 Report Share Posted September 2, 2013 it is a holley 750 and ....so if it needs 7 to 7.5 can i run a fpr without a return Yes, it'd work. But like Rick said, it's a little hard on the pump. You do know that 750cfm is way way way to much carb for a 305? And it's going to lack response on the street. Quote Link to comment Share on other sites More sharing options...
gt-titan Posted September 3, 2013 Author Report Share Posted September 3, 2013 well it came off a stock 5.0 ford motor and it was good on it...the carb was jetted down and setup to work on a stock motor... so i was told..i have a holley 650 on standby just in case.... Quote Link to comment Share on other sites More sharing options...
gt-titan Posted September 3, 2013 Author Report Share Posted September 3, 2013 Yes, it'd work. But like Rick said, it's a little hard on the pump. You do know that 750cfm is way way way to much carb for a 305? And it's going to lack response on the street. heres another one that im being told...that i can run a fpr with a fuel line in and two fuels lines out...and run one of the out as the return... is this possible Quote Link to comment Share on other sites More sharing options...
gt-titan Posted September 3, 2013 Author Report Share Posted September 3, 2013 Not that I know anything about carburetors. But wouldn't that be hard on the pump? An electric pump is giving full flow at all times regardless of throttle. A mechanical pump on the block would slow down and pump fuel slower at idle and speed up with throttle providing more fuel to fill the float bowl. I would think that at idle when the motor is using the least amount of fuel your electric pump would burn up while it spins, but very little fuel passes through to cool it. Also, as the engine idles and burns less fuel you might see a spike in the fuel pressure since the pump is still running, but has nowhere to go. I could be completely off base, I don't have any experience with this. If it was me, I would put a regulator with a return in the line and run the system they way it was designed to run. I wouldn't be comfortable running it as a non return system. thanks man...deff something to think about... Quote Link to comment Share on other sites More sharing options...
Cordell Posted September 3, 2013 Report Share Posted September 3, 2013 Okay let me tell you a story. Some years back I had an S10 with a 2.5L 4 banger. I got sick of not having any adjustment to the stock TBI system so I decided to swap on a 2 barrel holly carb. While this is not the same exact scenario here's what I did, the stock fuel pump puts out about 15 psi so I installed a cheap holley FPR and blocked off the return line. Using a fuel pressure gauge I adjusted the FPR to about 5 psi. Basically the fuel pump would deadhead against the regulator. Drove the truck about 4 years like that before the body rusted off, the engine and carb set up still worked great. Right or wrong it will work. If it was really a high pressure system I wouldn't even try it, but the pump is not strong enough to push past the regulator and as much as I drove mine the wear and tear couldn't have increased much. Quote Link to comment Share on other sites More sharing options...
gt-titan Posted September 3, 2013 Author Report Share Posted September 3, 2013 Okay let me tell you a story. Some years back I had an S10 with a 2.5L 4 banger. I got sick of not having any adjustment to the stock TBI system so I decided to swap on a 2 barrel holly carb. While this is not the same exact scenario here's what I did, the stock fuel pump puts out about 15 psi so I installed a cheap holley FPR and blocked off the return line. Using a fuel pressure gauge I adjusted the FPR to about 5 psi. Basically the fuel pump would deadhead against the regulator. Drove the truck about 4 years like that before the body rusted off, the engine and carb set up still worked great. Right or wrong it will work. If it was really a high pressure system I wouldn't even try it, but the pump is not strong enough to push past the regulator and as much as I drove mine the wear and tear couldn't have increased much. good info bro....thanks,,, Quote Link to comment Share on other sites More sharing options...
Richard Cranium Posted September 3, 2013 Report Share Posted September 3, 2013 Okay let me tell you a story. Some years back I had an S10 with a 2.5L 4 banger. I got sick of not having any adjustment to the stock TBI system so I decided to swap on a 2 barrel holly carb. While this is not the same exact scenario here's what I did, the stock fuel pump puts out about 15 psi so I installed a cheap holley FPR and blocked off the return line. Using a fuel pressure gauge I adjusted the FPR to about 5 psi. Basically the fuel pump would deadhead against the regulator. Drove the truck about 4 years like that before the body rusted off, the engine and carb set up still worked great. Right or wrong it will work. If it was really a high pressure system I wouldn't even try it, but the pump is not strong enough to push past the regulator and as much as I drove mine the wear and tear couldn't have increased much. Alrighty then, we have an answer. Experience beats out theory every day of the week. Quote Link to comment Share on other sites More sharing options...
gt-titan Posted September 3, 2013 Author Report Share Posted September 3, 2013 Alrighty then, we have an answer. Experience beats out theory every day of the week. u said that right!!!! i seen a car with a holley fpr with a fuel line in with two fuel lines out...one went to the carb one to the return line.... he told me it takes alot of stress off the pump.... and he has had the same pump for 3 years and he drives it almost every day.... it was showing 8 psi..... now i have two choices...lol... Quote Link to comment Share on other sites More sharing options...
Richard Cranium Posted September 4, 2013 Report Share Posted September 4, 2013 Either way, looks like you're going to need a pressure regulator. I got the feeling your original question was whether or not you could feed the fuel line straight to the carb from the pump at full pressure. Quote Link to comment Share on other sites More sharing options...
gt-titan Posted September 4, 2013 Author Report Share Posted September 4, 2013 Either way, looks like you're going to need a pressure regulator. I got the feeling your original question was whether or not you could feed the fuel line straight to the carb from the pump at full pressure. lol.......no i was trying to fig out if i really needed a fpr with a return line out. or if i could run one without.... but i think i got it now...lol thanks everyone.... Quote Link to comment Share on other sites More sharing options...
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