luvemfast Posted May 10, 2012 Share Posted May 10, 2012 My dad is close to getting his Z running, converting from EFI to triple 44PHH. So he has an EFI fuel pump. He has a choice of either 6 PSI or 4.5 PSI. Which would be best? No regulator and a return line. Thanks. Quote Link to comment Share on other sites More sharing options...
madkaw Posted May 10, 2012 Share Posted May 10, 2012 Neither-you want 3.5psi. Maybe 4psi at th most, so you will need a regulator Quote Link to comment Share on other sites More sharing options...
luvemfast Posted May 10, 2012 Author Share Posted May 10, 2012 4.5 pump would get pressure drop from tank to carbs though? And with a return line, that would work ok wouldn't it? Quote Link to comment Share on other sites More sharing options...
ctc Posted May 10, 2012 Share Posted May 10, 2012 4.5 pump would get pressure drop from tank to carbs though? And with a return line, that would work ok wouldn't it? You will want to get the regulator and a good fuel pressure gauge. My Webers like to live best at 3psi. without the regulator I had drivability issues. Quote Link to comment Share on other sites More sharing options...
Leon Posted May 10, 2012 Share Posted May 10, 2012 You can run the current EFI pump using a return line (equal in size to feed) and an inline pressure regulator. Quote Link to comment Share on other sites More sharing options...
Lazeum Posted May 10, 2012 Share Posted May 10, 2012 (edited) You can run the current EFI pump using a return line (equal in size to feed) and an inline pressure regulator. A friend of mine tried this solution when he switched his ZX with Carbs. He ended up being lean because of fuel delivery. It seems that pressure regulation is reducing flow rate as well making the pump running out of fuel. He ended up removing his EFI fuel pump for carb specific pump. For $100, I wouldn't skip this step. Carter 4070, Mallory 4070lp, Facet Red Top, etc. All would run 70gph at around 4 psi, good enough for 250whp. Edited May 10, 2012 by Lazeum Quote Link to comment Share on other sites More sharing options...
Tony D Posted May 10, 2012 Share Posted May 10, 2012 A friend of mine tried this solution when he switched his ZX with Carbs. He ended up being lean because of fuel delivery. It seems that pressure regulation is reducing flow rate as well making the pump running out of fuel. He ended up removing his EFI fuel pump for carb specific pump. For $100, I wouldn't skip this step. Carter 4070, Mallory 4070lp, Facet Red Top, etc. All would run 70gph at around 4 psi, good enough for 250whp. He did something VERY WRONG then! The stock EFI fuel pump will fuel triples using a backpressure regulator to well over 300HP! The flow rate of the stock Bosch-Licensed pump goes through the roof at 3psi. I ran (and still do) this system to 375HP in turbocharged form and with a simple jet or regulator setting change immediately flood the engine to the point of sinking the floats and fuel pouring out the carburettor throats! If someone "ran lean" using mere triples and the stock EFI pump---then either the pump was shot to begin with, or they did something VERY WRONG in setting up the system---first thought to mind by the way it was phrased was 'pressure regulation is reducing flow' meaning he DID NOT use the REQUIRED backpressure regulator. And FYI: the EXACT same thing will happen to a carb pump if you use that style regulator! A backpressure regulator ALWAYS has full pump capacity available to deliver fuel to the carbs or injectors. Any regulator placed between the pump and the fuel delivery source is ALWAYS going to be a potential bottleneck in delivery through orifice size or malfunction. Quote Link to comment Share on other sites More sharing options...
Leon Posted May 10, 2012 Share Posted May 10, 2012 A friend of mine tried this solution when he switched his ZX with Carbs. He ended up being lean because of fuel delivery. It seems that pressure regulation is reducing flow rate as well making the pump running out of fuel. He ended up removing his EFI fuel pump for carb specific pump. For $100, I wouldn't skip this step. Carter 4070, Mallory 4070lp, Facet Red Top, etc. All would run 70gph at around 4 psi, good enough for 250whp. Yes, it's clear he did something totally wrong. The EFI pumps are designed to flow at high pressures. As you go down in pressure on the pump curve, the flow rate will increase. There is no way you should run lean with a properly regulated EFI pump, pouring rich maybe but not lean. Quote Link to comment Share on other sites More sharing options...
luvemfast Posted May 11, 2012 Author Share Posted May 11, 2012 thanks folks, bottom line is. He needs a regulator Quote Link to comment Share on other sites More sharing options...
Lazeum Posted May 11, 2012 Share Posted May 11, 2012 (edited) Yes, it's clear he did something totally wrong. The EFI pumps are designed to flow at high pressures. As you go down in pressure on the pump curve, the flow rate will increase. There is no way you should run lean with a properly regulated EFI pump, pouring rich maybe but not lean. I would have agreed with you. I even advised him to go this route but facts have proven that EFI was running low on fuel with regulator. It has been observed on dyno with AFR reading. Car was running great on 1st, 2nd & 3rd gear but not anymore (= super lean) on 4th & 5th. So now, I don't advise it anymore. Luvemfast, Get a regulator, run the car with EFI pump & report on results. Worst case scenario you'll buy a low pressure pump later on Edited May 11, 2012 by Lazeum Quote Link to comment Share on other sites More sharing options...
Leon Posted May 11, 2012 Share Posted May 11, 2012 I would have agreed with you. I even advised him to go this route but facts have proven that EFI was running low on fuel with regulator. It has been observed on dyno with AFR reading. Car was running great on 1st, 2nd & 3rd gear but not anymore (= super lean) on 4th & 5th. So now, I don't advise it anymore. Luvemfast, Get a regulator, run the car with EFI pump & report on results. Worst case scenario you'll buy a low pressure pump later on Then he either set it up wrong, or something went amiss. There is no reason that a properly working, properly regulated EFI pump should not be able to supply enough fuel at low pressure. We are talking physics here, not anecdotal evidence. Quote Link to comment Share on other sites More sharing options...
Lazeum Posted May 11, 2012 Share Posted May 11, 2012 I agree with you regarding the physics. His pump may have been shot for awhile. Quote Link to comment Share on other sites More sharing options...
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