Sharp drop in fuel pressure
02-08-2009, 08:06 PM
#1
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Sharp drop in fuel pressure Hey
I'm working on a LT1 with a vortech blower. Power is in the 560-570 rwhp range and its using a stock fuel pressure regulator. Injectors are 60 motrons.
For a fuel system it has a racetronix in tank pump with a vortech T-rex inline pump.
Fuel pressure goes from 40 psi to 52 psi during the run then at about 6300 RPM the fuel pressure drops very quickly back to 40 or less.
I just wanted to make sure there was nothing goofy with LT1 buckets or anything that would cause it to starve. I've seen pumps give a gradual drop in fuel pressure but this falls almost immediately.
I'm working on a LT1 with a vortech blower. Power is in the 560-570 rwhp range and its using a stock fuel pressure regulator. Injectors are 60 motrons.
For a fuel system it has a racetronix in tank pump with a vortech T-rex inline pump.
Fuel pressure goes from 40 psi to 52 psi during the run then at about 6300 RPM the fuel pressure drops very quickly back to 40 or less.
I just wanted to make sure there was nothing goofy with LT1 buckets or anything that would cause it to starve. I've seen pumps give a gradual drop in fuel pressure but this falls almost immediately.
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02-09-2009, 08:48 PM
#9
You should never run pumps in series. This does not increase flow.
You need pumps in parallel to properly increase flow.
A bigger second pump will be restricted by the first.
The supercharger makers supply inline pumps to help increase pressure when running an FMU. This only serves to increase pressure within the limits of the standard flow rating.
You need pumps in parallel to properly increase flow.
A bigger second pump will be restricted by the first.
The supercharger makers supply inline pumps to help increase pressure when running an FMU. This only serves to increase pressure within the limits of the standard flow rating.
02-09-2009, 10:31 PM
#10
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You should never run pumps in series. This does not increase flow.
You need pumps in parallel to properly increase flow.
A bigger second pump will be restricted by the first.
The supercharger makers supply inline pumps to help increase pressure when running an FMU. This only serves to increase pressure within the limits of the standard flow rating.
You need pumps in parallel to properly increase flow.
A bigger second pump will be restricted by the first.
The supercharger makers supply inline pumps to help increase pressure when running an FMU. This only serves to increase pressure within the limits of the standard flow rating.
At the HP levels he's quoting....a single 044 inline is a bandaid that will work if the Walbro is in proper working order. The pressure head in the Walbro intank will be less than the inline pump....inline pump takes the FPR hit...intank pump isn't exactly in a freeflow state...but it sees much less pressure and it's ability to flow more will increase big time based on the flow curve.
02-10-2009, 12:25 AM
#11
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I don't really agree that series pumps are a bad idea. The principle is as old as time. Just the way you can run a 9v battery with a 1.5v to make a 10.5 potential you should be able to stack pump work with some effectiveness. *if I remember right, been a while.. a pumps work = m_rate * density * (dp) with two pumps we are just sharing the change in pressure. If there is a helper pump one pump should be pumping to some 1/x of the system's pressure where the other pump would be pumping the remainder. The problem is these pump manufactures do not publish any real data on their pumps. We don't know if a walbro flows 300lph at 20psi or 258lph.
Regardless, I don't know if theres some resonance or anything else weird going on between the two pumps so I'll eliminate one this week and see if the problem goes away.
One thing I think is really weird going back and looking at my logs/dyno sheets this car had the same sharp drop in fuel pressure with the old setup that made 80 less rwhp. The difference is I went with a racetronix setup with a brand new T-rex. What I find strange is that the drop happens right at the same RPM, same boost, etc. The 80rwhp came from a cam/exhaust change. I wonder is something is going on with the FPR. The FP starts at 43psi at the start of the run and rises to about 53 during the run due to boost pushing the FPR up then at 6300 RPM and about 13psi it just snaps back to 40 psi. Its a stock FRP, all the vaccum lines going to it are zip tied to keep them from swelling under boost.
Regardless, I don't know if theres some resonance or anything else weird going on between the two pumps so I'll eliminate one this week and see if the problem goes away.
One thing I think is really weird going back and looking at my logs/dyno sheets this car had the same sharp drop in fuel pressure with the old setup that made 80 less rwhp. The difference is I went with a racetronix setup with a brand new T-rex. What I find strange is that the drop happens right at the same RPM, same boost, etc. The 80rwhp came from a cam/exhaust change. I wonder is something is going on with the FPR. The FP starts at 43psi at the start of the run and rises to about 53 during the run due to boost pushing the FPR up then at 6300 RPM and about 13psi it just snaps back to 40 psi. Its a stock FRP, all the vaccum lines going to it are zip tied to keep them from swelling under boost.
02-10-2009, 08:45 PM
#12
Your analogy is a little misleading....
Increased voltage makes the pump spin faster & therefore more output.
The "battery in series" example you are relating to is more like HP.
Series pumps have more total power, (more pumping pressure at a given volume), but will do little to increase total flow above its rated pumping volume.
This is just like an engine that makes more power, but will not rev any higher. It will accelerate a car or go up a steep hill faster, but will not go faster than its predetermined rpm limit... unless it originally did not have enough power to reach max rpm.
For a pump that is rated at 255lph at 45psi, 2 pumps in series will still only flow roughly 255lph at the same pressure, but may be capable of flowing (a guesstimated example) 200lph at 75psi compared to 150lph with only 1 pump at the same pressure.
2 pumps in parallel will flow twice the amount at their rated pressure.
Increased voltage makes the pump spin faster & therefore more output.
The "battery in series" example you are relating to is more like HP.
Series pumps have more total power, (more pumping pressure at a given volume), but will do little to increase total flow above its rated pumping volume.
This is just like an engine that makes more power, but will not rev any higher. It will accelerate a car or go up a steep hill faster, but will not go faster than its predetermined rpm limit... unless it originally did not have enough power to reach max rpm.
For a pump that is rated at 255lph at 45psi, 2 pumps in series will still only flow roughly 255lph at the same pressure, but may be capable of flowing (a guesstimated example) 200lph at 75psi compared to 150lph with only 1 pump at the same pressure.
2 pumps in parallel will flow twice the amount at their rated pressure.
02-11-2009, 10:33 AM
#13
easy now, how about checking the filters first.. seen it happen
also a possibility of a kinked/crimped line up around the tank.. seen it happen
what kinda a/f you targeting? you could be at the limit of the pump because you are being too conservative with the tune.. seen it happen
is the alternator charging well, and no i dont mean via the dummy gauge. seen it happen
check in the tank for that dumb *** white straw to be split open and pissing fuel out the side.. seen it happen
see that the relay is wired right, clean grounds etc. dirty ground kills. my pumps are wired straight to my battery ground.
who put in the pump? if its in the wrong spot on the hanger it MIGHT be bottomed against the tank and the inlet blocked.
if this guy only cares about getting it finished and is ok with a bandaid, look at the walbro flow charts vs. pressure and you can see that if you even add a second walbro inline, that when you divide the 52psi fuel between them (26 each) that they can meet the demand... and i say easily do able with the bosch 044 in line.
with the 044 thought you are throwing a lot of money at it and as lonnie says the money much better spent on adding another walbro in the tank to get way more flow.
also a possibility of a kinked/crimped line up around the tank.. seen it happen
what kinda a/f you targeting? you could be at the limit of the pump because you are being too conservative with the tune.. seen it happen
is the alternator charging well, and no i dont mean via the dummy gauge. seen it happen
check in the tank for that dumb *** white straw to be split open and pissing fuel out the side.. seen it happen
see that the relay is wired right, clean grounds etc. dirty ground kills. my pumps are wired straight to my battery ground.
who put in the pump? if its in the wrong spot on the hanger it MIGHT be bottomed against the tank and the inlet blocked.
if this guy only cares about getting it finished and is ok with a bandaid, look at the walbro flow charts vs. pressure and you can see that if you even add a second walbro inline, that when you divide the 52psi fuel between them (26 each) that they can meet the demand... and i say easily do able with the bosch 044 in line.
with the 044 thought you are throwing a lot of money at it and as lonnie says the money much better spent on adding another walbro in the tank to get way more flow.
02-11-2009, 10:53 PM
#15
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The more I think about it the more I think I'm just out of fuel. I haven't tested fuel pressure between the pumps but seeing how both are 255lph pumps I'm going to take a stab and say between the first pump and second pump should be ~25psi and should be ~50psi after the second.
Thats still about 255 lph for the first pump and about the same for the second pump. Lonnie is right, and its really due to the pump performance curves. You do see a slight stack in flow rate when you run them in series but its nothing to write home about.. What I was banking on was the pump would flow quite a bit more when its head was cut in half. Not really the case.
1. I took for granted how much this car was going to make.. It picked up 100rwhp with a cam and exhaust change, we honestly expected half of that. Worse of all it did it at high RPM.
2. Never really bothered to look up the pump performance curve. I'm used to and expected to see a 1/2 drop in flow rate with twice the change in pressure. Not the case at all. These things are pretty efficiently till about 60psi.
Heres the pump performance graphs if anyone needs them in the future
http://www.vortechsuperchargers.com/...-265_graph.gif
http://www.gnttype.org/techarea/fuel.../gss307340.gif
Now the question lies with what fuel system should I do now. We are mid 570's now with a LT1 car shooting for a 11.5 AFR. Thats at 13psi too, I hope to eventually be in the 18 pound range!
Lonnies has some nice systems.. Just got to make a decision on how wild I want to go.
Thats still about 255 lph for the first pump and about the same for the second pump. Lonnie is right, and its really due to the pump performance curves. You do see a slight stack in flow rate when you run them in series but its nothing to write home about.. What I was banking on was the pump would flow quite a bit more when its head was cut in half. Not really the case.
1. I took for granted how much this car was going to make.. It picked up 100rwhp with a cam and exhaust change, we honestly expected half of that. Worse of all it did it at high RPM.
2. Never really bothered to look up the pump performance curve. I'm used to and expected to see a 1/2 drop in flow rate with twice the change in pressure. Not the case at all. These things are pretty efficiently till about 60psi.
Heres the pump performance graphs if anyone needs them in the future
http://www.vortechsuperchargers.com/...-265_graph.gif
http://www.gnttype.org/techarea/fuel.../gss307340.gif
Now the question lies with what fuel system should I do now. We are mid 570's now with a LT1 car shooting for a 11.5 AFR. Thats at 13psi too, I hope to eventually be in the 18 pound range!
Lonnies has some nice systems.. Just got to make a decision on how wild I want to go.
02-11-2009, 10:58 PM
#16
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BTW.. Am I the only one disappointed in that a GSS340 only flows 255 at about 15psi? At 60psi its only 225lph. The Vortech pump flows 255 right at 40psi.
I don't know maybe my source is way off??!
I don't know maybe my source is way off??!
