[ProCharger]

Originally Posted by parish8

600+hp with gasoline should not be an issue with all stock fuel system.

Not all of the HPFP's are created equal.

I have seen many run out before that.
Yet others hang one to 650.

NOTE: the other day I had a stock LT4 not even be able to keep up with the 9% overdrive balancer. Literally hardly any power increase at all, and preso-chango she was already out of HPFP. He just got one of the unlucy "dud" pumps.

[exxit]

Originally Posted by ProCharger

Not all of the HPFP's are created equal.

I have seen many run out before that.
Yet others hang one to 650.

NOTE: the other day I had a stock LT4 not even be able to keep up with the 9% overdrive balancer. Literally hardly any power increase at all, and preso-chango she was already out of HPFP. He just got one of the unlucy "dud" pumps.

I wonder if there is a common denominator between these pumps... A factory or batch or something.

[Atomic Ed]

Interesting comments on the variability of the HPFP. It does make sense. Going from roughly 60 psi to 2100 psi in a single stage positive displacement pump is tough to do and keep the variation to a minimum, as well as cost.

[Chevy71]

I may have some info to help here. I work for a Caterpillar dealer and have for some time now. Started life as a mechanic and have worked on everything from trucks, machines, and compression engines. DI with a high pressure system is the main staple of fueling for almost all of the newer cat engines (natural gas being the only series that doesn't use it). This may help simplify the system and make it easier to understand the short comings. The HPFP has nothing to do with volume, it takes whatever volume the LPFP system sends it and increases the pressure. It will move whatever volume you send it and the injectors expell. The HPFP is fixed displacement that only varies by engine speed, it's purely mechanical. The HPFP can only lose performance from injector problems, internal problems within itself, or fuel coming to it causing cavitation that could harm the output. The LT4 pump will not move any more volume, only increase the pressure it's being fed by the same LP pump (this system is slightly, larger so it will move some, but it's minimal). Typically the low side pressure will actually drop if you put a larger high side pump on, or larger injectors. The low side is usually variable (electric driven and varies by electric supply) so it can keep up with changes in the system (injector clog or leak, bleed off from HP pump internal issues).

With all this said, in our applications (and about every DI engine I've worked on) to support more boost and more fuel, the LP pump is where to start. I've been doing a pile of research on the LT1/4 actual components trying to decide what I should do with my current build. It's very hard to get true data on the parts, but I can say most HP pump failures are probably because the system has got hot or went dry causing extreme wear internally on the HP pump. Adding the LT4 pump alone will do next to nothing for what fuel you put out because it's still trying to come out of the same tubes and the same injectors which completely prevent the gains the LT4 offers. The LT4 system only gains some psi and looks to gain very little volume. If your system is running out of fuel, your biggest gain will be the low side pump. The high side and LT4 injectors will gain some, but the gain isn't worth the $$$, and it's near nothing without the extra volume from the LP. You can turn up the output on the stock LP system to get more out of it, and the ZL1 LP has a better range. Again, this system does not perform much better than stock and you will hit a wall again shortly. I want a system that can support 1000hp comfortably and run around 750-800. That duty cycle will last and will always perform top notch. That's the way all of our engines are designed and I have never dyno'd one that ever came close to running out of fuel, both on the flywheel and the chassis dyno. So that's my .02 with my experience on these types of fuel systems and what I have learned on the LT1 system.

[ProCharger]

Originally Posted by Atomic Ed

Interesting comments on the variability of the HPFP. It does make sense. Going from roughly 60 psi to 2100 psi in a single stage positive displacement pump is tough to do and keep the variation to a minimum, as well as cost.

I have been around an absolute boat load of LT car and trucks now since they started hitting the dealership lots.

I know the internet has all sorts of "theories" on this and that.
But what I can say for absolute 100% fact are two things.


1)
I have only seen ONE fuel system failure on a stone stock car. (new vette, that even bone stock could hardly maintain 900psi of fuel pressure at peak TQ) dealer swapped the pump out, car still awesome to this day.

So other then that one rare car, it's a very good system. The pumps can obviously keep up well for stock cars, and even ones that are tracked and abused.

2)
Every single car/truck I have logged after getting a blower kit has different abilites to keep up with fuel demands. Never ONCE have I seen two cars in a row have the same HPFP, and LPFP values when the 100% stock system is retained.

Everything has a mechanical variance. So that variance really comes into play when pushing things to the limit. Hence why anyone pushing the power limits really needs to have a tuner that is dialed into what to look for... to replace the parts that are needed. Otherwise, you will be shot gunning parts at the car.

If I had a dollar for every person that was sold LT4 injectors "to fix their fuel issue".... when the actual issue was the HPFP... I would have at least enough money to enjoy a good dinner and movies adventure. And to me, that is upsetting to know people spend big bucks on injectors, when in reality a simple fuel pump would have fixed their issue.

Or the guys being sold really expensive "fuel systems"... when a $250 boost-a-pump would have cured their issue.



If you are going to change parts on your fuel system.
Work with a good tuner that knows these DI cars and trucks inside and out.
Thats my best advice.

[Atomic Ed]

Originally Posted by ProCharger

I have been around an absolute boat load of LT car and trucks now since they started hitting the dealership lots.

I know the internet has all sorts of "theories" on this and that.
But what I can say for absolute 100% fact are two things.


1)
I have only seen ONE fuel system failure on a stone stock car. (new vette, that even bone stock could hardly maintain 900psi of fuel pressure at peak TQ) dealer swapped the pump out, car still awesome to this day.

So other then that one rare car, it's a very good system. The pumps can obviously keep up well for stock cars, and even ones that are tracked and abused.

2)
Every single car/truck I have logged after getting a blower kit has different abilites to keep up with fuel demands. Never ONCE have I seen two cars in a row have the same HPFP, and LPFP values when the 100% stock system is retained.

Everything has a mechanical variance. So that variance really comes into play when pushing things to the limit. Hence why anyone pushing the power limits really needs to have a tuner that is dialed into what to look for... to replace the parts that are needed. Otherwise, you will be shot gunning parts at the car.

If I had a dollar for every person that was sold LT4 injectors "to fix their fuel issue".... when the actual issue was the HPFP... I would have at least enough money to enjoy a good dinner and movies adventure. And to me, that is upsetting to know people spend big bucks on injectors, when in reality a simple fuel pump would have fixed their issue.

Or the guys being sold really expensive "fuel systems"... when a $250 boost-a-pump would have cured their issue.


If you are going to change parts on your fuel system.
Work with a good tuner that knows these DI cars and trucks inside and out.
Thats my best advice.

That's the kind of insight I like to see here. Thanks.

[Perdieu]

Originally Posted by ProCharger

I have been around an absolute boat load of LT car and trucks now since they started hitting the dealership lots.

I know the internet has all sorts of "theories" on this and that.
But what I can say for absolute 100% fact are two things.


1)
I have only seen ONE fuel system failure on a stone stock car. (new vette, that even bone stock could hardly maintain 900psi of fuel pressure at peak TQ) dealer swapped the pump out, car still awesome to this day.

So other then that one rare car, it's a very good system. The pumps can obviously keep up well for stock cars, and even ones that are tracked and abused.

2)
Every single car/truck I have logged after getting a blower kit has different abilites to keep up with fuel demands. Never ONCE have I seen two cars in a row have the same HPFP, and LPFP values when the 100% stock system is retained.

Everything has a mechanical variance. So that variance really comes into play when pushing things to the limit. Hence why anyone pushing the power limits really needs to have a tuner that is dialed into what to look for... to replace the parts that are needed. Otherwise, you will be shot gunning parts at the car.

If I had a dollar for every person that was sold LT4 injectors "to fix their fuel issue".... when the actual issue was the HPFP... I would have at least enough money to enjoy a good dinner and movies adventure. And to me, that is upsetting to know people spend big bucks on injectors, when in reality a simple fuel pump would have fixed their issue.

Or the guys being sold really expensive "fuel systems"... when a $250 boost-a-pump would have cured their issue.



If you are going to change parts on your fuel system.
Work with a good tuner that knows these DI cars and trucks inside and out.
Thats my best advice.

GREAT info for everyone.
Hope we can provide a little more info with my car to help others make the right choice for fuel upgrades

[parish8]

I read a comment on a hptuners thread. the poster has experience with di 4 cyl motors and pumps.

he said if you are dropping high fuel pressure at peek tq you are out of hpfp. if you are dropping high fuel pressure at higher rpms you are not feeding it enough fuel with your low pressure fuel system.

even though you may not see a drop in low side fuel pressure it still may not be enough to feed the hpfp at higher rpms.

[Chevy71]

Originally Posted by parish8

I read a comment on a hptuners thread. the poster has experience with di 4 cyl motors and pumps.

he said if you are dropping high fuel pressure at peek tq you are out of hpfp. if you are dropping high fuel pressure at higher rpms you are not feeding it enough fuel with your low pressure fuel system.

even though you may not see a drop in low side fuel pressure it still may not be enough to feed the hpfp at higher rpms.

That is 100% correct, and the same thing I see with DI cat engines on the dyno. The HP pump can't make volume and without the volume can't make pressure. High rpm is the most demand for fuel.

[Atomic Ed]

Originally Posted by parish8

I read a comment on a hptuners thread. the poster has experience with di 4 cyl motors and pumps.

he said if you are dropping high fuel pressure at peek tq you are out of hpfp. if you are dropping high fuel pressure at higher rpms you are not feeding it enough fuel with your low pressure fuel system.

even though you may not see a drop in low side fuel pressure it still may not be enough to feed the hpfp at higher rpms.

Still trying to wrap my head around "the why" of this.

[parish8]

Originally Posted by Atomic Ed

Still trying to wrap my head around "the why" of this.

my understanding for what it is worth...

being mechanical the hpfp output should be tied to rpm. at 6000rpm it should put out twice as much fuel at at 3000rpm. i believe the most fuel for a given rpm that you will need is at peek tq. above that point your fuel needs compared to rpms will actually go down.

if you make it thru peek tq without dropping fuel pressure then that is the most fuel/rpm that you should need. as rpms go up the pump output goes up and you should be covered. that doesn't mean you wont need more fuel. you will need more fuel but the rate of rise of the hpfp output should go up faster than the needed fuel.

that being said if you are not feeding it enough fuel to work perfectly its output will drop up top. it will require twice as much fuel feeding it at 6000rpm as at 3000rpm.

think about whatever orifice they have going into that hpfp and how much fuel it can flow. now bump that up to an lt4 hpfp or even a big bore lingerfilder pump with the motor spinning at 6400rpm. then even add some stroke to it with a 32% larger cam lobe. you are going to have to really hit the hpfp with some low pressure fuel to not starve it.

my plan just to play it safe is build an excessive low side and feed that hpfp with ~70psi any time i am under boost.

[Chevy71]

Originally Posted by parish8

my understanding for what it is worth...

being mechanical the hpfp output should be tied to rpm. at 6000rpm it should put out twice as much fuel at at 3000rpm. i believe the most fuel for a given rpm that you will need is at peek tq. above that point your fuel needs compared to rpms will actually go down.

if you make it thru peek tq without dropping fuel pressure then that is the most fuel/rpm that you should need. as rpms go up the pump output goes up and you should be covered. that doesn't mean you wont need more fuel. you will need more fuel but the rate of rise of the hpfp output should go up faster than the needed fuel.

that being said if you are not feeding it enough fuel to work perfectly its output will drop up top. it will require twice as much fuel feeding it at 6000rpm as at 3000rpm.

think about whatever orifice they have going into that hpfp and how much fuel it can flow. now bump that up to an lt4 hpfp or even a big bore lingerfilder pump with the motor spinning at 6400rpm. then even add some stroke to it with a 32% larger cam lobe. you are going to have to really hit the hpfp with some low pressure fuel to not starve it.

my plan just to play it safe is build an excessive low side and feed that hpfp with ~70psi any time i am under boost.

You're close, but not exactly. Volume and psi go hand in hand, but they are not the same thing. The HP pump is fixed, it's output is fixed, the fuel it boost goes up with RPM. The volume needed is at max at your highest RPM not peak tq. Peak tq requires the highest pressure not necessarily the highest volume. That volume is supplied by the low side pump. The stroke of the HP pump can change with your lobe, and increase its performance but that means nothing if the needed volume of fuel (supplied 100% by LPFP) isn't there to begin with.

[Perdieu]

Originally Posted by parish8

is build an excessive low side and feed that hpfp with ~70psi any time i am under boost.

That's what I've been told to do by 5 different tuners that have cars in the 900+ range which is what I'm looking to achive.

Reason I went with the Cordes Lowside set up is it's a plug and play and James is a nice guy LOL

[Jonru]

I have a 2017 zl1 4k miles about a month I had a 2.31 upper pulley,thermal insulator plates and long tube headers installed ,same day my tuner spent 3 hours on the dyno trying to tune it but at wot pass 4k rpms the car would lean out and he said something about the low side fuel pump could be the problem ,I have to take it back to him at the end of this month so he can figure out what the problem is.