EFI fuel pump, problems being too big?

[RabbitHoleSS]

81cutlass explained the idea of the returnless setup better than I can.

Regarding boost, and why the need for a boost referenced FPR, when boost pressure is present in the manifold it is also applying pressure to the injector tip. And that pressure has to be overcome - basically,
there is a pressure differential between the manifold and fuel system. The fuel supply end of the injector has fuel pressure on it and the other end has manifold pressure on it. The difference between the two is referred to as ‘pressure differential’ in this discussion.

The goal of the referenced FPR regulator is to keep the pressure differential between manifold and fuel system the same for all boost levels. For example , you have a system that runs at 43psi base fuel pressure (set at atmospheric pressure with the engine off.) 43 is now the value to be set as the pressure differential number. At 10 psi of boost the FPR adds that same 10psi to the fuel system to generate 53psi of fuel pressure. At 20 psi of boost the fuel pressure becomes 63psi. I’m sure you get it, but the important piece of puzzle is that the injector is now in a constant pressure differential of 43 psi all the time. And this occurs in vacuum as well, hence the reason why the fuel pressure drops in vacuum to a negative psi.

The negative psi number starts becoming confusing because rarely does anyone reference pressure in negative psi. The most common unit of measure that is simplest is kpa due to the scaling of it. And kpa infers ‘absolute’ pressure rather relative pressure. But that’s another discussion if needed.

Onto injector data consideration and how fuel pressure affects injector flow. All injectors’ flow characteristics are not the same as fuel pressure varies. A Siemens Deka flow rate flow rate change due to fuel pressure variance might be 5-10% more than a Bosch, Multec, Delphi, etc. This makes tuning an injector swap even more demanding at a varying fuel pressure differential. So again, a constant fuel pressure differential across the injector makes for very linear, predictable and most importantly - consistent - tuning.

One variable that is tuned by most every ECU is flow rate changes due to voltage changes. The varying flow rates due to voltage changes are what is entered into most every ECU as ‘injector data’. With this in mind, consider running with a consistent fuel pressure that doesn’t take fuel injector pressure differential into account. Now you are having to adjust for both voltage change and pressure differential change. This situation turns into a 3 dimensional aspect of the tune rather than a 2 dimensional aspect (aspect implies a table). Perhaps the newer factory ECM’s can handle this, and I’ll guess they can, but that is because they have at least one of two things going on or both - they have very specific injector data for all 3 dimensions and/or they have the O2 sensor commanding wild injector duty cycle changes. The factory ECM is probably doing more than what I just referenced

This leads to a simple question. Why not put in a 1 to 1 vacuum/boost referenced FPR and make this very easy - so easy in fact that all of the big name aftermarket ECM manufacturers can handle - I.e Holley, Haltech, Big Stuff, Fuel Tech, Megasquirt, etc.?


I referenced absolute pressure via relative pressure a couple of paragraphs back. Having a full understanding of the difference between the two is extremely important when trying to understand what is happening in your fuel system and inside your intake. I only mention this, because I either didn’t understand or overlooked this when I first started messing with tuning cars. It was something taught in most every chemistry and physics class through my high school and college classes, but dang, that was 25 years before I needed to know how it applies to tuning a motor on earth lol.

p.s. I typed this post on my IPhone - I’m trying to force myself to be better at using this damn dinky key pad 😉

Thanks for the detailed explanations.
I do not fully understand the the absolute vs relative pressure. My head went to the concept of dew point vs RH% measurements. Or like the way a weatherman measures fronts, but how it coincides with tuning, or how it effects fueling, idk.

Yeah basically returnless that's not vacuum referenced has in effect non continuous flow rates. The injectors get 'bigger' as the manifold vacuum increases as you gain relative fuel pressure.

In a manifold pressure reference set-up NA you have 42.5 psi of fuel pressure at wide open throttle, no vacuum or with the engine off. At idle with 28" of vacuum you have about 30 psi of fuel pressure relative to the air you breath but it's actually 42psi relative to the air in the manifold because it's at a vacuum.

Returnless setups can be harder to tune because if it's not manifold pressure reference the effective fuel pressure at idle is say 56psi which makes the injectors roughly 10% larger. You have to ramp the injectors size as the air pressure in the manifold changes.

And yeah, walbro or TTI pumps are great but there are a lot of fakes. If you go with one from a reliable seller, I got mine from highflowfuel or from racetronix, where I get my bigger wiring bulkhead parts from, you should be fine. But Amazon and eBay are yikes.

I have a question about your fuel pump wiring video. I have a 10ga wire from my relay, so do I just split that into 2 14ga wires a little before the pigtail?
Then put both 14ga wires off the 4pin bulkhead into the pin for the fuel pump pigtail?
Thanks for the returnless setup breakdown.I understand what your saying. All this makes me wonder how much I would've struggled trying to tune the returnless setup N/A.
Doesn't really matter now. I ordered the tank and sender from rockauto, that fpr from Amazon, plus the pump and everything needed to install it from racetronix(no sales tax). It was around $600, includes tax and s/h. The fuel system will be completely new now. I think I have about 750 in the whole fuel system.

 

[64nailhead]

1 bar = 14.7 psi = 100kpa = atmospheric pressure at sea level (what we live in - yes we are pressurized all of the time.) KPA is kilopascals.

Everything is measured in absolute pressure. 100/14.7 is very close to 7. So every 7 kpa is equal to 1psi both whether negative or positive psi (boost). Google kpa to psi conversion and you’ll find a table or conversion algorithm. The only reason I 1st learned KPA rather than psi is that Megasquirt only references KPA so I was chronically converting KPA to psi. And if you want throw another number in the mix convert kpa to inches of mercury (what old school vacuum manometers measured.)

With the above equation, in regard to boost, we all measure boost in positive numbers of psi. So an absolute pressure of 0 kpa is -14.7 psi, 100 kpa is 0 psi and 200 kpa is 14.7 psi. Basically, a pressure measurement in absolute pressure is the same on the moon as it is in earth because the moon has no atmosphere. It’s similar to the differences in measurement between mass and pounds. Mass does not consider our atmosphere or gravitational pull. Absolute pressure measurement does not account for out atmosphere.

Another mind bending aspect of this is the difference in elevation. 100kpa is atmospheric pressure at sea level.
At my home the kpa is 96, in Denver it’s somewhere around 88-90. How is this tuned in a car where there is a changing elevation? Most every ECU has the ability to have a table to offset the difference in sea level vs current kpa - basically a table that has a built in offset to account oxygen changes as the elevation changes.

In my most recent escapades I was disappointed that I didn’t have my car sorted out when I was in Bradenton,FL because that track is about 10’ above sea level implying the air is extremely dense (more oxygen than most anywhere I run - everything is faster there because of the extra oxygen in the air.)


Regarding your wiring size question - the longer the length of wire the more resistance there is in the wire, so larger wire is needed for longer runs to carry the same amount of current. IMO, more important than the positive wire is the ground. A larger ground will cover many inadequacies of the positive wire. I run a 10 gauge ground wire and it will keep a 12-14 gauge positive wire functioning without melting the positive wire that is twice the length of the ground. You can run a 10 gauge positive wire to your pump, and if the ground is inadequate then the heavy gauge positive wire will over heat and fail.

 

[64nailhead]

What are you using for a secondary fuel filter?

 

[Supercharged111]

1 bar = 14.7 psi = 100kpa = atmospheric pressure at sea level (what we live in - yes we are pressurized all of the time.) KPA is kilopascals.

Everything is measured in absolute pressure. 100/14.7 is very close to 7. So every 7 kpa is equal to 1psi both whether negative or positive psi (boost). Google kpa to psi conversion and you’ll find a table or conversion algorithm. The only reason I 1st learned KPA rather than psi is that Megasquirt only references KPA so I was chronically converting KPA to psi. And if you want throw another number in the mix convert kpa to inches of mercury (what old school vacuum manometers measured.)

With the above equation, in regard to boost, we all measure boost in positive numbers of psi. So an absolute pressure of 0 kpa is -14.7 psi, 100 kpa is 0 psi and 200 kpa is 14.7 psi. Basically, a pressure measurement in absolute pressure is the same on the moon as it is in earth because the moon has no atmosphere. It’s similar to the differences in measurement between mass and pounds. Mass does not consider our atmosphere or gravitational pull. Absolute pressure measurement does not account for out atmosphere.

Another mind bending aspect of this is the difference in elevation. 100kpa is atmospheric pressure at sea level.
At my home the kpa is 96, in Denver it’s somewhere around 88-90. How is this tuned in a car where there is a changing elevation? Most every ECU has the ability to have a table to offset the difference in sea level vs current kpa - basically a table that has a built in offset to account oxygen changes as the elevation changes.

KPA is plain easier to work with, I think absolute pressure is the biggest thing for a n00b to wrap their brain around. That and understanding an engine's need for fuel/timing based on RPM/load and how little it can sometimes fluctuate. As for elevation, well, a guy who lives in Denver said he sees 82-84 which is reasonable for a mile high as I see 78-80 here at 6500. It's a big old kick in the nuts. I think where I was in Rapid City, SD was in the 88-90 range close to 3000'. Back in MI around 700' I see 96-97. By that math, the top of Pike's Peak ought to be 58-60kpa! Now that I said that I want to go log it, it's right in my back yard.

 

[81cutlass]

Thanks for the detailed explanations.
I do not fully understand the the absolute vs relative pressure. My head went to the concept of dew point vs RH% measurements. Or like the way a weatherman measures fronts, but how it coincides with tuning, or how it effects fueling, idk.

I have a question about your fuel pump wiring video. I have a 10ga wire from my relay, so do I just split that into 2 14ga wires a little before the pigtail?
Then put both 14ga wires off the 4pin bulkhead into the pin for the fuel pump pigtail?
Thanks for the returnless setup breakdown.I understand what your saying. All this makes me wonder how much I would've struggled trying to tune the returnless setup N/A.
Doesn't really matter now. I ordered the tank and sender from rockauto, that fpr from Amazon, plus the pump and everything needed to install it from racetronix(no sales tax). It was around $600, includes tax and s/h. The fuel system will be completely new now. I think I have about 750 in the whole fuel system.
View attachment 216945

Does this help explain? Single big 10 gauge into 2 14 gauge wires in a butt connector.

 

[RabbitHoleSS]

What are you using for a secondary fuel filter?

Well I was closer to knowing then I thought lol. The kpa part i was clueless about. Still kinda am but atleast now I have an idea of what I need to learn. Thanks.
The fuel filter is out of an 02 v8 express van. My filter is in the back on the rail so I could use something like he has below if it ends up being a problem.

Does this help explain? Single big 10 gauge into 2 14 gauge wires in a butt connector.

Yea, thanks, it's what I thought you had. I like your filter setup too, for use and changing it out.

KPA is plain easier to work with, I think absolute pressure is the biggest thing for a n00b to wrap their brain around. That and understanding an engine's need for fuel/timing based on RPM/load and how little it can sometimes fluctuate. As for elevation, well, a guy who lives in Denver said he sees 82-84 which is reasonable for a mile high as I see 78-80 here at 6500. It's a big old kick in the nuts. I think where I was in Rapid City, SD was in the 88-90 range close to 3000'. Back in MI around 700' I see 96-97. By that math, the top of Pike's Peak ought to be 58-60kpa! Now that I said that I want to go log it, it's right in my back yard.

That's pretty awesome you live that close to pikes peak. I figured that's why guys run turbo setups up there, they can put more atmospheres in the intake. Do you have any books or educational material you'd recommend? I've never really tried to learn those things unfortunately, I just settled on "engine get fuel/air/spark, go boom".

You know you can get the factory rails for an early Gen 3 than have a fuel return built into them - with two Amazon fittings that slide onto the supply and return you’re all set with a -8 or -10 supply and a -6 return? I ran that setup to my 1st high 9 second pass before I swapped to the Trailblazer intake. I used the built in FPR without issue. And if you get a Deka injector, then you can space the rails with a thick plastic washers from Lowe’s (that’s my back up plan in the basement).

Shoot, I don't know how I missed this post, but yea I have a gen 3 return setup in the basement, I never thought to use the rails without an aftermarket fpr. It sounds to me like I could've skipped that aero fpr?
I have a few different intakes, some 823 heads and gen 4 recport intake/rails down there too.

 

[64nailhead]

This is the budget oriented fuel filter setup. The 595-5 filter is E85 compatible and this beetch flows a ton of fuel.

$25-30 for the filter and housing. I tig’d a mounting bracket to the top for easy installation.

Replacement filters are $8-10.

Can find at Tractor Supply online or Amazon.

 

[Shinobi68]

I'm gathering parts to do my LS1 swap into my '85 3.8 Grand Prix. I was on the Holley site and noticed the OEM in tank pumps that are available. The description states that the return is built into the pump assembly to maintain constant pressure and good to 550hp (255lph mump). The swap motor is a 2004 LS1 Corvette 5.7. I plan to keep this stock with no modifications. Will the '04 LS1 tune work with the Holley In Tank pump w/built in return like the '04 Vette LS1 fuel system (return is built into fuel filter)?

 

[64nailhead]

Are you using a Holley ECU or stock ECU?

 

[Shinobi68]

Are you using a Holley ECU or stock ECU?

Stock ECU