Fuel pressure Regulator Location (Gen 3)

[petepetrolhead]

I was just wondering where folks have mounted their fuel pressure regulators for an SBF with EFI setup? Presumably in the engine bay not below the trunk? On the firewall (back or side?) or on the frame (where?)?

Thanks for your help :-)

[TTimmy]

The common practice is to mount them in the engine compartment. This also seems to be the recommendation of those that make produce the products. Many folks will also remove the glass pressure gauge after the engine is sorted over fire risk concerns.

It is my understanding that mounting in the engine compartment is favorable as the pressure is regulated closer to the point of fuel consumption, thus ensuring a more consistent pressure to the fuel rail, etc.

Another, maybe minor, consideration is the potential for vapor lock is reduced as the fuel in in the lines closest heat sources is recirculated, thus reducing the chances of it heating up and vaporizing. If the regulator were mounted in the rear, the full forward fuel supply would be subject to heating. How much of an is it this really? I'm not sure.

[PNWTim]

The common practice is to mount them in the engine compartment. This also seems to be the recommendation of those that make produce the products. Many folks will also remove the glass pressure gauge after the engine is sorted over fire risk concerns.

It is my understanding that mounting in the engine compartment is favorable as the pressure is regulated closer to the point of fuel consumption, thus ensuring a more consistent pressure to the fuel rail, etc.

Another, maybe minor, consideration is the potential for vapor lock is reduced as the fuel in in the lines closest heat sources is recirculated, thus reducing the chances of it heating up and vaporizing. If the regulator were mounted in the rear, the full forward fuel supply would be subject to heating. How much of an is it this really? I'm not sure.

I have been thinking about this quite a bit for my coupe (this is how I fill my time; jonesing on details that are pretty minor and probably not worth the brain power) and I was under the impression most go engine compartment simply for the ease of setting initial fuel pressure. Since most remove the gauge after setting it becomes somewhat of a moot point. I am more inclined to place it back by the fuel tank since I will be doing first start and go kart with the body off. Setting the FP will be simple and as long as I orient it to be accessible for the future I see no reason to install in an already crowded engine bay.

I can't really comment on the vapor lock. I'm not sure the residence time in the fuel line is long enough for the fuel to really warm up but that's just a WAG. I won't be using metal fuel lines either so hopefully there is some insulating quality with PTFE and woven covering (I think).

[burchfieldb]

Does your EFI screen show the fuel pressure? I have an MSD Atomic 2 that shows it.

[edwardb]

Ok, another country heard from... On my two Coyote builds, I did the traditional setup with the adjustable regulator on the firewall and supply and return lines back to the tank. On my truck build, I decided to simplify and mounted the exact Aeromotive adjustable regulator I'd used previously in the back by the tank. This picture shows the setup. So fuel out of the tank to the Trick Flow filter. Then a short run to the regulator. Then out of the regulator, the return line back to the tank (guessing 16-18" long) and a single supply line along the chassis to the front for the engine. I haven't taken the time to see where a similar regulator location could be used for a Roadster or Coupe, but I'm confident a similar location could be found.

Advantages: One line the length of the chassis instead of two and one less thing to locate and clutter up the engine compartment.

Disadvantage #1: Not convenient to set and monitor the pressure. My experience driving the two Coyote powered builds for multiple years and the truck build for one year, once the pressure is set it doesn't change. So a little inconvenient at first to set, but then you're done.

Disadvantage #2: Technically, there is some pressure loss through the line up to the engine. So the pressure at the fuel rail isn't exactly as shown on the gauge. I didn't take any fluid dynamics courses (not smart enough... not my major...) but my uneducated guess and experience is it's minor and not enough to make a difference. Plus my opinion is the recommended PSI settings (65 for the Gen3 Coyote, 60 for the LS) are conservative. It would be easy enough to bump up the pressure at the rear regulator if you knew the actual loss and it was enough to matter. I would do this setup again if I were to do another build.

I will also add it was common practice with the Gen2 Coyote to use a GM/Corvette fuel filter/regulator at the back by the tank and again only run one line to the front. That piece isn't typically used any more as it's fixed pressure and less than the 65PSI required for the Gen3. So the basic idea here isn't new or untested.

[Skuzzy]

The worst case scenario is during hard acceleration where the mass of fuel in the fuel line exerts pressure to the regulator causing a drop in pressure at the injector. How much? Okay, I am going to put on my geek hat. Here we go:

First calculate the volume of fuel in the line. You need the length of the line from the regulator to the engine and the radius of the line. Using the following formula:
Length of line X 3.14159 x Radius Squared = Volume of fuel
Example: If you are using a 3/8 inch (0.375) diameter fuel line, and it is 12 feet (144 inches) long then the volume is;
144 inches X 3.14159 x (3/16 x 3/16) = 15.9 cubic inches.
Convert that to gallons: 1 cubic inch = 0.004329004 U.S. gallons.
15.9 cubic inches X 0.004329004 = 0.068831 gallons

Now the weight of that fuel needs to be calculated. I am going to assume room temperature as that impacts the density of the fuel which impacts the volume. I am also going to approximate based on blended fuel used in the U.S. It is slightly lighter than pure gasoline.
With all that said, I'll use a specific gravity of 0.72 (0.75 is pure gasoline +- 0.02) and a per gallon weight of 6.075 pounds.
The weight of the fuel in the line is calculated as follows:
0.068831 gallons X 0.72 specific gravity X 6.075 pounds per gallon = 0.301 pounds (0.136531 kilograms).

Take the weight and multiply it by the g-force during acceleration and deceleration to come up with the potential pressure change at the injector.
Assuming 1G of acceleration or deceleration, the variation of fuel pressure given a 12 foot, 3/8 fuel line will be approximately +- 0.301 pounds with the regulator located at the tank.

Check my math folks.

[edwardb]

The worst case scenario is during hard acceleration where the mass of fuel in the fuel line exerts pressure to the regulator causing a drop in pressure at the injector. How much? Okay, I am going to put on my geek hat. Here we go:

First calculate the volume of fuel in the line. You need the length of the line from the regulator to the engine and the radius of the line. Using the following formula:
Length of line X 3.14159 x Radius Squared.Amount of fuel
Example: If you are using a 3/8 inch (0.375) diameter fuel line, and it is 12 feet (144 inches) long then the volume is; 144 inches X 3.14159 x (3/16 x 3/16) = 15.9 cubic inches.
Convert that to gallons: 1 cubic inch = 0.004329004 U.S. gallons.
15.9 cubic inches X 0.004329004 = 0.068831 gallons

Now the weight of that fuel needs to be calculated. I am going to assume room temperature as that impacts the density of the fuel which impacts the volume. I am also going to approximate based on blended fuel used in the U.S. It is slightly lighter than pure gasoline.
With all that said, I'll use a specific gravity of 0.72 (0.75 is pure gasoline +- 0.02) and a per gallon weight of 6.075 pounds.
The weight of the fuel in the line is calulated as follows:
0.068831 gallons X 0.72 specific gravity X 6.075 pounds per gallon = 0.301 pounds (0.136531 kilograms).

Take the weight and multiply it by the g-force during acceleration and decelertation to come up with the potential pressure change at the injector.
Assuming 1G of acceleration or deceleration, the variation of fuel pressure given a 12 foot, 3/8 fuel line will be approximately +- 0.301 pounds with the regulator located at the tank.

Check my math folks.

If the math is correct (no reason for me to think otherwise) this confirms what I suspected. Thanks for doing that and posting all the details. The loss while measurable isn't enough to make a difference. The rear mounted regulator was good enough for the engineering types at GM in the Corvette and a bunch of builds on here. Down to just the basically one-time inconvenience of setting the pressure with the advantages I referenced.

[Skuzzy]

If the math is correct (no reason for me to think otherwise) this confirms what I suspected. Thanks for doing that and posting all the details. The loss while measurable isn't enough to make a difference. The rear mounted regulator was good enough for the engineering types at GM in the Corvette and a bunch of builds on here. Down to just the basically one-time inconvenience of setting the pressure with the advantages I referenced.

The only thing I failed to mention is during any pressure change, there is less (drop)/more (increase) fuel squirted by the injector, unless the system compensates for pressure changes and varies the duration of the injector cycle accordingly. Then again, small pressure changes may be beyond the resolution of the electronics.

I always assume people will check the math, but I never fail to ask. Never hurts to have more than one set of eyes on these things. No need to thank me. Math is a fascinating hobby of mine.

You would not believe how much math I have done while building this car. Fun stuff!

[petepetrolhead]

The common practice is to mount them in the engine compartment. This also seems to be the recommendation of those that make produce the products. Many folks will also remove the glass pressure gauge after the engine is sorted over fire risk concerns.

It is my understanding that mounting in the engine compartment is favorable as the pressure is regulated closer to the point of fuel consumption, thus ensuring a more consistent pressure to the fuel rail, etc.

Another, maybe minor, consideration is the potential for vapor lock is reduced as the fuel in in the lines closest heat sources is recirculated, thus reducing the chances of it heating up and vaporizing. If the regulator were mounted in the rear, the full forward fuel supply would be subject to heating. How much of an is it this really? I'm not sure.

Thanks TTimmy - that's very helpful :-)

[petepetrolhead]

Does your EFI screen show the fuel pressure? I have an MSD Atomic 2 that shows it.

That's interesting - i haven't actually purchased the EFI yet so that's a good consideration :-)

[petepetrolhead]

Ok, another country heard from... On my two Coyote builds, I did the traditional setup with the adjustable regulator on the firewall and supply and return lines back to the tank. On my truck build, I decided to simplify and mounted the exact Aeromotive adjustable regulator I'd used previously in the back by the tank. This picture shows the setup. So fuel out of the tank to the Trick Flow filter. Then a short run to the regulator. Then out of the regulator, the return line back to the tank (guessing 16-18" long) and a single supply line along the chassis to the front for the engine. I haven't taken the time to see where a similar regulator location could be used for a Roadster or Coupe, but I'm confident a similar location could be found.

Advantages: One line the length of the chassis instead of two and one less thing to locate and clutter up the engine compartment.

Disadvantage #1: Not convenient to set and monitor the pressure. My experience driving the two Coyote powered builds for multiple years and the truck build for one year, once the pressure is set it doesn't change. So a little inconvenient at first to set, but then you're done.

Disadvantage #2: Technically, there is some pressure loss through the line up to the engine. So the pressure at the fuel rail isn't exactly as shown on the gauge. I didn't take any fluid dynamics courses (not smart enough... not my major...) but my uneducated guess and experience is it's minor and not enough to make a difference. Plus my opinion is the recommended PSI settings (65 for the Gen3 Coyote, 60 for the LS) are conservative. It would be easy enough to bump up the pressure at the rear regulator if you knew the actual loss and it was enough to matter. I would do this setup again if I were to do another build.

I will also add it was common practice with the Gen2 Coyote to use a GM/Corvette fuel filter/regulator at the back by the tank and again only run one line to the front. That piece isn't typically used any more as it's fixed pressure and less than the 65PSI required for the Gen3. So the basic idea here isn't new or untested.

That's a great thought Edward - thank you! I do like the idea of just a single fuel line to the engine bay. I'm sure I can find a fitting that will go on the fuel rail to attach a pressure gauge which pretty well addresses both disadvantages?

[petepetrolhead]

The worst case scenario is during hard acceleration where the mass of fuel in the fuel line exerts pressure to the regulator causing a drop in pressure at the injector. How much? Okay, I am going to put on my geek hat. Here we go:

First calculate the volume of fuel in the line. You need the length of the line from the regulator to the engine and the radius of the line. Using the following formula:
Length of line X 3.14159 x Radius Squared = Volume of fuel
Example: If you are using a 3/8 inch (0.375) diameter fuel line, and it is 12 feet (144 inches) long then the volume is;
144 inches X 3.14159 x (3/16 x 3/16) = 15.9 cubic inches.
Convert that to gallons: 1 cubic inch = 0.004329004 U.S. gallons.
15.9 cubic inches X 0.004329004 = 0.068831 gallons

Now the weight of that fuel needs to be calculated. I am going to assume room temperature as that impacts the density of the fuel which impacts the volume. I am also going to approximate based on blended fuel used in the U.S. It is slightly lighter than pure gasoline.
With all that said, I'll use a specific gravity of 0.72 (0.75 is pure gasoline +- 0.02) and a per gallon weight of 6.075 pounds.
The weight of the fuel in the line is calculated as follows:
0.068831 gallons X 0.72 specific gravity X 6.075 pounds per gallon = 0.301 pounds (0.136531 kilograms).

Take the weight and multiply it by the g-force during acceleration and deceleration to come up with the potential pressure change at the injector.
Assuming 1G of acceleration or deceleration, the variation of fuel pressure given a 12 foot, 3/8 fuel line will be approximately +- 0.301 pounds with the regulator located at the tank.

Check my math folks.

Interesting calculation Skuzzy! By +/- 0.301 pounds do you mean 0.301 psi? If so, for an EFI running at 40 to 60 psi that's fairly inconsequential?

[petepetrolhead]

Ok, another country heard from... On my two Coyote builds, I did the traditional setup with the adjustable regulator on the firewall and supply and return lines back to the tank. On my truck build, I decided to simplify and mounted the exact Aeromotive adjustable regulator I'd used previously in the back by the tank. This picture shows the setup. So fuel out of the tank to the Trick Flow filter. Then a short run to the regulator. Then out of the regulator, the return line back to the tank (guessing 16-18" long) and a single supply line along the chassis to the front for the engine. I haven't taken the time to see where a similar regulator location could be used for a Roadster or Coupe, but I'm confident a similar location could be found.

Advantages: One line the length of the chassis instead of two and one less thing to locate and clutter up the engine compartment.

Disadvantage #1: Not convenient to set and monitor the pressure. My experience driving the two Coyote powered builds for multiple years and the truck build for one year, once the pressure is set it doesn't change. So a little inconvenient at first to set, but then you're done.

Disadvantage #2: Technically, there is some pressure loss through the line up to the engine. So the pressure at the fuel rail isn't exactly as shown on the gauge. I didn't take any fluid dynamics courses (not smart enough... not my major...) but my uneducated guess and experience is it's minor and not enough to make a difference. Plus my opinion is the recommended PSI settings (65 for the Gen3 Coyote, 60 for the LS) are conservative. It would be easy enough to bump up the pressure at the rear regulator if you knew the actual loss and it was enough to matter. I would do this setup again if I were to do another build.

I will also add it was common practice with the Gen2 Coyote to use a GM/Corvette fuel filter/regulator at the back by the tank and again only run one line to the front. That piece isn't typically used any more as it's fixed pressure and less than the 65PSI required for the Gen3. So the basic idea here isn't new or untested.

BTW Edward, looks like you're not using the stock Mustang fuel pump hanger? Is that a Pro-M Racing hanger, or a Quantum? Or maybe something else?

[Skuzzy]

Interesting calculation Skuzzy! By +/- 0.301 pounds do you mean 0.301 psi? If so, for an EFI running at 40 to 60 psi that's fairly inconsequential?

You know, in this context yes, psi is fine. I cannot come up with a really good analogy to explain this better.

[edwardb]

BTW Edward, looks like you're not using the stock Mustang fuel pump hanger? Is that a Pro-M Racing hanger, or a Quantum? Or maybe something else?

Pro-M. I've used it on all my builds with a Walbro pump. Highly recommended setup.

- Paul B.

[Presdough]

On hot days mine will vapor lock when it is shut off and the fuel lines heat soak. I made some footbox hear shields out of aluminum cookie sheets and ran the fuel lines between the heat shields and the footbox. I prefer the regulator in the engine bay as I can bleed pressure off easily when servicing the fuel system.

[lewma]

Be careful with the cheaper fluid filled regulator gauges. They do not report an accurate reading in a hot engine bay. Saw this first hand. Had my fuel pressure set to 58psi cold, took the car for a long drive, engine bay was hot, opened the hood, fuel pressure gauge was reading around 40psi. Swapped it out with a Moroso gauge that is not filled with fluid. Rock solid now.

[petepetrolhead]

On hot days mine will vapor lock when it is shut off and the fuel lines heat soak. I made some footbox hear shields out of aluminum cookie sheets and ran the fuel lines between the heat shields and the footbox. I prefer the regulator in the engine bay as I can bleed pressure off easily when servicing the fuel system.

On a learning curve here, so please forgive any dumb questions! If I understand correctly, you have the regulator in the engine bay? So you're running a return line from the regulator to the tank? I would sort of expect the pump to be able to push liquid fuel to displace the vapour lock, but that doesn't happen?

[lewma]

On a learning curve here, so please forgive any dumb questions! If I understand correctly, you have the regulator in the engine bay? So you're running a return line from the regulator to the tank? I would sort of expect the pump to be able to push liquid fuel to displace the vapour lock, but that doesn't happen?

pete, that's exactly how i have my system setup.

[edwardb]

On a learning curve here, so please forgive any dumb questions! If I understand correctly, you have the regulator in the engine bay? So you're running a return line from the regulator to the tank? I would sort of expect the pump to be able to push liquid fuel to displace the vapour lock, but that doesn't happen?

Not saying vapor lock is impossible. More common with low pressure carb setups. Modern EFI and the pressures they run make it unlikely. It's rarely mentioned on here and I've never experienced it with five builds and thousands of miles.

[Presdough]

It runs like crap when first started but will smooth o0ut when the air gets pushed out of the rails.

[Alphamacaroon]

FWIW, I did the exact same thing as EdwardB did on his truck build on my Coupe build. I think a few people recommended against it when I first proposed the idea, but I decided to go with it anyway and have not had any regrets. It's been fully dyno tuned and there were no reports of any fuel starvation or pressure loss of any sort.

I will say that it may be responsible for the tiniest bit of vapor lock— when I shut down the car at full temp and start it up before it's had a chance to cool down, it does take a couple of seconds longer to start it up. But I think this could also be easily fixed by commanding the PCM to run the fuel pump a little longer during the priming phase (or whatever they call it) right before startup. It's also possible that it's something completely unrelated too. Point being, it's such a minor thing that it's not even really worth doing anything about it, and the simplicity (and added safety) of running one fuel line was worth it in my experience.

Also I'm trying to remember, but I think I was able to mount my regulator in such a way where I could access the adjustment screw from the access hatch in the trunk area. I'll see if I can find a picture. But the reason I can't remember exactly where I mounted it was because I have never needed to look at it, let alone touch it again after adjusting it the first time.