Fuel pressure regulator, simple mod idea?

[qsiguy]

I still need to check my fuel pressure but I've been thinking about a simple way to increase the fuel pressure using the stock FPR. I want to install a needle valve on the return line after the stock FPR. Any reason this wouldn't work or would create a problem? Seems to me it would work fine. It's variable and still allows the stock FPR to change with load. I believe it would just offset the pressure by however much restriction you place on it. Has anyone heard of this done or done it? Maybe it's common knowledge but I haven't read about this being done.

Also, to check the pressure I can easily install a gauge on the line but do I need to have the gauge readable while driving or can I just rev the engine up in park to get an accurate reading? If it's sitting in park and I rev the motor up will it show the max fuel pressure or do I need to be driving under a load?

[T45]

Are you running a fpcu? I think that may affect the fp at idle vs. wot. As for guages you can pick up an elec fp gauge so you can read it while driving. They are pretty expensive but it's an option.

[SuperHatch]

I still need to check my fuel pressure but I've been thinking about a simple way to increase the fuel pressure using the stock FPR. I want to install a needle valve on the return line after the stock FPR. Any reason this wouldn't work or would create a problem? Seems to me it would work fine. It's variable and still allows the stock FPR to change with load. I believe it would just offset the pressure by however much restriction you place on it. Has anyone heard of this done or done it? Maybe it's common knowledge but I haven't read about this being done.

Also, to check the pressure I can easily install a gauge on the line but do I need to have the gauge readable while driving or can I just rev the engine up in park to get an accurate reading? If it's sitting in park and I rev the motor up will it show the max fuel pressure or do I need to be driving under a load?

You would end up with erratic fuel pressure using this method. The fuel pump delivers a constant flow of fuel, with the exception of the high/low flow voltages. However, the fuel used by the engine is constantly varying depending on engine load and RPM. The FPR maintains a ~43.5psi rail/manifold pressure differential regardless of load. If you measure the flowrate in the return line you would be suprised to see how much it varied.

Adding a restrictor post-regulator would increase fuel pressure when the engine is at low load and the return fuel flow is high, but at high load when the return flow is low, there would be significantly less of a pressure increase.

What you need is either an aftermarket fixed rate adjustable fuel pressure regulator so you can raise the base pressure to achieve a differential greater than 43.5psi, or an aftermarket rising rate regulator that will increase the pressure differential x psi for each psi of boost gained.

[Q45tech]

When the WOT plenum pressure exceeds the 13-14 psi pressure from atmosphere because of positive boost from super/turbo then the FPR raises the rail pressure.

If 8-8.8 psi at cruise yield 34 psi in rail and 13.0 psi [WOT] yields 43.4 psi.........this is a rising rate regulator with a 2:1 ratio so a 5 psi boost might raise rail pressure by 10 psi to 53.4 psi..................about a 10% mass flow increase.

Important to understand the real positive pressure being applied to the FPR so called vacuum port..........

[Q45tech]

When the WOT plenum pressure exceeds the 13-14 psi pressure from atmosphere because of positive boost from super/turbo then the FPR raises the rail pressure.

If 8-8.8 psi at cruise yield 34 psi in rail and 13.0 psi [WOT] yields 43.4 psi.........this is a rising rate regulator with a 2:1 ratio so a 5 psi boost might raise rail pressure by 10 psi to 53.4 psi..................about a 10% mass flow increase.

Important to understand the real positive pressure being applied to the FPR so called vacuum port..........

A vacuum can only exist in space or lab............using the term on a vehicle leads to all sorts of confusions.

[qsiguy]

Thanks for the input. Tech, can you summarize the data you posted, I'm not sure if are saying my idea is feasible or not. I understand the data but not sure if you are stating facts or answering my question.

As far as including atmospheric into the calculations, I agree it's much more accurate but it is much simpler to use gauge readings for these basic things. Plus, if it is necessary to include atmospheric you must know what that is in your current location at the time you are taking the readings. In my opinion this is rarely necessary. For most it is understood that atmospheric is factored in. I'm sure you won't agree but that's ok

SuperHatch, your example make sense. The needle valve is just for restricting flow and since the flow will actually decrease during high load conditions the mod would be counter productive.

[John Dixon]

Why not just buy an adjustable FPR, they're pretty cheap.In the past I've squashed stock ones in a vice to increase the pressure on the spring, works OK but a bit hard to calibrate!!

[Q45tech]

The difference between a mechanic and and automotive engineer is the use of ACCURATE measurements.

The is no vacuum even in space, just a lower pressure. It has a pressure of 1.322 × 10**-11 Pa or about 1 hydrogen atom per cm3.

Measure the rail input and output psi while the return line is blocked off squeezed shut to gain some insite into the pumps capacity...............watch out for the in pump pressure relief valve which limits to 65 psi depending on gasoline viscosity.

It is all a tuned system even down to oem inside diameter of metal lines and rails. Screw with one component and there may be unintended changes.

Japanese FPR are filled with Japanese reference air in bellows on the day of manufacture.

[SuperHatch]

The difference between a mechanic and and automotive engineer is the use of ACCURATE measurements.

The is no vacuum even in space, just a lower pressure. It has a pressure of 1.322 × 10**-11 Pa or about 1 hydrogen atom per cm3

If you really want to get technical there's no such thing as deceleration either... only negative acceleration.

The real point is that there is absolutely no reason whatsoever to nit pick over terminology on these forums to the nth degree. It only serves to piss off the people that are trying to learn something.

[qsiguy]

I did find a way to make my idea work with a small modification. I'm not sure I will try it or not but there is no reason it shouldn't work.

Same needle valve idea but have a bypass loop around the needle valve that is open during low load conditions. Have a relay/switch wired to trigger at high loads based on MAF voltage that would close a solenoid that shuts the bypass loop and forces the return fuel to pass through the needle valve. You will then have higher fuel pressure only during high load conditions. It's actually a pretty simple mod. An adjustable FPR is probably still a much better way to go.

Thanks for the input guys.

[John Dixon]

Much easier and more predictable anyway. I just got one for about $60US, check ebay, there are loads for sale, just need some plumbing to fit.

[qsiguy]

Which one did you pick up John? There are a lot of different variations to choose from. Curious what you went with. What's yours going on?

[John Dixon]

Vacuum's a pretty commonly used term in all forms of engineering, it may be a conceptual thing but everyone understands it!Never seen one with sealed bellows either, the reference is through the sense line to the FPR. Any sealed unit wouldn't account for atmospheric changes or altitude changes. At the end of the day, an FPR is nothing more than a needle valve with it's opening controlled by a bellows and return spring, nothing mysterious or particularly clever

[John Dixon]

Which one did you pick up John? There are a lot of different variations to choose from. Curious what you went with. What's yours going on?

I just got a generic one with 1/4" NPT ports on it. Mine's going on my VH50DE. Here's a similar one (with cut-aeay pic): http://www.demon-tweeks.co.uk/...1-C-B

[npez]

Shane,

If you don't mind spending some coin (about $240 USD) this is the one I am considering.

http://www.cartech.net/fmu2020.htm

Cartech is very reputable (developed their first FMU in 1975) and have some features I couldn't find in other FMUs specifically:- Adjustability of fuel pressure to boost ratio; most I've seen are fixed at 1:1,7:1,12:1, etc.- Additional adjustability for fuel pressure increase at onset of boost

If these things aren't important to you though, then the one John suggested and others on the market as he suggested should do what you're looking for.

Just my $.02.

Thanks,Nick.

[John Dixon]

For what it's worth I'd stick with a 1:1 ratio.Especially if you're using the stock ECU as if you have rising rate then the AFR numbers in your map will get inconsistient as TP (& boost) rises.Just get an adjustable, inrease the base pressure then adjust the k value in your map and re-scale the TP scales accordingly.

[npez]

John,

I hadn't thought about it that way - since the ECU tuning will take place anyway all we would really need is an adjustable FPR versus a rising rate one. That's a great point! and saves quite a bit of money on the part as well.... Are you aware what the pressure limit is on the TT/Q45 pump? I would think it should be around 60-65psi but wasn't sure. All I'm looking at running is around 47psi - <10% more than the regulated pressure.

Thanks,Nick.

[John Dixon]

Tech had said 65psi relief valve on the pump so you need to keep the (baseline pressure + boost pressure) lower than that.

[tmorgan4]

I know I posted something about it a while back, but the fuel pressure regulator I'm using is off an RX-7. I was working on mine late one night trying to find out why it won't start and the fuel pressure regulator is clogged and not letting any fuel through. I brought it over to the race shop across the street and they managed to find one off an RX-7 that was almost identical. Same flange, same o-ring, bolted up to the fuel rail perfectly.

My point being, if you want to keep your stock fuel pressure regulator location (it's unfortunate that you have to pull the plenum to access it) there are tons out there that will bolt up. The Nismo adjustable one is probably a quality unit and wouldn't be a bad idea.

[qsiguy]

I'm in no hurry to pull my plenum again so if I change my FRP it will be an add on model. So if you get a 1:1 ratio adjustable that basically means it's not a rising rate model. You just set it for whatever pressure you want and it maintains that?

As far as stock ECU I assume you are referring to stock fuel maps? I'm not really worried about the tuning as I could retune the fuel maps for whatever fuel adjustments were required. What I'm trying to accomplish is lowering the injector duty cycle a little while maintaining good AFR's. To do this I just need a bit more fuel pressure specifically at full throttle/boost.

Nick, I'm pretty sure that is the same FPR that Siju is using on his turbo Q. He's running the stock ECU/tune and ~6 psi of boost and maintaining good AFR's.

[npez]

I'm in no hurry to pull my plenum again so if I change my FRP it will be an add on model. So if you get a 1:1 ratio adjustable that basically means it's not a rising rate model. You just set it for whatever pressure you want and it maintains that?

1:1 is still rising rate. We'll just need a fixed adjustable one. The set and forget variety. The Nismo unit is like that.

As far as stock ECU I assume you are referring to stock fuel maps? I'm not really worried about the tuning as I could retune the fuel maps for whatever fuel adjustments were required. What I'm trying to accomplish is lowering the injector duty cycle a little while maintaining good AFR's. To do this I just need a bit more fuel pressure specifically at full throttle/boost.

Nick, I'm pretty sure that is the same FPR that Siju is using on his turbo Q. He's running the stock ECU/tune and ~6 psi of boost and maintaining good AFR's.

I'm in the same boat somewhat. When I go boost I'll swap to my Nismo 555cc injectors so the duty cycle will go way down and AFRs should be ok with fuel map tuning. It's in phase 2b running 16psi that I will run into the duty cycle problem I'm mostly thinking ahead for the fuel pressure regulator. As far as your situation, I believe that yes it's as you said. Set the fuel pressure higher and adjust your fuel maps accordingly to maintain the AFRs you need - in theory your duty cycle will go down as you're expecting.

Thanks,Nick.

[tmorgan4]

Do these "set and forget" units go off manifold pressure?

[qsiguy]

Yes, I'm pretty sure all FPR's need to change with manifold pressure as the fuel requirements change the regulator must open or close accordingly. This is why my original idea of just putting a needle valve on the return line would not work. I'd have higher pressure at low load and lower pressure at higher load.

[maxnix]

The real point is that there is absolutely no reason whatsoever to nit pick over terminology on these forums to the nth degree. It only serves to piss off the people that are trying to learn something.

That's like saying if one is too lazy to think about the phenomena's model accurately, don't worry, the unverse will conform to one's stupidity!

Good luck! I hate to break it to you, but the Earth is neither flat nor the center of the universe.

A difference in pressures does not constitue a vacuum.

[npez]

I think shane gave a great answer above - yes they do. If you look at the Nismo fuel pressure regulator you'll be able to get a visual:

http://www.courtesyparts.com/M...710US

You still have the manifold pressure affecting fuel pressure depending on load, etc., however the maximum fuel pressure will now governed by what you set with the adjuster and lock nut on top of the adj fuel pressure regulator. On our stock ones this maximum pressure is preset, on this one you can set it and forget it.....

Thanks,Nick.

[npez]

Ok - lets stop the hating as all three of you are correct. In general terms a vacuum is considered anything less than atmospheric pressure and what some have been discussing. Under the strictest scientific interpretation and philosophical terms it is a condition/state completely void of any matter (and hence it's latin root). The latter is an absolute vacuum which practically doesn't exist; the more general term is what's being used in this forum, your A/C guy pulling a "vacuum" on your A/C system, "vacuum" tubes, etc.

You can argue the degree of vacuum all you want but that's how the scientific community looks at it and the general consensus. It's analogous to the absense of gravity on earth. My brother worked at NASA and they actually did tests in micro-gravity environments not zero-gravity.

Just my $.02.

Thanks,Nick.
Modified by npez at 6:14 PM 5/18/2008

[John Dixon]

What I normally do is adjust the fuel pressure then trim the K value to about where you think it should be and rescale all TP/TTP max etc tables accordingly. Do a run carefully monitoring AFR and see if the actual AFR's are now back where they were before the mods. If not, rescale k until they are.If you don't do this then the values in the map will go miles away from reality so 11:1 on the map may actually be 9:1 or something.

[npez]

What I normally do is adjust the fuel pressure then trim the K value to about where you think it should be and rescale all TP/TTP max etc tables accordingly. Do a run carefully monitoring AFR and see if the actual AFR's are now back where they were before the mods. If not, rescale k until they are.If you don't do this then the values in the map will go miles away from reality so 11:1 on the map may actually be 9:1 or something.

John,

That's a great tip! I'll keep it in mind when I have to do mine....

Thanks,Nick.

[SuperHatch]

1:1 is still rising rate. We'll just need a fixed adjustable one. The set and forget variety. The Nismo unit is like that.

1:1 is not rising rate. 1:1 is a fixed rate. For every 1psi of manifold pressure (positive or negative) the fuel pressure will change by 1psi. That is why you set the base fuel pressure with the engine off. Injectors are sized at ~43.5psi or 3bar. So a 370cc injector flows 370cc's of fuel per minute at 43.5psi operating pressure when wide open.

When at idle there is a negative pressure in the manifold below the outlet of the injector. If the rail pressure were still 43.5psi with a -13psi pressure in the manifold at idle. The pressure differential across the injector would be 56.5psi causing the flowrate of the injector to increase and a rich condition at idle. That is why we apply vacuum to the diaphram of the FPR to reduce the fuel pressure to 30.5psi at idle, resulting in a 43.5psi differential across the injector and the injector to still behave like a 370cc injector while the manifold is experiencing a negative pressure.

The inverse is true for an engine under forced induction. If the fuel pressure was fixed at 43.5psi and the pressure inside the manifold increased from atmospheric to a positive 13psi, the pressure across the injector would only be 30.5psi, and the injectors would behave like a lower CC sized injector. That is why the boost pressure is applied to the diaphram on the FPR to increast the pressure to 56.5psi, keeping the pressure differential constant and the injector functionting like a fixed CC value.

That is why John said a 1:1 ratio is the best for keeping a steady K value on your tune. If you had a FPR with no manifold pressure reference the target AFRs in your maps would be worthless because the "size" of your injector will vary with manifold pressure. It would be very difficult to map indeed.

The same goes for a rising rate FPR, which could (depending on the rate) raise the fuel pressure by 15psi when you are only running 10psi of boost. This would make your 370cc injectors act like 370cc injectors at 0psi, but like a larger injector at boost and all different sized in between. Again, very difficult to map.

That is why what qsiguy wants to but is perfect. A fixed rate 1:1 adjustable FPR. You adjust the BASE fuel pressure to 47psi, and it will maintain the pressure differential at 47psi under all positive and negative pressure conditions. Like John said, you just adjust your k value to compensate (like you've installed larger injectors) and you're on your way.

[npez]

Steve,

Thanks for the concise explanation of the 1:1 FPR. I was under the impression, and now I understand incorrectly so, that any kind of increase in the fuel pressure due to boost whether 1:1, 2:1, etc. made the FPR rising rate. I can now see how 1:1 is considered fixed.

Thanks a bunch for the explanation. That's why I love this forum I learn something new every day!

Nick.