Fuel Pressure Relating To Hose Size
Fuel Pressure Relating To Hose Size
(OP)
I'd really appreciate some help with the design of a fuel supply for a fuel injection conversion of an engine currently fuelled by twin carburettors. The engine is a 4 cylinder 1.2 litre Honda from the 1970s. It currently has 6mm ID fuel lines and hoses feeding twin 34mm CV carburettors. For the conversion I will be fitting 4 x 38mm individual throttle bodies that were sourced from a 2006 Honda CBR600 motorcycle. The use of these types of throttle body assemblies has become commonplace on the later series 4 cylinder Honda engines, but to my knowledge only one person has done such a conversion on the 1.2 litre engine, and with great success. Fortunately I have a good relationship with this person, but his engine was developed for full race conditions alone, whereas my application will predominantly be for the street.
My problem is the selection of fuel line and hoses. I was hoping to retain the original fuel line from the fuel tank to where it enters the engine bay. From that point on I plan on using a 6mm ID to 8mm ID fuel line adapter, and run 8mm ID hoses from there. In the first instance it will feed into a large FRAM HPG-1 fuel filter, which is often used in this application as it doubles as a surge tank, and from there the fuel line will lead directly to the fuel rail attached to the throttle bodies and injectors. My question is, how much of a restriction will the 6mm fuel line be to fuel pressure supplied to the throttle body rail? The volume of fuel is not an issue, as the engine itself will not use much more fuel than it did with the twin carburettors fitted, it's whether the pump will be able to supply a minimum of 50psi to the rail. The fuel pump is to be located next to the fuel tank, at the lowest point possible, while still safely positioned, where it will push the fuel up to the fuel filter and fuel rail. There will also be a small pre-filter immediately before the pump to protect it from 60 micron and above sized particles, whereas the aforementioned FRAM HPG-1 filters down to 10 microns.
Hopefully this makes sense. It'd be ideal if there was a formula, or some way to calculate the pressure reduction that occurs due to a reduction in fuel line size? For example, if a pump were capable of supplying 90psi through a 10mm ID pipe, what pressure would it be capable of supplying through a 6mm ID pipe, or an 8mm ID pipe?
Thanks,
Steph
My problem is the selection of fuel line and hoses. I was hoping to retain the original fuel line from the fuel tank to where it enters the engine bay. From that point on I plan on using a 6mm ID to 8mm ID fuel line adapter, and run 8mm ID hoses from there. In the first instance it will feed into a large FRAM HPG-1 fuel filter, which is often used in this application as it doubles as a surge tank, and from there the fuel line will lead directly to the fuel rail attached to the throttle bodies and injectors. My question is, how much of a restriction will the 6mm fuel line be to fuel pressure supplied to the throttle body rail? The volume of fuel is not an issue, as the engine itself will not use much more fuel than it did with the twin carburettors fitted, it's whether the pump will be able to supply a minimum of 50psi to the rail. The fuel pump is to be located next to the fuel tank, at the lowest point possible, while still safely positioned, where it will push the fuel up to the fuel filter and fuel rail. There will also be a small pre-filter immediately before the pump to protect it from 60 micron and above sized particles, whereas the aforementioned FRAM HPG-1 filters down to 10 microns.
Hopefully this makes sense. It'd be ideal if there was a formula, or some way to calculate the pressure reduction that occurs due to a reduction in fuel line size? For example, if a pump were capable of supplying 90psi through a 10mm ID pipe, what pressure would it be capable of supplying through a 6mm ID pipe, or an 8mm ID pipe?
Thanks,
Steph





RE: Fuel Pressure Relating To Hose Size
You are asking the wrong question and also not supplying enough data to answer the question you are asking.
With no flow, the pressure will equalise no matter what the diameter of the pipe. Once flow starts, the calculation for pressure drop from flow rate is complex.
The question you should be asking is, will the flexible portions of the hose designed for use on a carburetor system that probably never exceeds 10psi still be suitable and safe at 50psi.
How are you going to accurately measure MAP to tune the thing for part throttle cruise.
Regards
Pat
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RE: Fuel Pressure Relating To Hose Size
In essence, my question is, will the diameter of the hose effect pressure, or as I suspect, just the volume alone. I think I already know the answer, but I was looking for some reassurance, and perhaps a formula that I would have imagined included the area of a circle as a part of it. Intuitively, I'd expect 6mm ID hose to only flow 56% of what 8mm ID hose is capable of at the same pressure, based purely on cross sectional area alone. So the pressure should remain the same, and volume alone varies. Correct?
As far as individual throttle bodies go, setting up a MAP sensor with individual throttle bodies is a bit more of a challenge, because the transition between a low-load and full-load reading has the potential to occur very quickly with only the slightest movement of the throttle. As far as part throttle cruise goes, it's still early days in the research side of things, but I haven't come across anything making specific reference to this issue, but I suspect it one and the same to what I just described. Can you further enlighten me? For reference, I'm employing a MegaSquirt 2 as the engine management system for this project.
RE: Fuel Pressure Relating To Hose Size
RE: Fuel Pressure Relating To Hose Size
The Fram filter will be completely useless as a surge tank. If this idea came from the expert then you need to find a better expert...
RE: Fuel Pressure Relating To Hose Size
RE: Fuel Pressure Relating To Hose Size
1) A steel tank that always remains full and has no pressurised bladder cannot change volume beyond the stretch in the steel so it cannot act as an effective accumulator or surge tank.
2) EFI with a good pump and pressure regulator on the fuel rail needs no surge tank.
3) Pressure drop in the fuel line does not matter as the pressure in the rail is what counts and that will be controlled by the regulator.
A Walbro 255 HP will have more than enough fuel supply for your engine.
Regards
Pat
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RE: Fuel Pressure Relating To Hose Size
You have no idea what I know. I do know you didn't both reading the rules or obeying them when you posted. I know lots of people that do something for a living yet I wouldn't trust them to do anything for me. So, what's your point besides trying to insult.
I will stand by what I posted. Using your description of plumbing from the tank to the pump to the filter to the fuel rails means the filter will not work as a surge tank. Any expert that has told you it will has proven they're not an expert on that topic.
RE: Fuel Pressure Relating To Hose Size
I completely agree.
I made an error of judgement when I replied. I will fix it.
Regards
Pat
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RE: Fuel Pressure Relating To Hose Size
You can fix this without opening up the tank, but it'll cost you at least another pump and a separate tank.
Norm
RE: Fuel Pressure Relating To Hose Size
You mean a real surge tank.
Regards
Pat
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RE: Fuel Pressure Relating To Hose Size
Of course, you probably wont notice the pump because of the wonderful intake noise of the four throttle bodies!
RE: Fuel Pressure Relating To Hose Size
Sir, I think you need to read the original post.
The poster says, and I'm paraphrasing,: a "coarse filter" between the inlet of the electric pump and the fuel tank, and a "fine (fram/(surge tank)filter" at, or near the fuel rail.
Tank - coarse filter - fuel pump - fuel line to firewall - fine filter- fuel rail.
Seems perfectly reasonable to me, altho I agree the "surge tank" business is a bit of a stretch.
And he's going to need a return line to the tank from the fuel rail regulator, I would think.
RE: Fuel Pressure Relating To Hose Size
Norm
RE: Fuel Pressure Relating To Hose Size
RE: Fuel Pressure Relating To Hose Size
"Seems perfectly reasonable to me, altho I agree the "surge tank" business is a bit of a stretch."
again:
"surge tank" business is a bit of a stretch."
If we eliminate this surge tank business,(while keeping the Fram filter to do it's (filtering) job, where is the fatal flaw in this set up?
RE: Fuel Pressure Relating To Hose Size
The biggest flaw in this project is the OR has virtually zero knowledge of fluid dynamics to the extent he has no clue as to how to evaluate the advice given.
There is a fatal flaw in the logic that Pascals Principle does not apply when the system is static.
There is a fatal flaw in not understanding that pressure losses vary with flow rate when dynamic.
There is a fatal flaw in not understanding that if the pressure is regulated at the exit to the fuel rail, the injectors will see the pressure set by the regulator or very close to it so long as the fuel pump is big enough to supply an excess so as to overcome the pressure losses as they occur and so supply enough for the regulator to control the system.
There is a fatal flaw in the concept that a fuel filter will function as a surge tank.
There is a fatal flaw in giving ANY credibility to anyone who tells you that a filter is a surge tank.
There is even a flaw in the concept that this needs a surge tank. There are millions of late 80s to early 90s EFI OEM Hondas out there with no surge tank and many thousands of them have been modified to over 250hp on stock steel fuel lines and quite a few to over 400hp all without surge tanks.
As for damage to the pump from surge in the main tank, sure a surge tank supplying a remote pump will protect the remote tank from running dry, but what protects the pump that feeds the surge tank from running dry.
I know that running an electric pump typically used for EFI systems dry is reputedly harmful, however I and several family members have or have had quite a few EFI D series Hondas of about 1990 vintage that have never ever had a fuel pump fail and in every case they where at least 250,000kms old and up to 400,000+ old. I regularly push the limit on range and run the tanks very low, sometimes to he point of an engine stutter during hard corners. Still never a pump failure.
There is a flaw in thinking that journalists who write technical books and get published automatically know what they are talking about.
There is a fatal flaw in the concept that individual throttle bodies will perform better on a daily driver than tuned length runners from a plenum with a single throttle body. It can be done to get better response, but at considerable expense in other regards unless you have the knowledge of a team of good factory engineers and a lot of support facilities. It is VERY obvious that this won't be the case in this instance.
The biggest hurdle will be a stable but responsive MAP signal.
Another hurdle is the disruption to airflow by each throttle body in the heavily pulsating high peak speed airstream in the runner as opposed to the more constant lower peak speed airflow of a throttle body feeding a plenum.
The proximity of the throttles to the inlet valve do potentially give a slightly quicker response, but in reality it is a few turns of the engine, probably in the magnitude of 0.01 or less of a second difference.
Bottom line is almost negligibly better air flow response for loss of total airflow and a significant loss if engine management system response to changes in fuel requirements.
A Walbro 255HP will flow enough fuel to support a 300+hp engine through the stock Honda 6mm steel fuel lines. They are cheap and the normal high performance replacement for a Honda fuel pump on engines up to about 400hp.
Regards
Pat
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RE: Fuel Pressure Relating To Hose Size
Anything with OE EFI would already have a baffled tank.
Doing hot work on a 35 year old tank sounds a mite iffy. I wouldn't/didn't.
It is still possible through an extreme combination of low main tank fuel level and sustained hard maneuvering to empty a smallish surge tank if you're supporting a bit more power than 1.2 liters worth.
Norm
RE: Fuel Pressure Relating To Hose Size
Open the hood, four individual throttles, topped with gold anodized velocity stacks,and one of these:
ht
Chromed & mounted on the firewall with stainless steel internal wrenching fasteners.
Lots of faux aeroquip hoses, & a "billet" oil filler cap.
It's a hobby car!
RE: Fuel Pressure Relating To Hose Size
The ratio of air to fuel is IMP
You have to calculate Lambda factor
Lambda air=amount of air transferred to cylinder/(the amount of air fit to displacement volume*normalised pressure)
and Lambda fuel is similar and it is ratio of relative fuel supply
then you you find lambda=lair/lfuel
l<1 is a rich operation and mixture
Regards
www.adhengineering.co.uk
RE: Fuel Pressure Relating To Hose Size
I am fully aware of the wank factor. If I m honest I am trying to bait the OP into admitting it so we can stop wasting time on faux technical questions.
Norm.
I know OEM EFI has baffles, but I still got surge from sucking a bit of air despite the baffles and till never had a pump fail.
I do agree a better tank would be good and I think trying to fix the OEM tank would be difficult and dangerous.
Despite my comments to TTF, my thoughts run to a maybe one gallon tank close to the front centre and slightly below the bottom of the OEM tank with a couple of well placed large bore pipes with non return valves connecting them as a gravity feed also with a breather connecting to the filler neck. Install the pump into this tank.
Regards
Pat
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RE: Fuel Pressure Relating To Hose Size
The world has failed to end in the four years since the installation. The only problem is that, when the fuel is down to the last two or three gallons in the (wide, flat) tank, hard left-hand cornering sloshes the fuel away from the pickup and the engine will cut out momentarily. The fuel pump does not seem to care about running dry for that brief period of time, and to be honest, if it did have a problem with that, I'd start looking for a better pump!
The problem with running low on fuel is mainly an issue with in-tank pumps, which tend to be far underbuilt relative to external pumps. Modern cars have an internal surge tank to always keep the pump immersed in fuel so even this isn't much of a problem anymore.
RE: Fuel Pressure Relating To Hose Size
If I had known that not bothering to describe a second irrelevant filter to issue of the Fram filter being a surge tank would be such an issue then I would have included it. The configuration changing from;
tank -> pump -> Fram "surge tank" filter -> fuel rail
to
tank -> filter -> pump -> Fram "surge tank" filter -> fuel rail
Makes absolutely no difference in my comment of the Fram filter not funtioning as surge tank.
Apparently, I should have just followed my first instinct and hit the red-flag link and reported this post as a hobbiest post.
RE: Fuel Pressure Relating To Hose Size
Rodger that!
Instead we get rage and vindictive over a non-issue, from you, and the OP.
Of course it's not a surge tank.(I've also heard surge tanks referred to as "header tanks")
It's a filter. This is simply a matter of (as you say) a hobbyist being confused over technical terms he has heard from others in his peer group, whom he respects for their accomplishments, and became defensive when someone attempted to correct him.
At the risk of starting more controversy, I submit that a "coarse filter" at the pump inlet is not a "second irrelevant filter", but one intended to protect the high pressure pump from FOD, and is good practice whether you are "Ricer" or an OEM.
If I have offended you, or anyone else, I apologize.
RE: Fuel Pressure Relating To Hose Size
I'm working on an EFI system that uses three TBI (GM throttle body injection) units.
Each TBI contains it's own fuel pressure regulator. I could feed fuel to all three units in parallel, but getting the FPR settings to match seems like an ordeal. I could remove two FPRs and series the string of TBI to let the last one control pressure. Or, because the fuel return passages are pretty small on the TBI, I could parallel the two non-FPR units and series the return to the third unit for regulation.
Most systems I've seen use one FPR to control the entire system. For those of you who actually know something about EFI, what seems to be the least troublesome?
RE: Fuel Pressure Relating To Hose Size
RE: Fuel Pressure Relating To Hose Size
I was not aware, that a post could be edited, "once out there" .
http://www.eng-tips.com/viewthread.cfm?qid=249557
Such edits do in fact "confuse" the readers, as stated in answer #3 in the above link, (which explains why posts cannot be edited).
Gosh, I'm REALLY confused now!
How does one edit a post?
RE: Fuel Pressure Relating To Hose Size
TTF - I would suppose the post was red-flagged and asked to be changed.
RE: Fuel Pressure Relating To Hose Size
potteryshard.
There is an outside chance your thread might remain if you ask intelligent questions (which it seems you have) and you show some ability to understand the answers and some appreciation for them AND if you start your own thread rather than hijack someone elses thread, especially one of very low quality.
Regards
Pat
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RE: Fuel Pressure Relating To Hose Size
I forgot what I was going to say