Ham
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posted on 20/2/08 at 08:14 AM |
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Fuel pressure
Hi all,
I am currently changing my fuel pump from mechanical to electric, I have purchased a facet solid state pump(mounted at the tank outlet),
Do I need to install a pressure regulator?
Engine is a X Flow running twin 40's
Cheers
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Mr Whippy
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posted on 20/2/08 at 08:35 AM |
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not normally as they cut out once up to pressure. Some also allow you to adjust the cut off.
Fame is when your old car is plastered all over the internet
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Jenko
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posted on 20/2/08 at 08:37 AM |
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A pressure reg is always recomended - you are lookin for around 3.5 psi at the carbs......
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britishtrident
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posted on 20/2/08 at 08:49 AM |
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You do not need a pressure regulator with this type of pump and DCOE carbs.
Regulators are a bad idea if not required as they place a restriction on the flow.
Xflo mechanical fuel pump is also fine to use with DCOE carbs.
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Mr Whippy
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posted on 20/2/08 at 09:20 AM |
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Bet your glad you asked
I used that type on the Falcon after using the point’s type (unreliable). Never bothered with a regulator with either type and had no issues. If
you’re using a fuel return I'd use the standard mechanical pump as due to the pressure never building up the electric pumps just run and run.
The solid-state pump you interested in is designed for standard float carbs so won't flood them.
Fame is when your old car is plastered all over the internet
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Ham
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posted on 20/2/08 at 09:23 AM |
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Thanks guys,
This pump is non adjustable, the reason I am replacing the mechanical pump is that on long straights on the track at around 6500rpm I experience fuel
starvation .
The new pump does not give output pressure, if more than 3.5 psi what will happen?
Cheers
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Mr Whippy
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posted on 20/2/08 at 10:14 AM |
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if the float valve is not seating right it might force fuel past the valve and flood the float chamber. You'll soon know about it as the car
will feel like the choke is on and get a bit smelly. Unlikely to be a problem though and you can get exactly the same problem with the original
mechanical pump.
Fame is when your old car is plastered all over the internet
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alexdj125
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posted on 20/2/08 at 11:06 AM |
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I've got a xflow with dcoe 40's and a facet fuel pump and I was told that I HAD to use a pressure reg, seems to run ok, or should I pull
it off?
Thanks, Alex.
If it ain't broke- it soon will be!
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Mr Whippy
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posted on 20/2/08 at 11:58 AM |
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Who said you had to and why, did they even give a reason? Feel free to fit one if you like as there is no downside so long as it can keep up with the
flow rate.
I would not bother myself as if it runs then no problem. The only thing I'd suggest is you fit the inertia kill switch used in fuel injection
cars to stop the pump in the event of a crash and the fuel line being cut. You wouldn't like fuel spraying all over the place would you.
Fame is when your old car is plastered all over the internet
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alexdj125
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posted on 20/2/08 at 01:31 PM |
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Hmm, good point, I can't remember being given a reason! think I'll go pull it off and see what happens!
If it ain't broke- it soon will be!
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britishtrident
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posted on 20/2/08 at 02:33 PM |
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quote: Originally posted by alexdj125
I've got a xflow with dcoe 40's and a facet fuel pump and I was told that I HAD to use a pressure reg, seems to run ok, or should I pull
it off?
Thanks, Alex.
Depends which pump you fit different Facet pumps produce different output pressures the normal Road Facet Pump solid state produces 2.5 to 3 psi.
http://www.completeautomobilist.com/parts/fuel+system/
Fitting a higher pressure pump and a regulator is pretty pointless.
I am very much against regulators because they are not 100% reliable. Internally they have moving parts which wear, if the regulator is worn it will
leak and especially in a no flow situation the pressure will build up to full line pressure.
In contrast in a fuel pump the output pressure is dictated by spring in compresion --- the pressure cannot rise above the rated pressure of the
pump.
The higher pressure Solid state Facet pumps are i theory rated at a higher flow rate but this isn't true in practice because if you reduce the
line pressure with a regulator you are in effect putting in a restriction that chokes the fuel flow back down to the same as standard road solid state
pump.
What really determines the max fuel flow rate of a pump undr perfect conditions is much the same as what determines how much power an engine develops
--- basically the size x number of strokes per minute.
To maximize fuel flow it is essential to pay attention to the suction side of the system.
Any restriction on the suction side will lead to vapour locks forming due the fuel instantly turning to vapour when the pressure is reduced much below
atmospheric.
The fuel line from the tank to the pump should be adequately sized. Only relatively coarse "screen filters" should be used on the suction
side. And the tank should be properly vented to avoid a semi-vacuum forming inside the tank.
[Edited on 20/2/08 by britishtrident]
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PaulBuz
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posted on 20/2/08 at 02:34 PM |
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I'm running twin 40 DHLA's on my engine.
I also have a fast road Facet pump (4.5 psi?)
Without a regulator , the pressure overcomes the float needle, with fuel pouring out of the carb.!
ATB
Paul
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britishtrident
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posted on 20/2/08 at 02:40 PM |
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quote: Originally posted by PaulBuz
I'm running twin 40 DHLA's on my engine.
I also have a fast road Facet pump (4.5 psi?)
Without a regulator , the pressure overcomes the float needle, with fuel pouring out of the carb.!
When going through tuning parts catalogues you have set aside mind set that words such "high pressure" and "competition" have
any meaning.
A high pressure fuel pump is pointless if the carbs can't cope with the extra pressure when the engine is stopped but pump switched on.
Much the same goes for the high pressure oil pumps sold for Xflos -- they only give higher pressure because the relief valve spring has a spacer
under it, a bit of a con really.
[Edited on 20/2/08 by britishtrident]
[I] “ What use our work, Bennet, if we cannot care for those we love? .”
― From BBC TV/Amazon's Ripper Street.
[/I]
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Jenko
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posted on 20/2/08 at 05:52 PM |
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Sorry, I'm going to disagree with those who said you don't need one......
Weber's like having a consistant flow of fuel, Something like a filter king is designed for the job (plus adds some more filteration to the
fuel).....Depending on which pump you have, those facet pumps can deliver upto 8 PSI, which is way too much....
A reg helps with any surge you may see, and ensures that the needle valves in the carbs never get overpowered....
If you have a <4psi pump then it's not stricktly required, but generally good practise.....
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britishtrident
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posted on 20/2/08 at 07:21 PM |
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quote: Originally posted by Jenko
Sorry, I'm going to disagree with those who said you don't need one......
Weber's like having a consistant flow of fuel, Something like a filter king is designed for the job (plus adds some more filteration to the
fuel).....Depending on which pump you have, those facet pumps can deliver upto 8 PSI, which is way too much....
A reg helps with any surge you may see, and ensures that the needle valves in the carbs never get overpowered....
If you have a <4psi pump then it's not stricktly required, but generally good practise.....
A filter king won't make a difference to pulsation --- fuel is more or less incompressible. The only way to reduce pulsation would be to fit
something like the huge double pumper low pressure SU pump as used for many decades by Rolls-Royce.
Provided the maximum pressure on the float valve is not exceeded Webers only care about the level of fuel in the float chamber.
Regulators without a return bleed cannot be depended on in non flow situation.
The non-flow situation cannot be regulated reliably because all regulators contain a valve with wearing parts which will at some point leak.
[I] “ What use our work, Bennet, if we cannot care for those we love? .”
― From BBC TV/Amazon's Ripper Street.
[/I]
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Jenko
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posted on 20/2/08 at 07:55 PM |
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Thats a fair point, but it's the higher than 4psi pulses that can have an effect on the needle valve...Too much pressure can effectively stop
the floats returning...I'll admit you would need a very specific set of circumstances to get this if you had a low psi pump.........
The purpose of the reg is to ensure this never happens, so you have to be 100% sure that your fuel pump is incapable of producing no more than
4psi.......Even the 'fast road' Facet pumps are rated between 4 and 5.5 psi (which means they are especially stable), and strictly
speaking thats too much for a weber.................
I would always go for a higher rated pump and fit a reg...that way, you can 100% guarantee you are getting the correct pressure at all
times.........
Paul.
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britishtrident
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posted on 21/2/08 at 07:36 AM |
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Normal road Facet pump output of 2.5 to 3.0 psi.
Fitting a Fast Road or Competition pump won't make the car go faster. If more flow rate is needed a bigger pump and or fuel lines is the answer
not a higher pressure pump.
Most fuel starvation issues arise because of problems on suction side not the high pressure side of the pump.
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Jenko
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posted on 21/2/08 at 10:20 AM |
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Of course more pressure does not make you go faster!......
Read any weber spec, and it shows that around 3.5 - 4psi is the optimum Fuel pressure......Anything over this and it 'CAN' effect the
needle valve and float operation.#
So, the specs are below...Unless said person has the smallest rated pump, then there is a possibility of over pressure........By fitting a pump giving
slightly higher pressure than required (and regulator), you fully cover yourself for any fuel requirement, plus, if the engine is ever upgraded, you
don't need to worry about fuel.....
Spec Road Road Fast Road Competition
Pressure2.0-4.0 3.0-4.5 4.5-7.0 7.0-10.0
Clearly anything above fast road must have a reg...
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Stu16v
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posted on 21/2/08 at 11:12 PM |
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Plus, whilst the pressure of the smallest pump will probably be more than adequate speeds and on a rolling road, it is quite possible that fuel
starvation might manifest itself if the car is capable of accelerating hard (which is exactly what seveneques are all about). Mainly because the fuel
pump is now trying to push a 'column' of fuel against the acceleration.
IMHO that is why it is best to have a pump of slightly higher pressure than required, and mount the regulator as close too, or better still in front
of the carbs
Dont just build it.....make it!
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