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John L

PI Fuel Pressure

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Here's a Tech Bulletin from a American pump manufacturer called Aeromotive regarding pre filters when using an in line filter, makes interesting reading and makes sense to me.  I have been quite happy with my Bullitt filter which has a metal filter that can be cleaned. I take it out every year and give it a good clean and am happy that I am getting full flow to the pump over the next year.

https://aeromotiveinc.com/wp-content/uploads/2014/12/TB_101_InletFilter02.pdf

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1 hour ago, Rogcastle said:

Here's a Tech Bulletin from a American pump manufacturer called Aeromotive regarding pre filters when using an in line filter, makes interesting reading and makes sense to me.  I have been quite happy with my Bullitt filter which has a metal filter that can be cleaned. I take it out every year and give it a good clean and am happy that I am getting full flow to the pump over the next year.

https://aeromotiveinc.com/wp-content/uploads/2014/12/TB_101_InletFilter02.pdf

Not that relevant to this situation as 1 its a different type of pump altogether and 2 they are selling their own product.

Stuart.

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Oh dear I didn't mean to open a can of worms...….

Can anybody advise what the thread size is of the tank outlet, I want to fit a push on 8mm hose adaptor, I have seen them in carbuilder solutions, as there seem to be many threads to choose from.  I know Malcolm used to make them but he never replies to my mails asking for one.

Is the sytec filter small enough to protect the pump and MU and injectors? I presume so if Stuart is using them.  Is it necessary to then fit a finer pressure filter after the pump.

The problem I had with the PRV, after fitting the better battery, the pressure had increased.  I also notice that when the engine speed is increased the pressure increases more volts, but surely the PRV should keep the pressure the same whatever the increase in volts, this is what makes me think that the return flow from the PRV must go back open into the tank free flowing.

John

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From the earlier posts, I had the pressure set at 110psi with my then current battery, when that one failed, and fitting a new battery I did just recheck the pressure and found it to be 125psi, so I can only conclude that the new battery does have much more poke in it. The supply does use go thru a relay, so a bit concerned the new battery is well up on power, where the old one  wasn't.

The pressure has be reset to the required amount.

John

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Hi  John

I don't know the thread size for a large bore tank outlet, but TRGB sell them for £7.50.

https://parts.trgb.co.uk/products/large-bore-fuel-tank-outlet-pipe?_pos=1&_sid=05dc95fb0&_ss=r

A post filter of around 10 micron is recommended by most of the suppliers for a PI . :rolleyes:

 

 

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Hi John,

a friend machined a barbed ferrule for me from an 1/2” UNF bolt. This thread size fits nicely in the standard tank outlet, but I think it is another thread originally, others will know for sure. I used a Loctite sealant for fuel on the thread. The advantage of using a bolt is the high tensile stress (yield- if you like) of this material, allowing a bigger bore for better flow. 
 

Opinions differ about pre-and post filters on this forum. I wanted to protect the pump, so have a not so coarse suction filter. I selected the largest I could find, and it will filter out anything that the pump, MU and injectors  could damage. 

An additional filter on the pump outlet would in my opinion only catch pump-wear particles, which should be minimal. So I did not install that 2nd filter, but others think different, each to his own.

I realise a coarser suction filter reduces the potential for cavitation, if large enough, but the filter size I have should be sufficient.

If you use the search function you can find days of reading on this forum about filters:)

Cheers,
Waldi

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Further to my intention to change my existing fuel system, I want to fit the return from the PRV into a new fitting in the tank, should this just be vented direct into the tank or should it have a drop tube attached so as the return the fuel to the bottom of the tank and hopefully not to have too many bubbles this way. Am I thinking correctly?

John

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Return hot fuel into the top so that the pump takes nice cool supply.

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I return the fuel at low level to a nozzle on the far (passenger) side of the tank from the pump pickup. I don't like splashing fuel through air due to sparks from static electricity - just something I was taught when I used to design fuelling systems for the RAAF. 

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If the pressure is reading 125 psi something is wrong with the PRV (or less likely its return to the tank) Your pressure should be 100-105psi. Running at 125 psi will make most Bosch pumps groan!

It is either set too high or it is stuck and unable to vent the excess fuel. Take it apart, clean and reset or replace with a reconditioned one.

The impact of pre-filters and post filters doesn't change the fact that the fuel pressure is too high.

A too restrictive prefilter may give normal fuel pressure at low demand (tick over) but will restrict fuel and the pressure will fall at full throttle and high revs.

A clogged post filter will have the same effect.

What pre-filter to use? The consensus is that the Bullet filter with the coarse mesh is fine in that it protects the pump from significant debris and swarf)

The important thing as far as filtration is concerned is the post filter of which many of the high pressure Bosch injection applications such as fitted to Ford CVH cars, Saabs and many others.

Is the size of you tank outlet critcal? Not convinced at teh flow rates needed for the TRs. The vendor who sold a larger outlet for the PI tanks was (at the time) promoting a glass prefilter that had a significantly smaller bore than the standard tank outlet! Said vendors then changed to the Bullet filter when the level of testiculation was pointed out.

Yes a big bore outlet and unrestrictive prefilter is a good thing but probably not essential. Likewise mounting  the pump below th tank is better but contrary to many statements most of the bosch pumps are able to suck enough to self prime. Back in the day many a TR6 was run using a Bosch pump taken from a scrap XR3i mounted where the Lucas pump was using the original CAV filter and worked fine. What's best and what is essential are 2 different things.

 

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On 11/21/2019 at 5:30 PM, John L said:

From the earlier posts, I had the pressure set at 110psi with my then current battery, when that one failed, and fitting a new battery I did just recheck the pressure and found it to be 125psi, so I can only conclude that the new battery does have much more poke in it. The supply does use go thru a relay, so a bit concerned the new battery is well up on power, where the old one  wasn't.

The pressure has be reset to the required amount.

John

The key issue with power supply to the pump is volt drop. When a battery starts to die this is often when the problem starts if you are adjusting the PRV as you will not get a correct reading for a new battery when fitted. Also size of alternator will also effect the reading, in my view only fit an 18 ACR which has a 45 amp output or larger. The original 15 ACR in my view is useless as it is not much better than a C40 dynamo! Supply wire size is very important. BL modified the size of wire in summer 1972. I went for 39amp wire (4mm2) to combat volt drop and have never had any more trouble, powered through a 30 amp relay.

Bruce.

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Good point. A simple check is to see how much the voltage at the pump connection rises if you increase rpm from idle (850) to say 2000 rpm.

Waldi

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