DIY split fuel rails Reply #3

[titian]

 evowrx said:

Dwight started to explain something like this IIRC. Was he telling you this? He said no2 was tuned especially too for a different reason to 3 which he wasnt going in to.

Understand what Dwight is saying perfectly!! For the same reason...He does tune Group N motors this way to compensate because you are not allowed to alter the fuelling system.

Phew...Looks like you are understanding the reasons for fuel temp control consideration :)

[funkytown]

my first point was - fuel temperature variances have been proven a few times to account for nothing. nada. zip.

Go look on an RB motor - they run 6 in series... even in aftermarket set up, and they dont do bearings anywhere near as much as EJ's do.

think your talking more rubbish

Oh and regardless of the injector / split rail configuration. we run a retard on #3 for our cars regardless, makes more power and safer. Fuel temps - i think not.

[titian]

 funkytown']

my first point was - fuel temperature variances have been proven a few times to account for nothing. nada. zip.

Concerned about fuel temps - install a swill pot and run four tanks with four pumps and four swill pots to individual injectors, with 4 fuel regs with thermos at the injector tip adjusting the rate of fuel pressure by temp and fuel reg variance... *yawn.

If fuel temps are not the concern lets continue with the rest of your argument.

[quote name='titian said:

Why does No3 have BE failures = leaness/detonation.Why?..As above. Less burnable volume BUT the same quantity admitted compared to other injectors,In particular the first one serviced in the supply line flow, (No2 in OEM setup)

Equal temp of fuel for each injector is as important as correct pressure control and volume of supply. esp when WOT is being used a lot. or when achieving higher than OEM powers for longer than the OEM car.

/quote]

We are talking about split rails here - so the above No3 argument is out the door. both 3 and 4 are the last in line (with two factory regs) or even one with teed return lines.. In my case i did a BEB on #2.. go figure that one out in your logic buddy. #2 is first in line.

Attributing BE failure on fuel temps is pretty out there dude.. You notice that phase 2 motors onwards (particularly v8 onwards) that change to a modified

sump (headers i know) and a rear thrust crank do far less bearings than earlier revisions? On your logic i can attribute the BE failure to center trust cranks as much as i can fuel temp. The late model ones still run an inline fuel system as well in case your wondering. Oh on that note..

Go look on an RB motor - they run 6 in series... even in aftermarket set up, and they dont do bearings anywhere near as much as EJ's do.

*yawn.

Yep i give up too!!But im sure scottspeed will back me up. :)

There is a 20 dg C difference across the EJ motor on the fuel rail...By the way read the post throughout and understand it before climbing into my comment. > I Did clarify WHY BE failures occur. Thats WHY the split rail concept is it not?

[funkytown]

a split rail has the ability to do SFA - as per RB's and others.

What a split rail does is peice of mind to bring the 3rd and 4th closer and in equal proportion to the 1st and 2nd in line (for fuel) to maintain an equal pressure.

Historically people think its to reduce pressure drop across the fuel line between the first and last.

Which back to the whole point of what we are talking about in the first place - even two factory regs if slightly different will after the car has fired and equalised have a balanced pressure across the two rails.

you can refute this all you like - but many many people have run two regs to great success. As i have on my build running the best part of 500hp. (Yes its recently failed, it failed as i built it for 350hp and way over extended what it was capable of holding and abuse).

it is not fuel temp or flow they are concerned with. I would be interested to see your test rig to measure temp variances across an EJ fuel rail.

[titian]

 funkytown said:

a split rail has the ability to do SFA - as per RB's and others.

What a split rail does is peice of mind to bring the 3rd and 4th closer and in equal proportion to the 1st and 2nd in line (for fuel) to maintain an equal pressure.

Historically people think its to reduce pressure drop across the fuel line between the first and last.

Which back to the whole point of what we are talking about in the first place - even two factory regs if slightly different will after the car has fired and equalised have a balanced pressure across the two rails.

you can refute this all you like - but many many people have run two regs to great success. As i have on my build running the best part of 500hp. (Yes its recently failed, it failed as i built it for 350hp and way over extended what it was capable of holding and abuse).

it is not fuel temp or flow they are concerned with. I would be interested to see your test rig to measure temp variances across an EJ fuel rail.

AS you mention...Pressure will always be constant from filter to reg...Be that a one or two reg system. Equal proportion! correct. Remove the differences and create balance.

Two regs cannot be balanced (flow wise)..Pressure however will be correct.

Given that two regs will not balance and allow equal flow to pass through each rail.One rail will be unbalanced..As in the temp will be different,Therefore volume will be different.

I measured the temp using a non contact thermometer..On a std setup and after driving and coming to a stop checked the temp of each rail at idle...20 degC difference.

I used the same thermo to check my setup..0.3Deg C difference..Balanced!(almost!) Incidentally my setup was also checked periodically during Dyno tuning and also found to be balanced.

I have not checked temp on a two reg system.

[rex-leggy]

so pressure will be correct in a 2 reg system ...... you have not measured temp in a 2 reg system ..... comments seam redundant then without proof.

was the rail that was hotter happen to be the drivers side rail which is next to a hot turbo?

[Koom]

 titian']

[quote name='evowrx said:

Dwight started to explain something like this IIRC. Was he telling you this? He said no2 was tuned especially too for a different reason to 3 which he wasnt going in to.

/quote]

Understand what Dwight is saying perfectly!! For the same reason...He does tune Group N motors this way to compensate because you are not allowed to alter the fuelling system.

Phew...Looks like you are understanding the reasons for fuel temp control consideration :)

Also can't touch the ports. So how much of the tuning differences in certain cylinders is due to the V.E. differences due to that horrible dogleg exhaust port that Subaru heads have creating unbalanced V.E. ?

Another question: The common Walbro fuel pump flows as per this chart stolen from the internet (there's a few out there showing similar numbers) and they have HP instead of L/hr but we all know its a 255L/Hr rated pump.

As well as, if you are making decent power and pushing ~20psi. And we'll make a guess that our bigger aftermarket injectors are flowing about 650cc at that point. Then the injectors are consuming 156L per hour and that leaves about 25% of the fuel to return if the fuel base pressure is 45psi (+20psi manifold pressure). Then if this is all flowing through a factory side feed setup, there is a measurable pressure drop across each injector in the rails. So, the pressure at the filter is actually higher than the pressure at the regulator i.e. the last injector gets the least pressure (and least resulting volume of fuel flowing through it). I've tested this using a standard two injector rail and installing a 440cc and a 740cc injector then rating them. Then swap their positions and rate them again. They always flow more when they are earlier in the rail.

(This is in the very early EJ20 rails where the rail runs through each injector. I am still yet to re-run this test on one of the later rails that runs slightly offset from the centreline of the injectors or with a larger bore aftermarket rail).

So what I'm trying to say is that I reckon there is more to it than just fuel temp variations in the rail.

[Swindog]

Would the simple answer be if you could balance flow and volume across the two rails you wouldnt have a problem?

I somehow doubt you would need to compensate #3 for a temp variation of 20deg...that would mean that corner of the block sits hotter constantly.....and you have to find that temp at varying throttle settings.

My simple builder mind says that if you can get as much fuel as possible to each injector equally you therefore eliminate the risk of #3 failing due to lean out.

To do that you need pressure and volume, in my mind. But of course its all relative to your injectors for the volume and fuel pump for the pressure - or regs if you run them.

My setup i 'was' going to run had two regs but also equalise the pipe length across the block to the rails so to reduce 'lag' of the fuel to the far side if any was going to be present in the fuel lines. Equalising the line length would reduce a dramatic variance in the reg settings and allow a higher flow rate across the 4 injectors.

Again, in my mind.

Kooms mechanical mind may disagree but i think the theory was correct. I just never got round to building it.

[titian]

Mr Koom ..I agree with you..There is more than one reason to split the fuel rails for subaru..Pressure drop reasons and temp rise across the OEM system.

Balance is what is required.

so pressure will be correct in a 2 reg system ...... you have not measured temp in a 2 reg system ..... comments seam redundant then without proof.

Mr Rexleggy

A two reg system cannot be balanced for FLOW, I have tested this.

. .Therefore i did not setup or test temp balance on the two reg system! WOFT!

Mr Swindog...Test the two reg system for flow balance..it cannot be achieved.With OEM regs or aftermaket adjustables...Repeating what i have said already ::)Your line one says it all.

Balance! of FLOW and PRESSURE and TEMPERATURE is what we want is it not?.

Balance everything you can on any motor and you will achieve reliability.

Summation:- Balance the Pressure and the Flow in both rails. The temp will also be equal in both.

Best way for me to check equal flow? ??? Temp check on both rails.

[funkytown]

nah dude - you've still missed it. there is no way, if you have a split tee under the manifold, in a two OEM reg system, using equal length system .. of about--- 30cm? hose to the rail inlet is going to cause ANY temp variances that will affect volume and leaning on #3 or any particular cylinder.

If a FACTORY ONE reg serial set up i can see how by #3 you might increase the temp somewhat coupled with the pressure drop Koom has described, but not 20degs worth of heat alone causing the issues... imo.

So, if we've agreed the pressure will be equal, and as above the temp diff is nada, and we've split the rail in either fashion to give a more even pressure drop on to the 2nd inj in the rail its irrelevant that the flow may be different dude. the flow will alter to BALANCE the pressure and make for happy times. But lets be clear.. there will always be positive flow past the reg that is blocking more flow.. which is fine.

THUS... and il say it again.. going back to the 2 factory reg vs one single aftermarket reg to acheive a split rail.. is not a single bit different.

You're argument is so circular and pointless.

[madmike]

I like potato's... They are nice mashed...

[Guest]

 madmike said:

I like potato's... They are nice mashed...

Much better Roasted.

[Johnnynz]

Potato Salad mmmm...

[madmike]

 Johnnynz said:

Potato Salad mmmm...

+1

[titian]

:::)test your two reg setup...equal flow is NOT possible at all....Of course pressure in the rail will be equal.

Flow not equal?...Equals different temp...Therefore different volume.

Simple science really : :

Balance of both in all respects ..Just HAS to be better End of Statement of truths :-*

[madmike]

 titian said:

:::)test your two reg setup...equal flow is NOT possible at all....Of course pressure in the rail will be equal.

Flow not equal?...Equals different temp...Therefore different volume.

Simple science really : :

Balance of both in all respects ..Just HAS to be better End of Statement of truths :-*

I still like potato...

[funkytown]

you keep make this logic jump that unequal flow equals unequal temp???

eveeeen if this was true and i cant see how, for the two hose lengths of 30cm and the rate of flow of fuel.. that there is such a very short period of time where the fuel could even deviate in temp.

[Swindog]

Whats the flow rate vs pressure of a standard sti fuel pump? until you know that i dont think theres a way to control it.

Equal line length across the block plus allowance for loss across the injectors i dont see how you couldnt adjust it so it was equal.

If you have 20deg across a cylinder....somethings seriously wrong...considering you have to take into account air flow factors.