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Discussion Starter · #1 · (Edited)
Guys,

Just a quick one....

Has anyone modified their fuel system to run a returnless setup, rather than the original setup?

Reason i ask is because i'm going to run a fuel cooler and at the same time i'm thinking of going returnless.

Cheers, Ian
 

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Discussion Starter · #3 · (Edited)
The idea is that pressure between the injectors and pump remains at the correct level by stopping and starting the pump...........this means you are not circulating warm fuel from the rail back to the tank.
This is normally adopted on new cars due to the EVAP system not being able to cope with all the HC's that try to escape the warm fuel, hence increasing emission output.......but i'm thinking of just tryin to run a cooler fuel setup!

In order to make our cars quicker, it seems we spend great chunks of money on reducing the air inlet temp by adding larger intercoolers, then inject it with warm fuel.

I'm thinking a fuel cooler is a simple mod to help this, so why not go one step further and go returnless.

Any discussion welcome.
 

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I know the Jag V12 A/C the fuel rail, but its in a very hot place between the V.

Could you not just continuously run the pump, and somehow use a pressure regulator valve to supply the rail with fuel. I don't think you need to up the fuel pressure when on boost, you can just run a higher pressure all the time.

An interesting point, have you thought about the fact that the fuel gets cooled returning to the tank under the car, and then the cool fuel cools the fuel rail upon its return.

Does the fuel not get cooled when it gets forced through the injector and then cooled again by the cool air.

Sorry for not sounding convinced, I'm sure there is lots more to this then meets the eye..

It's certainly 'fuel for thought':)
 

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Discussion Starter · #6 ·
Seems i am not the only one thinking about returnless systems - had an interesting email from Mark @ Abbey....
Defo gonna lob a cooler on there while ia m studying this item.

Update to follow.

Ian
 

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Sorry, but isn't a returnless fuel system going to make your fuel hotter?

Reason being that instead of running a loop to and from the engine (where it gets cooled on the way there and back, especially if you have a cooler), it sits in the rail and heats up?
 
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The fuel is used in the rail with a returnless system noting is returned via a return line


On a normal system approx 85% of the fuel supplied to the rail is returned to the tank via the fuel pressure reg.( this depends on running of the motor i.e full throttle etc etc) so the heat in the engine etc heats the fuel.

A returnless system runs the reg etc in the fuel tank , the only problem must returnless system run static fuel pressur ei.e it doesnt rise with manifold pressure so you need extra big injectors to allow you to run the correct amount of fuel and fuel pump/s to run then.

most modern cars run the returnless system like the 350z and the Honda Civic type R
 

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The fuel is used in the rail with a returnless system noting is returned via a return line


On a normal system approx 85% of the fuel supplied to the rail is returned to the tank via the fuel pressure reg.( this depends on running of the motor i.e full throttle etc etc) so the heat in the engine etc heats the fuel.

A returnless system runs the reg etc in the fuel tank , the only problem must returnless system run static fuel pressur ei.e it doesnt rise with manifold pressure so you need extra big injectors to allow you to run the correct amount of fuel and fuel pump/s to run then.

most modern cars run the returnless system like the 350z and the Honda Civic type R
Good comments Mark, id like to add some aswell.

A true returnless system modulates pump speed to change pump delivery pressure (ie rail pressure) and hence there is no regulator. Obviously you would need a more capable ecu such as a motec to control this, a fuel pressure sensor, map sensor and a pump capable of being pulse width modulated (expensive).

Static fuel rail pressure not only means you require a larger set of injectors but there is now not a constant pressure differential across the injectors with increasing manifold air pressure. It decreases. This means inorder to flow the same amount or more of fuel, the injector pulse width increases. This screws with your tuning alot, as it now changes with boost pressure and mass flow. You also need to adjust your fuel injection timing table, not just pulse width table.

However too cool a fuel could result in combustion problems.

However a returnless system does have its many benefits, just at increased complexity and cost.

Hope this helps.
 

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I have seen fuel coolers fitted to a number of modern cars, They are normally just located in the return line, They seem to be more common on diesels as apparently if you return hot fuel to the tank it can froth up...

Does the same thing happen with petrol ? Im just wondering if this would be even more reason to go returnless.
 

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If you read the top fuel injection companies blurbs, they will tell you the fuel pump is largely responsible for heated fuel. This is why many powerful cars come with a 2 stage fuel pump, and aftermarket ones do a full fuel pump speed controller (see aeromotive).
If you consider a 1000hp fuel system. An idling car might use only 20-30hp worth of fuel, but the pump is supplying 1000hp worth. 980hp worth of fuel gets sent back to the tank, and continues to go round and round, all for the sake of the need to supply 1000hp for say a 10 sec run every now and then.

Many fuel pumps are fuel cooled.

The rising rate thing is not a neccessity, you could run 5-6bar rail pressure all the time if you wanted, you would just get less fuel resolution at idle (decreased injector pulse) which shouldn't be a problem for a decent ECU.

Wouldn't an aeromotive fuel speed controller, work to perhaps not to returnless standard, but much closer to?
 

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The rising rate thing is not a neccessity, you could run 5-6bar rail pressure all the time if you wanted, you would just get less fuel resolution at idle (decreased injector pulse) which shouldn't be a problem for a decent ECU.
It might not be on a standardish car, but when you're approaching 1litre injectors it will be.
 

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It might not be on a standardish car, but when you're approaching 1litre injectors it will be.
I think it would, I use 1000cc injectors, and have had the base pressure upto 4.6bar. Idled nice and smooth.
If you fitted the correct type of injectors (high impedance) or a peak and hold driver, you would have even more control than the bastardised inline resistor (read that as sluggish) thing the Japs tend to use.:confused:

However, you would only have to up the pressure if your injectors weren't flowing enough. The need to increase fuel pressure to counteract boost pressure is a myth.
 

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Its often 44psi on pretty much all pulsed injection systems, The continuous injection system uses about 60psi.

Its when you get onto modern common rail diesel systems it goes to silly figures up to 25000 psi.
 
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