My boredom = Fuel Rails (390cc DSM)

[SATAN]

crowbar wrote: I believe they are brass. Stainless Steel would be a better choice.

I agree, thin stainless at that. However, can you imagine trying to machine stainless for fuel rails? That would be costly just on the tooling.

[Andrevas]

composite fuel rails FTW

Skunk2 has them for popular applications (Honduh...)

[G-E]

I suggest using those thick slurpy straws and for added reinforcement some spray foam around it...

[SKOLJACK]

Or how about utilizing the fuel injector cooling fan from other z31's???

[crowbar]

The greatest problem is heat soaking. That is, after some nice accelerations/boost/etc., the car comes to an idle and that heat is just 'glowing' off the lower intake plenum. (think about dyno pulls also, heh)

Aluminum will soak this up and the fuel will act like an internal 'radiator' carrying that heat further into the pressurized fuel.

A fan would have to carry mucho heat away faster than the liquid gasoline can soak it up internally. Not very likely. I have some thermal pics of the lower plenum. Its filled with 'coolant' that is coming off the heads.

The aluminum should not physically touch the car. It should be thermally isolated from the car's heat by using insulators at the mounting points. Perhaps the rail can also be coated with something that is thermally isolating. Like a clear coat.

It would be neat to build a pressure bypass switch that 'douches' the rail. You hit a switch and the fuel in the rails is bypassed around the fpr to the gas tank. So the rails 'refresh' with cooler fuel. The bypass is two takeoffs from right before the FPR that join in a 'Y' and there is a solenoid that can be opened (driver douche-button). Another possibility is to have a means to boost the voltage to the fuel pump for a 'spurt'. This will raise the fuel pressure and the FPR will allow the most energetic (hot) fuel molecules to go back to the fuel tank.

[SKOLJACK]

crowbar wrote: The greatest problem is heat soaking.

I understand that, but don't you think after increasing the fuel rail ID size from the factory (less than) 5/16" to 1/2" that it would take the fuel rail longer to heat soak the fuel on a "return-style" fuel system with fuel being constantly circulated via the fuel pressure regulator?

[G-E]

[quote]SKOLJACK wrote:

The greatest problem is heat soaking.
I understand that, but don't you think after increasing the fuel rail ID size from the factory (less than) 5/16" to 1/2" that it would take the fuel rail longer to heat soak the fuel on a "return-style" fuel system with fuel being constantly circulated via the fuel pressure regulator?

no he wouldn't, he's just talking out his ass again...

you'll be fine, the fts and hot-start conditions are accounted for by the ecu to avoid any problems.... once the fuel flows it will no longer boil in the rail

[crowbar]

[quote]SKOLJACK wrote:

The greatest problem is heat soaking.
I understand that, but don't you think after increasing the fuel rail ID size from the factory (less than) 5/16" to 1/2" that it would take the fuel rail longer to heat soak the fuel on a "return-style" fuel system with fuel being constantly circulated via the fuel pressure regulator?

It would almost certainly be dictated by the return flow rate at idle.

I never said the fuel is 'boiling'

[G-E]

I never said you said it boils... you intoned that the heat is bad somehow, and why would the heat be greatest "after some nice accelerations/boost/etc.," ? because the air isn't flying around the engine bay as much right?

crowbar wrote: The greatest problem is heat soaking. That is, after some nice accelerations/boost/etc., the car comes to an idle and that heat is just 'glowing' off the lower intake plenum. (think about dyno pulls also, heh)

....

It would be neat to build a pressure bypass switch that 'douches' the rail. You hit a switch and the fuel in the rails is bypassed around the fpr to the gas tank. So the rails 'refresh' with cooler fuel. The bypass is two takeoffs from right before the FPR that join in a 'Y' and there is a solenoid that can be opened (driver douche-button).
think about when you use fuel... when you stop accelerating and start cruising or return to idle, that is when the MOST fuel is BYPASSED in the fpr and therefore will have the highest flow rate within the fuel rail

crowbar wrote: Aluminum will soak this up and the fuel will act like an internal 'radiator' carrying that heat further into the pressurized fuel.
you're suggesting fuel loiters around in the fuel rail long enough to take up that heat, except that due to the multiples of atmospheric pressure, the fuel can withstand being heated quite a bit without expanding significantly, and unless it is significant the engine will not be affected

crowbar wrote: I have some thermal pics of the lower plenum. Its filled with 'coolant' that is coming off the heads.

now do you have any thermal pics showing the fuel rail heat in relation to the plenum heat "after some nice accelerations/boost/etc.," ?

crowbar wrote: The aluminum should not physically touch the car. It should be thermally isolated from the car's heat by using insulators at the mounting points. Perhaps the rail can also be coated with something that is thermally isolating. Like a clear coat.

you mean isolated like the factory rail ?

crowbar wrote: Another possibility is to have a means to boost the voltage to the fuel pump for a 'spurt'. This will raise the fuel pressure and the FPR will allow the most energetic (hot) fuel molecules to go back to the fuel tank.

only the most energetic molecules? I suppose you've learned how to communicate with the fuel molecules and nicely asked them to stand in the correct line?

disclaimer: no I didn't calibrate my toaster this morning to +/-0.001C

[Jason84NA2T]

Crowbar does have a point... but here is my reasoning.

I agree there should be at least maybe some rubber washers between the rail mounts and the lower intake if you're looking to keep heat out of the rails. This is also to "cushion" the injectors and rail from engine harmonics/vibration but that's another story. The only problem with heat in the rails is the RVP of the fuel being used and how it relates to hot starts. Winter blended gasolines being run in warmer months (or on warm days in the winter) are the primary reasons OEMs build so much hot start protection into their systems (FPR solenoid, FTS, cooling fan).

The simple fact of the matter in my mind is:
1. OEM's go fo overkill on most systems
2. I never put winter blended gas in my Z

So with that said, I see no issues with his fuel rails as is, unless he encounters hot start issues.

To mince words... fuel does actually partially vaporize in the hot rail... not boil.

[DrewZee87T]

If you are that concerned about it just put a cool can in the car to ice the fuel. Cheap, simple, effective. Or you could build some crazy fuel rails with heat sinks on them. Maybe hook up some big zalman cpu coolers to it ...haha

[SATAN]

DrewZee87T wrote: If you are that concerned about it just put a cool can in the car to ice the fuel. Cheap, simple, effective. Or you could build some crazy fuel rails with heat sinks on them. Maybe hook up some big zalman cpu coolers to it ...haha

Cool can, simple and easy. No need for all the super tech ways to cool the fuel.

[G-E]

Jason84NA2T wrote: The only problem with heat in the rails is the RVP of the fuel being used and how it relates to hot starts. Winter blended gasolines being run in warmer months (or on warm days in the winter) are the primary reasons OEMs build so much hot start protection into their systems (FPR solenoid, FTS, cooling fan).
exactly, the only time the fuel should actually be hot is a hot start where the fuel hasn't moved and has heatsoaked....

Jason84NA2T wrote: To mince words... fuel does actually partially vaporize in the hot rail... not boil.

figured people would get that

[Firehawk]

I think many are worring about a problem that does not exist. I have tracked cars that have the rail attached to the intake manifold and never had a problem of any kind. Not that much heat is going to be transfered across so little contact area of the mounts, and not enough to worry about from heat from the air.

[crowbar]

It would be easy enough to test.

On a 90 degree day, sitting next to a 210+ degree heat source, that aluminum piece would heat soak to at least the underhood temp plus some.

The only heat removal would be from internal fuel flowing through it. At idle, when PWM is small, the car is using minimal fuel. That leaves the fuel pressure regulator.

There is also another route. The fuel that is heated can be replaced by the 'upstream' fuel molecules. That is, heat is also drawn further back into the hose section. This is an insulator. In other words, heat is moving into the fuel supply no matter what.

Anyone ever measure the flow rate of the regulator back to the tank at idle? I know some people state that the pressure guage fluctuates at idle (perhaps from spurts of fuel pressure relief). A good idle is certainly needing constant pressure to some degree. Just as a turbo car, with its smaller pwm at idle needs injectors that are flow matched. Its more critical for them.