Fuel rail test

[GasGunR]

I'd like to see a test performed to determine if a front cross over on the fuel rails is helpful or needed in order to prevent fuel starvation of the number 1 cylinder.

Test 1. Flow match 8 injectors, preferably some of the bigger guys like Blue Giants or Purple SRT-4s.

Test 2. Flow test a complete set, (pair) of stock rails and the injectors from test one with the stock fuel rail inlet and rear cross over.

Test 3. Flow test a complete set, (pair) of aftermarket rails and the injectors from test 1 with a rear center feed fuel line.

Test 4. Flow test a complete set, (pair) of aftermarket injectors from test 1 with a rear center feed fuel line and front cross over line.

Preferably the test would run for several minutes in order to add accuracy to the test quantities.

Thanks,

Don

[roswald0511]

Damn good idea

[JonW]

Due to the pressure of the fuel system, you need the injectors mounted into the rails and then either attached to the manifold or inserted into a test stand that can be secured. The easiest way I can see for you to do this is to have an intake manifold off of the vehicle and have it positioned above a set of 8 graduated cylinders. You will also need to use a pump with a regulator so you can dial it up to 59 psi. You will then need a set of injector drivers to run all 8 injectors simultaneously.

[mhigham]

Testing flow you can just wire the injectors for power and run 100% duty cycle. Not the best for the injectors, get a donor set.

We run mineral spirits for tests like that.

Mike

[GasGunR]

I think this is worth fabbing a test stand designed to hold the rails over graduated cylinders.

There has been enough unproven conjecture about the number 1 injector being short on fuel. This test will prove or dispell that theory.

[GasGunR]

Update... Billet Technology has graciously offered their fuel rail pressure test fixture for modification to do this test.

It would be nice if Jason or Matt would post up here and let us know if this test might be on the list.

Also folks, hopefully the rest of you guys have been thinking of things that need to be tested during this MOFO. Please give it some thought and post your rideas up in this forum for discussion. Jason / Matt, if you'd rather have them posted elsewhere let us know where.

Thanks!

Don

[Super T]

Silly idea... Stuff pipes/tubes/whatever into the injector ports of the rails... copper, plastic, steel, glass, whatever, as long as they seal. In said tubes, install tees with pressure transducers. At the ends of the tubes, cap them and drill small holes to choke the flow down to something resembling what the injectors might take at 100% duty cycle on a big horse engine. It would be a pretty friggin small hole. But then all you have to do is measure the pressure in each tube to determine whether the flow is unequal (pressure differentials are what make fluid flow... well that plus gravity, but we know that one will be constant on all 8 tubes... at least I hope it will...).

Pressure transducers are a lot cheaper and more readily available than any flow measuring device... I don't even know where to get a flow measuring device that can measure the low quantities we're talking about here. Plus this would save us having to buy injectors.

Thoughts? If nothing else, go this route w/ pressure transducers and then stick injectors at the ends of the tubes... that way you have the most accurate flow rates possible but you still have the ease of measurement. The tubes can be turned on a lathe or whatever needs done to make them nearly identical and reduce the possible introduced error.

[Cam]

Thoughts??................yup, take a look at your plugs...........whatta ya think of that

[Blown7]

Well you have to remember also only 2 injectors are firing on opposite banks in sequence and the PCM will modify the timing of the injector pulsewidth to not create standing pressure waves in the fuelrail.

So my question is how can you duplicate the test to match the PCM injector pulsewidths and internal timing???


Jeff

[GasGunR]

Frankly I think it sucks. Doesn't tell you if its an injector, a fuel rail pressure problem or an intake head combination that moves more air to one cylinder.

Thoughts??................yup, take a look at your plugs...........whatta ya think of that

[GasGunR]

WHy do all that when all you need is a set of injectors, which I'm sure we can come up with... I'll loan a set of Blue Giants if necessary.

You and I know that it would take a huge pressure differential differnce to significantly affect flow as the flow will only change at the square root of the pressure change, but it would be easier to convey to those not interested in learning pump laws by just using graduated containers wouldn't it? No reason for fancy flow measuring devices.

I think the test as laid out above with all 8 injectors fllowing 100% duty cycle at the same time will speak volumes, (pun intended). A simple test, no reason to get complicated unless - the test shows there is a shortage of flow to cylinder #1 and we want to see what the actual limits are. I doubt that will happen, but who knows unless we do the test?

Silly idea... Stuff pipes/tubes/whatever into the injector ports of the rails... copper, plastic, steel, glass, whatever, as long as they seal. In said tubes, install tees with pressure transducers. At the ends of the tubes, cap them and drill small holes to choke the flow down to something resembling what the injectors might take at 100% duty cycle on a big horse engine. It would be a pretty friggin small hole. But then all you have to do is measure the pressure in each tube to determine whether the flow is unequal (pressure differentials are what make fluid flow... well that plus gravity, but we know that one will be constant on all 8 tubes... at least I hope it will...).

Pressure transducers are a lot cheaper and more readily available than any flow measuring device... I don't even know where to get a flow measuring device that can measure the low quantities we're talking about here. Plus this would save us having to buy injectors.

Thoughts? If nothing else, go this route w/ pressure transducers and then stick injectors at the ends of the tubes... that way you have the most accurate flow rates possible but you still have the ease of measurement. The tubes can be turned on a lathe or whatever needs done to make them nearly identical and reduce the possible introduced error.

[Super T]

Well you have to remember also only 2 injectors are firing on opposite banks in sequence and the PCM will modify the timing of the injector pulsewidth to not create standing pressure waves in the fuelrail.

So my question is how can you duplicate the test to match the PCM injector pulsewidths and internal timing???


Jeff

I don't believe the car controls the injector timing as a function of anything, only the pulse width (aka duration). And that's more or less fixed at WOT for a given tune. True you only fire 2 at at time on the car... but the hardware to duplicate that in a test would cost mucho dinero. The injectors are open/close, they don't modulate, so you can't use a controlled voltage to simulate 1/4 flow in all injectors (same as full flow in one).

I think if a certain cylinder has trouble keeping up, running all 8 @ 100% would exaggerate the problem and make it more pronounced, at least verifying that there is indeed a problem. If you wanted to, you could take the required flow rate for, say, 600 horsepower, and find injectors that flow 1/4 of that. Since the object of the test is the rail setup, not the injectors, this might be a viable alternative.

[GasGunR]

Or you could just put power to one, two or three injectors perside at a time... engineers always complicating things

[Super T]

Or you could just put power to one, two or three injectors perside at a time... engineers always complicating things

Yes you could. But I believe that all four flowing more closely simulates real life conditions. At, say, 6000 RPM, each injector is firing once every other revolution, so 3000 times per minute, or 50 times per second. Since it would be cost prohibitive (unless someone has ideas on actually controlling the injectors a la PCM) to get "real" flow that would have the rapid fluctuations of an in-service system, I would say that, at 50 times a second staggered across four injectors on a rail, constant flow through them would be the closest approximation. I dunno, maybe not. The effect of the pulsing pressure would depend on the velocity of the fuel in the rail.

There's a though... at the back of rail 1 (drivers side), the rail is carrying four injectors worth of flow, while at the front, it's only carrying one cylinder worth. That means the average velocity at the back of the rail would be four times that at the front. Granted, even that should be a very low velocity since the rails should act basically as fuel plenums. But maybe they don't...

[Hemi31]

Well,we saw some proof while tuning my car but nothing that would be believed here.The fuel trims from the right and left bank were uneven with the stock rails in place and after the new rails and crossovers went on they evened up.Now I know thats not a pressure and flow test like you guys want but it is another piece of evidence that a balance tube makes a difference.At least on a modded motor.