Fuel Rail design

[wedge]

Okay, now that I've decided what injectors I'm using, I can move on to the next step which is the fuel rail.

I've got a pretty good idea already, and I've done up a design using Google Sketchup.
The parts I'm looking at are from Ross Machine Racing, using their -6 extrusion and universal clamps.
It looks to me like it will work perfectly, and should be pretty easy to do. Since the factory mounting holes on the Opel injector plates are in a straight line with the injectors, those universal clamps should be a perfect fit.
Clearance looks good too. I did up that design as accurately as possible, it will be a tight fit, but I think it will all fit without even having to grind any material off those clamps.

Does anyone more experienced foresee any problems with any of this, or have any suggestions how it could be improved?

[neuropel]

Looks like a nice design. Keep in mind there are a number of options previously posted on the site regarding fuel rail designs. One option is to go to www.extrudabody.com and check out their extruded fuel rails. They offer a service where you can give them the measurements and they'll make the fuel rail to your specs. It's pretty nice stuff, with nice mounting options, reasonably priced, and complete with AN fittings.

Search the site here and you'll see how other members have handled fuel rail design.

[wedge]

Hmm... I've been pondering it, and I do have a thought/concern. I don't know enough about fuel system design or performance to really know if it will make a difference or not. But I'm concerned that with the layout of the injectors for this engine, being paired together at opposite ends of the rail like that. Would that cause there to be any fuel pressure drop from the first pair to the second pair? That's based on the fact that one end of the rail is the inlet and the other end is the outlet.
But what if I were to try this: put a Y-adapter on the fuel feed line, and have both ends of the rail as feed in, then drill a 5th hole in center of the rail which would go out to the FPR.
Actually, as I understand it, that's more or less how the stock "rail" is plumbed anyway.
So would there be any benefit to doing it that way or would it be a waste of time?

[jordan]

Hmm... I've been pondering it, and I do have a thought/concern. I don't know enough about fuel system design or performance to really know if it will make a difference or not. But I'm concerned that with the layout of the injectors for this engine, being paired together at opposite ends of the rail like that. Would that cause there to be any fuel pressure drop from the first pair to the second pair? That's based on the fact that one end of the rail is the inlet and the other end is the outlet.
But what if I were to try this: put a Y-adapter on the fuel feed line, and have both ends of the rail as feed in, then drill a 5th hole in center of the rail which would go out to the FPR.
Actually, as I understand it, that's more or less how the stock "rail" is plumbed anyway.
So would there be any benefit to doing it that way or would it be a waste of time?

The fuel pressure regulator should be mounted inline on the return line end of the fuel rail for end feed rails, this is what will cause the pressure increase. The amount of pressure drop at the last 2 injectors due to the prior injectors wont lead to an appreciable amount for the power level that most will be at.

[markandson]

Hmm... I've been pondering it, and I do have a thought/concern. I don't know enough about fuel system design or performance to really know if it will make a difference or not. But I'm concerned that with the layout of the injectors for this engine, being paired together at opposite ends of the rail like that. Would that cause there to be any fuel pressure drop from the first pair to the second pair? That's based on the fact that one end of the rail is the inlet and the other end is the outlet.
But what if I were to try this: put a Y-adapter on the fuel feed line, and have both ends of the rail as feed in, then drill a 5th hole in center of the rail which would go out to the FPR.
Actually, as I understand it, that's more or less how the stock "rail" is plumbed anyway.
So would there be any benefit to doing it that way or would it be a waste of time?

With the proper sized injectors, fuel pump, supply and return lines, you should have little issue with pressure drop except possibly at WOT for an instant when the demand peaks before the pump can catch up. A good solution for that particular problem is an accumulator that is available from Marren (and probably others).

[wrench459]

I'm going to take a stab at this and I'm sure it won't come across right.
As long as the injectors are on the same dia. of the rail it wont matter.
One of the laws of hydraulics.
How are you planning on tuning the fuel curve ..with what software?
Is this a street car or a max effort race engine?

[wedge]

I'm going to take a stab at this and I'm sure it won't come across right.
As long as the injectors are on the same dia. of the rail it wont matter.
One of the laws of hydraulics.
How are you planning on tuning the fuel curve ..with what software?
Is this a street car or a max effort race engine?

It's somewhere in between street and race. The car is for Targa Newfoundland. So it's going to be tuned as powerful as possible, but it's got to survive a week long endurance race. And some of the fuel that's available out on the rock is a bit questionable, so it's going to be tuned with safety margin, in case of bad gas. Tuning will be done via Haltech E6K

[RallyBob]

It's somewhere in between street and race. The car is for Targa Newfoundland. So it's going to be tuned as powerful as possible, but it's got to survive a week long endurance race. And some of the fuel that's available out on the rock is a bit questionable, so it's going to be tuned with safety margin, in case of bad gas. Tuning will be done via Haltech E6K

I assume you're running N/A, so that'll be fine. If you had some huge turbo with big boost and gigantic injectors, then I'd want to see a larger diameter fuel rail (like -10AN).

When really BIG injectors open under full load, there can be a substantial pressure drop in the rail and subsequent loss of fuel volume to the next injector in line to open. But I'm talking about 800 cc to 1000 cc injectors (of which one probably flows more than all 4 of your injectors!).

You shouldn't have any problems.

[wrench459]

wedge
Its looks like you've got the hardware and knowledge to handle this.
I like to force the pcm into open loop then tune the fuel curve after subtracting timing to a safe starting point. This is for WOT conditions with a good A/F ratio. After getting the max numbers with the fuel I'll start adding
timing back into the car slowly.
I like 39.5 lbs. tip pressure and with the wideband it will tell the story.So far I've not been able to tell where the volume problem lyes if the ratio goes lean.
Then we get into the PITB part. Driveability on the street.

[wrench459]

wedge
Its looks like you've got the hardware and knowledge to handle this.
I like to force the pcm into open loop then tune the fuel curve after subtracting timing to a safe starting point. This is for WOT conditions with a good A/F ratio. After getting the max numbers with the fuel I'll start adding
timing back into the car slowly.
I like 39.5 lbs. tip pressure and with the wideband it will tell the story.So far I've not been able to tell where the volume problem lyes if the ratio goes lean.
Then we get into the PITB part. Driveability on the street.

This might help out somewhat with you endeavor.


Injector Comp Batt Volt

15.938 0.563 --- 0.906
15.000 0.563 14.000 0.906
14.000 0.625 13.000 1.000
13.000 0.750 12.000 1.156
12.000 0.875 11.000 1.406
11.000 1.000 10.000 1.688
10.000 1.219 9.000 2.031
8.000 1.844 --- 2.594
6.000 3.188 7.000 3.531

This is just an example NOT real world numbers

[wedge]

Just thought I'd share my finished product.

First pic shows the outgoing manifold and rail (from the previous owner of the car) side by with the new one.
Second pic is the full assembled FI manifold.