What size fuel rail do i need?

I have used a calculation program to determine that with E85 fuel I need 52lb/hr injectors to be able to support 300hp so to give a small comfort margin I am planning to get 65lb/hr injectors.

What size fuel rail do I need?

I have seen some ranging from 1/2" to 1"

I have not found any calculations to show what size fuel rail will support what size rail.

Can anyone shed some light on this?

Thanks in advance

Mark

I think you need a slightly smaller injector.

Using a BSFC of .8 for E85, I get:

300 x 0.8 x 1/6 x 0.8 = 50 lbs.

Except that injectors actually flow volume not weight and E85 is slightly denser than gasoline by .78 vs. 75 so:

50 x (.75/.78 ) = 48# lbs/hr.

I have seen BSFC numbers as low as .72 (1.3 x the standard 0.55 for boosted gasoline applications) for E85. That would drop the required injector size to 44#

I'm not saying my numbers are right and yours are wrong but I think you need to research a little more to determine the actual number.

As for the fuel rail size:

P = (.000273 x V x L x Q) / (D^4)

Where P = pressure drop in the line
V = viscosity of the fluids
L = length of the line in feet
Q = flow in GPM
D = Inside diameter of the line in inches

For your purposes, we know that a stock 5.0 Mustang fuel rail is completely adequate for at least 350 HP so if we ignore the differences in viscosity and length and look at 30% more flow due to the higher BSFC of E85, a fuel rail diameter which could accommodate 390 HP on gasoline would work for 300 on E85. If you crank the proportions, it's about 7% larger in diameter.

If you were to use something the ID of a 5.0 rail and fit an adjustable regulator so you could crank it up to 45 PSI or thereabouts, you should be fine. Since you're fabricating your own, you could always just make something with a few thousandths larger bore. I'd be much more concerned about the several feet of line from the tank to the fuel rail than I would be about the rail itself.

This is going in a late model Fox body Mustang that already has EFI.

The only thing I really need to change is to a Walbro 255LPH in tank pump.

IIRC stock fuel pressure on the Fox Mustangs with EFI is 42lbs pressure.

I would just run some 1/2" or larger tube if fabbing one (welded) or just some of that AL extruded stuff (it is all pretty heafty sized)

I would go with around a 42 or 44, the 42 is very plentiful, if you use it past 80% for any length of time I will be amazed, I started with 36 and went to 30 blown at 10lbs and from 24 to 19 N/A, a to large injector is a drag at idle.

Don't forget the actual fuel line sizes

Broncitis":2avoivjg said:

I would go with around a 42 or 44, the 42 is very plentiful, if you use it past 80% for any length of time I will be amazed, I started with 36 and went to 30 blown at 10lbs and from 24 to 19 N/A, a to large injector is a drag at idle.

Click to expand...

Remember this is for E85. That takes 30% more fuel by weight than gasoline.

I had to start all over on this post because I get to factual and political about ethanol or its by products, it just drives me insane that some think ethanol is a viable product and yes on top of it, not as efficient. I still think he may get by with 42's, I actually ran mine blown with 24's for awhile and did not see much difference, just my experience with actually having done it with that engine, I did the #'s for mine and it should have been 39's, I have to be running 275 horse at a very conservative minimum. And every time I went smaller it got easier and easier to tune, but also I had a huge amount of injectors to choose from and they aren't cheap, perhaps around 50 is the answer with ethanol to be on the safe side, I just can't imagine anything past that with my personal expereince.

I was looking at E85 for its cooler burning properties and the fact that its rated at 106 octane.

Im also still planning on running a Negasquirt II Version 3.57. The 2.3L guys are having very good luck getting their turbo 2.3L 's to idle with the bigger injectors due to the Megasquirts faster CPU ability to process the info faster and compensate with a narrower pulse cycle on the injectors.

Your right in what you are using it for, I just get all messed up about the whole energy thing with ethanol, don't pay any attention to me, I knew why you were using it and that is very legitimate, its part of why ethanol does not have the energy of gasoline that its ping rating is higher or lower, depending on how you look at it, meaning octane rating, anytime you add octane booster, you are simply trying to reduce the ability of the fuel to ignite in simple terms.

StrangeRanger":1qvucffe said:

Broncitis":1qvucffe said:

I would go with around a 42 or 44, the 42 is very plentiful, if you use it past 80% for any length of time I will be amazed, I started with 36 and went to 30 blown at 10lbs and from 24 to 19 N/A, a to large injector is a drag at idle.

Click to expand...

Remember this is for E85. That takes 30% more fuel by weight than gasoline.

Click to expand...

E85 averages about 26% less energy efficiency per unit volume than petrol doesn't it? So injectors need to be 135% of petrol rating.

Anlushac11 it might be easier if you just worked in cc/min rather than lbs. However for 300 ponies with an 80% duty cycle the petrol injector rating would be 34.4lbs and for E85 46.4lbs. There is no need to exceed this rating and infact you may compromise MLPT and DFR if you do.

And the other thing, if you should be so lucky to run a 42 at 90 %, just how long will that be in reality, definately not long enough to hurt the injector, your talking about spinning this thing at about half the rpms to produce 300 hp most of the time, just saying if it were mine I wouls start with 42's, just because you can find them cheaper perhaps, FIC has balanced remans for half the price.