Stock Fuel Rails, why they don’t keep up

[16GoManGoHC2]

I think I stumbled on to why stock fuel rails don’t keep up especially once on corn. I switched to corn back in September, a Flex Fuel tune. I installed a dual 285 fuel pump set up on dual FPCM’s but stuck with my already tuned for on 93 ID1050X injectors. Tuner said it could be done on the 1050’s and it can be. But as I’ve inched up to about 925 wheel now on tested 85%E and now cold weather set in with DA in the -1000 to -1500 range I’ve notice my fuel rail pressure dropping from commanded 90 psi to 80 psi and pump commanded at 89% which is max and my injector Duty Cycle go from an OK 75% to 85-86% which is about the max safe limit to push them too. In discussion with Rick at tapped he told me change to fore rails and their feed line and I’ll gain back 10-15% Inj DC and fuel pressure back because the stock rails are limiting flow. So I decided to try this verse the expense of going to a bigger injector and also having to retune for such which on a flex tune is like starting from scratch again. I just happened to then score on a set of Fore Rails with feed line and factory sensor for a killer deal and was looking forward to trying out Ricks suggestion. Well unfortunately that deal fell through because the seller could not get the feed line uncoupled from the fuel line from the tank and ended up having to sell the car with the Fore rails as there was no way to get the coupler out of the stock fuel line without destroying it, BIG BUMMER!! So it was back to watching out for another Fore setup. Well today in the shop I was doing clean up and organizing and had a set of stock rails for my spare blower sitting out and I wanted to seal them up and box them for storage. Well during this process I decided to look them over for what makes them restrictive, and I found it!!! And how stupid it is!! So we equip the car with 1/2” fuel lines but at the main rail feed connection fitting the tube is rolled over snd necked down to .303” of an inch!! Worse yet further down the tube where it’s connected to the rail the hole into the rail for ALL the fuel to go through is .277” of a inch!! WTF where they thinking?? And it gets worse!! So the main line feeds into the Passenger Side rail which then feeds the Drivers Side rail through a 3/8 tube fitting, they couldn’t stay 1/2”?? Ok, 3/8, not too bad BUT this fitting is rolled over on its end as well and has a inlet diameter of only .246” of an inch, smaller then 1/4”!! And believe it or not it gets worse!! That tube where it’s welded to the tube it’s supplied from the supply hole is only .213” in diameter!! Holy F$#k no wonder the system can’t keep up!! And now yet there’s even one more restriction!! The bung where each injector is fed from? Well each is restricted to feed through a 121” diameter hole!!! OK, I can relate to a bit of why this is, to help keep a more even feed pressure in the entire rail and regulate a flow to each injector but dam who would ever think to look in there and see this! Just think if you where trying to feed 1700’s through this little hole, definitely a pressure drop would be in that area between injector inlet and fuel rail!!


So....., I’m going to “port” these restrictions out and make these fitting be the max inside diameter of each tube which for the 1/2” tube is appx .420” and the 3/8” tube appx .310”, a BIG difference!! And see if I gain fuel pressure back and some injector Duty Cycle back!! But unfortunately I don’t know if I’ll get to test them in the near future as it’s now snow and salt season here in Pa So.... I’m looking for a volunteer that is in about the same boat as me, dual 285 pumps and 1000-1050 size injectors running E85 and getting to just about max Inj DC and seeing fuel pressure drop below commanded at the rails. @Speedy! I I think you may be close in fuel and injector DC as well in cool weather?You want to try a set of “Ported” stock fuel rails and see what it nets? If yes I’ll ship them out to you once completed. The mod won’t weaken or compromise them at all, their welded on the outside not any where near where material will be removed. The orfice in each injector port will be opened up to the same size as Fore Rails are. They should only take maybe 1/2-1 hour to change out. If no volunteers I may postpone pulling my blower and trans as planned for some upgrades and cross my fingers for a warm day (35-40F will do)in early January in Pa and being the Mexico boarder is only 1/2 mile from my house and I only need a 2-3-4 to 6500 rpm 12 second pull with data log to find out apples to apples get my just detailed for winter storage cat dirty to find out, I gots ta know!! Any one game to try a set of ported rails and see what it nets? Just think, this could save big bucks by not having to layout $650 for Fore rails and feed lines and more so the in ability to use the fancy valve cover covers which in switching to the Fore rails won’t fit any more. This could be a EUREKA finding here, need a tester!! Anyone game??

 

[BULL]

Warning, .02 ahead.

When thinking about fluid dynamics, a "temporary" reduction in pipe diameter is not the same as thinking about a long run of pipe at a given size.

i.e., if you take a 1/2 pipe and neck it down to a 3/8 pipe, that is an obvious reduction in flow. But this is not the same as a "temporary" reduction in pipe size, say going from 1/2 to another 1/2, but with a short 3/8 reduction in diameter such as a restriction from a crimp, etc.

This is NOT to say that you can't improve the flow by porting what you've got. I'm just saying that you shouldn't try to think of a crimped area measuring at 3/8 (example only) as the same thing as a 3ft length of 3/8 pipe.

Warning, .02 behind.

 

[16GoManGoHC2]

Warning, .02 ahead.

When thinking about fluid dynamics, a "temporary" reduction in pipe diameter is not the same as thinking about a long run of pipe at a given size.

i.e., if you take a 1/2 pipe and neck it down to a 3/8 pipe, that is an obvious reduction in flow. But this is not the same as a "temporary" reduction in pipe size, say going from 1/2 to another 1/2, but with a short 3/8 reduction in diameter such as a restriction from a crimp, etc.

This is NOT to say that you can't improve the flow by porting what you've got. I'm just saying that you shouldn't try to think of a crimped area measuring at 3/8 (example only) as the same thing as a 3ft length of 3/8 pipe.

Warning, .02 behind.

Thanks for the heads up. A reduction in size will limit and reduce max flow possibilities, if it didn’t changing jet sizes in a carburetor would have little to no effect on fuel flow down stream of the reducing jet correct? Same principle, the pressure on the down stream side of the restrictions is going to get less and less compared to upstream of the restriction as flow is opened up to equal what the open ended pipe can handle. The fuel pressure should be as equal as possible in each rail and with these kind of restrictions I’m sure it’s not helping such. Each restriction also induces turbulence as well which will lead to flow losses as well. Opening up these restrictions has got to make an improvement. Unfortunately 12-16” of snow is forecast here for later this week here which once that much is on the ground here it’s heat reflective traits keeps it cold and crappy in January usually. Need a tester!! I’ll be working on these soon and they’ll be ready for testing.

 

[Speedy!]

Interesting observations, but I'm honestly not keen on testing fuel rail changes like that in "production" as it were. Something on a flow bench would be better as if there were an issue it's bad news in "production" LOL. I am close on my setup as well with ID1000s hitting 80% DC on full E85 in 40 degree air and 1900 aircharge. I plan to run E70 in the cooler temps to mitigate that, and still get 99% of the benefit of E85, no sense spending all that money on more injector or bigger fuel rails when E70 is really good.

I'm still chasing why my fuel trims have seemed to go positive in the cooler air. Mike found a couple things I've been testing that seem to work.

Having said that I have been on the hunt for a passenger side fuel rail for an idea I had if anyone comes across one.

 

[Mike L.]

Warning, .02 ahead.

When thinking about fluid dynamics, a "temporary" reduction in pipe diameter is not the same as thinking about a long run of pipe at a given size.

i.e., if you take a 1/2 pipe and neck it down to a 3/8 pipe, that is an obvious reduction in flow. But this is not the same as a "temporary" reduction in pipe size, say going from 1/2 to another 1/2, but with a short 3/8 reduction in diameter such as a restriction from a crimp, etc.

This is NOT to say that you can't improve the flow by porting what you've got. I'm just saying that you shouldn't try to think of a crimped area measuring at 3/8 (example only) as the same thing as a 3ft length of 3/8 pipe.

Warning, .02 behind.

Comparing oranges to apples here,But. In my transmission business working with 5/8 steel cooler lines I've had customers go to custom made 5/8 hydraulic lines with improper fittings that measuring 3/8 at the ends and instantly overheated their transmissions because of the bottle neck. We rectified the problem by just changing the fitting to 5/8. Your thoughts?

 

[BULL]

Comparing oranges to apples here,But. In my transmission business working with 5/8 steel cooler lines I've had customers go to custom made 5/8 hydraulic lines with improper fittings that measuring 3/8 at the ends and instantly overheated their transmissions because of the bottle neck. We rectified the problem by just changing the fitting to 5/8. Your thoughts?

Well first is that empirical evidence outweighs my silly conjecture.

Second would be that if they had used 3/8 fittings AND 3/8 hose, it would have been much worse, faster, which is the point I was trying to make above. Think of it this way, put one hand around someone throat and squeeze, or put two hands around their throat and squeeze. (Actually, not a great analogy, but it was fun to say...)

 

[Mike L.]

Thanks for the heads up. A reduction in size will limit and reduce max flow possibilities, if it didn’t changing jet sizes in a carburetor would have little to no effect on fuel flow down stream of the reducing jet correct? Same principle, the pressure on the down stream side of the restrictions is going to get less and less compared to upstream of the restriction as flow is opened up to equal what the open ended pipe can handle. The fuel pressure should be as equal as possible in each rail and with these kind of restrictions I’m sure it’s not helping such. Each restriction also induces turbulence as well which will lead to flow losses as well. Opening up these restrictions has got to make an improvement. Unfortunately 12-16” of snow is forecast here for later this week here which once that much is on the ground here it’s heat reflective traits keeps it cold and crappy in January usually. Need a tester!! I’ll be working on these soon and they’ll be ready for testing.

How much, if at all, might opening these restrictions help a stock fuel system with no tune? I would imagine if it helped at all it would be at WOT.

 

[16GoManGoHC2]

How much, if at all, might opening these restrictions help a stock fuel system with no tune? I would imagine if it helped at all it would be at WOT.

Stock engine with no tune the system as is is ok to supply the needs of a stock engine. It’s when running high % ethanol with a automatic 30% increase in fuel needed along with the needs of increased boost and air flow even more fuel is needed and its then the stock system can’t deliver the fuel needed at the injectors even with dual fuel pumps. These restrictions in the fuel supply lines don’t help that situation. Going to Fore Fuel Rails and cross over lines usually cure the issue up to a certain point but they cost $660 and then the valve cover covers don’t fit any more. I’m trying to avoid both these issue by removing these restrictions in the stock fuel rails.

 

[AeroF16]

I'd be very careful experimenting with this. Not saying don't do it, but be careful. Messing around with fluid dynamics is not always as obvious as it seems and sometimes is counterintuitive. Especially when you are talking about messing with one piece of an entire system that was designed for this $70k car.

 

[Mike L.]

I wonder if any of the big tuners have played with this or have any thoughts.

 

[Speedy!]

The fluid dynamics piece is what gave me pause trying it in "production". Flow bench would be wise.

I heard a while back about someone messing with the holes around the injectors, but I can't remember the outcome.

 

[16GoManGoHC2]

I'd be very careful experimenting with this. Not saying don't do it, but be careful. Messing around with fluid dynamics is not always as obvious as it seems and sometimes is counterintuitive. Especially when you are talking about messing with one piece of an entire system that was designed for this $70k car.

That’s for the advice. I’ve been involved in industrial machine design, troubleshooting, upgrade, repair, and making shit fly for almost 40 years, probably longer then you’ve been walking this earth. I was responsible for over 100 million dollars of equipment at one time and gave it up to have a life. This is a no brainer and simple task, the rails themselves aren’t the issue, it’s their supply design snd build. Sufficient for stock delivery but not to much beyond. I’ll make the injector feed ports the same size as on Fore Rails that actually have a smaller ID then the stock rails. Their difference? The supply tubing is free flowing AN fittings without these restrictive crimps and weld on connectors with margin for placement error on the tube for automated welding. I’ll try them on my car with confidence or I would not have even thought of letting someone else, I wasn’t looking for a guinea pig I was looking for quick data since I’ll be snowed in for a while.
70,000$ Engineering brilliance netted a harmonic damper drive that a simple woodruff key would have made it bullet proof, instead they choose to use clamp load and a fancy washer and we drill and pin it with a hand drill. I’d be more worried about a failure there from doing that then drilling out these restrictions to the the size they should be, match the tube ID. They won’t be weakened at all either as their welded on the outside not inside.
Fore rail injector feed ports have 1/4” hole to each injector, if it’s good for them it will be good for these as well. That was done to help equalize pressure at each injector at 600-700cc flow not 1050-1300cc flow, Fore knew they had to be bigger for such so I’ll use their engineering and match their hole size. I’m not just poking and hoping here, there’s engineering behind it, I’m an electrical engineer but mechanics came along with that schooling baking with 40 years of real world experience. But I do appreciate the concern and advice

 

[Speedy!]

I for one hope it works. Will be an easy upgrade so.

 

[16GoManGoHC2]

I for one hope it works. Will be an easy upgrade so.

That’s the hope!!
The stock fuel rail is a whooping .650” ID, the Fore Rail is 1/2”, around .500”. So there’s no reason stock rails can’t keep up once the restrictions are removed. I’m going to mod these in the next few days, but unfortunately this upcoming snow storm is really going to put a dent in getting out to test them under extended WOT top of 4th gear 1/4 run in same conditions as previous runs.
Here’s looking down the barrel of a Fore Rail, stock rail ID calculated from OD minus .050” wall thickness of tube used to make them.


Here’s what’s coming



YUK!!

 

[Jack_Toepfer]

Yes, make the holes bigger, as big as you can go. Your observation with the Fore rails is spot on. The only job the hose and rails has is to supply the injector with the required flow at a pressure determined by the FPM. Let the injector decide how much it uses, not the orifice that preceded it.

 

[Magnified]

Awesome. This is why I come to this site. It doesn't get better than this. Creativity, ingenuity, and cooperative scientific and experimental know how solving problems.

 

[TrackDay]

The only concern I'd have is cleaning out the rails after drilling them. Flushing them perfectly may not be super straight forward and any debris at all into an injector can have bad results, obviously.

 

[Mean Cat]

Man, if a fuel injector cleaning shop could test them b4 & after drilling out the fuel rails, would be good, to see flow difference & any issues.

 

[Phast Hemi]

Interesting observations, but I'm honestly not keen on testing fuel rail changes like that in "production" as it were. Something on a flow bench would be better as if there were an issue it's bad news in "production" LOL. I am close on my setup as well with ID1000s hitting 80% DC on full E85 in 40 degree air and 1900 aircharge. I plan to run E70 in the cooler temps to mitigate that, and still get 99% of the benefit of E85, no sense spending all that money on more injector or bigger fuel rails when E70 is really good.

I'm still chasing why my fuel trims have seemed to go positive in the cooler air. Mike found a couple things I've been testing that seem to work.

Having said that I have been on the hunt for a passenger side fuel rail for an idea I had if anyone comes across one.

Close at 80% IDC on id1050 running e85 at 1900 aircharge?
Must have some massive fuel pumps in the trunk or car is running on 4 cylinders. Those numbers don't mesh with any setup I've seen... That thing should be pulling way more fuel.

The whole chasing positive fuel trims in good air thing may not be a chase that needs to happen depending on how positive they get. Just my .02

 

[16GoManGoHC2]

The only concern I'd have is cleaning out the rails after drilling them. Flushing them perfectly may not be super straight forward and any debris at all into an injector can have bad results, obviously.

Already had a plan for this. I Drilled one out today, I pressurized the rail with clean and dry compressed so all the chips flew out as they where generated. I drilled them out about .015” at a time, I still need to debur the holes in the injector bungs which I have a plan on how to debur both sides of the holes already as well but I’m elated how they came out. The inlet feed looks the part now for a 1/2” line!!
Primary inlet went from a .277” restriction at the inlet of the rail to a whopping .413”!! the feed port out of that rail that feeds the drivers side rail went from .213” to .302”!!. I drilled the injector bungs out from .113” to .204”, I stopped when I started getting close to the spot welds that hold them to the rail but they are brazed in place as well and no compromise in strength what so ever. The hole is now almost twice the diameter at .204” and will be plenty as it now almost matches what the feed port to the entire drivers side rail was originally!! I wish they were both done today as I would have gone out tonight and tested them before the snow storm starts tomorrow of which now projections are 18-24” in my area, yuk yuk yuk yuk YUK!!!!

Tomorrow drill and debur, and blow out from a bunch of different ways, fluid flush into a fine screen so I can see how if even one chip was left in the tubes them get them in the car and waiting for this crap to melt for testing.