I have seen people discussing fuel rails in other thread (it wasnt on this topic), there isnt a thread specificly about this so I made one.

some of the things that would be nice to cover.

When? and Why is this needed?
What is the benefit of them?
What brands/models are good/bad?


Also could talk about other fuel components

:banana:

Paralleling fuel lines can be troublesome. If the fuel rails are not designed properly, a parallel system can create air pockets [....]

Agency Power's original side feed fuel rails had this problem. Let's continue this in another thread.

Do their current side feed rails have this problem?

APS or Perrin???

the stock rails dont spread fuel evenly,a.market rails are for safe fuel delivery first.
perrin,turbo xs both make great rails.

At what point are they beneficial and whats the gain from them?

what does everyone think about perrin top feed rails? or what top feed are reccomended (has to be affordable)

I have the Perrin's and I love them. Install was easy and fit and finish was awesome.

I'd also like to know at what point the stock fuel rails become a problem. I'm running 565cc DW injectors just for reference.

for some reason the fuel delivery is not even on the stock rails,
if you are runing 300whp and up change rails,mind you the rubber hoses that comes with those kits usually cracks after some time(not a lot of time),you will need metal hoses for reliability.

for some reason the fuel delivery is not even on the stock rails,
if you are runing 300whp and up change rails,mind you the rubber hoses that comes with those kits usually cracks after some time(not a lot of time),you will need metal hoses for reliability.

300whp? What!? I've only known folks to swap out their rails for over 500whp, never heard anyone needing rails for 300whp.

lol i run 850cc with a 255 pump on the stock fuel rails...talk to your tuner first before you spend money on something you might not need.

well perrin rail kit comes with ss lines.

lets say I put 680cc with perrin top feed, walbaro 255 (on 07 sti engine, vf43) would the rails be beneficial or over kill? what gains would be made?

I know that if I run them on top of intake mani i will get colder fuel wich means more hp.

The benefit is more even fueling from cylinder to cylinder. With more even fueling, you no longer have to worry that one cylinder might not be getting as much fuel as the others. This means that the car can be tuned leaner for a little extra power.

Less heat into the fuel lines is a nice little perk too.

Do their current side feed rails have this problem?

not that I am aware of.

However, I can't be certain. I have a friend close to AP that said they redesigned them after having issues. For all I know, he could have been making it up.

I do know for certain that the first gen rails had issues with repeated misfires due to vapor pockets. For the first gen rails, I just convert them to series feed instead of parallel and they work great. It's really easy and you only need to get 2 1/4" NPT plugs to do the job. Even in the series config, they are still better than the factory rails.

I too have found this on one of my customer's car. It was an 02 WRX with the 1st gen rails. The car was getting misfires on 1,3 and 4 along with a bad tune. After retuning the car, the misfires were still happening so I switched out the rails back to stock and misfires went away.

Now, with my car, I have the 2nd gen AP topfeeds and am having some issues with occasional random misfires and the car going lean upon tip-in. I've tried various tip-in settings as well as played around with the injector settings. Several ID injector owners have gotten pm's from me asking what their settings are so I'm at the point of replacing the rails rather than mess around anymore with tuning changes.

not that I am aware of.

However, I can't be certain. I have a friend close to AP that said they redesigned them after having issues. For all I know, he could have been making it up.

I do know for certain that the first gen rails had issues with repeated misfires due to vapor pockets. For the first gen rails, I just convert them to series feed instead of parallel and they work great. It's really easy and you only need to get 2 1/4" NPT plugs to do the job. Even in the series config, they are still better than the factory rails.

to my knowledge sti's (sidefeed) rails will fuel up to around 450whp, around 400 they start to starve cyl #3 if i remember correctly.

personally I would NEVER run perrin parts on my car, I ordered the APS fuel rails and should have them installed hopefully this summer along with my new turbo setup.

aps ftw

I too have found this on one of my customer's car. It was an 02 WRX with the 1st gen rails. The car was getting misfires on 1,3 and 4 along with a bad tune. After retuning the car, the misfires were still happening so I switched out the rails back to stock and misfires went away.

Now, with my car, I have the 2nd gen AP topfeeds and am having some issues with occasional random misfires and the car going lean upon tip-in. I've tried various tip-in settings as well as played around with the injector settings. Several ID injector owners have gotten pm's from me asking what their settings are so I'm at the point of replacing the rails rather than mess around anymore with tuning changes.

try plumbing them in series and see if the problem goes away first. It would be great data for all of us (and yourself).

Will do! That's less work than swapping them out.

try plumbing them in series and see if the problem goes away first. It would be great data for all of us (and yourself).

to my knowledge sti's (sidefeed) rails will fuel up to around 450whp, around 400 they start to starve cyl #3 if i remember correctly.

personally I would NEVER run perrin parts on my car, I ordered the APS fuel rails and should have them installed hopefully this summer along with my new turbo setup.

Why would you never install any perrin parts on your car? Please explain..

http://www.aeromotiveinc.com/products.php?prod=144
http://www.aeromotiveinc.com/products.php?prod=282


These can be found on Ebay for 160ish. If your somewhat smart you can see how the fuel runs through the system. Fab your own lines and you have the best of both worlds. Cheap (compared to other options), lots-o-fuel, metal braided, and sexy with anodized fittings.

I'm waiting for some actual information in this thread... we have one guy saying to keep the rails in line while everything I read otherwise up to this point said that a parallel system would be safer for the engine. Have any of the OP questions been answered? And why wouldn't you use Perrin products 06njsti? I just bought v2 perrin sidefeeds for my build and would like any information about them you can provide for me. It's just that i've been refreshing this thread for 2-3 days now and people have seem to forgotten about it....

it's all about the supply and the load. If the rails are large enough and you have sufficient supply, it doesn't matter if they are parallel or series. Series helps prevent any issues with vapor pockets if fuel temp and rail temp get high enough to vaporize the fuel at the base pressure of 43psi.

The boiling point of fuel varies from 100 - 400 degrees (based on the kind of fuel and additives in it) at atmospheric pressure. Pressurizing the fuel raises the boiling point. This is why carburetor engines are usually the only ones you hear about having issues with vapor lock as they run a very low fuel pressure (6-8 psi in the lines and atmospheric in the fuel bowls).

there are also other factors that will affect the performance of a fuel rail. Did the V1 AP rails cause misfires from vapor lock? I don't know. However, the problem was surely there. The other factor could easily be the pressure pulse in the fuel rail from an injector opening and shutting. If the fuel rail diameter isn't right, the pressure pulse in the rail could cause a low pressure at the same time the next injector opened. My guess is that this is the real cause the original rails had issues. Larger injectors cause a larger momentary drop in fuel pressure in the rail followed by a subsequent rise in pressure. Similar to "water hammer (http://en.wikipedia.org/wiki/Water_hammer)".
This is the same reason we have BOV/BPVs on our turbo engines. My guess would be that if the V1 rails were used with a larger fuel pressure regulator (like an aeromotive) they might not have had any issues at all. The larger control surface and diameter of the diaphragm in the controller would likely stabilize fuel pressure faster and more efficiently than the small factory regulator.

So, the reason you don't feel like you've had "any real answers" is because the real answer is: It depends.

i'm a newb to this so. can i just get perrin v2 fuel rail kit and then upgrade my injectors/pump and call it a day? (07 sti engine with vf43) or do i need to get a better fpr? if so what pressure should i set it to? what is the range of good fuel pressure? or does it solely depend on injector size?


i'm just afraid of getting a performance fpr and putting in the wrong settings

I'm running factory fuel rails and regulator with 1000cc injectors and a GT35R on my 07STi. Is this a good idea? Probably not. Am I going to upgrade my rails? absolutely. I'm just waiting for us to finish our rails so I can run our own brand.

I think factory top feed fuel rails and a walbro fuel pump will do you just fine up to an FPGreen and 800cc injectors.

^ thanks for making me feel good about my set up :)
i'll send you a pm about something off topic

it's all about the supply and the load. If the rails are large enough and you have sufficient supply, it doesn't matter if they are parallel or series. Series helps prevent any issues with vapor pockets if fuel temp and rail temp get high enough to vaporize the fuel at the base pressure of 43psi.

The boiling point of fuel varies from 100 - 400 degrees (based on the kind of fuel and additives in it) at atmospheric pressure. Pressurizing the fuel raises the boiling point. This is why carburetor engines are usually the only ones you hear about having issues with vapor lock as they run a very low fuel pressure (6-8 psi in the lines and atmospheric in the fuel bowls).

there are also other factors that will affect the performance of a fuel rail. Did the V1 AP rails cause misfires from vapor lock? I don't know. However, the problem was surely there. The other factor could easily be the pressure pulse in the fuel rail from an injector opening and shutting. If the fuel rail diameter isn't right, the pressure pulse in the rail could cause a low pressure at the same time the next injector opened. My guess is that this is the real cause the original rails had issues. Larger injectors cause a larger momentary drop in fuel pressure in the rail followed by a subsequent rise in pressure. Similar to "water hammer (http://en.wikipedia.org/wiki/Water_hammer)".
This is the same reason we have BOV/BPVs on our turbo engines. My guess would be that if the V1 rails were used with a larger fuel pressure regulator (like an aeromotive) they might not have had any issues at all. The larger control surface and diameter of the diaphragm in the controller would likely stabilize fuel pressure faster and more efficiently than the small factory regulator.

So, the reason you don't feel like you've had "any real answers" is because the real answer is: It depends.

Thank you for this post and the link. Was the last line directed at me? My post wasn't really meant to be taken as if I thought there was no useful answers/info in the thread already.. I thought this was a thread about fuel rails in general not just weather in-line rails were better than parallel rails. My main concerns were also the statement made about Perrin products.. seeing as I just got some perrin fuel rails I wanted to know if there was something wrong with their setup? Thanks again.. looking forward to learning more. :banana:

I don't know why Subaru doesn't do this but rotary engines have the same fuel rail design, two rails in series with two injectors each, and the same problem with fuel pressure dropping when one injector opens and then jumping when it closes. So they put a fuel pulsation dampener "FPD" on the end of the last fuel rail. It's just a rubber diaphram with a spring pushing on it. When the fuel pressure drops the diaphram pushes in and equalizes it, and when the fuel pressure rises it pushes the diapham back out. Rotaries are extremely inefficient with fuel so they have to run larger injectors for the same power levels and that's how they do it without getting wacky fuel pressures and vapor pockets inside the rail.
But these rubber diaphrams tear and it lets the fuel leak out and start the engine on fire. A lot of second gen RX7's have burned because of this. Before I fixed mine I would get a fuel smell if I pushed it hard.

While we're on the topic of fuel rails, I have another question to pose: What all is necessary to perform a side-feed to top-feed conversion? Is there anyone that sells such a kit? I want the new ID 1000's, but I'm having trouble finding information on EXACTLY what I would need to make this swap happen. Thanks, everybody, for the info (especially Maxwell. Your posts are always superb).

Topfeed TGVs, topfeed fuel rails(including fpr), injectors. There are other misc stuff such as vaccuum hoses but the 3 I listed are the major ones.

While we're on the topic of fuel rails, I have another question to pose: What all is necessary to perform a side-feed to top-feed conversion? Is there anyone that sells such a kit? I want the new ID 1000's, but I'm having trouble finding information on EXACTLY what I would need to make this swap happen. Thanks, everybody, for the info (especially Maxwell. Your posts are always superb).

Topfeed TGVs, topfeed fuel rails(including fpr), injectors. There are other misc stuff such as vaccuum hoses but the 3 I listed are the major ones.
that is correct. You can use either 07STi top feed fuel rails or an aftermarket rail. The Perrin rails fit well, but I don't like the method that is used for attaching the fuel lines. I haven't tried any other brands, but it appears to me that the Agency Power rails will also work. They are skinny enough that they don't interfere with the AVCS solenoids.

While we're on the topic of fuel rails, I have another question to pose: What all is necessary to perform a side-feed to top-feed conversion? Is there anyone that sells such a kit? I want the new ID 1000's, but I'm having trouble finding information on EXACTLY what I would need to make this swap happen. Thanks, everybody, for the info (especially Maxwell. Your posts are always superb).
thank you.

Just wanted to add that if you go with aftermarket rails, you can use your factory STi Fuel Pressure regulator.

I finally bought the necessary parts to switch the parallel setup to series and installed them this weekend. I havent driven the car yet but only to pull it out the driveway, wash it and drive it back in. The car starts right away on the 3 times I fired it up. Before, it would sometimes take long cranks and even me stepping on the gas pedal before it would fire up.

I have a little bit of fuel leaking from one of my fittings so I'll have to fix that before I drive it around.

try plumbing them in series and see if the problem goes away first. It would be great data for all of us (and yourself).

I finally bought the necessary parts to switch the parallel setup to series and installed them this weekend. I havent driven the car yet but only to pull it out the driveway, wash it and drive it back in. The car starts right away on the 3 times I fired it up. Before, it would sometimes take long cranks and even me stepping on the gas pedal before it would fire up.

I have a little bit of fuel leaking from one of my fittings so I'll have to fix that before I drive it around.


hopefully this fixes your problem for good.

lol i run 850cc with a 255 pump on the stock fuel rails...talk to your tuner first before you spend money on something you might not need.

Correct, we run 600WHP on the stock fuel rails without any fueling issues.

Don't fix it if it aint broken... unless you just want to sepend some money ;)

Team Crawford

Bump. Good discussion.

When you go with Perrin parallel rails, you're basically forced to change fpr. Is there a consensus on a reliable (preferably value) fpr?

I made myself a parallel set.
Cost me under 100$, including all new lines, and the connectors on the filter and FPR.
http://i159.photobucket.com/albums/t144/DutchScoob/IMG_0722.jpg

http://i159.photobucket.com/albums/t144/DutchScoob/IMG_0055-1.jpg

Correct, we run 600WHP on the stock fuel rails without any fueling issues.

Don't fix it if it aint broken... unless you just want to sepend some money ;)

Team Crawford

the only reason why many would consider it is because in the winter those fuel lines shrink or something and you start smelling fuel...

I made myself a parallel set.

http://i159.photobucket.com/albums/t144/DutchScoob/IMG_0055-1.jpg
Interesting take on the parallel rail setup. I would have thought running separate lines to each rail would be better, but I guess the lines feeding the rail would be T'd somewhere anyhoo (unless you ran twin pumps and lines :P).

You don't have a list of parts required to do this do you? I wouldn't mind doing it, but once I start I have no car until it is finished, so I need to ensure I have everything to do it or I'll be be using public transport until it is sorted lol.

Leslie

...
You don't have a list of parts required to do this do you? I wouldn't mind doing it, but once I start I have no car until it is finished, so I need to ensure I have everything to do it or I'll be be using public transport until it is sorted lol.

Leslie

and the FPR that you're using :)

Much obliged