buying up injectors for my 28rs setup, but this is kinda something that I don't want to buy now only to replace later so I'm wondering if I can get the 630cc injectors now and get a 440cc tune from unitronics, not very familiar with the way injectors and fuel pressure works so is this possible? or would I have to decrease fuel pressure to force the 630cc injectors to act like 440cc injectors. Also, I've seen some threads say the stock fuel pump is fine for base 28rs setups and some threads state that an in-line pump is required, at the moment I really just kinda want to get it running, an extra $40 for future-proof injectors is one thing, but I'm trying to shave off the big ticket items if I can, so I'm using the stock 102,000mile engine, I've got a atp knock off mani, a stage 5 southbend clutch, new 20lb flywheel, goodspeed IC and atp 3" DP(and the gt28rs of course..), and I'm using the 2.5">2.75" milltek that I've had(just cuz it was so frecking expensive don't want to replace it after only 2 months use lol). I figure it probaly won't even see 300+ awhp.. so anyone have opinions on this? I'm trying to avoid the extra $300-400 I'd have to spend on a AFPR and in-line pump. Also, I'm a little confused about the VR6 MAF people talk about, do you acutaly use the MAF sensor element that comes with it or re-use the stock A4's element and just use the housing because its 3" in DIA.? I've seen a couple variations on this that never really have clear answers, one thread says to drill a hole in the VR6 maf and re-use the stock sensor and another says to straight use the VR6MAF. I've been searching the vortex forums, audizine and these forums for a week or two now so if I've missed a thread I apologize.

thanks for any input.

 

I would use the 3" vr6 maf housing and put your internals back in it.

 

No one uses "inline" fuel pumps on the A4 since it doesn't do anything to add fuel since you are still limited by what fuel pump you have in the tank. So the better choice is to just upgrade the intank pump so that your only running 1 pump.


No such thing as "drilling a hole" in a VR6 maf to use your stock maf. If you plan on using a VR6 maf you have to make sure to get the corrrect one so that your stock maf mounts into it.

You cant just throw 630cc injectors and expect the car to run on a 440cc tune. If you want to run 630cc injectors buy a file that was tuned for them.

 

^ not 100% true. you can change the fuel pressure to cause fuel injectors to flow more or less (to an extent). check out this calculator:

http://www.csgnetwork.com/fiflowcalc.html

conversion from cc to lb/hr is approximately divide by 10.5, so 440cc ~ 41.9 lb/hr and 630cc ~ 60 lb/r. now i dont know what stock fuel pressure is on these cars, but if you do you can calculate what theoretical fuel pressure you need to run in order to get them to behave as expected.

 

honestly, if you dont have the money for all of these "little ****" items.. then you really shouldnt be trying to do this setup.

as far as injectors, just buy the ones your tune reccomends, there is a market for used performance parts, and you will make a decent amount of money back off of them

 

Stock fpr is 4bar which is the highest pressure you want to run on these cars and you dont want to go below 2.5 bar.

You could never get 440cc injectors to flow the same as 630cc and here is why. Plus I said that he could never get 630's to flow like 440's which was 100% correct.


est
440cc at 4 bar = 48.5 lbs/hr or 510cc
630cc at 4 bar = 69.5 lbs/hr or 730cc

So get the 440cc injectors to flow like 630cc you would have to raise the fuel pressure to 89.5 psi asa base fuel pressure. That isnever going to happen.

To get the 630's to flow like 440's you would need to run the fuel pressure at 22psi and that is well below the lowest pressure you would ever want to run.


Using fuel pressure to do this stuff only works when the injectors are much closer in size and is really only used for fine tuning a set of injectors with the tuning.

I have been using this site for years http://www.rbracing-rsr.com/fuelinjectors.htmand I run 1000cc injectors in my A4 with around a 3.5 bar base fuel pressure since the 1000cc injectors were maxed out with a 3 bar fuel pressure.

 

^thats a good site for fuel stuff mike.

 

^^ fair enough. i put "(to an extent)" because of those limitations on going too high or too low that I didnt want to get into.

so youre saying stock fuel pressure is 3 bar, but the stock fpr can accomodate 4 bar? i wasnt sure if thats what you meant...

 

The stock FPR in the A4 1.8t is rated at 4 bar (58psi). If you are running boost at 25psi your fuel pressure also goes up 25psi, this means you then end up with fuel pressure that is 83psi and most fuel pumps fall on their face at that type of pressure.


The 440cc and 630cc are the ratings of the injectors at 3 bar.

 

alright, i see what youre saying. i thought you meant that the stock fpr was adjustable thats where i got confused with 3 bar versus 4 bar.

so youre obviously running an aftermarket fpr to keep your base lower than 4 bar right? thats cool, it gives you the extra headroom as well to up the boost without worrying about the fuel pump falling behind