550's or 680's

[wpg87turbo]

Just wondering at what point do you need to upgrade to higher then 550cc injectors? I'm looking at gettin a Holset HX-35 or H1C turbo, going to be running approxiametly 15psi, and I'm just wondering at what point do I need to upgrade from 550's. I haven't purchased them yet, but I'm wondering if i should just skip the 550's and go right to 680's. Any help or input as always is appreciated.

 

[aye mate]

General rule of thumb is 440s are good for 400rwhp, 550s = 500, etc etc. How much power are you wanting to make?

 

[wpg87turbo]

500whp is approxiametly where I would like to be after all is said and done, is there anything else I should be looking at as far as fuel delivery? Is a AFPR necessary? I've got a walbro 255 in a RCI engineering fuel cell, and I live in canada so I really don't have to worry about emissions, is there any other benefit to the fpr?

 

[Kyle87T]

I am also curious about this. I remember seeing a a formula of how to calculate it. Anyone would like to post it up?

 

[GrimJack]

Pretty certain that was posted by SupraCentral in the FAQ section, how to calculate how much fuel you need...

 

[suprarich]

Nice calc. on RC's web site.

 

[JB91389]

can some one post the link

 

[suprarich]

http://www.rceng.com/technical.htm#WORKSHEET

Here you go...

 

[JB91389]

Thanks

 

[wpg87turbo]

Ok so got that issue solved, now as for the issue of whether or not to use a AFPR, can anyone solve this mystery for me? Explain the benefits and that kind of thing?

 

[Clifton]

Ok so got that issue solved, now as for the issue of whether or not to use a AFPR, can anyone solve this mystery for me? Explain the benefits and that kind of thing?

Not really a mystery. Just has become popular on mkiii boards, just as egt's were a few years ago were a wideband was really needed. Get an safc or safr instead. Adjusting the fuel pressure to change your afr is a bad idea as it changes it across the board. Unless you are running twin pumps and the stock fpr can't return enough you don't need it. Also get a wideband.

 

[drjonez]

Not really a mystery. Just has become popular on mkiii boards, just as egt's were a few years ago were a wideband was really needed. Get an safc or safr instead. Adjusting the fuel pressure to change your afr is a bad idea as it changes it across the board. Unless you are running twin pumps and the stock fpr can't return enough you don't need it. Also get a wideband.

i disagree.

an AFPR is a very useful tool- think of it as a global AFR scalar. use it to get you close, then use an AFM scaling device to fine tune. the less AFM correction you make, the better.

 

[Clifton]

Fine tune? That's what the ecu/piggy back is for. Injectors need to run at a set pressure. Going up or down a few psi isn't neccesary. Going down being worse as you loose flow. If one knows how to tune the ecu/piggyback they are not needed.

 

[drjonez]

Fine tune? That's what the ecu/piggy back is for. Injectors need to run at a set pressure. Going up or down a few psi isn't neccesary. Going down being worse as you loose flow. If one knows how to tune the ecu/piggyback they are not needed.

on the stock ECU, your only way to "tune" is via AFM scaling. remember timing is also calculated based off of mass-flow. so your fuel "tuning" is resulting in a timing change, this timing change is especially responsible for the large gains sometimes seen by "leaning it out" (less airflow = MORE timing). this is the reason behind my previous statements- get close w/FP, keep AFM corrections to a minimum.

 

[wpg87turbo]

Ok so basically what im getting is, "its useful but not necessary". I have a SAFCII and a wideband, so this should be enough correct?

 

[drjonez]

depends on how many tuning parameters you want....

 

[Clifton]

on the stock ECU, your only way to "tune" is via AFM scaling. remember timing is also calculated based off of mass-flow. so your fuel "tuning" is resulting in a timing change, this timing change is especially responsible for the large gains sometimes seen by "leaning it out" (less airflow = MORE timing). this is the reason behind my previous statements- get close w/FP, keep AFM corrections to a minimum.

The ecu has no problem correcting for 550's under closed loop so there isn't a need to correct fuel at any there. Only plavce you would want to maybe pull some is under load. If you need to pull that much larger injectors aren't needed. I never ran 680's with the stock ecu to coment on them. As far as timing correction. You'll need to limit the afm signal just before fuel cut anyways. With an fcd I was still was at the 96% duty cycle at redline. Any more afm signal and I wouldn't of been able to run 20psi (lex). Just saying pulling a little afm signal isn't that big of a deal. I ran what many on here would say is dangerous (fcd) and shouldn't be done (always 27 psi) on the stock ecu and had no issues for 2 years with pulling signal and a stock fpr. Car idled at stoich and cruised there. Hated the low rev limit or I would still be using it. Money is better spent on many other things before an afpr, so many other things I have yet to get to needing one.

 

[drjonez]

The ecu has no problem correcting for 550's under closed loop so there isn't a need to correct fuel at any there. Only plavce you would want to maybe pull some is under load. If you need to pull that much larger injectors aren't needed. I never ran 680's with the stock ecu to coment on them. As far as timing correction. You'll need to limit the afm signal just before fuel cut anyways. With an fcd I was still was at the 96% duty cycle at redline. Any more afm signal and I wouldn't of been able to run 20psi (lex). Just saying pulling a little afm signal isn't that big of a deal. I ran what many on here would say is dangerous (fcd) and shouldn't be done (always 27 psi) on the stock ecu and had no issues for 2 years with pulling signal and a stock fpr. Car idled at stoich and cruised there. Hated the low rev limit or I would still be using it. Money is better spent on many other things before an afpr, so many other things I have yet to get to needing one.

the important thing to remember is that you have a clue as to what you're doing and 90% of those that will read this don't. i tend to cater my advice, etc. to the uneducated masses.....

 

[Halsupramk3]

also remember that when you increase boost, which you will do if you are needing 680s, that with each pound of boost you will need another pound of fuel. If you are running 23psi boost that is about 15 psi more boost over stock and your stock FPR will need to supply more fuel over stock fuel pressures. I do not know if the oem FPR is designed to handle that much fuel presure. Many are using it with no problems.

What blows head gaskets? Not enough fuel or improper a/f; and too much boost which is related to the a/f problem.

Clifton
you can run that oem ecu and max it out with piggy backs but if needing injectors over 550s i would feel safer with a stand alone or a emanage type ecu. I would think that it would be difficult to idle 680s on the oem ecu since the duty cycle minimum is 3%. My 720s on my aem idle rich at 1%. I lowered my base fuel presure from 40 to 38 lbs to help lean out the idle and uped the fuel in the map.

dont cheap out on managing the fuel. high boost is not dependable if you skimp on fuel management to go with it. Spend $100 on a AFPR and avoid a weak link.

 

[Clifton]

also remember that when you increase boost, which you will do if you are needing 680s, that with each pound of boost you will need another pound of fuel. If you are running 23psi boost that is about 15 psi more boost over stock and your stock FPR will need to supply more fuel over stock fuel pressures. I do not know if the oem FPR is designed to handle that much fuel presure. Many are using it with no problems..

Sounds like the beginings of a rumor. Stock fpr is fine to whatever psi you want to run. I've pegged my 30 psi boost gauge.

What blows head gaskets? Not enough fuel or improper a/f; and too much boost which is related to the a/f problem..

Knock, which leads to extremely high cylinder pressure. Too lean can lead to deto but you would have to be 1 psi or so away from knock to begin with. Too lean at lower boost and nowhere near the knock threshold will just melt a hole in the crown.

dont cheap out on managing the fuel. high boost is not dependable if you skimp on fuel management to go with it. Spend $100 on a AFPR and avoid a weak link.

It's not a weak link. You are assuming that, just as you are about it being able to handle higher boost. It' sjust a diaphram with a spring. The only benift to an after market one is it can return more and is adjustable. I agree with spending more on fuel managment though (electronics)