injector sizing...

[1fast97gsx]

I need some help and advice here. I am near the end of my project and I just need to match up the right injectors still. I was running some 650s before ... but I need bigger now. I have a fully built motor and an sc61 turbo. I plan to run around 25 psi or so daily ... but at the track crank it up to 30 - 32. I am only using an safc for tuning right now becuase I am out of money. I know a standalone would be better ... but like I said no money. What max size injectors could I run with the safc and a 255 pump and afpr? Thanks.

 

[VRMAN]

Max a SAFC will support are 720s.

Sounds like time for a VPC+880cc injectors.

 

[1fast97gsx]

just curious .. why do you say 720 is the max? Won't the safc go to like -50? I had my 650s at only -20 at the lowest point? I'm not argueing ... just wondering. Thanks.

 

[VRMAN]

To be honest, I forgot the verbage but anything over 720s wouldn't allow for sufficient tuning abilities with the correction factor. It is pretty well documented that 720s are max for SAFC. Some people say they wouldn't even run those w/o some other for of A/F correction but they were a small margin.

 

[1fast97gsx]

so then what would be my cheapest option to run some 880s or something of that size?

 

[white 2g awd]

Originally posted by 1fast97gsx
so then what would be my cheapest option to run some 880s or something of that size?

couldn't you find an eprom ecu, and try a keydiver chip with the injector compensation?? that and safc should help shouldn't it??? and granted its not as good as standalone, but cheaper, and hey, since you have an eprom, later on you could go with something like dsmlink.

Dustin

 

[herostar]

If you've already got the safc dsmchips.com might be able to do something to your ecu. I believe it's 125 for the whole package. The guy should be able to compensate for 880's, but fine tuning w/ the SAFC would help alot. Maybe he could make a chip for 650's, then you could tune out the 880's... I dunno, jsut an idea.

 

[1fast97gsx]

yea that sounds like a good idea .. anyone have more info on this?

 

[sunflashx]

If you have a compensated chip or DSMLink go straight to 950's and most likely you'll never have to worry about it again.

DSMLink + FIC 950's and the car idles and runs smoother than it ever did on the any of the Denso injectors I had (450's, 550's, and 660) I had before. That was back when I had a SAFC, Keydiver chips didn't exist and going too big was a bad thing.

 

[pneumo]

Keydiverchips.com and DSMchips.com are the same guy. Like White 2G AWD said, you need an eprom ecu first, then keydiver can replace the eprom chip with a modded chip.

Another option is to raise the fuel pressure with your AFPR by 5 or 10 psi. That will make your 660's squirt more fuel, acting like slightly bigger injectors.

 

[white 2g awd]

yea, like i said, you can get a keydiver chip with the injector compensation like you want, if you get the 880 compensation, and end up getting 1000, you can compensate the extra 120cc with the safc...kinda like guys with 550's do...i have the keydiver chip, and i couldn't be happier, i have 550's on the stock t-25, and it runs just like stock....i had to adjust my safc roughly at 3%, i haven't fine tuned yet either. and also, if you do go this route, you can always go dsmlink too, and don't have to worry about getting a eprom ecu, cause you allready got one, then you can turn around and sell the chip, and make money off that too. but its up to you, and the more experienced (can't spell while i'm drunk ) members on here, but if it were me, thats what i would do, and....wait, thats what i did....i plan on going bigger, but since i got the 550 comp. i can go to 660's next year, and not have to set my safc as far as most people do.

Dustin

P.S.- here is his link: http://www.dsmchips.com/

 

[pneumo]

Cool. I have a keydiver chip, too. I got it with the 550 injector compensation so my AFC settings were close to zero. Then I got rid of the 550's and got 720s and my AFC settings went down, but they're still closer to zero than if I didn't have the chip. I could probably go up to 850's and still be OK with the AFC. I could esaily send the chip back and get it adjusted for any size injector.

 

[1fast97gsx]

Originally posted by pneumo
Keydiverchips.com and DSMchips.com are the same guy. Like White 2G AWD said, you need an eprom ecu first, then keydiver can replace the eprom chip with a modded chip.

Another option is to raise the fuel pressure with your AFPR by 5 or 10 psi. That will make your 660's squirt more fuel, acting like slightly bigger injectors.

I'm new to fuel mods like this ... what exactly happens if I raise the pressure by 10 psi. you said my injectors will spray more fuel ... but how much more? And is it safe to do that or is it going to ruin the injectors?

 

[KPWSerpiente]

650cc injectors flowing at 53.5 (10psi above stock) would flow about 800cc, by my calculatamations.
Someone can correct me if I am wrong.

-T

 

[pneumo]

800cc seems a little high.

From my calculations, raising the fuel pressure from 43 to 53 with 650 injectors makes them flow 721cc. B+M (of B+M fuel pressure raiser fame) provides a handy formula for calculating injector flow and fuel pressure differences.
P2= P1 X (F1/F2)^2

solving for F2 gives us
F2=F1 X square root of (P2/P1).
where
F1 is stock injector flow
F2 is New injector flow
P1 is current fuel pressure
P2 is new fuel pressure

An added benefit of running higher fuel pressure on smaller injectors is they still have shorter deadtime, giving you a better idle and making them easier to tune.

Injectors wont have any problems with raising the fuel pressure by 10 psi. I've even used an extra 15 psi with no problems. I wouldn't want to go much higher since the spray pattern gets narrower at higher pressures and the injector has to open against the added pressure.

 

[1fast97gsx]

ok so if I raise my fuel pressure and then mess with the safc ... if I get into the +s for the correction then I will mess up the injectors? So in other words set the boost so my settings are still negative .. or how far positive can you go??

 

[pneumo]

oh crap you're confused!

To raise your fuel pressure you need an adjustable fuel pressure regulator. The SAFC has no effect on fuel pressure.

If you have 650's and you use positive settings on the AFC, then you car will run terribly.

"set the boost so the settings are still negative"?
NO! raising boost does not change the air/fuel ratio. Do not raise the afc settings to compensate for raised boost. That's not how it works. The afc changes the air/fuel ratio. raising boost does not change the air/fuel ratio. You can raise and lower boost all day long and the a/f ratio won't change, unless you raise it so high that your fuel system can't supply enough fuel, but with a walbro 255 pump that won't be a problem.

 

[Scrymerr]

I am running 720s on a 14b with no problems at all, thanks to the MAFT, FPR and AFCII.

 

[1fast97gsx]

Originally posted by pneumo
oh crap you're confused!

To raise your fuel pressure you need an adjustable fuel pressure regulator. The SAFC has no effect on fuel pressure.

If you have 650's and you use positive settings on the AFC, then you car will run terribly.

"set the boost so the settings are still negative"?
NO! raising boost does not change the air/fuel ratio. Do not raise the afc settings to compensate for raised boost. That's not how it works. The afc changes the air/fuel ratio. raising boost does not change the air/fuel ratio. You can raise and lower boost all day long and the a/f ratio won't change, unless you raise it so high that your fuel system can't supply enough fuel, but with a walbro 255 pump that won't be a problem.

I did say I have a fpr. I am talking about boosting 30 psi .... obviously the 650s won't be able to handle that ... that's the reason for this thread!!! I was asking ... IF I raise the fuel pressure AND THEN tune with the safc as long as I'm not in the positives on the safc and my air / fuel is fine then I'm good right???

 

[white 2g awd]

Originally posted by 1fast97gsx
I did say I have a fpr. I am talking about boosting 30 psi .... obviously the 650s won't be able to handle that ... that's the reason for this thread!!! I was asking ... IF I raise the fuel pressure AND THEN tune with the safc as long as I'm not in the positives on the safc and my air / fuel is fine then I'm good right???

yes, that would mean that your injectors are too big, which is a good thing, and with the more positive you go, the better the chances for fuel cut i believe, and if you had a keydiver chip, you could eliminate fuel cut like i did... actually, with my stock t-25, 190walbro, 550's, and 550 inj. compensation, i have my safc roughly tuned to -4%. which also tells how good keydiver is, cause 550's are way to big on a t-25 at 14-15 psi boost. (i'll probably get flamed for this though... )

Dustin

 

[nanokpsi]

Raising the base fule pressure will effectively increase your injector size. Like the calculations show with 10 more base psi your 650s will flow like 720s. The limitations of the afc are still present as you would have to re-tune like you had 720s. If you already have an afpr that can raise base pressure you will be fine (up to 53 base psi-10 more than stock). Then you will be flowing more than teh afc can controll. With 720s you may not be able to lean the mixture out enough on race gas though. I don't know because I have dsmink.

 

[1fast97gsx]

alright ... so with the 650s and an additional 10 psi fuel pressure should I be able to run 25 psi or so and not be running lean? I know every car is different ... but is it possible at all? Also ... 30 psi should be possible then on race gas? Or is my only other option to turn up the fuel pressure ... use the 650s and run race gas all times? :thumbdown

 

[Mike 99GSX]

Originally posted by 1fast97gsx
alright ... so with the 650s and an additional 10 psi fuel pressure should I be able to run 25 psi or so and not be running lean? I know every car is different ... but is it possible at all? Also ... 30 psi should be possible then on race gas? Or is my only other option to turn up the fuel pressure ... use the 650s and run race gas all times? :thumbdown

I really think you are underestimating the flow potential of the 65 lb/min hairdryer that you just put on. I can't possibly see you having enough injector to run it at 25PSI on pump. I really think you need to fork over the cash for big injectors, keydiver chip, and eprom ECU.

No offense, but its a situation where you should not have bought a turbo this huge if you can't support it. I'm sure you bought it because you didn't want to get something in between if you are going to get the fuel mods anyway when you have the cash. The car is just going to be very slow in the inteum until you can do the support right. What turbo are you coming from that you were using the 650s with?

 

[1fast97gsx]

had a 16g and was looking to upgrade to a 20g. Ended up building the motor so I figured ... why not slap on an even bigger turbo. That's how I ended up with this turbo.

 

[Mirage2LTurbo]

I ran 750cc's on my AFC, and have seen 880's idled and tuned just fine on an AFC. That's called the difference between real world experience and book knowledge.