Injector Sizing Options

[turbohcar]

Alright boys. Here's my debacle now. I just picked up a Supra sidemount with 2.5in inlet/outlets. I've got 2.25in upper and lower intercooler pipes, a GM MAFT for a blow-through setup, and stock 14b @16psi. I'm wanting to purchase a Walbro 255lph pump, Aeromotive FPR, injectors and the necessary fittings to make it all work and rewire the fuel pump at the same time. What I need help with is the correct injector size. I did some playing with RC Engineering's FAQ page and came up with something in the 650-680 cc range. Does that sound right? I want to have plenty of room for adjustment without pushing the injectors too hard. Right now I'm already at my limit with the stock MAS, the stock injectors are maxed out, and I desperately need an Eprom computer to eliminate fuel cut. So, post up your thoughts and concerns please and let me know what you think.

What I need:
Eprom computer
Aeromotive FPR
Injectors
Walbro 255 pump

What I've got to put on:
GM MAFT with translator
2.25 intercooler piping upper and lower
Supra Sidemount

It may not be until Spring when I finally get all of this together and put on but, I atleast want to know what to work for. On a side note, my eventual plans for the car are to go to a fully forged bottom end, cams, and a .50 trim turbo (or maybe something bigger with ball bearings). Right now, I only have enough non-fuel modifications to run 25 lbs of boost and under 400 hp. So, everything's going to change before I go for the really big setup anyway but I thought it might be important to know anyway. I was thinking of going with an EVO III 16G or a 20G turbo after the fuel modifications are done though for an "in between" turbo. Thanks guys

[natedogg]

For a 14b 680's are overkill, but if you are planning on upgrading to a larger turbo before too long, 680's are probably the way to go.

[turbohcar]

Well, the shifting problems, fuel upgrades, Eibach springs, the sidemount, and blow thru setup will all come first before a bigger turbo. But, knowing me, the car monkeys will start filling my head again and I'll have it before next season.

Thanks Nate. Well, now that I think about it, would 680s be big enough for a 20G? Or would something bigger be in order for it? I'm thinking why stop at a 16G if I can run 25lbs. I just have to make sure I don't run over the 400hp mark for the sidemount IC.

[natedogg]

To play on the safe side for a 20G, I'd look at some 780's or the like. The 680's should handle a 20G at sane boost levels, but would probably max out much past 25 psi. That said, I ran 650's on my BR500 for quite a while before finally going larger.

[turbohcar]

Well, I'll just go with some 750-780's to be on the safe side. I don't like to just get by if I can help it. I'm already running 110% on the stock injectors but I'm also running incredibly rich. Rich enough to see some rich knock at cruising speeds anyway. No knock at WOT though.

[turbohcar]

What were you/are you running for fuel management if I may ask?

[jvb6806]

i ran 510's from a galant when i was still on the 14b at higher boost levels with a chipped ECU and an AFC. that seemed to get the job done. if i were you i would pick up and eprom and have a chip burned for your injectors (no matter what size you get) it has made things alot easier for myself and a buddy of mine that was having issues with his MAFT.

550's would be fine for high boost on a 14b or get the job done on a 16G. 720's if you are going to get a 20G.

[turbohcar]

Thanks JVB, I think I'll be going bigger than that though. I've heard too many problems with the 550cc injectors and a 16G. I'll probably skip to a 20G after this before I go to the .50trim though so I'm just going to get a set of huge injectors and I'll just grow into them. BTW, the Eprom is on the "to get" list.

[fastclipse82]

STOCK, stay with the 450's and just do a fuel pump rewire. Run 16 psi like that and make sure your log you car for knock, if you get knock then, then go with 550's. And what bad things have you heard about a 16G and 550's, its one of the best street setups there is. Also if you go with a 20g get a buschur 20G

[turbohcar]

Well, all the 16G/550cc injector threads I've ever read, they're usually maxing the injectors out or they're really close to it. So, if possible, I'd like to go with a little bigger injector and have plenty of room for adjustment.

[natedogg]

Well, all the 16G/550cc injector threads I've ever read, they're usually maxing the injectors out or they're really close to it.  So, if possible, I'd like to go with a little bigger injector and have plenty of room for adjustment.

This is true. 550's are only about a 15% increase in flow capability over the 450's. That doesn't give much head room for tuning. Especially on an Evo3 16g which is capable of outflowing the 16g's of old by quite a bit.

I think you're on the right track, Brett. Always best to be a bit conservative and play it safe when it comes to tuning and fuel management.

Right now, all I use to tune the injectors is the MAFT. I plan on going with a DSMlink soon though.