I am currently running an EVO III B16g and the stock 450s, uip, GM MAF-T, 3" exhaust, Walbro 255, etc. Well as you may have guessed, I have maxed out the 450s and am now looking for what to upgrade to. The options I'm looking at are 550s and 680s from either FIC or PTE. I'd like to stick with the same turbo for a while, even after a built motor goes in. Now the question is, will I max out the 550s with this turbo (running ~25psi)? I have a friend here at school that has a B16g, FMIC, etc and 550s and is convinced he has maxed them out at ~22psi.

Also, if I were to go with the 6xx injectors, would I need a burned chip to compensate for the idle or would I be able to iron things out with the MAF-T?

680's are perfect for an EVO III 16g, and the MAF-T will get you about where you need to be with those injectors.

680's with a stock fuel pressure and the stock 9.4:1 AFR tune in this weather would be almost right on 80% duty cycle. 680's are only 630's with stock fuel pressure.

Nate's AFR is ~13.5:1 if I remember correctly, plus he's running more than stock fuel pressure.

550's will work fine combined with a higher pressure fuel regulator.

You seem to do well enough at tuning these things from results.

Here's another way to look at it:

Marcus's car with 450's and a 14b put roughly 325hp to the ground. An EVO III 16g on a built motor can push over 400hp to all four tires. Marcus's car was notoriously lean. 550's are only a 22% gain from 450's. There's a 23% max gain in possible horsepower going to an EVO III from Marcus's setup. The fuel pressure regulator would make it just passable to run 550's on a truly maximized Evo III 16g from the numbers I've seen.

If you're not looking to absolutely max out the Frank 3, you'll be fine with 720's and a fuel pressure regulator. You should also be fine to max out the 20g on the 720's. The fuel pressure makes a much greater change the larger your injectors get.

I have no solid opinion on how much a stock 6-bolt bottom end can take. A stab in the dark says about 500whp on a perfect tune.

Buschur says 400hp, 500hp if you shot peen the rods. It's more a matter of opinion and what condition your car was in before you started putting all this stuff on it.

With my 650's 80% duty cycle is about the most I've seen at 9K RPM at a boost pressure of 27 psi. If I start turning the boost up beyond that, the duty cycle does tend to get higher. I could probably use larger injectors in the future, but the 650's are about perfect for me now. Plus, like Eric said, I can always turn up my fuel pressure. I'm pretty sure the BR500 has more in it than 650's can take care of, if I truly want to max it out. I just don't think my poor stock bottom end engine can handle 35+ psi.

I think dsm-performance.com has some equations that will work out what the effective cc is for a given injector and fuel pressure. I used to have a duty-cycle map over RPM, that I worked out for my injectors. I'll have to see if I can dig that up.

The setup I had was built for 500whp and could have easily done it had I had traction to do it.

720cc injectors +walboro 255lphhp pump + frank 3 = 500whp @ ~26-29psi depending on who tunes it.

Good god Spy. Aren't those injectors dead yet?

What's the safe duty cycle, <90%? So to be safe, should I go with the 680s or pick up some 550s and turn up my fuel pressure?

Wow! Thanks for using my crude HP for comparison Eric. I'm honored.

BTW - My injectors were as good as staticly open when at WOT. My 450's never seen the double digits like they are supposed to. Don't try this at home...do the math, spend the money and you won't have to get another a daily driver.

I don't know if 'honored' is quite the right word since I was using you as an example of what happens with little injectors and big power.

Interesting how far past 100% idc these cars go. At cordova, with a 14b on a 9:1 bottom end, I was consistently in the 130% range with race gas.

Depends on how the duty cycle is measured, if its measured againsts the smallest possible window, which occurs at redline, then its entire possible to run the injectors over 100% 'duty cycle' and still have accurate fueling. If its measured dependent on the RPM, over 100% means you're stuck at static, and your ECU wishes it could run more.

I have no idea which method the Pocketlogger uses to display injector duty cycle. I know MMCD is RPM dependent, so it goes to right around 100% max.

I say honored because you remember something that old and technologically insignificant to compare to today.

However, that combination lasted over a year on the $300 junk yard engine. It only melted the #1 piston ringland when I got greedy on a humid Cordova night after a year of beating that engine sensless.

You can make these things work with small injectors, but its a needless and very frustrating limitation.

From what I've seen, the pocketlogger actually calcutes the DC in two different ways depending on whether you are looking at the real time number display or the logged graph. When I was running 450's a while back I'd see DC as high as 130% on the real-time display, but when I looked at the graph of the same run the DC would top out at maybe 101% or 102%. It may be taking the standard deviation of samples to produce the graph. That would eliminate most of the "peaky" readings to give a smoother graph.

Anyone have an answer for this? Can I max out 550s with an EVO III B16g?

but wort also recommended six eighties...

so, my guess is yes your evo 16 would eventually max em out.

There are a couple of people on DSMTuners that have maxed out 550's on a 2G pressure regulator (43.5 psi vs 37 psi of stock 1G regulator) on an EVO III 16g, but you have to run 26psi on a motor with cams/ported heads to get there.

I'd prefer to have the room 660's or 680's offer, but 550s and an EVO III 16g will work. I've been tuning my Buick for years with injectors that have always been too small, and its a nightmare.

That's what I was looking for, thanks guys

Lawn...it sounds close.

With that info I know that 550's could be maxed out with a 16g. There is a lot of useable injector under that max though. It's your decision, but I would go big and tune down.

Plus larger injectors allow you to tune your fuel control down such that it makes the ECU think the MAF is reading less air than it is truely flowing which can eliminate Fuel cut in the most effective way I've seen to date. If your the Wortdogg with custom EPROMs you don't need this kind of injector voodo but for the rest of us it's a blessing!

To me, a bigger benefit that fuel cut control is the greater timing advance that accompanies a lower perceived airflow. The very short time I ran 550s on my 14b, I had the afc tuned pretty far down. This set-up netted far better timing advance than the same boost on 450s, because the ecu is registering less airflow and therefor believes there to be no reason to retard.

Sounds good. The next step is, with 680s am I going to need a custom chip to get the idle right or will the apfr and the MAFT-T do the trick?

With bigger injectors and fuel control you get more of everything:

More Fuel
A larger range of fuel tuning
More safety with fuel rich tuning
More Air from more boost possible before fuel cut
And of corse - More Power!!!

The MAF-T will make the bigger injectors idle like stock...

If you already have a larger fuel pump, a MAFT and an AFPR/fuel pressure guage will do the trick for larger injectors.