zguy36

I know that this is an age old question, but the search function on this site provides many difficulties.
Has anyone upgraded their stock turbo injectors to something larger while still using the stock ECU? I realize that you cannot just slap in big injectors without making modifications. I plan to tighten the spring in the AFM to compensate for bigger injectors. I want to know the point at which the linearity of the spring constant in AFM spring changes and will no longer give a linear response with tightening. In other words, how much larger of an injector can be used while still getting the same bottom end performance from the AFM. I do no want to sacrafice rich or lean conditions under vacuum conditions.
-jeremy-

duckyz

You can solve the AFM issue with a BMW ('84-'86 325 (?)) AFM. They're both made by Bosch and should hook right up. There may be two wires that need swapped, but that's all. Don't ask me which, I haven't done the swap...yet.

Look on hybridz.com. They can tell you more.

zguy36

Do you know what size injectors that BMW AFM uses? This swap should be able to be accomplished while retaining the stock AFM. The stock AFM is 3" inlet and outlet, so finding something bigger would probably be difficult. I am going to attempt fuel injectors in the range of 350-400cc range and try it with the stock AFM. I just wanted to know if someone had stepped up this large and still used the stock AFM.
-jeremy-

lifegrddude

I'm using 370cc injectors on a stock 82ZXT ecu. Running the same afm, just tightened up a bit. It runs a bit rich, but nothing too bad, in fact I need an adjustable fuel pressure regulator to increase the fuel pressure when the boost is hitting in the higher rpm since the stock efi likes to run lean past 5300rpm.

Bleach

I want to know this too because that is what I plan to do. Just a minor upgrade from stock but still run the factory ECU. At work I have a link to some flow charts of various injectors from other cars that fit the L28 manifold.

zguy36

Before I started this upgrade, I wanted to get some baseline numbers from the stock system. I found that the stock ECU doesn't even make use of the stock injectors. When the AFM flap is wide open, it only triggers the stock ECU to run the injectors at 43% duty! But since I do not have money yet for a standalone, I will upgrade the injectors to make use of the stock ECU.
-jeremy-

Bleach

...then maybe a rising rate fuel pressure regulator is the next stop to bump up the "duty cycle" or something. That sucks that the stupid ECU only runs them at that level. I would go Megasquirt but I figured with my horsepower goal I would be able to use the stock ECU and save myself some money and a LOT of time.

lifegrddude

The 370's are off of an SVO Mustang turbo, although 2 of them are also from a Thunderbird turbo coupe. They are the brown top ones rated at 35lb/hr. The later green tops were only 30lb injectors which aren't much of an upgrade from stock. About the a/f ratio, at 9psi, I was running crazy rich, ~10.0 from 3000-4000 before it started to lean and kept going leaner the higher the revs. By the time the pull was over (6000 revs) the a/f had leaned out to 12.8. At 12psi, I can't do an extended blast on the freeway as it starts to ping. I have to crank the boost down to 10, I hate Cali gas! Can't wait till I can buy an adjustable fuel regulator this summer...

John

zguy36

BleachZ- What is your horsepower goals for your motor? I am pretty sure that some good numbers can be found with the stock ECU, though it might be a bit sloppy. I borrowed a wideband 02 sensor and drove my z around at different levels of boost. With my setup (t3/t4, larger front mount, stock ECU), the maximum level of boost that the computer can handle is 9-10psi. I watched the injector duty cycles as they varied with rpm, and they didn't peak out. Above 9-10 psi, the injector duty cycle would peak out and not raise with rpm. At 15psi, the stock ecu is maxed out at 4800 rpm. It sure pulls like hell below that though. The stock maps for the ecu are **** though. Even functioning properly at 8psi, the map leans out 2 air/fuel points at 5000 rpm and is a bit rich below. I think I might have plugged injectors or somethign as well, since it runs really lean 17:1 at cruise and idle. Probably a plugged injector, since the AFM hasn't been adjusted from factory settings.

Larger injectors can be used, with the stock fuel rail by converting an O-ring seal to a barb fitting. Just grind off the plastic around the O-ring seat and touch up the steel underneath to make yourself a nice barbed fitting.

I do not think a rising rate regulator would provide good drivability conditions. Our problem is more rpm based than boost related. The stock ECU can handle high boost at lower rpm, and low boost at high rpm. An rising rate would just dump more fuel when it isn't needed, but also when it is needed. It would make the car faster, but less fun to drive.

-jeremy-

Camd810

How r u mounting the other injectors? Or do they just go right on? What cc for the factory injectors. Trying a ct26 turbo on my rwd maxima.