10cc larger injectors + stock ECU = bad idea?

I recently found a set of 235cc/min Bosch Type III injectors from a Volvo S80 2.9L for cheap. I am in the middle of replacing the O-rings and filters on them and cleaning them out. I was thinking of installing them into my Alfa 164 24V, as they use the more modern multi-hole spray pattern instead of the older pintle injectors the Alfa currently has and are quieter. Both the stock and Volvo injectors are high impedance. The Type IIIs are a near drop-in for the stock injectors, you just need to cut a small notch in the plastic for the mounting clip. The stock fuel pump can handle the extra flow - it's the same type used in some 90's V-12 Ferraris! (I also got a good look at Ferrari's price gouging compared to RockAuto- holy markup, Batman )!

However, I am still running the stock ECU and the stock Alfa injectors are only rated for 225cc. Later Alfa V-6 models used Type IIIs like the Volvos but rated for 225cc, and are much harder to find on this side of the pond. I want to run this by the GRM brain trust before I do it just to be doubly sure it's a safe upgrade. If not, what kind of trouble will the larger injectors cause?

i have gone from 35lb injectors to 46lb injectors in an old ford turbocoupe with no ill affects, and thats a significantly larger increase than what you are thinking about. my opinion is that you will be fine.

Note: i even got 33mpg on those 46ers...

-J0N

You're talking about a 5% difference. That's so minor as to make no difference in the real world.

In my experience, going to larger injectors made it sometimes harder to start in the morning. I had to blip the throttle a little, and it would fire right up. Otherwise, the thing ran like a dream. I'm an advocate for upgrading to multi-hole injectors. You'll hear the difference in the exhaust note immediately.

FWIW, the multi hole injectors are a help up to an engine temp of about 150F, once there, the effects of the spray pattern start getting overwhelmed by the fluid dynamics of hot fuel in an air stream. Start seeing some interesting effects as the fuel warms up, and eventually becomes flash vaporization.

For an Alfa, that takes some time.

So it may help get the engine started, assuming that it's spray pattern is reasonably close to the packaging. That part is often lost- most spray patterns are custom designed for an engine- to match injector location, orientation, and port design.

That's some good info.

Mrs. Oldtin's 928 has 24lb injectors instead of the stock (18lb IIRC) with stock ECUs (yes plural, it's a 928).

I know nothing about Alfas but in the DSM world the fuel trims are constantly being adjusted based on O2 sensor feedback during closed loop operation anyway and 5% is well within the range of adjustment. When you go open loop at WOT you'd be running that much richer. Easy to compensate for that with airflow sensor modification, piggyback ECU tuning, maybe even an inline resistor but probably completely unnecessary. If you've done anything to increase the volumetric efficiency, a little extra fuel may be your friend.

Not sure about the alfa, but most ECUs will "learn" the new flow rate and remap accordingly.

You can also quite easily tweak the AFM to lie to the ECU if the ECU doesn't take care of the difference on its own. Pretty common power/driveability mod anyway! The one nice thing about having a mechanical flapper AFM

Probably won't make any difference either way.

The ECM will just reduce the opening period to get the required amount of juice. Unless you goo so large that at idle the minimum opening period still chucks more fuel in there than the engine needs and it runs pig rich, you'll be OK. I doubt there will be any improvement in anything though.

curtis73 wrote: Not sure about the alfa, but most ECUs will "learn" the new flow rate and remap accordingly.

They don't, not in the high load sections, and it's not a "remapping" so much as adapting in real-time.

However, a 5% difference is minor. Let's look at it this way - the original injectors are probably flowing more than 5% less than they're supposed to.

Knurled wrote:

curtis73 wrote: Not sure about the alfa, but most ECUs will "learn" the new flow rate and remap accordingly.

They don't, not in the high load sections, and it's not a "remapping" so much as adapting in real-time. However, a 5% difference is minor. Let's look at it this way - the original injectors are probably flowing more than 5% less than they're supposed to.

Some try to extrapolate to learn errors out to higher loads. Others don't.