Fuel injector replacement/upgrade questions

[kung fu jesus]

My '88 325IS has about 185k on it and I am looking to replace the injectors.

I have been searching a number of e30/BMW forums to educate myself on the injectors, fuel pressure, different generations of Bosch injectors, spray patterns, upgrades, etc.

All I have on the car is a BAVauto BAV.m20.500 chip and Tri-flow cat-back exhaust. It's fine.

I would like to run a modern injector, something with a better spray pattern for better atomization. I have read people are using 19# m50 injectors that put them at ~17.x at the e30's 3 bar fuel pressure. That's fine, but the e30 wiki says the 14.5# are fine while others say they are running at a high duty cycle.

I am not unfamiliar with injectors and I do not want to run too rich and kill my economy and coke up the combustion chambers.

Can someone give me some real facts about which injector I should run and if there is a plug and play gen3 Bosch injector I can use to update? I am considering the Fiveo Motorsports variety, but If I can get part numbers or a vehicle they are found on that I can attain and have sent out for cleaning and matching, I would do that.

Thanks!

[digger]

stock ones are fine mate at stock or upto 200bhp, just need to be in good condition.

most people replace old clogged units with newer ones and that is why there is a improvement

[dnguyen1963]

Anything bigger than stock requires appropriate chip and tuning.

[kung fu jesus]

Excellent. Thanks!

[digger]

bigger will still work without a tune but it is just not required.

Reasons M20 community generally put bigger injectors usually because there are heaps of bigger injectors around and therefore they can be had for cheap. the other reason is due to misinformation that they are maxxed out and that more fuel gives more powe.

if you are going to retune then bigger upto sensible values has no downsides it comes down to cost

[kung fu jesus]

That is certainly understandable. Other cars I have had, there was a *little* room to go larger, but there was a point of diminishing returns on the stock ECU. The ones I had gone larger with were more for track use, and I would use an AFR plot to see if/where the the extra fuel was needed.

If the M50 injectors are 17# on the e36 @ 3.5 bar, that would essentially make them 14.5# at the e30's 3 bar fuel pressure, no? ( 3/3.5 x 17=14.5)

[Beau B]

I just purchased 17# green top injectors for my 88 325iS.. My understanding from searching was that the stock ecu can adjust within a certain percentage.. I am curious to see what everyone chimes in with.

[JMAL]

I just purchased 17# green top injectors for my 88 325iS.. My understanding from searching was that the stock ecu can adjust within a certain percentage.. I am curious to see what everyone chimes in with.

Let me know how that goes, i just got a set of green tops too. I have an ebay chip in my car. Let me know if there are any quirks with swapping them.

J

[efficient]

I just purchased 17# green top injectors for my 88 325iS.. My understanding from searching was that the stock ecu can adjust within a certain percentage.. I am curious to see what everyone chimes in with.

running 17lb green tops on my 2.5 with a 173 dme and it runs fine. ive never ran stock injectors so i cant vouch for them.

[Jaxx_]

That is certainly understandable. Other cars I have had, there was a *little* room to go larger, but there was a point of diminishing returns on the stock ECU. The ones I had gone larger with were more for track use, and I would use an AFR plot to see if/where the the extra fuel was needed.

Stock tuning already has a safety margin with the factory injectors. They will never hit 100% duty cycle on a stock tune. A shitty chip will do that, but really sketch to run injectors past 90% (85% is a better limit).

Yes, many factory ECUs will be able to adjust closed loop conditions, but usually don't have any adjustment for open loop, which is something like above 3.5k and WOT. Closed loop adjustment is probably not significantly more than 10-15%, but I'm not entirely sure. I don't know about motronic 1.0, but I don't think it alters the entire table according to closed loop values. What that essentially means is that with bigger injectors, the car will be running even richer than normal at WOT(great for your cyl walls ;)), and probably be slower.

You should understand that factory ECUs already have a huge amount of fuel safety in mind. They run rich to ensure no pinging or high temps(10.5:1 AFRs or lower are not uncommon), lower redlines, and duty cycle limits around 80-85%. With all of this info, it's safe to assume that the injectors that are in the motor from the factory are usually slightly bigger than they need to be. As you tune the fuel table with an aftermarket chip, these values are leaned out a bit and you can get away with the stock injectors, even with a higher RPM. Remember you make the most power at 12.5-13.2:1 AFRs.

You don't need more fuel unless you are somehow flowing more air. It's that simple. The only thing that would help is better atomization. With all other things equal, having bigger fuel injectors will never give you more power. You need real mods before you consider upgrading your injectors. Injectors are a supporting mod, not a mod in itself.

[digger]

there is apparently some long term correction factors that can affect the WOT AFR ive seen the effect way back when i cared about motronic....

you'll be hard pressed to hurt a stock M20 with lean mixtures and it is not uncommon with old engines and dirty injectors for AFR to be into the high 13-low 14 mark but doesnt causes knock or anything just runs a little hotter ( a local tuner told me he used to tune for 14:1 for more power but i suspect the actual AFR were closer to 13). these are low CR engines id be more worried about carbon buildup, combustion chamber oil conamination or bore wash than a slightly lean mixture on a low compression high mileage engine