fuel injector cleaning/swap??

[j.fro]

For those of you who have cleaned or rebuilt your fuel injectors, what kind of performance gains did you see afterwards? Smoother running? More torque/hp? Better MPGs?
Also, would there be any benefit to swapping my 2-hole injectors for the newer 4-hole injectors?

[BYprodriver]

Originally Posted by j.fro

For those of you who have cleaned or rebuilt your fuel injectors, what kind of performance gains did you see afterwards? Smoother running? More torque/hp? Better MPGs?
Also, would there be any benefit to swapping my 2-hole injectors for the newer 4-hole injectors?

Yes to all of the above. Obviously smoother throughout the whole RPM range, no testing to measure gains. I have not investigated what might need to be done to use the newer 4-hole injectors, I have a set waiting for a project.

[j.fro]

Any idea what the stock flow rate is for 3.2 injectors? How about the stock fuel pressure?

[BYprodriver]

Originally Posted by j.fro

Any idea what the stock flow rate is for 3.2 injectors? How about the stock fuel pressure?

2-holes are about 240cc per minute

I Forget the stock fuel pressue but it's about 35-38psi

[Gelbster]

I too am investigating this subject but am hesitating for lack of much discussion of this subject -so thanks BY.
Please correct me but I understand the upgrade injector is a Bosh Gen 3 ,part # 0280155890. The Porsche # is 996 606 120 00 ? This is a '4 hole' injector.
My originals work fine but as part of my engine rebuild I need either a repair kit or the upgraded injectors. The repair/service kit is $25 for all 6.If I send my originals out for service +flow test it is $300+. The 6 new,upgraded Bosch injectors are $315.
Check your injectors before you buy -if they are a dirty beige color and have "0280 156 053" on the side, they are 4 hole, Gen 3.The problem is you have to remove one injector to read this number.
"This Bosch injector replaces obsolete p/n 0290150455.
Bosch Part number: 0280155890
Flow specs: 22.7 LBS/HR at 3 BAR (172.4 g/min)
Fuel Nozzle: Modern 4-hole disc fuel atomizer
Spray Type: Narrow cone, maximum fuel atomization
Injector type: Saturated
Connector type: Jetronic
O-rings: Viton, 14.5 mm
Length: 74 mm
Coil resistance: 12.0 Ohms"

[The Radium King]

I sent mine to rce for refurbishment. they sent back a report detailing pre- and post-flow rates. according to them some needed more work than others. I have read that some cyls have higher wear rate than others - perhaps due to some cyls getting hotter than others.

I felt the engine ran smoother and travel through the power band smoother, but no noticeable increase in power. I got the injectors redone for two reasons; when triggering them with the durametric I found that I could not get one to respond and assumed it was not working. turned out there is a bug in the durametric software. the other reason was that I was getting a strong gas smell in my oil and thought it might be attributed to a leaking injector (and taking that a step further, gas in oil tends to break down lubricants and seals, which might lead to premature ims wear - perhaps bad injectors is the culprit). gas in oil smell was reduced after the work.

I don't know anything about the benefits of 2 vs 4 hole injectors, but the true test of flow rate and fuel pressure (there are 4 bar fprs on the market if you want to upgrade) would be afrs at wot. if your fuel system can maintain the design afr at wot then you don't need more flow or more fuel pressure. only way to test that is wideband o2.

[j.fro]

I haven't had the two types of injectors in front of me, but from my research it looks like the early (2 hole?) part number is 996-606-120-01 while the later is 996-606-122-00 (4-hole). This information came from Pelican. It also looks like the injectors for all Boxsters and 3.4 Carreras are the same. Not sure for 3.6 & 3.8 Carreras.

I'm very interested in learning how tuning through fuel pressure and injectors can augment intake airflow and exhaust mods.

[The Radium King]

it would be interesting. when under partial load, the computer tries to maintain a ratio of air to fuel of 14.7. the o2 sensors in the exhaust monitor this and are constantly correcting fuel delivery to match apparent air intake. these corrections get turned into fuel trims. so, fuel pressure and flow rate is a moot point during this closed loop operation, as the computer would adapt to the changes (up until the point when the fuel trims reach 20%, at which point you get an error code). of course, this won't address one bad injector, as the sensors monitor a bank of three cylinders each (computer can detect bad electrics on a single injector, however).

when the engine is at full load the computer adds a bit more gas (tries to maintain an air fuel ratio of approximately 12.5) to keep things cool and reduce detonation. the narrow band o2 sensors don't work at this mixture however, so the computer gets no feedback and operates open loop. basically, it looks at incoming air and applies what it thinks is an appropriate amount of fuel based on pre-programmed air/fuel/rpm maps. fuel pressure and injector flow become important at these high flow conditions, as the computer is getting no feedback on whether target fuel delivery is being met. worst case is that there is insufficient fuel flow during max flow requirements, resulting in a higher air to fuel ratio, engine runs hotter without the quenching from the additional fuel, and damage could occur (or computer detects detonation and throttles back operation). of course, reduced fuel flow also draws the air fuel mixture closer to the magic 14.7 ratio, increases power, and increases fuel efficiency. so, you may not want more fuel pressure ...

I don't think intake/exhaust mods will have much effect on the fuel delivery system, even at full load, as the computer is still monitoring the amount of air ingested. as long as the increase in airflow does not exceed the sensing ability of the maf or the data available in the maps things should be ok - again, as long as there is sufficient fuel pressure and flow available in the system. given that the same maf, fpr and injectors are used in the 3.4 L 996 making 300 hp stock, and that the computer has the ability to adjust up/down by 20%, I would presume that they are.

[Gelbster]

As far as pintle vs 4 hole differences are concerned: there are demos of the various types under the same pressure to show the spray pattern. The pintle and older types tend to have a narrow jet of fuel.The 4 hole ,like Bosch Gen 3 have an atomised cone shape.
The experts say the narrow jet is O.K. for turbo/s/c,racing. Four hole is best for our application and that is why the later cars use them.
"This Bosch injector replaces obsolete p/n 0290150455.
Bosch Part number: 0280155890
Flow specs: 22.7 LBS/HR at 3 BAR (172.4 g/min)
Fuel Nozzle: Modern 4-hole disc fuel atomizer
Spray Type: Narrow cone, maximum fuel atomization
Injector type: Saturated
Connector type: Jetronic
O-rings: Viton, 14.5 mm
Length: 74 mm
Coil resistance: 12.0 Ohms"
here is an easy read:
https://www.youtube.com/watch?v=7oTirEZNRw8
https://www.youtube.com/watch?v=Emnax2J4FX4
**
These may have been superseded by a 15.4 ohm update with # 0280 156 211 -but check first because these are rated at only 300 Kpa ,not 400 like the 0280 155 890 That is 43 vs 58 psi. The spray pattern is slightly improved from15 to 20 degrees - if that makes a difference to the M96?