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tasdrouille 01-30-2008 09:08 AM

Better injectors for better FE
I have read a bit here and there on various FE oriented sites since we bought the gasser but have not come across anything mentionning injectors.

I don't know if it could make sense for gassers, but diesels benefit a lot from aftermarket injectors.

On most of our manual TDIs, the stock injectors are 0.184 liters per minute with 5 holes. Lots of modders have been installing .205 or even .216 injector nozzles in their quest for performance. An interesting byproduct of this as also been better FE at light throttle. It appears that injectors with bigger holes allow to dump the requested fuel quantity in a shorter period of time than stock injectors, resulting in better effeciency.

The new trend now is to go with 7 holes injectors. These would appear to give even better atomisation of the fuel.

TomO 01-30-2008 10:43 AM

I agree that better atomization will help provide a more complete burn in the combustion cycle. Now, if you could get an aftermarket injector with the same flow rate but a better spray pattern (read atomization) that would be perfect.

These TDI owners that are swapping out for bigger injectors, what are they doing to tweak the ECU to compensate for the flow rate change?

NoCO2 01-30-2008 11:09 AM

You would likely need to compensate by increasing the amount of air that was delivered to the cylinder to get the optimal fuel/air ratio. I'm not sure about diesels, but I'm pretty sure that when you increase the fuel/air ratio, it's also a good idea to tweak the spark timings and cams. I know that diesels have glow plugs and not spark plugs, but I would assume you would need to compensate similarly, where possible.

tasdrouille 01-30-2008 02:58 PM

In diesels we don't absolutely need to compensate (up to a certain point) as our cars are designed to run lean and are cold when running lean. By default they are very underfueled so we can add some more fuel until the engine runs rich and you start seeing black smoke out the exhaust and the exhaust gas temperature goes up.

Nonetheless a lot of people will also go with a chip to use custom fuel/boost maps to increase power and control smoke.

What does the ECU do in a gasser when it sees it's running rich? Let more air in or reduce the injected quantity?

The key here is that you can get your fuel injected in a shorter period of time with bigger holes which has the potential to be more efficient (inject all of the IQ at the right time). Now it's up to you to keep a light foot if you're shooting for FE.

The better atomization part is a no brainer.

dremd 01-30-2008 07:12 PM

Warning : This post may not be 100% correct, but the principal is close.

Diesels benefit from injectors in 2 ways
1) better spray pattern
2) higher flow (more fuel injected near the optimal point for effectively increased timing)

Gasoline cars
1) Better spray pattern
2) SI (sequential injection) attempts to fire injectors only while air is flowing through intake manifold (mostly economy, no power because the pulses are far to long at WOT to restrict injection to the Intake cycle)
Check out the Megasquirt Site for great info on this.
3) (BIG MAYBE) smaller injectors on NON SI motor for better effective spray pattern.

diesel_john 01-31-2008 12:05 AM

IMHO vw uses the stock injectors because of noise and vibration concerns, in addition to engine life. i hate it when i run over my crankshaft.

jazzie604 01-31-2008 05:29 PM


Originally Posted by NoCO2 (Post 7507)
You would likely need to compensate by increasing the amount of air that was delivered to the cylinder to get the optimal fuel/air ratio.

most commonly you can use things that decrease the airflow signal to the computer. for eco guys, this is actually beneficial because a side effect is usually higher timing, which is nice.

not to high-jack, but I do have one of these "mystical" ;) items for sale. Its a SAFC-II for those who care.

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