VW AAZ two stage diesel injector

[Bean]

Canadian model VW TD's in the mid to late 90's came out with a mechanical 2 stage injector that had two pressure settings. First would pop at 155 bar to get the flame going with a small injection, then the larger injections follows right after at 220 bar. This two stage injection is supposed to result in easier starts, quieter running, and it's supposed to be more efficient.

MB guys have been using these injectors with Monark nozzles as an upgrade - but while most post that the engine starts nicer, and runs quieter - low end torque drops off, but top end power seems a little better.

I did a bit more research and it's possible the AAZ injector pump (VE pump as well) may have a special cam plate profile that ramps up the pressures precisely for the injectors. MB cars use a different pump that doesn't build pressure as rapidly as the VE pumps - so that might explain why they get a slight decrease in low end power / torque.

The big question for us now with VE pumps on our TD engines is if there is sufficient gain to warrant having the injection pump built with the VW cam plate, and run AAZ injectors.

I spoke to a local shop who said the AAZ 2 stage injectors are a PITA, and they replace them in the VW's with single stage injectors and you can't even tell.

I contacted Giless of www.performancediesel.ca and he really likes the AAZ two stage injectors. He's also recommended as one of the few shops that can set up the 2 stage injectors properly, AND he's an injection pump genius who is renowned for tuning pumps to give fantastic increases. From our brief e-mail exchange - he figured 150HP and 225 ft*lbs torque would not be a problem. (That's N9TE power - with 40 mpg (imp) highway)

The two stage injector is definitely peaked my interest along with a performance tuned VE pump to match - but that would be some serious cash for an uncertain outcome.

After much research - I plan on sticking with the single stage injectors that I can rebuild and tune myself easily, as well as keep the stock injection pump and use it's built in tuning features to get the car running as best I can.

Once I NEED to rebuild the injection pump - that's when I may consider trying the AAZ 2 stage injector set up.

Any comments?

Rabin

[andrethx]

a couple of thoughts

taking the comments of the local diesel guy and the expert together, it sounds like one only sees the benefit of the 2-stage injectors with proper tuning...no surprise there, devil in the details, etc.

also -- trading off low-end torque for top-end power & drivability makes sense in a diesel, but -- do you take a big hit in fuel economy when you do this? if you are going to great lengths to get the performance and fuel economy of a petrol engine, that would make this less appealing to me. however, if you end up with petrol-like performance but with still-better gas mileage, then it sounds much more worthwhile...just my 2 cents...

andré

[Bean]

The AAZ 2-stage injectors are only ever used on MB's which don't really have the right injection pumps to really make use of them. They ramp to pressure slower than the VE pumps that the Peugeot and VW have.

When they run them in the MB anyway - that's when they report the drop in low end torque. Economy is as good or better however.

And yes - I have no intention of sacrificing efficiency for performance. The two are tied however as it takes a very well tuned engine to make the most power - but that efficiency can work in your favor for fuel economy as well.

It'd be pretty expensive to do the custom hybrid IP, and the 2 stage injectors just to see, but it might be worth trying if you needed to rebuild your IP and rebuild injectors anyway.

Rabin

[Bean]

Did a bunch more research on this - and I'll definitely start collecting parts for an AAZ upgrade later. Found a research paper done by some engineering students that analysed the improvements to be had with proper tuning and the mechanical 2 stage injector were substantial. Performance, economy, and emissions were all greatly improved.

The more I look at it - doing the 2 stage AAZ injectors, custom pump set up, and VNT turbo w/stand alone controller, it pretty much realizes my plan to make it the cleanest, strongest, and most modern set up I can run in the car. It won't be HDI good of course - but with the 2.5L displacement and VNT it should be outstanding.

So while I get the current stock set up ironed out - I hope to keep an eye out on good deals on the VW parts necessary to do it. (AAZ injectors, AAZ 11 mm plunger injection pump, and a VNT turbo with a proper stand alone controller)

Rabin