Agreed. The turbo is a rather smallish KKK unit (not a T3) originally installed on a Mercedes 3.0L diesel.
Still, nozzles are directly related to your power goals. A 12mm pump head can be used to make some serious HP, but I really have no idea what you are looking for. A 12mm pump head is not a very good match for stock sized nozzles. This is totally different from the IDI diesels where the nozzles are large enough for whatever you might want to do - TDI engines are much pickier.
All of my experience stretching back over twenty years is with the old NA 1.5/1.6L VW and OM60X MB diesels, so the idea of adjusting nozzle sizes is a new concept, hence the questions. My concern is in adding a big pump head and then damming up the works with those tiny nozzles. This is going into a Vanagon, so it's not going to be a track demon, but I do want good solid torque delivery within a streetable powerband. It'll of course be monitored with a full complement of gauges and an over-built L2A IC. I just want some guidance about whether the auto nozzles will create problems, if even for a short duration.
Gotcha...
Basically on TDIs any given injector is good for about a 20-40HP range plus or minus. The factory nozzles were intended for a 90HP engine, so if you are intending to stay pretty close to 90HP then the factory nozzles are fine. IDI diesels are way less picky since their nozzles don't really atomize fuel all that well, they rely on the air swirling at high speed in the prechambers to "shear" the fuel droplets (more on that later)
There's a few things that come in to play with direct injection diesels (really even IDIs)
- atomization
- duration
- fuel volume
Direct injection engines don't have all that much swirl going on - they have SOME as a result of the shape of the intake runners and the combustion chamber in the piston, but nowhere near as much as you get when you force a large amount of air through a tiny hole in to a prechamber like on an IDI. As a result, direct injection diesels need the fuel to be atomized much finer than an IDI, and as a result they are very sensitive about the size of the nozzles.
If the nozzle is properly matched to the pump head then the fuel is atomized well at the right time. When the nozzle is too small, more injection duration is required to get the same volume of fuel in to the engine. The longer the injection duration the more the piston is moving in the bore. As we know from timing IDI engines too much advance causes problems, but so does retarded timing. If the nozzles are too small you will end up with a situation where you have advanced as far as you go but your timing is still essentially retarded when you have the pedal down, resulting in high EGTs.
If the nozzle is too large for the pump then atomization will be poor. The pump won't generate enough pressure to really get a fine mist going on, and the engine will have trouble burning the fuel completely. This will be particularly apparent at idle or low RPM use.
The combo of a large nozzle and a large pump is good in that it gets the fuel injected over a short period of time, but it also means that the injection duration will be very short. This will result in a lot of diesel clatter since the combustion will be happening over a very short amount of time.
That said, you've gone for a 12mm pump head. That means your pump is going to build pressure much faster, build higher pressure and is capable of delivering significantly more fuel in a shorter time. You might find that you have trouble controlling your pump at idle / low speed with stock sized nozzles since they weren't really designed to go with that big of a pump. The pump is going to be fighting the nozzles so it is going to be hard on the pump head, and you probably are going to end up with a lot of smoke as it will have a hard time metering down that low. I believe the stock automatic nozzles were also the smallest size. You will have awesome atomization, but your pump is going to be working really hard.
Most folks over on the TDIClub forum seem to recommend at least a Race520 (.260) nozzle with a 12mm pump. Any less can be bad for the pump head.
Is there an issue with the 11mm Land Rover pump head? An 11mm head is good up in to the mid 200HP range. A 12mm head provides nearly 20% more fuel than an 11mm head, so I'm a bit curious why you are going that route, especially in a heavy vehicle with a large wastegate turbo. To use the nozzles that are appropriately sized for your pump head you'll be rolling coal until you hit higher RPMs and have the turbo up to speed.
Topic: Where can I find Replacement nozzles for an automatic alh? (Read 4940 times)
