Which injectors?

[Baxter]

Is there a list of nozzle sizes anywhere?
I take it that the IDI responds well to larger injectors as the TDi's do?
Just curious.
If you've got a 1.6 is there anything to be gained by fitting injectors from say a 1.9? Or is it more involved than simply sneaking some injectors in your pocket from a breakers yard!

[Baxter]

Was it a silly question or does no one know?

[autobahn]

sometimes people answer
sometimes people flame
sometimes people post links to another page on this site where you can read and find the answer
http://www.vwdiesel.net/phpBB/viewtopic.php?t=998

[Otis2]

I find the answer kind of murky from reading that thread.  I meant to ask about it, but Bricky's post has reminded me.

In answer to the question of why there is no aftermarket performance injector sold for the IDI engines, Smog said,

because there is no need as you can tweak the pump to give more fuel. The point in changing the nozzles is more to restore the spray patern of the injectors; it will cure some of the smoke, bad mpg, bad idle,low power output. But the GTD nozzles will give more power than regular 1.6TD nozzles.  

I don't get it.  Either, hot ticket injectors do nothing at all for non-computerized IDI engines, and so manually cranking up the pump is the answer... Or, hot ticket injectors are the bees knees, as Quick TD has reported.  I expect that QTD had already tweaked his pump before the new injectors went in.

GTD nozzles shouldn't have any benecial effect at all, if the the first part of Smog's post is true.  But then he says that they do in the second part of that post.  So I'm confused - Smog's answers seems to have it both ways.

[vwmike]

My take on it:

Larger injectors do offer improved flow, but the gain (except in high boost turbo applications) isn't due to the fuel quantity so much as the timing.

As the engine increases in RPM, the injection pulse has to be initiated progressively earlier (this is known as advance) due to the fact that the time between the pump initiating the injection pulse and the actual injection event is fixed. If timing were fixed then the injection event would happen later and later as RPM increased. The engine would have a very limited working range.

A larger injector nozzle works to assist on this principal. The larger nozzle does not increase injection quantity considerably but rather allows the entire quantity of fuel to be injected in one short event rather than a long injection event which can sometimes extend through the entire combustion cycle (wasting fuel and causing lots of smoke out the tailpipe). So, injection timing becomes more exact which should net you some small gains, probably more towards the upper end of the rev range. Obviously if you're demanding a lot of fuel the gains can be much higher.

I actually have a shipment of GTD nozzles on the way so I'll be playing with them a bit and can comment a bit more before long.

[Patrick]

Almost, vwmike. The way I understand the timing thing, its not that things happen later, it's that they need to happen earlier at higher rpm in order for the burn to happen at the the right place in the cycle. If the burn takes, say, .1 sec, it has to happen earlier at 4000 rpm than at 1500 rpm in order to get power at the same point in the stroke. maximum burn just at or before top dead centre?

[vwmike]

Almost, vwmike. The way I understand the timing thing, its not that things happen later, it's that they need to happen earlier at higher rpm in order for the burn to happen at the the right place in the cycle. If the burn takes, say, .1 sec, it has to happen earlier at 4000 rpm than at 1500 rpm in order to get power at the same point in the stroke. maximum burn just at or before top dead centre?

I think we meant the same thing, it's just difficult to explain.  

But, yes the injection pulse must be initiated earlier so that by the time it hits the cylinder the piston will still be at tdc.