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Split shot injectors?

restoguy

restoguy

Active Member
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Location
NW Kansas
So I'm planning to rebuild my injectors in the next few weeks and reading about that has shown me 'split shot' injectors. Bosch made some mechanical split shots for mercedes and VW. Knowing that some of the parts are (almost) interchangeable, would it be beneficial to try to come up with split shots for us? Seems the ferd guys go away from them, but the quieter running might be desired by some. What are the pros and cons?

Discuss...
 
Yes. The merz/vw guys call then 2 stage, the ford guys call then split shot. Same thing as far as I can tell.
 
follows the same principle of the newer common-rail injectors, multiple 'shots' per stroke instead of one large fuel injection. Part of the reason why newer motors are so much quieter. Makes for a more complete burn of the fuel injected, possibly allowing more fuel to be injected/used during each cycle. How would it be done to the 6.2/6.5 injectors?
 
Yep. It's sort of a mechanical 'pilot' injection. Two springs in the injector. The lighter spring starts the injection earlier, at a lower pop pressure. Then the second heavier spring opens and injects the main charge into a cylinder (or prechamber in our case) that is already burning fuel. I think it might soften up the shock on the bottom end a little too. Might make blocks less prone to cracking and cranks less prone to breaking? Maybe not, but that's my thought. I read that the 'cali' model fords got them first for emissions reasons. They said it lowers peak combustion temp and reduces NOx (??).
 
I think if i remember correctly part of that was also built into the delivery valves in the pump, kinda like 2 stage delivery valves. But take the delivery valves out and machine them for single shot and you get more power and better economy....
 
That might be the case with the VW/Merz stuff. The fords got them in 97 in cali and all in 99 so they are HEUI injected. I read a couple threads about guys asking if they should use single shots in their cali spec truck when they were replacing them. Some performace places sell the split shots too, so I don't know if there's a peticular drawback or not. I was hoping someone here would be more familiar with them than I.
 
I don't think a split or injector with multiple injection points would work very well in an IDI engine. The VW, MERCEDES, and 97-99 FORD are all direct injected engines. In an IDI you want the flame front to build and move rapidly out of teh pre-cup and into the recardo piston bowl and combustion chamber. In a DI engine the fuel is injected directly at the piston bowl and combustion chamber, so the multi injection points is beneficial as it allows a larger flame front. Since there is no pre-cup hole for the flame front to travcel out, the expanded flame front can be utilized whereas in the IDI the expnaded flame front would just be wasted fireball as it still has to ball down and come out the pre-cup regardless.
 
littleboy said:
I think if i remember correctly part of that was also built into the delivery valves in the pump, kinda like 2 stage delivery valves. But take the delivery valves out and machine them for single shot and you get more power and better economy....
Click to expand...

I know YANMAR used a 2 stage injection system in there marine engines just before they went to common rail injection on the larger engines, and I believe they still use it on the smaller sail drive engines. They have found that the 2 stage injection system works quite well and helped power, increased milage, and reduced engine noise. Pilot injection has many advantages to it despite what many think. I've played with shutting it off, and lets say the ole DMAX turned into a slow smoke bellowing slug that took awhile to light the turbo. Turned pilot back on and she came right back to life. And yes I corrected my timing and rail pressure and still had poor results with it. The CUMMINS guys also started playing with shutting pilot off once EFILIVE came out, and I believe most of them have found that the pilot shot helps and have turned it back on for the most part.
 
The Mercedes OM617 is an IDI motor and I've seen people putting spit shot's in them. If I understand it correctly, they don't have multiple orifices like a DI injector. Just one orifice in the nozzle, it just shoots twice per cycle. Just like pilot injection.

I'm also getting conflicting reports on the pros/cons. The ferd guys say more power and better economy with single shots. While the VW/Merz crowd says the opposite! But most blue oval types get some kind of programing and 'stage 1' preformance injectors when they swap them out so it's not really a fair comparison.
 
restoguy said:
The Mercedes OM617 is an IDI motor and I've seen people putting spit shot's in them. If I understand it correctly, they don't have multiple orifices like a DI injector. Just one orifice in the nozzle, it just shoots twice per cycle. Just like pilot injection.

I'm also getting conflicting reports on the pros/cons. The ferd guys say more power and better economy with single shots. While the VW/Merz crowd says the opposite! But most blue oval types get some kind of programing and 'stage 1' preformance injectors when they swap them out so it's not really a fair comparison.
Click to expand...

Sounds like your thinking of 2 different technologies to me. When I think of split shot I think of an injector with multiple orifices in the tip of it. The 2 stage injection event is what is known as a pilot or pre injection and then a main power shot. This technology either requires a common rail injection engine where you can electronically fire the injectors, or a set-up where each injector supply nozzle has 2 ramps for the pump side to get 2 injection events. For a 6.5 you would need a custom pump to achieve this. As for an injector with multiple orifices that is doable, but I see no advantages to it for an IDI engine. The pilot system does have advantages to it as the pilot or pre shot is injected before the main combustion event and helps to fill the chamber with a fuel charge and get a softer ignition event instead of the more violent single event. Also since you are getting fuel furthur out into the combustion chamber before the ignition event you get a fuller combustion throughout the combustion chamber.
 
It is totally do-able with mechanical injection. And the pump isn't any different. The injector has two springs inside instead of one. The first is lighter pressure and 'pops' earlier allowing, say 5%, of the fuel to be injected. Then as the injection pressure rises, the second spring pops and injects the remaining 95%.

Here's a pic of VW diesel injectors. The top is an 'AAZ' 2 stage injector. The bottom is an older single stage.
imagesCA8B7RTO.jpg

The VW/Merz guys all talk about making sure your injection shop has the correct equipment and experience to test BOTH pop settings not just one. And they swap the injectors without any pump mods. At least none that they've ever mentioned.

The split shots the Ford guys talk about are also 2 stage injection, not mutliple orifice.(they are likely multiple orifice too, but...) I know this because they talk about getting different programing if you switch because the timing is different. And because I read the official explination as to why they were used in the commiefornia versions in 96/97, but not the rest until 99.
 
restoguy said:
It is totally do-able with mechanical injection. And the pump isn't any different. The injector has two springs inside instead of one. The first is lighter pressure and 'pops' earlier allowing, say 5%, of the fuel to be injected. Then as the injection pressure rises, the second spring pops and injects the remaining 95%.

Here's a pic of VW diesel injectors. The top is an 'AAZ' 2 stage injector. The bottom is an older single stage.
imagesCA8B7RTO.jpg

The VW/Merz guys all talk about making sure your injection shop has the correct equipment and experience to test BOTH pop settings not just one. And they swap the injectors without any pump mods. At least none that they've ever mentioned.

The split shots the Ford guys talk about are also 2 stage injection, not mutliple orifice.(they are likely multiple orifice too, but...) I know this because they talk about getting different programing if you switch because the timing is different. And because I read the official explination as to why they were used in the commiefornia versions in 96/97, but not the rest until 99.
Click to expand...

Dug a little deeper in my research, and I see they are indeed a single nozzle. The split shots actually are quite a bit bigger than the single shots are, and due to the early drizzle is why you have to change the timing. Looks like they use a design like your talking about where you get a small spray before the big spray to give a pilot type effect. I'm used to like my DMAX where it is 7 hole nozzles when I hear somebody say split shot. I would say it is doable, but would require retarding the timing back quite a bit down low, but keeping it high in the top end. Would be rather difficult to do with a DB pump I would think to get the timing curve you would want for the entire RPM range, but with a DS4 pump it would be very doable.
 
I have a Mercedes and VW injector,and can check if the 6.5 bottom,and Mercedes tops can thread together. I think the line thread size is different also.
 
Multiple injectons on a 6.5L? Oh man, now THAT would be awesome. There pretty quiet to start but having a pilot injection to start the flame front, then chase the flame down with a heavier dose of fuel would certainly make a big difference I think.

6.2 Turbo do you think something like this (if doable) would solve your issue with bending connecting rods? Perhaps a smoother initial injection make give you that extra room to build some additional power.
 
Sweet! Do you have an AAZ VW? Check and see what might interchange and what wouldnt. If the internal parts are similar maybe they can be swapped into the GM body? I might have to buy an AAZ if you don't have one

Also, can you do me a favor? See if the pop adjustment washer is the same diameter in the GM and the Merz? I need to get some to rebuild mine but it's proving impossible! I can find parts for Merz though...
 
I don't have any with dual springs. The shims are the same. I have some Mercedes nozzles with a built in pilot hole. These only used one spring.
 
Single stage Mercedes,and 6.5 will thread together,but the line size is smaller.
 
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