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In the next couple of weeks I'll be pulling the failing transmission out of my truck for a rebuild, and while its out I want to upgrade the injectors. I'm not looking for anything crazy just a nice towing injector, so between the 50 and 75hp rating. I realize that power all revolves around other mods, but take for example 75 horse injectors. Are they in fact good for at least 75 horse?

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In the next couple of weeks I'll be pulling the failing transmission out of my truck for a rebuild, and while its out I want to upgrade the injectors. I'm not looking for anything crazy just a nice towing injector, so between the 50 and 75hp rating. I realize that power all revolves around other mods, but take for example 75 horse injectors. Are they in fact good for at least 75 horse?

If they are rated for 75 horsepower they will be very close to that rating. I would recommend DAP or DFI injectors with full confidence.

I personally use DFI 7x.009 SAC injectors and love them but to make full use of them a larger turbo than the HX35W would be a must. A 75 horsepower injector would be on the maximum of what the charger could handle and keep EGT'S manageable. If you go the SAC injector route I would recommend a 50 horsepower injector due to the way the injector flows. A SAC injector will act and feel like a much larger injector and is a very strong injector.

Either way you should be just fine and you will enjoy the added power and economy over stock once the excitement subsides.

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I was on the DAP website earlier looking at their injector selection, for those that are running a bigger injector how are they for cold starts? Cold being below zero..

Below zero Fahrenheit or Celsius?

Larger injectors will start ok as long as they are not too too big. A 50 horsepower injector may be a better option if your worried about cold starts well below zero Fahrenheit. Another thing is keeping the batteries warm and using 5W -40 in those temps. A grid heater will also help tremendously.

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-19 deg F on the injectors in my sig and starts just fine!

The guys over at DAP use a 153° injector nozzle so the spray pattern is definitely correct.

Good to know that with marine pistons and DAP 125 SAC injectors the truck starts up in those temps.

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The pintile on a vco nozzle seats against the holes that atomize the fuel.

The pintile on a sac nozzle seats above the holes. 

Some say the sacs are dirtier.... I had the opposite experience. My 90 vco nozzles were much dirtier than the 125 sacs. 

While it's unlikely either tip will crack a vco nozzle is more prone to cracking due to where it seats. 

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The pintile on a vco nozzle seats against the holes that atomize the fuel.

The pintile on a sac nozzle seats above the holes. 

Some say the sacs are dirtier.... I had the opposite experience. My 90 vco nozzles were much dirtier than the 125 sacs. 

While it's unlikely either tip will crack a vco nozzle is more prone to cracking due to where it seats. 

 

There are 2 types of SAC nozzle to my knowledge, one is known as cylindrical blind hole and the other as micro blind hole. Cylindrical blind hole nozzles will have a large sac of fuel left in it after injection which usually causes the smoky burn. Micro blind hole nozzles will have a very tiny sac volume after injection and does not create a smokey burn. Another thing that helps is the correct spray angles which on a Cummins ISB 235 is 153 degrees. DFI uses a slightly narrower spray angle at 150 degree (not sure is this is all of DFI SAC injectors) this has a benefit when you begin using tuners because it will help keep the fuel in the bowl where it should be rather than making hot spots on the piston crown. The injector pintle seals the nozzle above the orifices, this offers strength but also a greater tolerance to contaminants. A SAC injector also will not get something known as (for lack of better term) pintle drift this is due to the injector sealing above the orifices. This means as the pintle is being pushed down by the spring to shut the pintle drifts over slightly causing the nozzle not to fully seal for or causes a delay to fully seal. This can happen from the beginning or after several thousand miles.

 

A VCO injector (Valve Closed Orifice) is what is used in stock applications all the way up to some fairly wild applications but has been known to crack once sizes go over 7x.010(150 horsepower) some have no problems all the way up to 7x.011(200 horsepower). To seal the injector pintle seats against all the holes in the nozzle. This can cause a number of possible issues over time or right from the beginning. VCO nozzles over time or right from the beginning can have pintle drift which of course would cause a rough idle, poor performance and possibly fuel in oil. Although this can happen it is not very common in stock applications but when the duration is pushed with a tuner this becomes much more of a potential to happen.  

 

The way these two injector nozzle designs spray fuel is very different from one another. A VCO injector spray penetration will be much greater meaning it produces a stream of atomized fuel from the point of injection all the way to the edge of the piston. A SAC injector spray penetration creates a dense atomized fuel spray over the top of the piston that has less spray penetration than a VCO nozzle design. This means the fuel is kept mostly over the piston rather than allowing the injector to spray fuel up to the cylinder walls potentially causing cylinder washout. 

 

In my experience my SAC injectors are just as clean as my big right foot allows :evilgrin: . Keep out of the skinny pedal and you don't smoke any more than stock. 

 

A great source of info and lots of pictures.

 

http://www.competitiondiesel.com/forums/showthread.php?t=88662

Edited by Vais01
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I posted it and the page refreshed and I saw your post and started laughing. Hey look, same size! (injectors). Have you lost any mpgs with those SACs?

I didn't see any difference between these and a dying set of Industrial Injection 7x.009 VCO injectors. I actually picked up 1 full MPG with Chris' injectors and lowered my cruising EGT about 50 degrees. After I got rid of the HE351VE and went to my 62/68/14 I dropped even more cruising EGT temps and my MPG went up about another .5 MPG

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