Thanks man! 
Project: The New CDD Shop Truck
- Thread starter Thewespaul
- Start date
While waiting on the crossover from the ambo to cool from ceramic coating, I got a chance to set up a few of the injectors.
It’s been fun, but really tough. As you drop in pop pressures, the smallest shims that would normally make a 50-75 psi change, start making larger and larger changes, and down at the pressures I’m bringing these to it becomes really tough to get a consistent batch.
I brought the pressure down till I started to notice a deterioration in the atomization, then brought it down till there was a fine spray but no atomization then met in the middle. Where that is I won’t say, but it’s a lower pressure than I’ve ever run in an idi injector. I probably wouldn’t ever sell an injector set this low, but it makes sense in my case since I’m trying to get as much fuel out of the stock pump as possible, and because it gives me a worst case scenario to test from as far as reliability.
Here’s a clip of the injector at more of a pressure I would feel comfortable supplying these at, but still a lower pressure than any idi injector ever came
It’s been fun, but really tough. As you drop in pop pressures, the smallest shims that would normally make a 50-75 psi change, start making larger and larger changes, and down at the pressures I’m bringing these to it becomes really tough to get a consistent batch.
I brought the pressure down till I started to notice a deterioration in the atomization, then brought it down till there was a fine spray but no atomization then met in the middle. Where that is I won’t say, but it’s a lower pressure than I’ve ever run in an idi injector. I probably wouldn’t ever sell an injector set this low, but it makes sense in my case since I’m trying to get as much fuel out of the stock pump as possible, and because it gives me a worst case scenario to test from as far as reliability.
Here’s a clip of the injector at more of a pressure I would feel comfortable supplying these at, but still a lower pressure than any idi injector ever came
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In THEORY, shouldn't that make an IP last longer? If they spray good at a lower pressure the pump wouldn't have to work as hard.
It absolutely would, and it would also mean that you could replace a set of worn out injectors with these and wouldn’t have any hot starting issues even though the pump is worn out, but would still have the better atomization
The_Josh_Bear
Full Access Member
First of all I'm following all your IDI threads closely and learning a ton. Thanks again!
I could be wrong, but I have read that the IDI uses a "splash ignition" concept where a stream of fuel fires across the pre-chamber and slams into the hot wall there, then splashes all over the place while spontaneously combusting. Doesn't atomization sort of violate that whole concept? Maybe it works perfectly fine and dandy, I dunno.
Could you offer some thoughts on all that? And why atomization would be beneficial for our pre-chamber setup?
It is a splash ignition, but still uses the swirl design where the combustive gasses tumble around the prechamber and into the cylinder. Ultimately at wot, how the injector fires as far as pattern and atomization doesn't matter because there is so much heat in the prechamber its igniting before the fuel even hits the wall. This is why db2 injection pumps have less injection timing as rpm and load increase, because naturally the ignition is happening earlier although the injection is happening sooner. It is counter intuitive, but the db2 is designed this way to keep the engine in its happy zone of ignition timing.
Back to the atomization, the only real reason we have a concern for atomization is for light load driving and cold start ups.Better atomization will give you a more responsive, less smokey throttle when you nail it from a stop and have little heat in the prechambers. It will also start much easier with a good pattern because it takes much less heat to ignite a mixture of mist and vapor than essentially a water hose.
Overall, these injectors dont ever real get to the "water hose" level, even at 150 psi they have a spray pattern of sorts, unlike say an E code that goes straight into injector ******* at 1500 psi
Back to the atomization, the only real reason we have a concern for atomization is for light load driving and cold start ups.Better atomization will give you a more responsive, less smokey throttle when you nail it from a stop and have little heat in the prechambers. It will also start much easier with a good pattern because it takes much less heat to ignite a mixture of mist and vapor than essentially a water hose.
Overall, these injectors dont ever real get to the "water hose" level, even at 150 psi they have a spray pattern of sorts, unlike say an E code that goes straight into injector ******* at 1500 psi
YJMike92
Full Access Member
Last edited:
I usually run about 5-6 on most setups, but have it bumped up slightly for this one
YJMike92
Full Access Member
I just replaced the stock mechanical pump before my trip to the east coast because it was leaking. I imagine it's pressure is about half what you normally run. I assume a little higher pressure into the injector pump = a little higher out.
In most cases it doesn’t affect the total flow but it does affect timing, I just aim for 5-6 psi because that is what pressure these pumps are calibrated at on the stand, at least that’s what pressure I use, I know Mel uses the 6.5 last I spoke with him
The_Josh_Bear
Full Access Member
Awesome, thanks Wes! That's really interesting and makes a lot of sense. I like less smokey idle and takeoff!
Got the rest of the injectors setup, used about a quart of calibration fluid just setting these up...
Pulled the R&D injectors out
3m injectors are in, retimed the truck and took it for a spin. Not going to lie I was expecting a runaway when I first started, and I was prepared for the worst with my pie plate, but it started up and idled smooth, smoother than it had in awhile. Timing really didn’t change much either. So far so good, it’s definitely got more fuel and more power, but I’m starting from zero with all the tuning I’ve done, and I’ve got a lot of fine dialing to do with the faceplate adjustments and timing. Boost didn’t change but egts are down 100*
Pulled the R&D injectors out
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3m injectors are in, retimed the truck and took it for a spin. Not going to lie I was expecting a runaway when I first started, and I was prepared for the worst with my pie plate, but it started up and idled smooth, smoother than it had in awhile. Timing really didn’t change much either. So far so good, it’s definitely got more fuel and more power, but I’m starting from zero with all the tuning I’ve done, and I’ve got a lot of fine dialing to do with the faceplate adjustments and timing. Boost didn’t change but egts are down 100*
YJMike92
Full Access Member
I see, Thanks.
I have quite a bit of automotive experience 40 years as a mechanic. Not much on these types of diesel. I'm trying to understand these a little better. As stated in this or another thread I have a 94.5 Powerstroke that will be for sale and I'm switching to an IDI truck. I do need the HP and Torque of a Powerstroke so I trying to learn as much as I can so I can achieve that goal.
YJMike92
Full Access Member
That’s awesome, I guess think of it like a carburetor fuel system, realistically you only need some positive pressure feeding the carburetor (injection pump) for it to perform properly, but you get a more consistent result if you have 5-6 psi through the rpm range
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