The argument for a real conversion injector

[Soup Nazi]

Resetting pop pressure to a lower value will help with a conversion injector, but it wont fix the inherent issues with spring rates and opening effort needed to keep the injector open when using a P7100 or similar mechanical pump with an injector designed for a VP44.

The issue becomes clear when one looks at the two springs side by side. This hit me like a ton of bricks back in 2004 and the rest as they say is history.

Of course the heavier and longer spring of the 24 valve VP44 injector is on the left and a standard 12V spring for the P7100 is on the right.

 

[Soup Nazi]

This is clearly an issue that is needing some attention if you want the system to operate in an optimal framework and deliver the fuel in a workable and tunable curve. A P7100 has a lower pressure curve when compared to the VP44. The 7100 may have the volume but the VP has the pressure hands down.

 

[Soup Nazi]

Here is the VP44 injector body ( nozzle holder ) and its companion spring.

 

[Soup Nazi]

Now, here is the VP44 holder with the 12V spring placed inside. This gives another view of the size comparsion of the two springs and helps one understand the issue of the spring' rates.

 

[Soup Nazi]

That tiny 12v spring is what the P7100 needs! This helps the injector open when designed and helps it stay open the length of time needed. A VP44 injector that is not converted will open slower and close sooner in nearly all applications. Lowering potential HP.

 

[Soup Nazi]

Getting the spring in the VP44 holder is the idea here. No rocket science degree needed. Just some common sense, machinery, and time.

The first conversion injectors we made took about 10 hours of machine time and added labor to a set of injectors above and beyond the normal build for VP44 stuff. I know it sounds crazy, but it is unfortunantely ( for us ) a true statement. Turning sleeves out of round stock on the lathe, machining the holder, the pressure pins and finally bead blasting and re-black oxiding all the parts eats time up. Not many poeple buy them, so we make very few sets and cant justify building a hundered sets a month or so to save time in set-up, etc.

Anyway, you get the idea here. Below is the 12 valve spring fitted in a holder as needed.

 

[Soup Nazi]

Of course the pressure pin used in the VP44 wont fit in the 12 valve spring and is too big to fit the now modified holder as well. The diameter must be machined in two locations shown below.

On the left is the VP44 and the right is the "modified to fit" pressure pin. Most can hardly hold onto these little bastards so it is a huge PIA.

 

[Soup Nazi]

One more shot of the pressure pins fitted to their respective springs for another view of the changes needed.

 

[Soup Nazi]

Once these bad boys are all machined up and fitted together the needed tuning adds another layer of hell ( as I call it ) This is where the nozzles are flow tested and lightly honed until they all flow the same volume under high pressure using diesel test oil. A time consuming step.

Final tuning is not done on on a some half assed pop tester, but a machine that actuates the injector as a complete assembly and measures its output. This allows us to tune each injector to deliver identical volumes. This involves changing springs, shims and sometimes plates and nozzles to get a matched set. We are not overly concerned about opening pressure or commonly whats called "pop" pressure as we are how much each delivers for a given pulse of fuel. One will sometimes find our injectors will "pop" at values that can vary as much as 20 bar.

For some added back-story: We have installed the same nozzle on on both the stock VP44 injector and the conversion injector using the P7100 spring and have measured considerable fuel amounts in favor of the converted assembly. Taking those tests out past 30 seconds will overfill the graduated cylinder with the converted assembly, but the same test with a standard VP44 style will have much room left to continue running. Pretty basic and totaly expected.


Finally, if you just cant get into a converted part ( for whatever reason), have your fuel shop set up the VP44 injectors to "pop" at under 240 bar. Perhaps 230-235 to start. It is a band-aid, but at least it'll idle decent.

 

[RonA]

If you ever need any of these made Don, let me know. But the way i read this, you are showing others how to do it so you can concentrate on the common rail stuff. I appreciate it, but if I make the pieces and do the mods, can you still do the nozzles?

 

[TheBigNasty]

Stupid question but wouldn't it just be easier to design a spring with the dimensions of the vp but with the rate of the 12v? Sure might take some capital outlay to design but sold in quantity would help.

 

[SmokinRamMike]

Stupid question but wouldn't it just be easier to design a spring with the dimensions of the vp but with the rate of the 12v? Sure might take some capital outlay to design but sold in quantity would help.

x2, wouldn't you be able to make a lighter spring, large enough to fit in the 24v body and use all other 24v parts? Or is in not that easy?

mike

 

[2141pete]

so these won't be availible for purchase anytime soon Don? I was hoping to buy another set of Mach 5's or 6's but I may hold off and save up to see if they will go into production if there is enough demand.

 

[Soup Nazi]

If you ever need any of these made Don, let me know. But the way i read this, you are showing others how to do it so you can concentrate on the common rail stuff. I appreciate it, but if I make the pieces and do the mods, can you still do the nozzles?

Seems to me the best program would be to make the holders up with the smaller diameter hole that would be a good fit for the 12V spring. This only leaves the pressure pins and those are not the end of the world to do alone.

Currently I have no plans to revisit these things ( as being built ) for months. I hate em. By the end of the day I want to strangle someone. LOL Kidding of course but they are no fun.

Having a body that is ready to go without a sleeve is going to make things much easier.

 

[Rods]

Don u must b getting old and rdy to retire , never seen so much info from u own injectors

mayb I can get talk Jon into this , I tried once b4 but WTH

 

[kscumminsdriver]

Currently I have no plans to revisit these things ( as being built ) for months. I hate em. By the end of the day I want to strangle someone. LOL Kidding of course but they are no fun.

The question then becomes, did you get the set of 7's done I ordered from Rip last month?? Is that what drove you over the edge??

 

[zstroken]

Would I know any about these pieces Don?

 

[GOT-Torque]

Very informative post, thanks for sharing Don.

Couple questions:

As someone stated above, wouldn't a new spring to fit the vp injector body but with the 12V length and spring rate be much simpler and cheaper?

For someone looking for high rpm performance (like sledpulling), it seems to me that a nonconverted injector would work better.
-so it opens slightly later (offset this with a touch more timing)
-so it closed sooner (fuel delivery is over a tighter window to support higher rpm operation, less fuel injected late in the stroke)
-not as much fuel flow as compared to a converted injector (step up in hole size or step up in pump cc delivery).

For a street driven truck, I would agree that two equal injectors (one converted and one not), that the converted one would perform better (more fuel), but for a high rpm engine, I don't see the benefit?

Again, thanks for sharing the info. I've held some of those pressure pins before and they are a bugger to hang on to...

 

[BgBlDodge]

I'm with Brandon on this one, wouldn't it be simpler to build a new spring that would work with the stock 24v parts instead of trying to build an entirely new injector?

 

[Soup Nazi]

Just a tick over 130 milliliters VS 85 milliliters for the same nozzle, but installed on two different injectors. The conversion and the standard VP44.

These are the flow test results of a complete injector, fully assembled and the injection pressure set at 300 bar or roughly 4300 PSI. The test was run for 30 seconds. Both injectors have the opening or "pop" pressure set at 270 bar.

Clearly the VP injector is injecting much less fuel in the same unit time using 300 bar. Before anyone asks; yes - as the pressure increases the differences become less pronounced, but it gives a great perspective as to the amount of force required to open the injector with a 300 bar injection pulse.

High performance engines need to spread the fuel charge over a longer number of crank degrees. This holds even more true for the P7100 pump systems because the injection pressure is so low compared to most others. One would be hard pressed to get 1100 bar out of the average P7100. Booo