NHC-250 Injector Size

[Lonnie]

I've looked extensively & cannot find any reliable injector size information for a NHC-250.
Does anyone have this info?

 

[simp5782]

Do you have top stops or non top stops? Or what is your esn?


I have the injector book and can tell you what your injectors are sized at. r you can call warren at premco in Texas with your ESN

 

[Lonnie]

Engine number is 10200712. They are non-top stop injectors.
Dated in 1987

I was contemplating installing larger ones from a NTC-350 since I added a turbo, but was not sure of the size difference.
This engine is # 10559780 dated 6-76. Fuel rate says 192 mm3/stroke on this tag.

 

[simp5782]

#3054250 injector

Barrel plunger # 3054532
Refer barrel # 3202184
Cup # 3012537
Cup holes -size/angle 8-.0065x18 degrees

Injector orifice .022-.023
Delivery- 112.5-114.5
Cam 189
Delivery flow- 121-122
120 psi
.020 seat orifices


If you want bigger injectors call premco. Warren can lead you right based on your setup.

You could get the esn from a 290 cummins and be able to cross reference those but Premco has new injectors built by them for $75 ea exchange.

 

[Lonnie]

Great info .... thanks.
I was considering going to a larger injector to get some more fuel, while also allowing me to reduce the peak fuel pressure I'm running.

 

[simp5782]

Great info .... thanks.
I was considering going to a larger injector to get some more fuel, while also allowing me to reduce the peak fuel pressure I'm running.

Bigger injectors will relieve some pressure off the camshaft.

You would maybe want to swap to top stop injectors. You would need 6 new clamps and washers, and plungers.

 

[simp5782]

One sizer larger non top stop injector would be part # 3054245 with a .024/25 orifice. Not much to it. Cheaper to have someone build it

 

[Lonnie]

I took your advice & called Warren. He was looking into a few things for my setup.
Hopefully I can get something safe but better performing without killing my budget.

I was using the reasoning that the harder you push the fuel pressure to get more flow, you also advance your timing, which is already advanced compared to the typical turbo engine. I could effectively reduce my timing by using a larger injector with a shorter duration shot of fuel, plus reduce my fuel pressure at the same time. Trying to keep a good balance of power & safety.

I didn't realize how spoiled I got tuning with EFI Live...

 

[simp5782]

I took your advice & called Warren. He was looking into a few things for my setup.
Hopefully I can get something safe but better performing without killing my budget.

I was using the reasoning that the harder you push the fuel pressure to get more flow, you also advance your timing, which is already advanced compared to the typical turbo engine. I could effectively reduce my timing by using a larger injector with a shorter duration shot of fuel, plus reduce my fuel pressure at the same time. Trying to keep a good balance of power & safety.

I didn't realize how spoiled I got tuning with EFI Live...

You have not advanced your timing. That requires the proper tools for shimming the rocker boxes. Unless you removed the compressor and accessory drive and jumped a few gears.

You messing with the flathead adjustment in the throttle shaft increases rail pressure which puts more pressure against the lever for a stronger push on the plunger to inject fuel. The more lever pressure it puts more wear on the camshaft lobe.

A larger flow injector gives more fuel with less pressure so it lets you keep rail pressure but at less force. This doesnt put so much pressure on the cam lobe

 

[simp5782]

This is timing on an NH855 engine. This is how you can set it to stock.or advance it.

https://youtu.be/gV4g8-d3IvA

 

[Lonnie]

Mechanically, the timing of the injection stroke is adjusted as you show above, but when the fuel flow actually starts is based on how much fuel in in the injector, which is determined by the amount of fuel pressure filling it.
I was referring to the duration of the injector pulse....

The end point of the injection pulse is always the same, when the injector physically bottoms out, but the injection start point gets earlier as you add more fuel.
At idle you have very little fuel & it is injected late in the stroke.

By increasing fuel pressure, you put more fuel in the injector, which causes a longer duration when the fuel is being injected. This causes the fuel to start injecting earlier in the mechanical stroke of the injector, effectively advancing timing as you add fuel. This is opposite of the ideal way to fuel an engine.