I did a BSFC comparison between the 305/555 and the 325/600.

The valve cover on my 325/600 engine says a stroke of 132 mm^3 @ 2900 RPM = 325 HP. My engine is CPL8423 built 08-04-04.

So...

132 x 2900/2 x 6 x 60 = 68.9 L/hr = 18.2 gallons/hr = 127 pounds/hour

127 pounds per hour / 325HP = 0.3907 lbs/hphr.

That is a little thirstier than I thought, but it is probably (a lot) better at peak torque. Then again maybe not.


A 305/555 has a stroke of 114 mm^3. CPL 8213.

So...

114 x 2900/2 x 6 x 60 = 59.5 L/hour = 15.722 gallons per hour = 110 poounds per hour.

BSFC = 110/305 = 0.3608. Not bad.


0.3907/0.3608 = 8% more fuel for the 325 versus the 305.

Note that these are full power numbers. The 325 would generally use a bit more fuel because it is delivering more power from the same cubic inches. The other thing to note is that the part throttle BSFC is what really matters.


Comparing fuel stroke per HP:

114mm^3 for 305 = x for 325. x = 121.5 mm^3. Post shot on the 325 must be about 10 mm^3.

I can think of 2 ways to removed the post shot. One would be to modify the ECM software. The other would be to install a piece of electronics between the ECM and the injectors to shut off the 3rd event.

Comments ?

 

A couple questions...

a) does the 3rd event serve to increase the exhaust temp or provide a reducing exhaust environment or both ?

b) where exactly is the 3rd event injected in the cycle ? close after the main event ? Near BDC ? On the exhaust stroke ?

c) If the answer to a) is to increase exhaust temps for proper cat operation, then what exactly happens when we put on big air cleaners and big exhaust and the ECM senses way more air in the intake under part throttle conditions ? Does it jack up the 3rd event volume ?

 

One more thing... lots of people claim the 12Vs are a lot better on fuel than the 3rd gens, but if you do the BSFC calc for them, they generally have higher numbers. But then again, it is the part throttle numbers that really matter.

Side comment: Now that fuel economy is becoming a big issue, I wonder if the dyno events will start running true traction dynos, measure fuel consumption and start comparing BSFCs instead of all out HP.

 

Great questions.

a.) yes, it is used to increase the exhaust temps to keep the cat clean and is there only because the decision was made to use this instead of adding cooled EGR.

I'm not too clean on " a reducing exhaust environment".

b) I'll have to look. There are probably alot of variables to this like it depends on when the pilot injection starts, how much total fuel is commanded for the entire event, temperature, etc. I would say its definitely as the exhaust valve starts to open (at bottom of power stroke) to get raw fuel to the turbine).

c.) The ECM doesn't sense airflow (no mass airflow sensor). It uses boost pressure and IMT to determine how much fuel to put in to keep it from going too lean.

 

Sorry, I'm not too CLEAR on the "reducing exhaust environment".

As I think about it more, I think its both. I bet the gas leaving the exhaust port is a little cleaner and the cat get hotter.

 

"The ECM doesn't sense airflow (no mass airflow sensor). It uses boost pressure and IMT to determine how much fuel to put in to keep it from going too lean."

There are two ways to sense engine air flow. One is to use a mass air flow sensor and the other is to deduce it from the air pressure/density in the intake manifold combined with a volumetric efficiency table. I'm sure Cummins uses the later. The 7.3 PSD does. If you read the engine parameters with a scan tool, one of them is air mass flow.

As far as keeping it from going too lean, you mean making the 3rd event rich enough to provide a reducing environment for NOx, right ? That is the whole thing with the post injection events/cat converters, a reducing environment and a catalyst converts some of the NOx back to N2 ?

 

Just thinking here. Now I don't have all the technical expertise some of you all have, so please forgive me if I'm talking out my rear!!! Eliminating the 3rd injection event (if it's there for the kitty temperature), wouldn't that cause the kitty to possibly plug with whatever. We don't want that do we???!!! I remember plugged kittys from the 80's with leaded and unleaded fuel etc. What a nightmare that was trying to figure out what it was!!! Also, this tone ring mod: we're advancing the injection cycle correct and nothing else???? Same question as above. Moving the 3rd injection forward; is that 3rd shot gonna do what it's supposed to (get the kitty hot enough to work)????? If the kitty is not hot enough to change these compounds, will it get plugged with something else????

 

Kittys operate on other trucks without a 3rd event. Sometimes kittys get lost too.

 

Superduty,
Contact Marco over on the TDR. He's an expert on the Cummins ECM and might be able to come up with something.

MikeyB

 

I'd bet there is a setting right in the ECM to shut off both pre and post injection events. You just have to find it I bet there is even a way to shut it off via the OBD port without reprogramming. Again, you just have to find it I have to wonder what else the BullyDog people know about that they aren't using?

I suppose you could come up with a hardware solution but that sounds like more trouble than it's worth. If you're a sharp guy you could build and program your own ECM! You could do without the pre and post injection events then, it would sound manly if nothing else!

Andy

 

Nope, no enable/disable for pilot or post injection events in software. It wouldn't run right (misfire).

 

What logic tells you that it would misfire? And how do you know it doesn't have such a thing?

Andy

 

"Nope, no enable/disable for pilot or post injection events in software. It wouldn't run right (misfire)."


Err... if you dig around enough in the software, you will find the routines that fire the post injection event. Not too hard to disable those. The ECM uses an MPC555 processor. It has a special Timer Processing Unit that generates the injector firing signals. If I had the flash code for a 555 and 6x0 engine, it might be pretty simple to disable it.

 

I disagree. The post injection would be like the pilot injection that is built into the base tables. It's not a seperate algorithm that can be disabled. You may be right about it running fine (better maybe) if you could cut the post off, but you would essentially have to "re-map" the entire fueling table for both quantity and timing (I should say tables, as in many tables).

 

First of all, I bet there is a column in the fuel table for pilot, main and post shots, because they aren't static values, they change with engine load.

Even if their isn't, the address of the TPU is known and it should be pretty easy to find code that writes to it. Actually, the TPU runs microcode, separate from the ECM. It shouldn't be too hard to find all the code that accesses the TPU and go from there. I'll bet there is a routine for firing the injectors that takes about 6 parameters: timing, pilot duration, main delay, main duration, post delay and post duration. The timing parameter will be a delay as well because the cylinder #1 mark reaches the crankshaft position sensor before physical TDC on cylinder #1.

Like I said... get me the flash code for a 555 and 6X0 and we'll see.