I was talking with another diesel guru today on some questions I have on making these things run more efficiently.

For instance on a mechanical pump truck, say a truck makes 300 h.p. with PODs and 30 psi of boost. you have a boost reference signal going to the pump to tell it this, but if you port the head and say make the same power at 25 psi, how does the mechanical pump know to pump a increased fuel amount for the increased airflow? Does anyone check A/F ratios on their truck?

Or if on the old rotary pumps if the aneroid is bottomed out a say 15psi of boost how does it supply more fuel at 30 psi? Depending on the turbo some arent efficient under 10 psi so down low the truck is over fueled...

I/C piping, this stuff is pretty small for the displacement of the engine. My turbo car with 135 cubic inches runs 3 inch pipe and has a Hx-40 on it, should these trucks run larger piping?

Can someone help me out here??

 

Air to fuel ratios are not critical for diesels the way they are for gasoline engines -- running leaner normally increases efficiency. They way we check our air fuel ratio is with the pyrometer -- if EGT gets too high, we just add more air , leaning out the mixture, and reducing temps. Technically, many of us are wasting energy, (and thus hp), pumping up higher manifold pressures than we really need at top rpm for our fueling level. (Hence some folks using a 16 housing over a 12 for better top end milage.) So, you are correct -- looking at my truck: the pump is giving max fuel at say 8 psi, efficient burn is at 17 psi, and max boost is 25 psi.

Practically speaking, most guys just tune their trucks for max hp at max rpm. So, they only care that the pump is putting out as much fuel at 3000 rpm as possible, that they have enough timing to get it all to burn before TDC, and that there is enough air flowing through the engine to get it to burn and not melt a piston. If you were trying to go for great drivability and fuel efficiency, then you would have to start looking more closely at the AFC pin, spring, and lever (which to be fair, IS what the old smokey pin does, but IMO it is limited by the inherent geometry of the pump governor levers, etc.) and the timing advance curve.

As for the flow of air through the IC pipes, bigger pipes effect turbo lag and spool-up, and the air in those pipes is at pretty high pressure, so I do not think that there is much to be gained by going bigger, but I have not done any analysis, that is just a guess. I think that the aftercooler is certainly the place to look first for improved flow, and improved efficiency in reducing the charge air temperature. Cold intake air also has a huge effect on turbo efficiency, so boxing in that BHAF so it draws fresh air maybe should be higher on our to do lists . . . Somone should do a test on straight BHAF vs CAB mounted BHAF . . .

I am not t true high hp experienced guy, and sometimes experience sheds a lot of light on theory . . . so, let's see what some other folks say.

 

I know at least in the gas arena on the 135 cu inch Dodge motors using a 72mm turbo 4 ich IC pipes are needed for good flow. I can tell you swapping from 2.5 to 3 inch really helped my engine due to the increase flow which reduced the pressure allowing the turbo to be more efficient and dropping intake temps. the harder the turbo has to work by beating the air to make pressure the more efficiency is lost. Since there is always air moving through the pipes, even at idle, boost lag shouldt be a issue, the gas burners even vent intake pressure (blow off valve) on shifts to reduce compressor surge and increase tubo life.

Now over fueling doesnt that effect spoolup? Makes me wonder if a guy could make a engine mgt system for these trucks? Is there a high/low ampedance injector used in the B series motor? It just looks like most throw a bunch of air and fuel in and hope it gets close

So many questions...

 

On the IC piping question, keep in mind these engines only run ~2500 RPM stock and the majority of trucks on here are staying under 4K RPM. The gassers run much higher RPM, thus flowing as much or more air as these trucks.

 

Even though the rpm is lower the pipes still have to flow the same CFM from the turbo wouldnt they? Has anyone tried bigger piping with a larger IC that has larger fittings? i know a number of guys use Cummins, power stroke and Isuzu NPR I/Cs on their car and minivans, makes me wonder if the IC needs to be bumped up especially when your making 300+.

Has anyone check pressure drop frin the inlet and outlet of the IC?

 

1st gen coolers are pretty restrictive... the 3" IC pipes aren't hurting anything, but the cooler could definately stand to be larger.

as for the original question, as long as your AFC is set to give full fuel before 25psi, there would be no change in max fueling, but it would probably come in later.

AFC is your boost:fuel setting

 

A 180ci engine at 6000 RPM, 10psi boost, volumetric efficiency of 85%, should flow ~34 lb/min air. A 359ci engine, 2500RPM, 20psi boost, volumetric efficiency of 85%, should flow about 40 lb/min. So they're flowing about the same, even though one engine is bigger and running twice the boost. I'm sure HOHN could comment further and more knowledgeably on this...

 

But boost isnt just boost. For instance you can take a stock T3 turbo at 13 psi and replace it with a T3T4 50 trim turbo at the same 13 psi and make 50 h.p. more on a gas burner due to the 50 trim delivering a larger cooler volume of air.

How did you come up with those flow numbers?

So if the AFC is set to max out at 20 psi, how do you deliver more fuel say at 30 or 35 psi, then again you cant make 30-35 psi without fuel, so somehow its getting there.

 

Doesn't it stand for "Air-Fuel Control"?

Or is that only laymens terms' for something Deustch?

 

Yes.

Mopar2ya - It might help you to think of the AFC as a device to decrease fueling rather than a device to increase fueling. The engine only gets as much fuel as the governor assembly is calling for. At low boost levels, the AFC lever is restricting the travel of the governor lever. Once the boost builds to a certain point, the AFC lever moves out of the way and the governor lever can move to the "full fuel" position - but only if the governor mechanism calls for full fuel, and that depends on engine speed and load.

On fuel ratios: A good rule of thumb on diesels is that if the smoke clears up at full boost, adding more fuel will make more power.

 

is that like crank the fuel pin until it melts than back it off 1/2 turn??

So is there a limit to how much fuel a injector can make. Say with stock 160 h.p. injectors and using a wastgated housing you make 25 psi and 1200 degrees, if you swap in PODs and leave the boost at 25 will it over fuel? My thinking is yes since the wastegate is controlling boost and rpm is the same, its just more fuel, if Im wrong...umm why?

 

In the situation you describe, yes, the POD's would be dumping in more fuel. The engine will make more power. Adjusting the wastegate to add boost would help with the EGT and smoke, and would give a small gain in power.

Gas engines fall on their face when you get out of a very narrow A/F mixture range. Diesels tolerate an extremely wide range of mixture, they have to because that is how engine speed is controlled.

An easy way to think about it is this: on a gasser, air + fuel = power. On a turbodiesel, fuel = power. It's hard to get a turbodiesel to the point where more fuel will not make more power. Usually before you hit that point, EGT has caused you to go out and buy a bigger (or more than one) turbo.

 

SO porting a head allows you to run a bunch more fuel and keeps the EGTs down by adding more air. Well then Gunrunner1 will have to tell me how this ported head and exhaust manifold I did for him drops EGTs and boost.

A ported head wont make power on a diesel like a gasser, all it will do is allow you to add more fuel and will keep the EGTs down. thereby allowing more fuel and more power? Power on a diesel is limited by EGT then?

BTW is there a firing order on these injectors?

 

You do reach a point of diminishing returns when adding fuel, and at that point more airflow will help the HP without adding more fuel. On a gasser the range of A/F ratios that makes good power is like a knife edge, on a diesel it's like an upside down frying pan.
1-5-6-3-2-4

 

and since the diesel has a divided housing has anyone made a pulse manifold/header for these? or is the ATS the only thing? If not the divided housing is a waste.