Shiftless, I don't mean to be argumentative, but you're thinking like a gas-engine Dude.
Your comments indicate that you expect increased efficiency from the incremental changes you are considering making to the intake restriction. On a diesel engine.
Everyone here knows that in a gasoline engine more air means more fuel, and thus, more power, because the fuel/air ratio is constant. But a diesel takes a full breath every intake stroke regardless of whether it's idling or at full load. One gets more power by injecting more fuel, up to a point. That point is reached when more fuel is injected than can be completely burned by the available charge of air, and smoke forms. That will only happen as you near maximum load.
A 6/1, 8/1, etc., at the appx. 2 kw load Selmawp mentioned isn't near that point. Providing more air under a partial load will only enrich the oxygen content of the exhaust stream; the extra available oxygen won't be burned. What decreasing intake resistance will do is it will allow the engine to produce more power before it begins to smoke. But you won't see any benefit at partial load. In another example of gas-engine-thinking, Millman56 mistook the 1 Hz increase in alternator frequency to indicate that providing more air resulted in more power from the same amount of fuel. What he was doing was simply reducing the pumping loss of the engine and slightly overpressurizing the cylinder. Go to any show and you'll find old dudes running small 4-stroke engines on compressed air simply by pressurizing the intake manifold.
What you propose has been talked about a few times, but I don't think anyone has ever done it and provided photos, and most important, reliable data.
Consider what's involved:
The 6/1 chugging along at 650 rpm takes a breath 325 times/minute. Its cylinder volume, is 87 cu. in. The airflow sucked into the cylinder on the intake stroke should be about 28,275 cu in/min, or about 16.4 cfm.
For the sake of comparison, at full roar, each cylinder of a 350 V-8 takes about 2500 breaths each minute at WOT with manifold vacuum near 0. Its cylinder volume is about 44 cu in. So it sucks about 110,000 cu in/min or about 64 cfm past each intake valve. That's almost 4 times as much air as the diesel breathes.
The intake valve on the V-8 is just under 2" diameter; about the same as that of the 'roid. All things being equal, and setting aside the complexities of boundary vs. turbulent flow, Reynolds numbers, and boundary layer thickness, what we’re talking about with such a short intake runner boils down to flow resistance. And the resistance to flow varies with the square of the area of the restriction.
Since the flow rate past the intake valve of a 350 V-8 is about four times as great as that of the diesel, and resistance varies as the square of the flow rate, any improvement you make to the restriction in the intake of the V-8 will be 16 times that of the same operation in the diesel. That’s why porting is always done in gasoline race engines, but is seldom mentioned with regard to diesels.
I think any gain in power that you might make by cleaning up the intake would be small. But it appears that you've already drawn your conclusions from your experiment which has yet to be performed.
I'm not saying don't do it; these engines are wonderful tools for experimentation and learning. I wish they still taught autoshop in my old high school; I would have donated one of my engines to the program.
Quinn
