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Air Box pressure in 2-stroke diesel engines

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Your Detroit Diesel Specs

Basic specs are open to everyone and include images, displacement, dimensions and weight, essential bolt tightening torques, the characteristics of the engine like its power and torque.
Essential bolt tightening torques are the main bearing cap bolt torque, the connecting rod cap bolt torque and the cylinder head bolt torques.

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Cases in which air box pressure affected engine operation

Twelve 20 Cylinder EMD's Lodged Useless

Image - EMD 20 cylinder engines

Why? The air box pressure was too low! - Read all about it!

What happened is that these engines originally operated at 900 rpm to produce electricity at 60 cycles. They were purchased collectively as an installation, and sold to generate power in South Africa where the national grid operates at 50 cycles. This meant that the engines had to now operate at 720 rpm and not 900 rpm. The necessary electrical changes were made, but on starting, the engines smoked excessively and would produce no power.

When we measured the air box pressure it was about 7 psi - no good! Far too low! We told the customer he had to upgrade his turbos, but he wanted proof before spending another cent. 220 million bucks is quite enough for a white elephant - Thank you!

Well now we proved it, with the help of huge hired compressors. We pumped air into those enormous air boxes and artificially increased the air box pressure to about 13 psi.

image 20 cyl emd 645 engine When the magic 13 psi happened - Hey Presto! Even those smaller turbos kicked in and normal power was produced and the engines ran normally with no excessive smoke.
When this happened the engines' own turbos sustained the power and maintained the air box pressure at 13 psi without assistance. Now the artificial source of air could be removed with no effect to the performance of the engine or change to the air box pressure.
In fact a type of 'terminal' air box pressure had been achieved, so that if you pumped air in or not it had no further effect on the air box pressure. That is, it neither rose when air was pumped in nor fell when the assisted air was removed.

However if the engine needed to be restarted the air boxes had to be primed again, and the air pressure had to rise to 13 psi, in order to get the turbos to kick in and produce power.

The net result was that the turbos were subsequently modified and the modified engines operated fine after the modification.

Facts about air box pressure

Article by Steve Barrington in response to many inquiries both general and specific. Air box pressure is a vital factor in the operation of two stroke cycle engines such as many Detroit Diesel, Brons, Wichmann, Sulzer and EMD engines employ. A vital factor in that, if air box pressures are too low they translate into loss of power or even complete failure of the engine.

Air Box Pressure

Basically sufficient air box pressure is required for:

If your engine has enough power and does not smoke excessively your air box pressures are probably within the normal ranges, or right.

Low Air Box Pressure

Insufficient air box pressure will cause:

Insufficient Air, low air box pressures are caused by:

High Air Box Pressure

Too much air box pressure may indicate problems with:

Power and Smoke Problems

If you have power or smoke problems with your engine, some basic checks may reveal the problem(s) very easily:

Basic air box checks and inspection:

Image - Barrington Diesel Club logo Full Load expected Air Box Pressures for Detroit Diesel engines 
Indicated in inches and mm of mercury
rpm 1800 2000 2100
Naturally aspirated N engines 1", 25 mm 4", 100 mm 5", 125 mm
Turbo engines 22", 594 mm 28", 756 mm 30", 810 mm
TI engines 27", 686 mm 32", 864 mm 35", 945 mm
 Notes: Measuring Air Box Pressure
  • Connect a manometer to one air box drain. Measure pressure at fixed RPM's
  • The above table gives an indication of what to expect, but air box pressures vary with altitude and from engine to engine, injector to injector, turbo to turbo; so take nothing as definitive.
  • If your air box pressures are close to the values listed in the table there is normally no problem in this area.
  • If you're at all concerned, contact the local agents with your model and serial number for further advice.

Barrington Diesel Club

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Page Revision #9.2R 02-17