quote:

Do you mind voicing your preference as to which diesel engines? Cummins, Detroit Diesel, Caterpillar,????

I've been absolutely delighted with my AMG (nee: DD, nee: GM) 6.5L TD. AFAIK, only 4 (all '94 28' Breakaways) had the OEM GM engine, and that was early in its career.

It had shortcomings, but AMG (who powered its Humvees with it) bought the rights and immediately improved it, with new metallurgy in the block (strengthening it 25%) and lowering the compression ratio from 21.1:1 to 18:1.

The engine has been further improved (now called the P400) with a forged crankshaft replacing the billet-cut crank.

Peninsular Engines (f/k/a Peninsular Diesel) built mine from the AMG base engine.

quote:

Originally posted by Rusty:


Rule-of-thumb is that best efficiency otherwise is at the engine speed is at the peak of the torque curve.

I used to believe that, and still like to drive right at the torque peak on my Barth, but some of my fuel injected vehicles with overdrive do way better at lower RPM if the throttle is kept light. The few that have had mileage readouts confirmed this.

A lot of "Rules-of-Thumb" have been OBE (Overtaken By Events).

Sometimes I feel a little OBE.

Would a charge air cooler be better?

http://www.fleetairtech.com/cac-function.php

quote: So if you are one of those people who has to have the ac on if it is 70 degrees or more, (i am not. Smiler), since it is on anyway, could you run an extra duct to dump cold air into the engine compartment to cool things down and improve combustion? Big Grin :unquote ???

Anything that cools inlet air that makes it more dense, containing more oxygen, is good. Some drag racers used to cool the intake by dumping ice on the intake manifold.

And, of course, blocking off the heat riser passages is good, both for power, mileage and cooler oil. The only drawback is a little slower carb warmup on really cold mornings. It is pretty easy to live with unless you use your Barth as a ski lodge. That was the only time I was unhappy with blocked heat riser passages.

BTW, speaking of cold air intake, later 454s have a flapper in the air cleaner snout that closes off the straight in air supply, and forces the engine to suck hot air from around the exhaust manifold. It can be checked on a warm engine by removing the vacuum hose from the top of the thermac on the snout. You should hear the flapper flap closed. You can also look with a mirror, or feel with your fingers, but have your fingers away when the hose is being pulled off. The vacuum is ported by a mechanical temp sensor in the air cleaner. If the vacuum line to the thermac is missing or bad, the engine is not sucking the coolest air it can.

On my Barth I have Thorley headers. Whoever installed the headers did not install the hot air shroud and duct that leads to the air filter horn. The EFE exhaust heat riser valve was also gone. (Fine with me, cause I'll be using Barth in mostly hot weather) However, flap in the horn was always closed due to one of several vacuum leaks.

I removed the offending vacuum lines and cut the air horn shorter to eliminate the flap entirely, which was by then just a restriction in the air supply, even when open.

quote:

Originally posted by Doug Smiley:
quote: So if you are one of those people who has to have the ac on if it is 70 degrees or more, (i am not. Smiler), since it is on anyway, could you run an extra duct to dump cold air into the engine compartment to cool things down and improve combustion? Big Grin :unquote ???

Losses in powering the A/C compressor more than outweigh any advantage of cooler induction.

Point was, Rusty, if someone is running the ac anyway, would running a duct to divert some of the cold air to the engine, help to either cool the engine, or improve performance by adding cold air to the intake.

Having a backround as a marine engineer, I pulled out my old thermodynamics text several years ago to see if there was any advantage to things like this.

First, disregarding losses and inefficiency, heat extracted from an engine is its work performed. Very much simplified, heat extracted is calculated using mass, combustion temperature, and exhaust temperature.

The first surprise for most folks is that the heat extracted is a percentage based in combustion and exhaust temps - but the temps used are absolute, so the calculations are adjusted to absolute zero.

Lowering intake temp is therefore a very tiny percentage compared to lowering exhaust temps; this is one reason why high compression engines are more efficient than lower compression engines - more heat is extracted.

An intercooler on a turbocharged engine can drop the intake temp by 50-200°F on the full air volume. Cooler air from an air conditioner might lower the temp 30°F for a tiny fraction of intake volume. A 500 cu. in. 4-stroke engine at 3000 RPM will use (0.5x500x3000)/1728 = 434 cu.ft./min. Your dash air blower probably produces ~200 cu.ft./min. Diverting 50 cu.ft./min would lower intake air temp by 2-3°, which is negligible...with ambient temp at 80°F, 537°A, that's 0.5%

BTW, there is a notion that gross power of an internal-combustion engine is calculated using cylinder pressure, since that's that makes the pistons go. However, output for any engine is calculated using thermodynamics, not physics, odd as that may sound. Calculations are done slightly differently for each of the internal-combustion engines: Diesel, Otto, Stirling, Miller, Wankel, etc.