I've been sitting here pondering my low dyno numbers and been wondering if maybe the colder weather had an effect on it. I've been driving this truck for almost 6 years now so I'm accustomed to it's quirks and this truck runs so much better when it's in the 70's and 80's than it does in the 40's and 30's. It's quieter, smoother, etc. It also feels faster and more responsive. Now, I don't have any data to prove this theory other than my own thinking but my thinking has me to believe that below a certain point the air is so cold that it's actually cooling the cylinder to much and isn't allowing a complete combustion. Any ideas?

 

Maybe it's not cooling the cylinder too much, but the air is too dense, causing an improper air/fuel ratio? Have you tried using a winter front at 50% on the dyno?

 

It's not that it's running too lean (a diesel runs with unrestricted air - how lean is it at idle?), but that the intake air can get too cold for good combustion. Remember, a diesel ignites its fuel from the heat generated by compressing the intake air in the cylinder. If the starting temperature is too low (the air temperature at the beginning of the compression stroke), the final temperature will be too low as well.

On many of the large diesel engines we built for arctic applications, the intercoolers were designed with 2 sections. One was a traditional intercooler that circulated auxiliary cooling loop coolant through it (used for the intercoolers and oil cooler) - the second section was a thermostatically controlled reheater that was controlled by air manifold temperature and circulated engine coolant through it to warm the air if the ambient temperatures fell too low.

Rusty

 

I think I read somewhere that diesel engines run better when on the hot side. The incoming air needs to be warm to compress and ignite properly. Gas engines have that darn spark to help. I don't know, just rambling........

 

That's what I'm talking about Rusty. I know cool air is good for combustion but is there a point as to which it's just to cold. I know the intercooler on these things is pretty dang good from the factory and the fan pulls massive amounts of air through it so maybe it's cooling the air to much when it's already cold outside.

 

The only way to be sure would be to have an IAT read out. Typically most industrial engines run at peak efficiency around 110 to 130°F intake manifold air temp.

On a dyno run, especially after a couple of pulls, your intercooler would be "heat soaked" and not cooling the air that much due to low or no air flow sitting still. In that case, even with cold air to the inlet to the turbo, the intercooled air is not going to be that low. You will notice on most dyno shows, the first pull is the highest, and then it levels off on each successive pull.

I would say, idling around town etc, where the intercooler is at ambient temp and boost is low, your IAT will be low and then it would affect combustion (hense the grid heater trip below 70°F). On the dyno, I have a hard time thinking the IAT is low enough to be a concern.

IMHO of course.

 

Blue, I think you could be right. If you can get back on the dyno, throw a big piece of cardboard in front of the intercooler and see what it tells you.

 

Lil Dog, last time I was on the dyno I was actually making more power as I made more runs. It was also 45* with a 20* head wind.

Totallyrad, that might be a little over kill considering that it's probably gonna be in the 70's or higher for the dyno. I'll let yall know.

 

maybe it isn't so much the air temp as is motor temp. a few weeks ago. temps here got to -10 below. first, i noticed low heat output. that i expected. but, i also noticed decreased mpg. i made a winter front for just the radiator out of .25" Plexiglas. heres what happened. heat way better, and the mpg came right back. now, the inter cooler isn't covered. but all of the radiator is- except for a 2" hole in the center. at 40* my temps are about 200-210 ish at 65-70mph. so, it could be that indeed that hotter = more efficient burn, and the cold air added allows for even more efficient burn = more power, better mpg

 

Sorry, I thought you were going to be on the rollers with the lower temps.

 

Blue, Are the numbers you posted corrected or uncorrected. When I dynoed it was in the 40's, my corrected numbers were lower than my uncorrected numbers. 30 hp difference to be exact. The dyno corrected down for the cooler temps. If my understanding of the correction factor is right. A correction factor is used to level the playing field so to speak, so dyno results no matter where you dyno will be similar.

With that said, I still would like to get back on a dyno when there is low humidity in the air and around 70 degrees to see what the difference would be.

Don M. has always said that he prefers to look at uncorrected numbers as diesels tend to be corrected too much.

 

My numbers are uncorrected as far as I can tell. I don't see anywhere where they state the correction factor.

Totallyrad, the last time I was on the rollers it was freezing cold outside. 45* with a 20mph wind. It'll be an interesting comparison next weekend.

 

Now that is funny 45 degress is now Classified as freezing cold

 

Hey, I'm from Texas. If it's below 70 we are shivering.

 

Tyler,

If you can make a real good friend at your local dealer you can get the DRBIII and be able to read all the parameters that the ECM reads real time. IAT happens to be one of those. The hottest I have seen my IAT is 135*F in the summer on a 90*+F day.

You may be on to something here.....