Anyone have info on the effect of altitude on mpg? I'd guess higher altitude would lead to a decrease in mpg but with the turbo ... ? Thanks.

 

My guess is that with a turbo, fuel economy would be somewhat unaffected. This is because you maintain the density of the air with boost and the effective mixture stays the same. You burn enough fuel to keep the power level where you need it to maintain your speed.

In turbocharged aircraft, the higher altitude is a benefit since the less dense air is less drag so more speed and less fuel consumed per hour. Assuming you're not taking hills, a higher altitude could give you better mileage for the same reason.

Edwin

 

I read someplace that the cummins is pretty uneffected by altitude compared with the earlier ford diesels. Ours are direct injection. I read that the fords lost 30% of their power over 6,000 ft. elevation. The fords had a pre-chamber I guess. Been awhile since I read it and I don't remember where I found the article. I don't know if it still applies to the newer ones.

 

Turbocharged vehicles will loose less power at altitude compared to naturally aspirated ones. As for fuel mileage, it is hard to compare because I live in flat.............. IL. You need to compare the same terrain type driving.

 

I drive in western Virginia/West Virginia at 500 to 1800 feet for part of the year, and in Nevada/Utah/Colorado at 5000-10000 feet for part of the year. Both areas have mountainous terrain and steep road grades, so I make good comparisons.

Yes, it makes a difference in fuel mileage and power. But not a big one, not nearly as big as a gas rig. Generally 1-3 mpg.

The big difference is EGT's. With the stock HX35 on my truck, an Edge and RV275's, EGT's would hold longer at about 200-300 degrees higher. When I went with the Dodgezilla, an HX40/35 hybrid, that helped the EGT's a whole lot, and I noticed a slight increase in mileage at higher altitudes, too.

 

the best miliage my truck has ever got has been from 6 to 10k feet it knocked down 20.47 mpg's. i filled up in roswell went to ruidoso, up and down the mountin a few times, out to white sands and back to ruidoso, up and down the mountin then back to roswell.

 

Gear Post, that's a good comparison. Thanks. I assume the 1-3 less mpg is for diesel?

 

I live at over 6k and frequently drive between 7 and 10k. My mileage doesnt seem to be too bad at all and have not noticed any big loss driving in the mountains here. Power is not bad either even at 10k though egts can get up there at that altitude pulling a load. Never had a power problem on even the highest passes. However anyone who says there is/should be no difference because of the turbo is a bit mistaken (not necessarily mileage I did not notice a big difference). I cant believe how much quicker the turbo spools up and the responsiveness at sea level. I went down to sea level last June(first time the truck had ever seen that kind of air) and I was amazed at the difference it was like driving a different truck. I guess at altitude you just get used to it because it isnt that bad at all especially compared to a gasser but there is definitely a difference in the way it feels at sea level compared to altitude.

 

I wonder if you could compemsate for the difference in altitude with a WG control to even out the boost? Since the boost gauge is balanced against air pressure you might have to add a bit at altitude to get the same absolute pressure.

Edwin

 

hmmmmm that is true.

If you are seeing 35 psi on your gauge at altitude it might actually be 37 psi actuall pressure in the intake horn....

Howver that is also dependant on barometric pressure in general... Even at sea level the presure is not always static.

 

I was familiar with aircraft turbos also...and was suprised that our trucks seem to respond differently. Aircraft hold sea level boost till they run out of turbo rpm. the CTD just looses boost as it climbs???
I could pull 50 psi boost at home (650') and in Colorado, at 6,000', could only pull 41 psi. Less power and a lot harder to control smoke in populated areas. All this has to hurt mileage some, I would think, but I was not up there long enough to track mileage.

RJ

 

This is likely due to the fact that the WG control diaphram has ambient air pressure along with the spring and as altitude increases the WG will open sooner and will lower boost when you need to increase it. Also, since the air is less dense, it gets more difficult to compress it.

9 PSI is a big difference! about 18% drop.

Edwin

 

Should have mentioned.....My colorado trip was before adding an external wastegate to my B-1 turbo.

RJ

 

What do you mean by external WG?

 

Mechanical spring operated by differential in air pressure feed from turbo compressor...no diaphram...mounted on exhaust manifold. Wasted air (exhaust) plumbed into downpipe. See my gallery.

RJ