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Old 09-06-2013, 11:17 AM   #149 (permalink)
owly
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Join Date: Jan 2010
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Quote:
Originally Posted by oil pan 4 View Post
The addition of my holset turbocharger boosted my mpg by 2 to 2.5 mpg and gave me tons of power.
The addition of my second turbocharger and intercooler added less than 1 mpg (more like a half MPG), it did not hurt MPGs but did increase drive ability.
They may hurt the diesel engine efficiency by its self but the over all system efficiency is higher.
You can get better MPGs from mods that give you more power, bigger free flowing intake or ram air intake will boost power and wont hurt MPGs (unless its very cold out). Big straight pipe exhaust on a turbodiesel helps too. A bigger more freely flowing shorter over all length exhaust did not appear to help MPGs back when I was running N/A and I wasn't expecting it to.
A turbocharger that has a 20 or 30 year newer design wont hurt anything.
I turned up my injector pump rate screw back in 2008 and MPGs were unchanged so long as I kept my foot out of it.
Let me point out that you ADDED a turbo.......... The Holset turbo kit didn't include low compression pistons........ did it? Factory turbo installations involved lowering compression ratio to stay within their parameters for head bolts and gaskets. They also include large nozzle injectors. Both of these HURT fuel economy. I personally would not put a turbo on a non-turbo engine. Having worked on diesels a great deal over the last 30 years, I've seen many of the internal changes that are used with factory installations. One such change is often a system which squirts a stream of oil through a nozzle carefully designed to bath the under side of the piston, as well as a larger oil cooler.

I don't disagree that many mods that give more power do not hurt MPG and may even help. You can fiddle around to make your pump deliver more fuel....... as you mentioned, and it will have no effect.......... It's the "nut behind the wheel" that costs fuel in that case. As long as you don't put larger injectors in, it will have no effect at cruise. Boost on an engine without lowering compression ratio as the factory does helps up to a point..... Diesels are mixture sensitive also, so there is a point of diminishing returns. Modern highly pumped up Cummins electronic engines produce vastly more power, and produce it at a higher efficiency......... But most folks get poorer mileage just idling down the road. You gain efficiency when pulling a big load.........but if you spend most of your time "loafing' down the road, you lose. It's just like we see with those high performance cams we used to play with......... you gain on one end........ lose on the other. Thus far I haven't read of anybody here who's trying to measure mileage based on pulling 20,000 down the highway on a gooseneck trailer............. Everybody is measuring mileage hauling their solitary butt down the highway!
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