Diesels are a strange animal when you start looking at cruise. they are all about torque, and run the most efficiently at a pointabout 80% of their max rpm, tho some variation on the type of diesel does effect that point. a high rpm diesel like yours seems to have it's best economy/power around 2800-3000 rpm, if you consider power vs speed.
You might want to poke around the various diesel sites like cummins, cat, yanmar, and you should be able to find power and fuel consumption charts for boosted and non boosted engines of identical displacement. tho the rated power of you motor is more akin to the 4 cylinder displacements, the 6 cylinders are similar in displacement and usually come boosted and non.
I'm really only familiar with them in marine applications, which is really a world apart form a car, in that it is a single speed transmission, so the propping is done to take advantage of torque to spin a larger higher pitch slower for maximum efficiency.
During the fuel price spike tho, I did hear of some people removing the turbos and intercoolers to increase fuel mieage, tho in that application, I don;t see how that is helping things if the boat was properly propped.

Unfortunatly its not that easy to compare my engine to other engines. Its an IDI (indirect injection) engine, and naturally aspirated, and makes its max power in areas that are not typical of diesels. It was designed as a light duty economy diesel. It was never meant for a bunch of power. (I personally think it was designed primarily for the military and trickled down to the civi trucks. Humvv's dont tow or make gobs of power, but they are heavy and need to be somewhat conservitive on fuel and work with all sorts of fuels. And im sure there are other reasons, but I believe this is why GM designed this engine. Not a power-house daily driver engine, but effiecent versitle military engine.
Not to mention this was GMs first production (from the ground up) diesel. I think they tried to give it gas like characteristics.

Anyways, Ive been poking around at the gm diesel forums, general automotive diesel forums and trying to find some books. Ive found the fuel consumption chart for the n/a 6.2 in the cucv trucks (1 1/4 ton military chevy c10). But there is no found info for the 6.5l td. Every other type of diesel I found charts for (even larger engines) all have better fuel consumtion rates than my engine.

Peak torque comes in around 1800-2100 rpm, and the 'magical mpg rpm' seems to be from 1600-1800 for non towing, and 1900-2100 for towing. This is based on others information from another forum. Yet peak hp is all the way at the govenor setting of 3800. (with a cam change, valve springs and other goodies, Ive heard theyll spin to 5500 safely, and to 8000 before it scaters heavy parts at people.)

quote Originally posted by merlot566jka: The 6.2l actuall IMPROVES gas mileage when boost is applied at cruise. Something about diesels making more trq as a load is applied?? (I would say more, but I feel a little retarded when it comes to how exactly making more power saves fuel. It can be read about on the banks website under the gm/6.2l sidewinder kit. I just dont want to sound like an idiot, cause I dont understand fully.) Its been proven on the Banks turbo kit increases fuel economy by 10% at cruise, and I believe even better mpgs while towing (towing vs towing turbo'd). While others who have installed the kit have seen up to 2.2mpg increase AFTER installing a turbo, some say thier mpgs went unchanged. But no one has ever said it went down. Odd, I know. Instead of researching it, I just accepted it and went after some boost.... The 6.5l pump is a direct bolt in. No retrofitting. (The 6.2l and 6.5l can be compared to the stock fiero V6 and the 94 camaro V6...in that they are the same basic engine, with a few upgrades like computer control, injection control, dis...bla bla bla) I am working on the angle of the hacked ecm. As of 2006 It looks like some one hacked it and offered tuning sultions for both obd1 and obd2. But with a price of $895 and $1300 respectivly, I feel that it has to have been done on an end user level somewhere. I am at work (in the navy, on an aircraft carrier, 24hr duty today) and the internet is painfully slow. When I get home tomorrow I should beable to find some more info on the ecm. I do belive it will be a key player here. Whether it be obd1 or obd2.

Good to hear about the ECM.

Not all boost is boost. Turbos and superchargers do different things for overall SYSTEM efficiency because they are driven differently. Turbos add back pressure and reduce IMEP, but improve intake side pumping efficiency. Superchargers subtract directly from BHP to improve intake pumping efficiency.

Mixture ratio rules in fuel efficiency. Gasoline engines use a lot of fuel in boost because they run richer mixtures. I hadn't thought enough about it, but it's probably more fuel efficient in a diesel to get a given power by adding more air to the same fuel than using less air and more fuel.

quote Originally posted by merlot566jka: This is based on others information from another forum. Yet peak hp is all the way at the govenor setting of 3800. (with a cam change, valve springs and other goodies, Ive heard theyll spin to 5500 safely, and to 8000 before it scaters heavy parts at people.)

LOL.

Link please to 5500+ RPM operation.

yeah, I'd like to see that also. Even high speed diesels have questionable reliability, and high speed right now is defined as 3800 rpm.

But then again, I'm looking at a much higher loading than a car, wher they might survive limited high speed bursts.

im lookin for the article....lol, it was from the diesel page......


after like 30mins of searching, im starting to think that was the duramax they were talking about.

Why not convert to a Bosch VE pump? Like the Stanadyne, it's a rotary style, but it offers more flow, and is capable of more than double the pressure.
The 6.2, while relatively inefficient, is a mileage engine. I can testify to having gotten 35 mpg in an '84 C-10 with a manual trans. However, exceeding 30 mpg with a Cummins in a Dodge dually is also easy, so I'm looking to install a turbo'ed 5.9, as then I could get any parts, anywhere, any time.

These are some serious fuel savers. 26mpg in a 6800lb suburban, people laugh when I tell them I get that kinda mpg. I laugh at the pump.

But they do have their price, $240 for a new starter, the old crapped out on me this morning before my E5 exam. not cool.

This engine is like the iron head 2.8, everyone has it, they all want something better, and I am going to try and make it a performer. ( i failed with the 3.4, 150hp and 190ftlbs)

Last time I went to pick-n-pull I found 3, they go for $150 each plus a $30 core charge. That'd make it easy to build a fresh one, since mine needs new valve seals anyway, and even the '89-'92 Cummins runs over $3000 around here.