12.7 Detroit need a new turbo (upgrade?), hauling light and best mpg?

Not really, the fuel is limited to protect itself from driver abuse. You must remember this engine was designed and marketed to fleets for great efficiency.

BTW making boost has everything to do with fuel. More fuel, more boost. A turbo simply does not just make boost, you can hang any turbo you want on there. It will do nothing without fuel and combustion.

 

If I'm working mine, I have zero concern cruising at 1800rpm.

 

@1200 rpm, you should not have your foot in it and making boost.

That style of driving hurts engines.

 

You and I aren’t communicating on the same page. I keep talking about a stock 500 12.7 while you keep talking about yours that is almost 100hp over stock and probably 1850 torque. I don’t argue the 702 isn’t a good enough fit for yours. I’m arguing that it is too big for mine.
Again, the 1.15 AR exhaust housing helped mine, and I believe the K-31 will help it more. I intent to find out within the next 90 days or so, with a slowdown in work permitting. Right now, I’m can to can’t with work...
I’ll let you know.

 

That might hurt YOUR turned up engine, it won’t hurt a STOCK engine. I don’t think you can hurt today’s engines... there isn’t enough fuel at that rpm to do it. Don’t forget that the 12.7 from ‘99 up came with the tiny Garrett wastegated turbo that will spool even quicker than the K-31, but is a known stopper backpressure-wise, not to mention they blew up regularly.

 

Disagree. I have ran a 17702 on a 470 program. Still a improvement over stock.

1200 rpm under load is dumb on any engine, but especially on a Detroit. Stock or tuned that is not a acceptable operating range. This is exactly what shortens engine life and adds to sunk liner problems. Even a Cat that will make power at 1200 shouldn't be luged like that.

Its a fleet penny pinching idea to run low that low of rpm.

 

man and here i thought running an engine over 1500 rpm shorted its life. i keep mine at 1600 because of the ratio but when i had a volvo d12 engine, it felt wrong to push it past 1500rpm. i did lug that engine at 1200 rpm same as my detroit but the volvo d12 would do awesome from 1200 to 1500

 

RPM does not hurt a engine. But my D12 experience stops with 2000 model years. So I dont have much to say about a D12

 

The D12 if I recall has a variable geometry turbo, meaning it spools great at low rpms while breathing well at higher rpms. Those are great turbo’s, and why it pulls down to that rpm without complaint. Also the D12 rolls back fuel past 1500 so drivers learn it is useless to try to turn it at high rpms.
Which brings me to my point I’ve been trying to make about what happens when a too large turbo is used. If you have the fuel to spool it, the 171702 is fine. If not, there are better turbos to match engine size and fuel rates.

 

To further bolster my point, Pittsburgh Power offers an expensive option to fit a variable geometry turbo to a D-Dec 4. It’s about 8K and I personally don’t want to spend that kind of money, plus the truck has to be done in their shop which is too far away and too much time off work.

They wouldn’t offer it if it made things worse.