I'd just drop 2500 on an old muscle car for when I wnated to go fast and leave the truck alone

but if you do this I want to see the pictures

 

well, the reasonin behind gettin the truck is that i need a good tow/haul rig to haul my other projects around. lol. and the mileage/power ratio cant be beat for the price.

 

Once you go above about 20 PSI, intake manifold gaskets, exhaust manifold gaskets and the exhaust pipe joints start having problems.

The 6.9 was never designed to run boost, but it can handle it fine as long as the numbers stay low.

In very round numbers, 14 PSI of boost is putting close to double the air in the cylinders, so that gives you a potential of about 50% power increase, which is low because of the increased intake air temps.

With a good intercooler, that number should be able to be closer to a 70% power increase if you can get enough fuel in the cylinders.

Also the high base compression ratio of the 6.9 22.5 to 1, has huge cylinder pressures as the boost increases.

if you consider the effective compression ratio of a stock 22.5 to 1 compression ratio engine running 20 PSI of boost, you are looking at an effective compression ratio of 53.1 to 1.

The same engine running 25 PSI is just under 61 to 1.

Now consider a Power Stroke with a base compression ratio of 18 to 1 running 30 PSI boost has an effective compression ratio of 54.73 to 1.

To run 25 PSI, I have head studs, intake studs, exhaust manifold studs and had to use gasket maker on the exhaust manifold gaskets, intake manifold gasket and come up with gaskets for the exhaust manifold to exhaust pipe connections befroe the engien would stay together plumbing wise.
I also milled the pistons to lower the base compression ratio to slightly over 20 to 1, which still gives me a higher effective compression ratio then a Power Stroke running 30 PSI of boost has.

Milling the pistons to lower the base compression ratio has a couple side effects that are not so desireable.
First is harder low temperature starting.
With everyting in top notch shape I have started using just glow plugs at -10F, but the engine was not happy for several minutes.
Manual glow plugs with several after glow cycles to keep the engine running once it started.
Second the lower compression ratio does cost you some low RPM torque, you will notice it when starting off with a heavy load when you try to ease out on the clutch.

Yeah, it is great once you are moving and the turbo is spooling.

Also when you have enough fuel to spool the turbo, you will also notice you leave more money at the fuel station, every time you visit one.

My best MPG numbers since I built my engine, right at 14 MPG, so that was a drop of about 4 MPG from what I used to get when it was a NA engine.

So the initial build price is not the final cost.

 

thats very informative dave! thank you! i was thinkin bout head studs and gaskets, and intake and exhaust gaskets, and runnin bout 15 lbs of boost through an intercooler with the fuel turned up just slightly over stock. the turbos are smaller and are commin off of 2.0L engines that dont make full boost till between 4 and 5000 rpms, so i should be makin plenty of lower end boost, and keep manageable temps. am i on track for a good, powerful, efficient motor, or off in lala land?

 

Dave, I can't help but wonder if some of your MPG loss comes from the DPS injection system you are running.

After having my injector pump "moosified" I actually seem to have picked up at least 1 MPG. I'm now averaging 18 MPG while towing @ 55-60 MPH. Thats mostly thanks to tall gearing, but I've never been able to break 18 while towing before the pump was rebuilt. Usually I was at 16-17.

I've seen reviews by those that have run both and they say the DPS version usually hurts fuel economy without pushing as much max fuel either.

Looking in your list there, my gut tells me the loss in MPGs you are seeing is not from the turbo or the dropped compression. At least not all of it.

 

The terrain here is also hurting my MPG numbers.

Speed limit increase on the interstate.
DPS injectors with lots of fuel cranked to the engine.
Steep hills everywhere.
Huge increase in the traffic volume on the local roads.

It all adds up to lower MPG.