[BabyDiesel]

Pgfpro - You're welcome Thank you for the support and valuable information! Everyone who is giving input is making this thread fun for me! Thank you all!!!

I have been messing around with the Borg Warner link you provided and it is very useful! I'm learning what everything means, so I am still on the learning curve.

I think I have been confused with all the information we have discussed. I remember use discussing engine size, and how the 2.0 is too large to run boost in lean burn unless I had AFRs of 40:1 or greater. Knowing that has made me "scared" of having any boost below 2500 rpm. The only way I can see a way around this is a larger turbo. Since this build is strictly for fuel economy, I can stand to have no boost until the mid-range. I haven't topped 2500 rpm in months!

I'll walk back through the turbo-talk we've had in the past couple weeks.

On your new theoretical car the fuel mileage would be around 108 mpg based on the very low hp needed from the car itself, but there is a major hurdle that wouldn't let this happen. Engine size. More on this later.

I understand this.

The 2.0 L engine size problem is that even at a needed 4 hp to 6 hp the 2.0L engine would have to be running in vacuum and could not utilize the turbos FE efficiency at this very light load. On my car I have to overcome AWD drive train loss and with a Cd of .29 so the hp that is needed is around 10 hp @ 55 mph.

So in your case the turbo could help with extra power when needed if you choose to run a 3 valve setup.

So no boost needed during lean burn, which is 1700-2300 rpm. I am going to run the 3.5 valve setup like you, so the turbo would help there when the rpms go up enough that I needed more flow.

It would be a normal turbo setup that would only make boost at mid and high load. So for FE the setup would be a lean burn N/A app. The results would still be awesome though!!!

This is what I have my mind set on; this set-up.

Nope 1 to 2 psi with the size engine you have won't work. You would have to extremely lean, above 40:1. Now this is based on the 4 to 6 hp needed.

See, no boost needed... boost is bad

The more I think it about it the more I like this idea. This would work awesome with a turbo for mid-load lean burn. See here I go again back to turbo world.lol

On my Talon the turbo gives me a 11% increase at 1psi in combustion efficiency over N/A. The more boost I run in lean burn the more the efficiency goes up.

So with your build you could run it in N/A at light load with a Atkinson cycle and at mid load still keep it in lean burn, but you would gain back some extra torque?

Hmmmmm. Must Ponder this.......

Alright here is the shift between our thinking. I'm still stick with N/A light load lean with boost seen in the mid range on up. You began to ponder mid-load lean... wait, you meant mid load as in the load on the engine, not the mid-rpm range correct?!? As in going from 50% load @ 2000 rpm to 65-70% load for a hill, the turbo spools up maybe 1-2 psi while still in lean burn, then I go back to N/A on the other side? If this is correct, then I am mad at myslef!!! How did I not catch this sooner??????

You wouldn't have to have the turbo wastegated at 2 psi and up to 6 psi. The proper choice in a turbo would only get you the low boost numbers, with out anything going through the gate.

With the low Cd it still looks like the you would be running in N/A even with a 1.0 L equivalent. This why i would run all four cylinders in a Atkinson cycle N/A and pull one tappet per cylinder to help with swirl. The when needed get into a mid-load and start making some boost in lean burn. This will accelerate the car up to speed and go back into light load steady state.

I see now... It all makes sense!

On my sons turbo Civic 1.5 L it had a fairly large frame turbo on it based on the engine size and we still manage to improve fuel economy. I couldn't make any low boost lean burn though do to what we are talking about engine size verses boost. What I did is setup the car for lean burn with a max around 18:1 A/F ratio and the car got great fuel mileage.

This is why I was told not to go with the 6.0 PS turbo. DANG IT!

If you drop your Cd down from what it is a sub-0.20 Cd then you will just use the turbo gain some HP when not in lean burn.

From above, it looks like I could make extra horsepower while lean burn too

So in this case i would run a much smaller turbo.

It allllll is becoming clear to me now!

In lean burn you are basically making a lean A/F hole in the fuel map. When i had my Del Sol with the 15g it worked great just enough to make around 1 psi at 22:1 A/F and i didn't have any problems pulling out of lean burn when needed.

It made boost when you pushed the go pedal down, opening the throttle plate, allowing more air in, which meant more expansion and this equaled the turbo making the 1 psi of boost while in lean burn. I get it now!!! The big turbo would not be able to do this, as you found out with the 5.9 Cummins turbo. A smaller turbo will make boost ONLY when I need it while in lean cruise conditions.

I am the smiley on top of this turtle -> I'm getting to the place of understanding, but veerrryyyy slowly LOL!!!