Ive heard in a couple of places that replacing stock GTP38 and running a 38R or kc38r will drop MPGs.
Ive heard the opposite in a couple places to & that MPGs will be the same or get better.

Any truth to either one if driving habits & location & fuel stay the same...in other words nothing else changes?

 

Too many variables. In theory you may get cleaner burn less unburnt fuel and a tiny mpg gain. possibly too small to notice. More likely to see a mpg drop due to stepping on the go pedal harder.

Driving habits and consistent fill ups are key.

 

Thank you for the reply. I tried to remove variables in my question when i wrote ---
(Any truth to either one if driving habits & location & fuel stay the same...in other words nothing else changes?)

 

I have no facts to base this off of, but here is my opinion.

Simply changing the turbo to a larger one is not the deciding factor on attaining more MPG's. I believe that the goal is to have air efficiently moved into and out of the engine with less throttle input while attaining the same level of work accomplished.

So, in my opinion yes, you can achieve more MPG's by changing the turbo out, but the turbo needs to be matched to the system and tuning.

The Brad posted this video on another thread and mentioned the time stamp of 27:41. I watched the entire video and took quite a bit of information from it. I was guilty of associating (not totally, but some) boost with power output by the engine to the wheels. That is not the case. This is why the higher boost numbers from some of the bigger turbos still produce higher EGT's and more heat, which would bring MPG's down.

Efficiency is the key and 1:1 is the goal. How you achieve that goal is entirely up to you. Some have gone with large injectors and the KC38R. Some have stuck with OEM injectors and gone with a Borg Warner/T4 kit. Education on the options and your personal goals for the truck is what matters.

 

A larger SXE turbo will decrease mpg in a linear fashion with the increase in tire tread loss. Fact.

 

As long as the intake and exhaust are not restrictive, more boost to take advantage of a turbo will in general increase mpg as long as your foot directs the same amount of power.

How the specific turbo fits into that equation depends...

So it all depends...

So I'm really not much help LOL.

OK, S&B intake, 4" exhaust, a good combination of parts from Riff Raff (by reputation, not experience), and injectors matching a Hydra tuning setup (again, reputation and not experience) with whatever turbo. I think the turbo and housing will have more impact in terms of lag and responsiveness (to that foot which hurts mileage) than to mileage directly. I'm still learning this stuff, but that is my general thinking from what I have read. And from what I have read, the foot gets heavier because it can. So mileage is actually likely to drop after all.

 

 

My fuel economy going from a stock turbo w/wicked wheel to a 38r was unchanged. It improved while towing.
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I know Barney on here had the 38R with the alum WW2 and the shaft broke on his after about 30K. So I would stay with the stock wheel on that turbo. Diesel o-rings also says that. He dose tow all the time with his F550.