New Ford 7.3 V8

JRscooby wrote:

LanceRKeys wrote:
A turbo big block 7.3 would require a huge fuel tank, a big fuel line, and some big radiators. The owner would need deep pockets.

I fail to understand your logic. Back in the day some trucks where sold with the same displacement diesel with and without turbos. Over time, and really a short time, the non-turbo was pretty much gone because of more power and better fuel mileage.
And doesn't Ford advertise their smaller turbo/gas engines as "Econo"?

He is right. Due to it's lower thermal efficiency, gas engines run much hotter and have much hotter exhaust than a diesel especially under load. Gas engines are regulated by air and have to stay around a 14.7:1 air/fuel ratio so the more air you put into a gas engine the more fuel it will burn along with the higher temps.

For example, just cruising down the road my diesel's EGT's right before the turbo are between 500-700F. On my old 3.5L Ecoboost, they would be between 1,000-1,200F under the same conditions. This heat is the main reason why gas engines cannot use variable geometry turbos like diesel's can without making the vanes with some exotic metal to handle the heat which increases the cost of the turbo significantly.

Diesels are regulated by fuel and since it has a much broader air fuel ratio it has to stay within(up to 70:1), it will use whatever air available to burn the fuel being added and will do it at much lower temps. This is why the more airflow you add to a diesel the more efficient it becomes and the lower the temps will be.

rjstractor wrote:

Diesel is a bit of a different animal, although it's a misnomer that the turbo engines get better mileage. Some of the early non turbo diesel pickups could get well over 20 mpg on the highway, but they had no power.

This is due to timing. Since the old diesels only had one injection event(which is what made them louder), their injection timing could be advanced more. Due to tighter emissions and NVH requirements, new diesels have multiple injection events which does not allow you to advance timing as much. Advancing the timing also creates more NOx. The only way to remove it is via tuning which will also increase your fuel mileage like the 2 mpg I gained via tuning alone.