I have an 85 f250 with a 6.9 (main bearing is knocking) so I'ma put a new engine in.
My questions:
As for fuel economy, people have said to me that the 7.3 turbo will do better fuel economy than my 6.9 non turbo.
Who thinks that's true? will a non turbo 7.3 be better or worse on fuel than my 6.9; than the 7.3 turbo?
Is turbo predominantly a fuel economy benefit or a power boost?

Thanks to all for the advice.

J

 

The 6.9 & 7.3 are the same engine just the 7.3 is bored out a little. The 6.9 w/turbo vs. 7.3 w/turbo isnt a big difference. The 6.9l is a little more reliable because the 7.3 is known for its cavitation issue from the cylinder walls being too thin and the coolant will cause pinholes in the walls causing a hydrolock which in turn ruins the motor. A turbo does increase fuel economy, but it is a predominate power booster. As long as you don't have clubfoot like me . You will gain HP and fuel economy. The 7.3 & 6.9l N/A will make the same power, same fuel economy and same everything else pretty much. The 6.9l and 7.3l had a power difference of 5 hp N/A. I would rebuild the 6.9 over buying a 7.3 because I trust the 6.9. My buddy has a 7.3 and I trust his rig, but I trust my 6.9 more. If you take the 6.9l rocker arms off it and throw on a set of 7.3 rockers, that makes the 6.9 even better. There are very subtle differences between my 6.9l w/Banks turbo (nonwastegated) vs Jared's(my buddy) 7.3 w/Banks Turbo (nonwastegated). We have the same gears, same turbo. I have a 4 spd manual, he has a E4OD so thats the only reason he gets better fuel economy than I do on the highway, but its 1 or 2 mpg. Nothing major.

 

Yea, its the turbo that CAN save you fuel... If you drive the same you would get better fuel economy.

Note on the strength of the engine though, a FACTORY turbo 7.3 engine is built tougher; they upgraded several major components (excessively, IMO) for the turbo, so it makes a difference whether you're swapping in a 7.3 with an aftermarket Vs. stock turbo.

 

Its just your foot that will end up making you loose money, I do. My engine acted as if it had a turbo from the way it would get really quiet after the new exhaust system. But the turbo is fun lol. I only have driven my buddy Jared's 7.3 and I could always hear that turbo wind up even on the highway, he has a 4" exhaust that was on when he bought the truck. I got on it one time and only got 15 mpg. I drove again to Billings and drove it careful for 930 miles roundtrip to Roundup(50m north of billings) and it got 19 mpg on the highway....

 

How do you know the main bearings are knocking on one of these engines. Mine has some knocking sounds at certain RPMs, but if I change the engine speed, the knocking sounds will go away. The sound is also faint and not very scary sounding at all.

I had a chevy cavalier with a 4 cylinder and when it started knocking it was so obvious that something terrible was going top happen any second if it wasn't shut down, but a diesel thats knocking might just sound normal to someone like me.

So I am being sincere when I ask, how do you know its got bad bearings and not just a normal sound, or faulty injector?