6.9 vs 7.3
6.9 vs 7.3
Senior User
Joined: Feb 2007
Posts: 191
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From: Denair, CA
The bore is different, the stroke is the same. I would not recommend boring a 6.9 out to the 7.3 size. You'd have very thin cylinder walls which could give you all sorts of problems. As it is, factory 7.3's suffer from cavitation issues.
Senior User
Joined: Mar 2007
Posts: 196
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I don't know that I would bore it all the way out.. i think that it would be about .100" bore.. I would go with .040" over hypereurtectic pistons. Leaves you some meat for your cylinder walls. The power difference between n/a 6.9L and 7.3L is not much. While you have it apart you should get the upgraded (& reusable) head bolts. If you go with a turbo that will trump any gain you might get from boring out to fit 7.3L
Post Fiend
Joined: Nov 2003
Posts: 21,285
Likes: 16
From: Nutter Fort, WV
A 6.9 bore is 4.000.
A 7.3 bore is 4.110.
Cavitation is less of an issue in the 6.9 because of the thicker cylinder walls, but it does still happen.
Since the 6.9 was not failing from cavitiation, SCA's were not used in them until the 7.3 started having problems.
So you may have a 6.9 block that has started the cavitation process, but still has lots of cylinder wall to eat through.
But at the same time, if you bore it 110 thousandths, you might run into the cavitation that has not come through the cylinder wall yet.
If you run into it, the block is junk or you install sleeves.
If you go the sleeve route, you might as well sleeve a 7.3.
A 7.3 bore is 4.110.
Cavitation is less of an issue in the 6.9 because of the thicker cylinder walls, but it does still happen.
Since the 6.9 was not failing from cavitiation, SCA's were not used in them until the 7.3 started having problems.
So you may have a 6.9 block that has started the cavitation process, but still has lots of cylinder wall to eat through.
But at the same time, if you bore it 110 thousandths, you might run into the cavitation that has not come through the cylinder wall yet.
If you run into it, the block is junk or you install sleeves.
If you go the sleeve route, you might as well sleeve a 7.3.
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New User
Joined: Aug 2007
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Will the old 6.9 drop right into my old 7.3 like a glove? I mean, will the intake and belts just bolt right up? and what is cavitation? and how do I look for it.
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Post Fiend
Joined: Nov 2003
Posts: 21,285
Likes: 16
From: Nutter Fort, WV
The 6.9 and 7.3 are interchangable.
Anything that bolts to one will bolt to the other.
Cavitation is cylinder wall erosion from the cooling jacket side of the cylinder wall.
You run and monitor SCA levels to prevent cavitation damage to the engine.
Cavitation is the result of vibrations of the cylinder wall because of the huge pressure differences between the intake and power stroke, which causes the cylinder wall to move.
Anything that bolts to one will bolt to the other.
Cavitation is cylinder wall erosion from the cooling jacket side of the cylinder wall.
You run and monitor SCA levels to prevent cavitation damage to the engine.
Cavitation is the result of vibrations of the cylinder wall because of the huge pressure differences between the intake and power stroke, which causes the cylinder wall to move.
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Freshman User
Joined: Aug 2006
Posts: 43
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From: Lilburn, GA
I'd like to hear more about the coolant and additives.
Last summer I lost the water pump on my F-350/7.3 on the way to Florida and promptly blew the top radiator hose from one clamp to the other. The temp gauge happily indicating "cool" the whole time.
By the time we got home to the NE Atlanta area, I had to have the engine re-built.
All that to say that when they ordered parts for what was labeled as, and was supposed to be a 7.3, turned out to have a 6.9 block bored .030 over. It runs like a champ, but I'm concerned about where I stand on cooling system protection. BTW Anybody know the system capacity on these?
Last summer I lost the water pump on my F-350/7.3 on the way to Florida and promptly blew the top radiator hose from one clamp to the other. The temp gauge happily indicating "cool" the whole time.
By the time we got home to the NE Atlanta area, I had to have the engine re-built.
All that to say that when they ordered parts for what was labeled as, and was supposed to be a 7.3, turned out to have a 6.9 block bored .030 over. It runs like a champ, but I'm concerned about where I stand on cooling system protection. BTW Anybody know the system capacity on these?
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New User
Joined: Aug 2007
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AIRTOMECH,
Do you like the 6.9 better than the old 7.3?
Any probs making everything fit with the 6.9?
I know these motors have alot of meat, but I like the idea of having extra with the 6.9. My motor is in a box truck, so mad performance is not my goal. Fuel eco. is what I want. I don't have a turbo and I can't seem to find a junk one. Is there anything that yall have found to be worth doing on the 6.9 other than a turbo?
Do you like the 6.9 better than the old 7.3?
Any probs making everything fit with the 6.9?
I know these motors have alot of meat, but I like the idea of having extra with the 6.9. My motor is in a box truck, so mad performance is not my goal. Fuel eco. is what I want. I don't have a turbo and I can't seem to find a junk one. Is there anything that yall have found to be worth doing on the 6.9 other than a turbo?
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mrblonde108
Pre-Power Stroke Diesel (7.3L IDI & 6.9L)
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Feb 3, 2008 10:28 AM