what's the difference between 6.9 and 7.3

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Jan 7, 2005 | 09:05 AM

greenego

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From: Brunswick, Maryland

what's the difference between 6.9 and 7.3

I've checked the books and both these engines are identical other than the exhaust valves. The part that puzzles me is that the bore and stroke are the same but the advertised displacement is different (6.9 and 7.3). How can they be different?

Jan 7, 2005 | 09:49 AM

barebackjake

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From: STEPHENVILLE,TX!!!!!

the differnce is .4

the combustion chambers in the 7.3 are larger and they put a differnt ex valve in it to compensate for it.

Jan 7, 2005 | 11:08 AM

greenego

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What does the size of the combustion chamber have to do with displacement?

Jan 7, 2005 | 12:25 PM

greenego

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Will the heads off of a 7.3 work on a 6.9?

Jan 7, 2005 | 01:05 PM

Pikachu

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From: Amarillo, TEXAS!

Quote:

Originally Posted by greenego

What does the size of the combustion chamber have to do with displacement?

The difference is 400cc, or 50 cc per cylinder. If one engine uses heads with 20cc combustion chambers, and the other engine's heads have 70cc combustion chambers, there is the 400cc difference.

Jan 7, 2005 | 01:51 PM

DannyP

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From: Gravel Switch, KY

I'm no 6.9/7.3 IDI expert, but there is a displacement difference. The 6.9 has 420 cubes and the 7.3 is 445 cubes. The 7.3 has a slightly larger bore than the 6.9, the thinner walls is why cavitation is primarily a problem in the 7.3. Or at least that's what I've been told.
Combustion chamber volume has nothing to do with displacement, even if the combustion chamber is cast into the piston as many diesels are. Displacement is figured as: 3.14 (pi) x bore radius squared x stroke length x number of cylinders. Compression ratio is: the volume of an individual cylinder divided by the volume of the combustion chamber : 1.
DannyP

Jan 7, 2005 | 02:06 PM

greenego

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From: Brunswick, Maryland

Thank you DannyP for your response and maybe the book that I was looking at had the wrong bore and stroke for one of these engines because it showed them as being the same for both. I still need to know if the heads are interchangeable from the 7.3 to the 6.9. Any info would be appreciated. Also , you are right, the combustion chamber size has nothing to do with engine displacement.