6.7 or 5.9 rebuild?

This thread is full of fail, when did this turn into Cummins Forum?

takedown95 said:
The head gasket can be an issue again because of the longer stroke and cylinder pressures.
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Or it could be the siamese water jacket.

takedown95 said:
The 6.7 head flows more then a 5.9 and can spool a bigger charger.
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Or it could be the larger bore.

takedown95 said:
They run the 5.9 crank to lower cylinder pressure and reduce torque saving the rods.
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Shortening the stroke will not necessarily decrease cylinder pressure.

takedown95 said:
....but if you're asking if a modded 5.9 will produce more hp and tq then a stock 6.7...of course it will.
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A modded 5.9L will produce more torque than a 6.7L? Didn't you just contradict yourself?

SPEAKSUP said:
Even 12V rod's in a 6.7 break at around 900 Bean's and Brown's have both destroyed them.
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Cast rods have held over 1200hp @ the crank with a 4.88" stroke, and both instances you mentioned the rods failed at well over 900hp.

SPEAKSUP said:
Also pushrod's in the 6.7 is another weak link when you want RPM .
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This takes the cake, I expect no less from someone that thinks using a longer rod increases cubic inch.
 
bracker8040 said:
This thread is full of fail, when did this turn into Cummins Forum?



Or it could be the siamese water jacket.



Or it could be the larger bore.



Shortening the stroke will not necessarily decrease cylinder pressure.



A modded 5.9L will produce more torque than a 6.7L? Didn't you just contradict yourself?



Cast rods have held over 1200hp @ the crank with a 4.88" stroke, and both instances you mentioned the rods failed at well over 900hp.



This takes the cake, I expect no less from someone that thinks using a longer rod increases cubic inch.
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I was under the impression that the 6.7 heads did flow a lot more than the 5.9 which I'm sure the 6.7 displacement helps with spoolup but the head has a lot to do with it correct?

Have there been a lot of rod failures before 750/1500 ish on the 6.7? I read the high hp 6.7 thread and saw a handful of guys above that level but not enough to make me feel safe.

What is your overall opinion the. On the swap or build?
 
For reference I have a stock 6.7 motor 2.6 puller making almost 900 to the wheels maybe more.. still doing stronk 4800 out of the hole 4100-4300 down track. Stock rods
 
smokeblack13 said:
I was under the impression that the 6.7 heads did flow a lot more than the 5.9 which I'm sure the 6.7 displacement helps with spoolup but the head has a lot to do with it correct?

QUOTE]

the same head port with nothing changed.... just change bore size and it flows more....always. the head itself is quite possibly not any better than the 5.9.
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bracker8040 said:
Or it could be the siamese water jacket.
I didn't say it was the only thing

Or it could be the larger bore.
Yes, the increased volume in the cylinder will also help spool a bigger charger

Shortening the stroke will not necessarily decrease cylinder pressure.
All other things being equal it will

A modded 5.9L will produce more torque than a 6.7L? Didn't you just contradict yourself?
I said stock 6.7 so, no I didn't
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Does that make you feel better? :Cheer:
 
smokeblack13 said:
What is your overall opinion on the swap or build?
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Rebuild the 5.9L, get a set of good cast rods, use the earlier piston/injector combo and common sense and you will be fine. And take everything you read on the internet with a grain of salt, including this.
 
takedown95 said:
Hmmm...now how might one decrease compression? Possibly by decreasing the stroke length?
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So you think it best for street use to drop the piston 0.080" down in the cylinder with a 5.9L crank yielding a 14:1 compression ratio? Or, are you using cynicism to hide the fact you are having to eat your words?
 
I love the idea of starting my daily driver with starting fluid when it's 95* out. Smart idea.
 
bracker8040 said:
So you think it best for street use to drop the piston 0.080" down in the cylinder with a 5.9L crank yielding a 14:1 compression ratio? Or, are you using cynicism to hide the fact you are having to eat your words?
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Excuse me? I never suggested he reduce his cylinder pressure. I simply stated why people do it.
 
takedown95 said:
Excuse me? I never suggested he reduce his cylinder pressure. I simply stated why people do it.
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You said;

takedown95 said:
They run the 5.9 crank to lower cylinder pressure and reduce torque saving the rods.
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Now this seems like the hardest way possible to achieve lower cylinder pressure, a simple head gasket change or piston crown machining would create the same results.

Back-pedal all you want, they're your words not mine.
 
I would just rebuild your 5.9 with better rods and a cam to go the easy way. Want to spend more do the 6.7 and let it eat.
 
takedown95 said:
Excuse me? I never suggested he reduce his cylinder pressure. I simply stated why people do it.
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Seems foolish to over suggest an over complicated set up when a factory rebuild will suffice with 12/24 rods.

I'm guessing you will suggest a billet block next.
 
If I ever had a choice between the two I'd go 6.7. As a matter of fact I have an 07 5.9 with 180k and exhaust Brake. Buy a 6.7 and this engine is yours.
 
My 6.7 pulls harder than the 5.9 did (the 03 in my sig). Same Smarty settings, the torque down low is very noticeable. The 351v is laggier than the 341, but that's possibly more a function of I can't get my computer and the VGT controller to work together, so it's non-variable right now.

It wasn't cheap; the engine was 6700 I think (including the 500 core; no 6.7 to send back so I ate that). Other than that, just the GDP intake horn and getting the 5.9 injectors tested is all I did. Oh and the cooler delete as well as a 5" exhaust. And South Bend clutch.
 
My buddy has a 6.7 with 530k miles on it. He uses it to pull a 3 car trailer several times a week. It pulls very well and still runs amazing, but I still have my doubts about reliable high horsepower 6.7's.
 
I think my plan is to build my 5.9 balanced bottom end 12v rods, head studs, intake manifold machined off, bigger valves, port work qsb 480 pistons, 03 exergy injectors, rocker studs. Any other suggestions? Should I forget the 12v rods and pony up the dough for billet?
 
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