6.7 vs. 5.9 - Page 2 - Dodge Diesel - Diesel Truck Resource Forums

3rd Gen Engine and Drivetrain -> 2007 and up 6.7 liter Engine and Drivetrain discussion only. PLEASE, NO HIGH PERFORMANCE DISCUSSION!

6.7 vs. 5.9

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Old 01-08-2007, 05:38 PM
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The emissions are lower for a bigger engine for the same HP? That doesn't sound right. Power shouldn't the deciding factor. They could have just derated the 5.9 power wise and re-done the head. I'm sure emissions would come more into line and the 5.9 would still work. The bigger CID because everyone else engine is that big. It’s nothing about lowering emission and saving fuel. If everybody was serious about lowering emission it would be criminal to adjust/tweak the engine period. How many new 6.7's are gonna have a new programs/fuel boxes and other power adding tweaks? Lots, so what are we really lower emissions. No. I work a lot with commercial power units in the states and know that they look’s at the Nox, and the co2 levels pretty closely. Lots of engines world wide are running at reduced power just cause of emissions. It will more than likely sometime in our futures, our vehicle emissions will have to be checked on a regular bases.
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Old 01-08-2007, 05:58 PM
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JKM:

Thanks for your input. This problem has been solved by way of "Admin. Editing!"

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Old 01-08-2007, 09:14 PM
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Theres an article in the new diesel power magazine, talking about what i posted, a larger engine doesnt have to work as hard to produce the same power, and thus lowers internalcombustion temps to lower nox emmisions. Wes
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Old 01-08-2007, 10:37 PM
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I understand that but their CO and co2 numbers go way up for the same power. Its a trade-off. I bet that they are using number of co vs mass air (engine air flow) flow to rate the engine for the new emission standards. Its just working the numbers. If they really want to do the right thing it would be to downsize the engine and put more gears into the truck. The europe is way ahead of us in this area.
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Old 01-09-2007, 12:28 AM
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I agree Mike.. Less Nox in ppm, but more millions of effluent. Net change=-100%. EPA is run by the petroleum companies and has nothing to do with being efficient. We are getting worse mileage today than in the 70's.
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Old 01-09-2007, 10:22 AM
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The main issue with the DC 6.7 engine (as I see it) is that the cylinders have been siamesed to allow for the increased bore without increasing engine length (introducing possible cooling and wear issues). Siamesed cylinder engines generally are not as long lived (e.g. chevy 400 small block), because the thermal expansion of cylinders under load is less symmetrical (increasing ring and piston wear). I hope this cost cutting move for the DC version doesn't doom the 6.7 to a service life more like its V8 diesel competition.
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Old 01-14-2007, 10:38 PM
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DC states the service life of the 6.7 is 350,000 miles. I believe that's the same as the 5.9.
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Old 01-15-2007, 06:25 PM
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You guys also need to realize that there is always a game called "bigger is better". You know " mine is bigger than yours" or I can haul more than you, or my ( read anything especially mileage) is bigger. All the auto industry plays this game. the big deal here is the 07 EPA emissions ruling. It's not just for pickups but the all diesels; marine, semi, generator, heavy equipment, public transportation, just like the unleaded deal in the 80's.
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Old 01-16-2007, 01:11 AM
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As an engineering student I have taken a few courses in thermo and internal combustion engines.... the reasoning for the larger displacement like others have mentioned is to lower the egt's which in turn will lower the nox formation since the reaction occurs at higher temps. And I wouldn't worry about the changes too much in regards to the boring out of the cylinders and them being siamesed (I think I've read that they actually arent... but anyways..). The engineers at Cummins aren't stupid and will have taken that into account when designing the block casting. It doesnt' take much to run a heat flow analysis to find out how much it deforms at high temps. I'm pretty sure they don't hire rookies like me either! Have faith, they've been doing what they've done best for how many years... you have to admit they are good at what they do!
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Old 01-16-2007, 09:29 AM
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Originally Posted by bigsnakebud View Post
You guys also need to realize that there is always a game called "bigger is better". You know " mine is bigger than yours" or I can haul more than you, or my ( read anything especially mileage) is bigger. All the auto industry plays this game. the big deal here is the 07 EPA emissions ruling. It's not just for pickups but the all diesels; marine, semi, generator, heavy equipment, public transportation, just like the unleaded deal in the 80's.
Fred
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Fred:

What is surprising to me is that Cummins goes to the 6.7 but their initial H.P./Torque ratings on these engines are not any higher than the 5.9 was??
I believe the H.P. will be initially "set" at 325, while Ford's new 6.4 PSD will be 350 and Chevy's 6.6 Duramax at 365 H.P. I have driven a new 07' Cab and Chassis and to be honest the power is not all that great. I do not feel that it is any better than my 06' was in stock form.

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Old 01-16-2007, 10:24 PM
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6.7 L controls increased temperature.

Increased combustion temperatures produce increased undesireable emissions in the exhaust. In the 6.7 L Cummins, a small percentage of its own exhaust gas is being recirculated into the fresh air intake to the combustion chamber in order to lower the temperature of the exhaust gas resulting from diesel fuel combustion. Less total oxygen in the total air charge means less burning fuel, resulting in less power for a particular displacement and less temperature rise producing less emissions. That is why the power output of the 5.9 L and 6.7 L are similar. The 6.7 electronic engine was introduce to be within the new emission standards, which the 5.9 displacement electronic engine could no further efficiently attain.

The competition performance boys will be able to take the 6.7 Cummins and wring enough torque out of her to unseat the new Duramax engines off her temporary pedestal. I do not care who is the leader of the competition events as long as it is an inline six cylinder configuration diesel engine in the lead. Bring on the New Cummins and show those V8 configured diesel engines that they are definitely not the best truck engines.
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Old 01-17-2007, 09:22 AM
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Originally Posted by John_P View Post
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Fred:

What is surprising to me is that Cummins goes to the 6.7 but their initial H.P./Torque ratings on these engines are not any higher than the 5.9 was??
I believe the H.P. will be initially "set" at 325, while Ford's new 6.4 PSD will be 350 and Chevy's 6.6 Duramax at 365 H.P. I have driven a new 07' Cab and Chassis and to be honest the power is not all that great. I do not feel that it is any better than my 06' was in stock form.

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John, your power numbers are not exactly right. The 6.7L in the cab & chassis with either transmission is 305/610. On the pick-ups it is 325/610 on 6-speed manuals, and 350/650 on 6-speed automatics.
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Old 01-17-2007, 09:53 AM
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John
Luke can correct me as I have not driven the new c&c out of fear of falling in lust and I want to see the "new" pickups later this year but I have been told the 6.7 combined with the asin and I hope the 68rfe are so smooth and quit that it doesn't feel like it is quick but the speedo tells another story.
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Old 01-17-2007, 10:22 AM
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Originally Posted by Mike Holmen View Post
I understand that but their CO and co2 numbers go way up for the same power. Its a trade-off. I bet that they are using number of co vs mass air (engine air flow) flow to rate the engine for the new emission standards. Its just working the numbers. If they really want to do the right thing it would be to downsize the engine and put more gears into the truck. The europe is way ahead of us in this area.
CO2 is not a "measured polutant" these days.
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Old 01-17-2007, 10:45 AM
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Thanks for all your input guys! I appreciate it.

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Luke:

You are probably right on the H.P. numbers you posted. I was getting my numbers from some early literature from one of the diesel rallies late last summer. Thanks for the help.

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