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6.7 Powerstroke vs 6.6 Duramax - Why I Chose Duramax (a research based comparison)
By: CowboyBenWade
They both perform equally well - this is not a performance comparison. I'm not going to talk about 0-60 times or which can tow up the Ike Gauntlet the best - if you want to see that type of content go watch TFL Truck on youtube. Both of these engines can do everything you would expect from a heavy duty truck. Comparing performance is just spitting hairs. However, these two engines differ significantly in design. I'm not a diesel mechanic, but I have assembled the following research that influenced my decision to go with the Duramax.
Powerstroke Selling Points & Innovation
Ford touts a number of technological 'advancements' to promote their Powerstroke 6.7 over the competition. Keep in mind that this is a relatively new engine that's newly designed by Ford for the 2011 model year. Previously, Ford's diesel trucks used Navistar engines. That's a whole separate discussion of what went wrong and all the issues with the navistar engines. Read more about Ford & Navistar here. Their notorious 6.0 liter was by far the worst. The 7.3 navistar was the most reliable, although underpowered.
After parting ways with Navistar, Ford needed a new large displacement diesel for their heavy duty trucks, so instead of finding another partner, they designed and built the 6.7 themselves from the ground up. This gave Ford the opportunity to innovate with the following features. This is not a full list; these are just major differences that I'm aware of.
- Reversed intake/manifold - Usually on a V8, the exhaust manifolds are on the outsides of the had. Ford has flipped this and now the exaust comes out where intake usually is. The turbo is between the two cylinder banks, and doing it this way puts the exhaust manifolds closer to the turbo. The goal is reduced turbo lag and better response. It may help to some degree, but I believe the effects are minimal. This is a major change in engine design for what I believe to be small benefit - Ford creating solutions to problems that don't exist. This optimizes turbo position, but now you have to route the intakes around to the outsides of the engine. If you look in the engine bay of the Powerstroke, it's full of tubes and stuff. The Duramax is a traditional design - intake in the middle and exhaust on the outside. The exhaust manifolds wrap around the back of each cylinder bank and empty into the turbo. I like the innovative thought process here with the Powerstroke, but I believe the complication it introduces is not worth what I see as marginal benefits.
- Steel pistons - Most engines use forged aluminum pistons for their strength and light weight. The powerstroke's pistons are made of steel and are much stronger. They used less material because steel is stronger than aluminum, so they are about the same weight as an equivalent aluminum piston. Does this matter? Not in any way that you're going to notice - it is a solution to a problem that doesn't exist. The Duramax uses aluminum pistons, and that's not a weak point on the Duramax. I just don't think the steel pistons make any significant difference.
- Compacted graphite iron (CGI) block - This material is 75% stronger than cast gray iron (which is what the Duramax block is made of). CGI is also lighter than cast iron. It's a better material, it's more advanced, and obviously higher tech than the Duramax block. But does this improvement matter to any degree that the owner would care? It makes the truck slightly lighter, but I doubt anyone would notice. The Duramax block is also extremely strong and can hold 1000hp without giving way.
Ford: Innovation without Improvement - a history lesson
Many people say that GM has not innovated - they still wax coat their frames (more on this later), and they still use pushrod V8 engines in their full sized trucks. It works why change it is the thought process at GM. GM v8 engines are simpler, reliable, and easier to work on.
Ford on the other hand, constantly chases new technology, and it's been a disaster. I don't believe Ford know how to make an engine. The Ecoboost line of small displacement turbocharged engines add mountains of complexity for no material gains. Compare Ford's 3.5 liter Ecoboost in the F150 to GM's 6.2 liter v8 in their full sized pickup - both are flagship engines. They are the highest power engines you can get in the F150 and Silverado 1500. Technically you could put the 6.2 in a 2500 pickup, but you could not do that with the 3.5. Ford doesn't even have a legitimate truck v8 engine. The 5.0 should never be in a truck because of the torque curve. It doesn't produce maximum torque until around 4500 rpm - not what you want in a truck. It's a sports car engine that Ford put in the F150 because they still wanted to have a v8 option.
The 6.2 GM v8 in the Silverado is an ideal engine for a truck - lots of low end torque.
I say all this to re-iterate the points above that Ford chases innovation but doesn't actually improve anything. Did Ford do the same thing with their innovative features of the 6.7 Powerstroke? From my assessment, it appears they did.
Ford on the other hand, constantly chases new technology, and it's been a disaster. I don't believe Ford know how to make an engine. The Ecoboost line of small displacement turbocharged engines add mountains of complexity for no material gains. Compare Ford's 3.5 liter Ecoboost in the F150 to GM's 6.2 liter v8 in their full sized pickup - both are flagship engines. They are the highest power engines you can get in the F150 and Silverado 1500. Technically you could put the 6.2 in a 2500 pickup, but you could not do that with the 3.5. Ford doesn't even have a legitimate truck v8 engine. The 5.0 should never be in a truck because of the torque curve. It doesn't produce maximum torque until around 4500 rpm - not what you want in a truck. It's a sports car engine that Ford put in the F150 because they still wanted to have a v8 option.
The 6.2 GM v8 in the Silverado is an ideal engine for a truck - lots of low end torque.
I say all this to re-iterate the points above that Ford chases innovation but doesn't actually improve anything. Did Ford do the same thing with their innovative features of the 6.7 Powerstroke? From my assessment, it appears they did.
6.7 Powerstroke and the CP4 fuel pump
Ford continues to use the Bosh CP4 fuel pump - a pump that's not designed to run on North American ultra low sulphur diesel. Sulphur provides some lubrication, and the CP4s eventually explode and send metal shards through the entire fuel system. This is a known issue - it's why GM stopped using the CP4 in the Duramax after 2017. Ram also stopped using the CP4. You would think Ford would do the same, since this is a widely know issue.
Ford has not switched to a different fuel pump because the 6.7 is designed around the CP4 from my understanding. I believe that fuel pump has been used in the 6.7 since it was introduced. To go to a different fuel pump, parts of the engine would have to be re-designed. New castings would have to be made, and it would be a big deal. Some say the failure rate is around 1%, but they given enough time, they are known to fail. It's hard to justify buying an expensive truck that has such a major issue that's been well documented for years. Diesel fuel pumps are a big deal - it's a major part of the engine. If it fails, it's a ten thousand dollar repair. And guess what - it has to be fixed with a new CP4 that may fail again. This issue alone makes me not want to buy a 6.7 Powerstroke.
Ford has not switched to a different fuel pump because the 6.7 is designed around the CP4 from my understanding. I believe that fuel pump has been used in the 6.7 since it was introduced. To go to a different fuel pump, parts of the engine would have to be re-designed. New castings would have to be made, and it would be a big deal. Some say the failure rate is around 1%, but they given enough time, they are known to fail. It's hard to justify buying an expensive truck that has such a major issue that's been well documented for years. Diesel fuel pumps are a big deal - it's a major part of the engine. If it fails, it's a ten thousand dollar repair. And guess what - it has to be fixed with a new CP4 that may fail again. This issue alone makes me not want to buy a 6.7 Powerstroke.
6.7 Powerstroke Oil Starvation
A very informative youtube video by Dave's Auto Center outlines bad engineering in the Powerstroke oil system. Dave details how, due to the way it's designed, oil has to travel a very long distance through tubes and passageways in the block before it reaches critical components. While it's doing that, air is being forced through the tubes which blows away previous oil films. He even shows how the camshaft and crankshaft should have better lubrication - the cam journals aren't lubricated through the main bearing journal holes like every other motor. Instead, the cam journals get their oil through a tiny little passageway in the cam itself.
I've read about a clatter on startup that Powerstrokes have because oil doesn't get where it needs to go fast enough. Dave, in the video, talks about spun main bearings that happen because they aren't getting enough oil. This seems like an issue that should not exist in this engine, and this really bothers me about the Powerstroke. I've read that it's quote "a 200k mile engine", and that's potentially due to this oil issue.
It just seems like this could be designed better. When I first watched this video, the first thing that came to my mind was the 3.5 Ecoboost and the cam phaser issues that happen around 60k miles. I've read things about that engine that suggest oil starvation, and that's why the camp phasers go so predictably.
There are lots of 6.7s with more than 200k miles, but get this. According to Google, Ford rates the Powerstroke to 300k miles, while GM rates to Duramax to go 500K miles. This is the manufacturer's estimated lifespan, and I suspect the Powerstroke is lower due to this oil starvation issue. It's going to wear those internal bearings for no good reason other than poor engineering. I genuinely believe GM knows how to make an engine that can lubricate itself effectively. The same cannot be said of Ford.
I've read about a clatter on startup that Powerstrokes have because oil doesn't get where it needs to go fast enough. Dave, in the video, talks about spun main bearings that happen because they aren't getting enough oil. This seems like an issue that should not exist in this engine, and this really bothers me about the Powerstroke. I've read that it's quote "a 200k mile engine", and that's potentially due to this oil issue.
It just seems like this could be designed better. When I first watched this video, the first thing that came to my mind was the 3.5 Ecoboost and the cam phaser issues that happen around 60k miles. I've read things about that engine that suggest oil starvation, and that's why the camp phasers go so predictably.
There are lots of 6.7s with more than 200k miles, but get this. According to Google, Ford rates the Powerstroke to 300k miles, while GM rates to Duramax to go 500K miles. This is the manufacturer's estimated lifespan, and I suspect the Powerstroke is lower due to this oil starvation issue. It's going to wear those internal bearings for no good reason other than poor engineering. I genuinely believe GM knows how to make an engine that can lubricate itself effectively. The same cannot be said of Ford.
6.7 Powerstroke Engine is More Complex
When you look at engine builders and people that re-purpose these engines for other things, what do they use? A Duramax. It's a simpler design than the Powerstroke even though both are V8 diesels. When I just look at the engines outside of the truck, I can instantly tell that I would rather work on the Duramax. It just looks like less is going on. From every year model of the Duramax, they are easier to rebuild, easier to put in other things, and less expensive to deal with.
The same has been true for GM V8s for decades. Nobody really used Ford engines the way they did GM small blocks and big blocks. And GM has a good, long history of making simple, well designed v8 engines. GM knows V8s, and for many decades they have been less complex than Ford's designs. And this is what I'm seeing with the diesels.
The same has been true for GM V8s for decades. Nobody really used Ford engines the way they did GM small blocks and big blocks. And GM has a good, long history of making simple, well designed v8 engines. GM knows V8s, and for many decades they have been less complex than Ford's designs. And this is what I'm seeing with the diesels.
Which one has a cleaner engine bay?
Open the hood on a Powerstroke, and it looks like tubes, pipes, fittings and stuff were just vomited out in random places. This has been an issue with Fords for a long time on many of their vehicles. The engine bay is just a disaster of wires and tubes. Even on an old Ford Ranger from 2001, I noticed this. That 4-cylinder engine had 8 spark plugs, and they provided no benefit. It still knocked so bad the piston chipped. The new ecoboost engines are just as bad - a mountain of tubes and wires. The Powerstroke is just another example of Ford just cramming everything into a small space without much thought.
The Duramax engine bay is pretty clean - far less stuff everywhere than on the Powerstroke. I like a clean engine bay. Part of good engineering is reducing the number of parts needed. The Duramax may still need to have the cab removed, but there just way less junk in there to look at when you open the hood.
The Duramax engine bay is pretty clean - far less stuff everywhere than on the Powerstroke. I like a clean engine bay. Part of good engineering is reducing the number of parts needed. The Duramax may still need to have the cab removed, but there just way less junk in there to look at when you open the hood.
Solid Front Axle(SFA Powerstroke) vs Independent Front Suspension(IFS Duramax)
Everyone knows that the solid front axle design is stronger and the independent front suspension rides better - I'm not debating that. Either of these two system are just as good as the other for the vast majority of use cases. The front suspension design is not a factor in my buying decision. I would actually prefer a solid front axle on these heavy duty trucks, but I'm fine with the IFS on the Duramax. The differences between these two are not significant for me.
If you are driving thousands of miles off road every month, maybe this might play into your decision making more than it does mine. I'm a regular user like the vast majority of people that buy these trucks. I'll be driving on the highway most of the time and towing on the highway. Maybe I'll go off road from time to time. Either system will work great for me.
If you are driving thousands of miles off road every month, maybe this might play into your decision making more than it does mine. I'm a regular user like the vast majority of people that buy these trucks. I'll be driving on the highway most of the time and towing on the highway. Maybe I'll go off road from time to time. Either system will work great for me.
Wax Coated Frame vs eCoat
I could not find any definitive information on forums as to which protects the frame better. The wax coat that GM uses is called Nox Rust - it's very good stuff, and it protects extremely well as long as it stays on. I've seen reports of it drying and flaking off. A company in Pennsylvania has a treatment for Nox Rust that it claims can keep it from drying and coming off. A lot of people do not like the Nox Rust, but again I've not been able to tell if trucks in the rust belt that use Nox Rust deteriorate faster than ecoated frame in the rust belt.
Ecoat is not without rust issues either. Since it is a hard coating, it will tend to flake off around welds and stress areas, and that's where rust will start. Ecoat is a much nicer finish, it doesn't collect dust and dirt, and ecoated frames I've seen generally look good. Everything rusts eventually; I don't have any real data on rust formation on ecoat. Ecoat is very thin, and rust does form on ecoated frames.
I prefer the idea of eCoat, but from the forums and reports online, I think Nox Rust is a great product. I would prefer my truck to be eCoated, but this is not going to affect my buying decision. I don't believe one is significantly worse than the other. A lot of people that have problems with the GM frame wax have sprayed fluid film or other oil based undercoatings on their frames - if you do this on a GM frame, it will dissolve the Nox Rust wax coating.
Ecoat is not without rust issues either. Since it is a hard coating, it will tend to flake off around welds and stress areas, and that's where rust will start. Ecoat is a much nicer finish, it doesn't collect dust and dirt, and ecoated frames I've seen generally look good. Everything rusts eventually; I don't have any real data on rust formation on ecoat. Ecoat is very thin, and rust does form on ecoated frames.
I prefer the idea of eCoat, but from the forums and reports online, I think Nox Rust is a great product. I would prefer my truck to be eCoated, but this is not going to affect my buying decision. I don't believe one is significantly worse than the other. A lot of people that have problems with the GM frame wax have sprayed fluid film or other oil based undercoatings on their frames - if you do this on a GM frame, it will dissolve the Nox Rust wax coating.
Diesel 2500 vs 250 Payload Comparison
If doesn't make sense to buy a diesel F250 - you should buy the f350 becuase the weight of the diesel engine in the Ford drastically reduces payload. It's very noticeable on the Ford for some reason. However, very little differences exist between the Duramax 2500 and the 3500 - payload ratings are very close. I don't have specific comparison numbers, but you can watch plenty of videos that explain this. They detail how for Ford and Dodge 2500/250 class, you would want to step up to the 3500/350. The exception is Chevrolet.
If you look under a Duramax 2500 and an F350, the rear leaf springs on the Duramax are way heavier - it has a lot more leafs. The F250 leap springs are not anywhere near as substantial. This is just speculation, but I'm guessing this has something to do with the impressive payload ratings on the Duramax 2500. I feel better about the heavier springs on the Duramax.
I would feel comfortable buying a Duramax 2500 off the lot, but I would really want to step up to the F350 if I was buying a Ford. Everyone knows they stock lots and lots of 2500s and F250s at dealership. You won't find a lot of 3500s or F350s just sitting around. You will have to special order those trucks. Also if you're buying used, a 2500 is going to be much easier to find.
These are my speculations as to by Chevrolet's Silverado 2500 does so well in payload. More payload is better, and you usually sacrifice ride quality for more payload. But this is just another mark in favor of the Duramax.
If you look under a Duramax 2500 and an F350, the rear leaf springs on the Duramax are way heavier - it has a lot more leafs. The F250 leap springs are not anywhere near as substantial. This is just speculation, but I'm guessing this has something to do with the impressive payload ratings on the Duramax 2500. I feel better about the heavier springs on the Duramax.
I would feel comfortable buying a Duramax 2500 off the lot, but I would really want to step up to the F350 if I was buying a Ford. Everyone knows they stock lots and lots of 2500s and F250s at dealership. You won't find a lot of 3500s or F350s just sitting around. You will have to special order those trucks. Also if you're buying used, a 2500 is going to be much easier to find.
These are my speculations as to by Chevrolet's Silverado 2500 does so well in payload. More payload is better, and you usually sacrifice ride quality for more payload. But this is just another mark in favor of the Duramax.
Which Diesel Does the Military Use?
Gale Banks is a famous diesel guy. He owns a shop, and he has a huge government contract to provided upgraded Duramax engines for the new JLTV (Joint Light Tactical Vehicle). This vehicle will replace the aging humvee. These diesels that banks is providing to the military are crate duramaxes that he is upgrading with products from his company. They won't have any emissions equipment because the military is exempt from those rules. OshKosh makes the JLTV - not GM. This means OshKosh chose the duramax as the powerplant over the Powerstroke. I obviously don't know if they had a choice or how they decided.
Why did the Duramax end up in military vehicles instead of the Powerstroke? I don't have the answers, but Gale banks prefers the Duramax. Gale Banks knows diesels perhaps better than anyone, so it's wise to consider his opinion.
Why did the Duramax end up in military vehicles instead of the Powerstroke? I don't have the answers, but Gale banks prefers the Duramax. Gale Banks knows diesels perhaps better than anyone, so it's wise to consider his opinion.
Why I Choose Duramax
Before I started researching, I wanted a Powerstroke 6.7. I was convinced they were a good product just by watching videos like TFL truck on youtube. But I didn't have any real mechanical assessments. Now that I know about the CP4 and the potential oil starvation issues, it's really hard for me to even consider getting a Powerstroke. The Duramax is built for longevity, and I have confidence in GM's ability to produce a V8 engine - whether diesel or gas - that lubricates itself well and holds up over time. I believe the Duramax is a simpler design and has less parts to fail.
About the Author
CowboyBenWade does interviews and lectures on a huge variety of topics, and he is an expert in a multitude of fields. His knowledge includes but is not limited to: engineering, chemistry, aviation, cooking, and farming.
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