I guess this is as good a place as any to make my first post on this site. As an owner of a 2009 Dodge/Cummins dually, and a driver of a 2011 F350 4x4 6.7 Cab & Chassis, I have experience with both trucks, and not just a 15 minute test drive around the block, or what someone's brothers friends uncle said, to compare each one to. Let me say that I'm not brand loyal, and have owned all 3 brands of trucks.

I've had the Dodge about 18 months now, completely trouble free, only visit to the dealer was for oil/filter change once, and a mandatory computer reflash. Consistantly delivers 14 to 16 mpg normal driving and have seen 17 on the hiway. Has never gotten 10 mpg as reported in this thread, even when hauling my 5000lb slide in camper. This is not the first Dodge/Cummins I've owned. My previous truck was an 02 2500 which I sold to my brother in-law. It currently has 179,000 miles and still going strong.

I work for a large utility on the west coast, and I've been driving Fords for my work trucks a little over 25 years now. I've been told that the company has purchased around 200 of the 6.7's to date from F250's up to the 550's. Hardly any problems have been reported according to a friend of mine who is a fleet mechanic. Mine has slightly over 6200 miles on it in the 3 months since I got it, and so far has been trouble free except for a major turbo lag Ford can't seem to fix yet. I understand the Cab & Chassis has a different turbo than the pickup does. The rest of the truck I really like, and I think Ford has done a great job with the 6.7 diesel. I will definately consider one when it comes time for a new truck.

As for comparing the 2 trucks, I'll just say it would be a tough choice if I had to choose one right now. Neither one in my honest opinion is clearly ahead of the other but your opinion may be different. Both have their advantages and disadvantages over the other but the differences are pretty small. Again this is only my opinion from driving both trucks daily, and comparing both brands in the driving I do.

I look forward to learning more about this truck, and hopefully hearing of an answer to the turbo lag issue.

Rich

 

Hey Rich1961, I've got a new cab/chassis only have 300 miles on it. I guess you are referring to a turbo lag on the same truck as mine. I guess I don't know about this turbo lag. But then again I've got no weight on truck just a frame with and engine and six wheels. I'll sure be interested to read anything you can post about other points of interest we may share with the cab/chassis. My driving routine is probably different than the vast majority of most, but still would like to hear anything you have to say. PM me if you prefer. Do you have 3.73 or 4.10?

 

I'm not discounting his story, especially since I have no experience with cab/chassis trucks and their unique turbo. That said, the majority of people who drive turbocharged engines have no real idea what turbo lag actually is. The common misconception is that is the engine has a turbo, and the driver experiences some sort of reproducible hesitation, that it's turbo lag. This simply isn't true.

Turbo lag is *not* a hesitation, or a lack of power for a short time. It's a *decrease* in power, or more correctly, a "slowness to increase in power". In a turbo lag scenario, the engine puts out power, usually about 60-75% of its potential at a given RPM, then surges to full potential after the turbo spools up. This is because without the turbo's forced air, the engine is producing less horsepower. Note that I said *less* and not *zero*. This is most commonly felt when going from idle or very low throttle to WOT, and it usually lasts about 1-2 seconds.

Our trucks have almost no turbo lag because of the twin vanes (on a single shaft) inside the turbo housing, effectively acting like a twin turbo. One set of vanes takes very little exhaust pressure to spool up the turbo, and the other takes full advantage of the high-pressure exhaust once it arrives. This means that the turbo is already spooled up at idle and while it's not creating much boost, it does not need nearly as long to spool up to its full potential. It's so quick, in fact, that only a trained driver would notice. I know that I don't feel any lag.

What our trucks *do* have is a built-in torque limiting mechanism. This is part of the computer's programming, and is done because going from 0 to 800 lb ft of torque in an instant would have very serious long-term effects on the entire drivetrain. It also give the transmission an extra few milliseconds to shift into the appropriate gear. Many drivers will interpret this as "turbo lag" because it shares a couple of the same symptoms.

The key differences are that in a turbo lag scenario, there is still 60-75% of engine power put to the wheels when "lagged", then a big surge of power. Also, this occurs even when going from part throttle (10-20%) to full. In a torque-limited scenario, there is no power to the wheels when limited, and the computer ramps power up in a much more linear manner, instead of the big "surge" of power. Also, it does not occur when going from part throttle to full, or when "rolling" the throttle.

I hope that helps clear it up... and I wish I could sticky that somehow so I don't have to keep typing different versions of it. Or, better yet, I wish paul would post an official explanation that is better than my former street racer / shadetree mechanic / computer geek version.

 

A rose by any other name...
Whether it is the turbo, the computer, or some combination of evil spirits, the delay in making power is annoying and sometimes dangerous.

I had a Corvette once, and it went from 0-max with no lag and the drivetrain never exploded. I am confident that drivetrain damage is not the reason for the lag, the loads the drivetrain sees would never exceed the torque needed to spin the back wheels, and the torque converter can buffer the rest.

 

this is not just another name for the same thing. Also, a corvette has nowhere near the same amount of torque that this engine does.

The reason that the differentiation is so important, is that turbo lag is unavoidable. The torque limiting mechanism *is* avoidable. It's also not dangerous, not even a little bit. Proper driving avoids this mechanism altogether - just roll the throttle instead of slamming it. Simple, right? I have almost 16k on my truck and I can't remember the last time I experienced and unexpected hesitation due to this torque limiter. I also have a very heavy foot.

Believe it or not, the torque converter is part of the drivetrain. that big of a change in torque stresses the torque converter... and the rest of the drivetrain, your confidence notwithstanding.

Now, perhaps the turbo equipped in chassis/cab applications does have some lag, I dunno.

 

FYI -- the 6.7L Diesel that comes in the cab chassis is rated at 300HP/660LB-FT & has a different Turbo (single stage) than the Pickup version.

 

Wow, that was interesting. Way over my head. I have noticed a little whining sound that you can hear at low speeds when accelerating. I don't know if this is the turbo or not. This darn truck is so quiet I hear sounds I never heard. My 04 diesel must have been noisier than I thought. I don't know if my chassis cab has turbo lag or not someone else would have to drive it and tell me. But I LOVE it. I do have a question about tire air pressures, but I'll start another thread and you guys can educate me..

 

Be careful not to engage the low range on your transfer case!!
It multiplies the torque by 3X, delivering around 2400 lb/ft to the drive train...talk about stress!

Also-My point with the Corvette was that the drivetrain is designed for the engine it is attached to, even the torque converter. I'm not sure how you thought I was implying I would put a diesel in a Vette, but you could with enough engineering time.

Actually, I wouldn't look down on Corvette torque, take a minute and look up the torque and HP for a new ZR1 and get back to us on how that compares to a new SuperDuty. It's lower but not much.

 

Thanks for a couple of informative posts. I have 22000 miles on my truck and I mostly agree with you. I can make my truck hesitate if I try but after driving it for a few thousand miles I learned to ease into the throttle for a second or so before going for the gusto...and I mean gusto. These trucks weigh over 8000 pounds. 800 lb ft of torque twisting at axle shafts and drive shafts from a standstill is a whole lot harder on the parts in a 8000 pound truck than a Corvette. Paul Bruckne said he was wondering what would break first when the tuners removed some of the programming safeguards. Don't get me wrong...I like the Vette...a lot

 

I must say that what djjoshuad described is exactly what my truck is doing. You have to use very light throttle, and after 1 to 2 seconds it's like flipping a switch when the turbo spools. Use heavier throttle and it just delays the time for the turbo to spool. It gets worse as you go up in altitude. Slowing down for a turn then trying to accelerate you get the lag, and then wham full boost with a transmission downshift. This can't be easy on the drivetrain either. Getting across traffic can be...exciting to say the least at times. I will add that it does this about 90% of the time. Sometimes it will accelerate what I would think it should be normally.
This is not my first turbo diesel. I've got over 200,000 miles driving 7.3's, and about 120,000 miles driving the Cummins. None of them behaved this way.
Rich

 

Jim,
Congrats on the new cab & chassis dually. That is going to be a very nice tow rig for you.
The truck I'm driving is a SRW 4x4 with 3.73's and the electric locker. 11,100 GVWR, weighs in at 10,700 with me, tools and equipment. Fuel mileage is averaging slightly over 14. Almost all of my driving is in the Sierras, so not the best area for getting good fuel mileage. But so far, I feel 14 is pretty good considering everything. So far,the reports I've heard from the fleet mechanics at work about the 6.7 are very positive, with hardly any issues.
Rich

 

Thanks Rich. Yeah I think it will be just what I've always wanted for pulling my 5er. It will be the truck's sole use. No pleasure driving as I have a little Ranger that is my everyday user. I'm still 6-8 weeks away from the bed being made and installed. With the hitch well being a "Special" modification I am kinda just waiting. I have the 4.10 LS in this and think it will offset any loss of power I have with the 300 HP engine. Is the whining noise probably the turbo? It goes away in like a half-second to one second when starting from a stop. I only really hear it when driving slowly. I actually like the sound, kinda sounds like what you think a truck should sound like. After reading this forum for several months, I can readily see how different my driving is from many who post here. Some of these guys will really find out what these engines can do. I have to chuckle at some of the things they do with these things. I guess they would be very dissappointed in my puny single turbo, de-tuned engine. Gosh it's quiet, great seats, great stereo and may even get decent fuel mileage. I LIKE it....OK maybe a little pleasure driving right now.

 

If you re-read my posts I thought I was clearly saying that drivetrains are designed for engine loads, suspension loads, weight loads etc. that the engineers anticipated for the application.

I did not say that a Corvette drivetrain was designed for or could handle the same loads as a HD pick up. But it would be very close.

I am taking exception to the concept that the Super Duty drivetrain is being protected by a designed in delay in power delivery. It isn't. Put your truck in low range and see how it responds to 2400 pound feet of torque.

Also-the correct term for how the vehicle (any vehicle) reacts to application of throttle from idle is called "throttle tip-in".

All new cars and trucks have programmed feel for throttle tip-in, mainly to avoid herky jerky when taking off. Most customers dislike erratic, sudden movements when they drive.

In the past, and maybe the present, GM would program their trucks with a much more abrupt tip-in to give the impression that they were faster than they really were. Ford has always programmed in a softer tip-in, mainly to please their older demographic.

Either way, my F450 has an erratic tip-in response, erratic response to varying throttle positions in general. I am hoping to re-flash and see if it helps.

Some have commented that all turbo engines have lag. Also not true.
The intake/turbo system can be designed for immediate response if that is the goal of the designer. Flash back to the Buick Grand National in the 80's. Big turbo, essentially zero turbo lag. You push the throttle, it ripped.

 

on one hand, you say that the vehicles are designed to handle the stress, but on the other say that there's no way that this stress-handling mechanism is part of the design.

Also, this is more than just simple tip-in. It is not present all the time. It is only in play when the driver gives are very large change in throttle input. It has been stated *by ford engineers* that this is a torque limiting mechanism. Why argue that point?

 

I was trying to stay out of this...

I completely agree here. These trucks are put through absolute hell during the design process to ensure they won't get broken when someone puts a load on it. There is no driving condition that should be possible with one of these trucks that will break driveline components. This is true even in 4-low.

Agreed with GM products. My '09 G6 I drive at work seems very fast of the line because of this. It's not bad at WOT, but the tip-in does imply more power at first impression.

I have only noticed an erratic tip-in when the engine is warming up. Last night when I started my truck at 16° F after sitting for a day and a half, the truck didn't want to give me any power. I feel this is normal, as this is the way it always behaves when the engine is cold. I believe this to be a protection feature to discourage making lots of power until it starts to warm up a bit. Disconcerting when first finding this out when pulling out into traffic, though.

Once warmed up I find mine to be very consistent. Is yours not this way?

I have not driven a GN, but I have driven several other turbo'd vehicles, including the new EcoBoost V6.

I strongly disagree with the statement that you can design a turbo engine with no lag. The simple physics of how it all works, how the turbo has to accelerate from essentially zero to upwards of 100,000 RPMs to provide peak boost in most cases takes time. Not much in most cases, but it will take time to spool up. An engine can't make peak power without peak boost in most cases, and the engine doesn't produce peak boost until the engine is given lots of throttle.

The easiest way I've seen to demonstrate turbo lag is at mid-range RPMs in "M" mode. Pin the throttle to the floor and the power comes on in a direct relationship to the boost pressure. It takes less than a second, but there is a bit of lag there.

I've done the same on an EcoBoost test drive, which has two very small turbos in comparison to what we have. And they still require time to spin up.

I highly doubt the GN had a faster spooling turbo than the ones on the EcoBoost engine, and I was able to notice some lag with that one. The modular V8s in comparison have no tip-in lag when at speed. When the engine is in 1st or 2nd gear at mid-range RPMs and you pin the throttle, it's like flipping a switch. No delay programmed in those circumstances.

I believe the tip-in delay is there to provide for a smooth driving experience as opposed to the herky-jerky driving seen in older engines with mechanical throttles. These trucks are relatively easy to drive smooth, and I think that's intentional.