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GM News: GM: Diesel For The Light-Duty Trucks Are Under Consideration


William Maley

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With Ram offering a small diesel and Ford announcing that next F-150 will be considerably lighter, GM is considering all options with their pickups to raise fuel economy. One of those options happens to be a 4.5L Diesel V8 that was planned to go into their pickups five years ago.

Steve Kiefer, GM's vice president of global powertrain tells Automotive News that GM is considering dusting off that engine and slip it into their new trucks.

"We are looking closely at diesel entrees in that segment. In fact, I heard the terms 'dust off' that 4½-liter at one point. That is certainly one of the options. Clearly, we have a portfolio of diesel engines," said Kiefer.

Source: Automotive News (Subscription Required)

William Maley is a staff writer for Cheers & Gears. He can be reached at william.maley@cheersandgears.com or you can follow him on twitter at @realmudmonster.


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YES YES YES, Put that bad boy into the Full Size SUV's line. Tahoe, Suburban, Yukon, Yukon XL and Escalade, Escalade ESV would do well with this.

Class leading HP, Torque and MPG would be awesome for GM.

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Forget the 4.5 Duramax Diesel -- the cost, complexity and mass of a four cam V8 isn't worth the specific output improvement. A very simple solution is to simply build on the Pushrod-32v Duramax 6.6 architecture. Instead of building a smaller V8, just take two cylinders off the Duramax 6.6. The resulting 4.95L V6 will make about 300 bhp / 575 lb-ft. That's close enough to the projected 310 bhp output of the 4.5 they were developing and more importantly superior in stump pulling torque (which is what really matters in a truck). While they are at it, why not a 3.3L V4 with 200 bhp / 383 lb-ft? The beauty of a cam-in-block + pushrod design is that you can use a V configuration with no penalty in terms of number of camshafts or phasers needed. The Duramax 6.6 and/or it's 6 or 4 cylinder engines are already reverse flow engines where the exhaust exits the valley of the Vee permitting the efficient use of a single turbo instead of two smaller ones flanking the engine. Unlike the 4.5, the 4.9 and 3.3 Duramax 6.6 derivatives will share the piston, connection rods, wrist pins, valves, springs, lifters, pushrods, bolts and a huge number of other parts with the 6.6L sibling.

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I agree with Dwightlooi, GM should just use the existing 6.6 and scale it down as a V6, V4 and really kick ass in the auto industry. People would buy up every 4.95L V6 powered Yukon Denali and Tahoe with this engine. I also can see huge sales in both full size and mid size pickups with a 3.3L V4 Duramax Engine.

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Forget the 4.5 Duramax Diesel -- the cost, complexity and mass of a four cam V8 isn't worth the specific output improvement. A very simple solution is to simply build on the Pushrod-32v Duramax 6.6 architecture. Instead of building a smaller V8, just take two cylinders off the Duramax 6.6. The resulting 4.95L V6 will make about 300 bhp / 575 lb-ft. That's close enough to the projected 310 bhp output of the 4.5 they were developing and more importantly superior in stump pulling torque (which is what really matters in a truck). While they are at it, why not a 3.3L V4 with 200 bhp / 383 lb-ft? The beauty of a cam-in-block + pushrod design is that you can use a V configuration with no penalty in terms of number of camshafts or phasers needed. The Duramax 6.6 and/or it's 6 or 4 cylinder engines are already reverse flow engines where the exhaust exits the valley of the Vee permitting the efficient use of a single turbo instead of two smaller ones flanking the engine. Unlike the 4.5, the 4.9 and 3.3 Duramax 6.6 derivatives will share the piston, connection rods, wrist pins, valves, springs, lifters, pushrods, bolts and a huge number of other parts with the 6.6L sibling.

What would the timeframe testing-to-production be like with this plan?

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Forget the 4.5 Duramax Diesel -- the cost, complexity and mass of a four cam V8 isn't worth the specific output improvement. A very simple solution is to simply build on the Pushrod-32v Duramax 6.6 architecture. Instead of building a smaller V8, just take two cylinders off the Duramax 6.6. The resulting 4.95L V6 will make about 300 bhp / 575 lb-ft. That's close enough to the projected 310 bhp output of the 4.5 they were developing and more importantly superior in stump pulling torque (which is what really matters in a truck). While they are at it, why not a 3.3L V4 with 200 bhp / 383 lb-ft? The beauty of a cam-in-block + pushrod design is that you can use a V configuration with no penalty in terms of number of camshafts or phasers needed. The Duramax 6.6 and/or it's 6 or 4 cylinder engines are already reverse flow engines where the exhaust exits the valley of the Vee permitting the efficient use of a single turbo instead of two smaller ones flanking the engine. Unlike the 4.5, the 4.9 and 3.3 Duramax 6.6 derivatives will share the piston, connection rods, wrist pins, valves, springs, lifters, pushrods, bolts and a huge number of other parts with the 6.6L sibling.

A few questions. I thought you had said on another thread that diesels benefited most from using DOHC due to the superior breathing offered from DOHC and the lack of air obstructions in diesels. It would certainly make intuitive sense that an engine that always runs lean would benefit most from using a DOHC valvetrain. Is the smaller packaging, lower parasitic friction of a pushrod V engine still sufficient to overcome the higher specific output / better breathing / lower reciprocating mass of a DOHC even in a diesel - at least in your estimation?

The upcoming Canyon/Colorado are going to offer a 2.8L duramax, which is VMRA208 puts out ~200hp (possibly less after US emissions are added) and weighs ~520 lbs. The ecodiesel that Chrysler is using in the Grand Cherokee and the Ram 1500 is a Vm Motori A630 which puts out ~240hp and weighs ~500 lbs. Dimensions really don't look like the I4 does much to save space over the V6. So, at the end of the day, if these were the two options why on earth would GM choose the I4 over the V6? Is it a cost issue? Volume production issue? Will an I4 with a lower power output produce better fuel economy numbers of a more powerful V6? My impression is that perhaps this would be true in a gasoline engine with a throttle, but without a throttle does this logic still apply to a diesel?

The dimensions of the ecodiesel, which is a DOHC 3.0L V6 are 695 mm (27.36 in) in length, 729 mm (28.7 in) in width and 697.5 mm (27.46 in) in height. Do you have the dimensions of the 6.6L duramax? And your proposed 4.95L smaller duramax, what would the proposed weight/dimensions of that engine be? Would it be appreciably larger and heavier than the ecodiesel?

Your proposal seems to be fantastic on its face. 2 different displacement diesel engines for the half tons which would *easily* give them best in class fuel economy across all models. What are the drawbacks to doing something like this? Is there any limitation from attempting to shrink the current duramax architecture? How difficult would it be to add balance shafts to a V6 at that angle? Does it being a heavier diesel engine make any difference with balance shafts / NVH? Very genuinely curious since on its face your idea seems to result in engines that put out near *perfect* power/torque numbers for a half ton pickup, all built on an engine architecture that already exists and could be extremely modular - thus significantly reducing costs.

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  • 2 weeks later...

Your proposal seems to be fantastic on its face. 2 different displacement diesel engines for the half tons which would *easily* give them best in class fuel economy across all models. What are the drawbacks to doing something like this? Is there any limitation from attempting to shrink the current duramax architecture? How difficult would it be to add balance shafts to a V6 at that angle? Does it being a heavier diesel engine make any difference with balance shafts / NVH? Very genuinely curious since on its face your idea seems to result in engines that put out near *perfect* power/torque numbers for a half ton pickup, all built on an engine architecture that already exists and could be extremely modular - thus significantly reducing costs.

It is not hard to add balance shafts... you can simply put one in the oil pan or above the camshaft. There is a difference between shrinking -- as in making the pistons, combustion chambers, valves, etc. smaller -- and simply removing two cylinders and changing the crank pin angles. The latter is easy because all the combustion and aspirational work is done. A diesel has heavier pistons and rods. They need bigger weights on the balancer. It doesn't affect refinement as much as it affects engine resposiveness. Still... the same applies to the 4.5 DOHC and the difference is immaterial between a 4.5 and a 4.95L engine. In fact, the 4.5 is trickier because it is a 72 degree Vee engine -- which is worse from a balance standpoint than a 60 degree (unbalance shafted) or a 90 degree (with balance shaft). This is why V6es are usually either 60 degree (for good intrinsic balance) or 90 degree (when derived from a 90 deg V8 or when it is desirable to stuff a supercharger or turbo(s) in the valley.The 72 degree angle was chosen entirely for packaging reasons to make the fat DOHC heads fit in the same width as a 90 deg pushrod design, and still be wide enough in the valley for the single turbo to fit

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They need a 3 liter V6 diesel in a bad way, they just don't see it yet. There are other diesel V6s out there with 240ish hp and 425 lb-ft, whether they be in an Audi A6 or a Ram 1500, the numbers are similar. That is the sort of engine GM needs, with an 8-speed transmission you can keep the engine in it's power band and you'd have adequate acceleration, plus the fuel economy.

Rumor is Ford is planning a diesel V6 with a 10-speed automatic for the F150, add that with the drop in weight and they are surely to have over 30 mpg in a pick up, if GM's best offering is 23 mpg, they are screwed.

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Forget the 4.5 Duramax Diesel -- the cost, complexity and mass of a four cam V8 isn't worth the specific output improvement. A very simple solution is to simply build on the Pushrod-32v Duramax 6.6 architecture. Instead of building a smaller V8, just take two cylinders off the Duramax 6.6. The resulting 4.95L V6 will make about 300 bhp / 575 lb-ft. That's close enough to the projected 310 bhp output of the 4.5 they were developing and more importantly superior in stump pulling torque (which is what really matters in a truck). While they are at it, why not a 3.3L V4 with 200 bhp / 383 lb-ft? The beauty of a cam-in-block + pushrod design is that you can use a V configuration with no penalty in terms of number of camshafts or phasers needed. The Duramax 6.6 and/or it's 6 or 4 cylinder engines are already reverse flow engines where the exhaust exits the valley of the Vee permitting the efficient use of a single turbo instead of two smaller ones flanking the engine. Unlike the 4.5, the 4.9 and 3.3 Duramax 6.6 derivatives will share the piston, connection rods, wrist pins, valves, springs, lifters, pushrods, bolts and a huge number of other parts with the 6.6L sibling.

A few questions. I thought you had said on another thread that diesels benefited most from using DOHC due to the superior breathing offered from DOHC and the lack of air obstructions in diesels. It would certainly make intuitive sense that an engine that always runs lean would benefit most from using a DOHC valvetrain.

IIRC; the emphasis was on 4-valve heads for air flow, not DOHC. Duramax is an IBC 4-valve design- best of both worlds in some instances.

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