New Duramax 4.5 Liter Diesel

Popular Mechanics just had this short article about GM's new lighter & more compact 4.5 liter V8 diesel with 310HP & 520 ft-# of torque. It has 70 fewer parts than GM's 6.6 ltr. diesel. "Compact Torque: Pickup trucks need better fuel economy, so automakers are responding with light duty diesels. GM's innovative 4.5 liter duramax V8 will be available on 2010 Chevy/GMC 1500 models and maybe others. The unique 72-degree V configuration allows for tighter packaging under smaller hood spaces. The block is compacted graphite iron, which is stronger than aluminum and lighter than traditional gray cast iron. The cylinder heads have integral exhaust manifolds, and the airflow is backward: The cam cover/intake manifold feed the cylinder heads' top ports, and exhausts directly into the V-valley. The EGR cooler, turbocharger and oxidation catalyst are mounted in the valley to maximize thermal efficiency and shave weight by eliminating parts. The goal? A better than 25% mpg bump over gas V8s."

I wonder why GM didn't use an aluminium block with cast iron cylinder sleeves. That'd be the ticket for lower weight, and strong cylinder bores.

Mr Mopar- one problem with al blocks is that the main bearing saddles are difficult to make last. The steel backed bearings tend to fret on the al saddle surface, ultimately losing crush. The difference in thermal expansion coefficients also can make for relative motion and fretting. Especially with the high bearing loads seen on diesels. I'm sure there are designs out there that work, but they are likely tricky

I like the idea of the exhaust going into the valley. A vee block turbo diesel has always been a plumbing mess with two manifolds and where the hell to put the turbo? Over the tire like a 6.5 gm?? But this only applies if you are committed to making a vee block. 4.5 liter v8? Why? 4.5 could be made in a smooth running straight six or even straight 5. Parasitic losses go up as you increase number of cylinders and keep displacement the same. I guess in-lines are out the window with pickup truck windshields extending half way over the engine bay. Styling trumps design again. Rats..

-Eric

Ski in NC said:

4.5 liter v8? Why? 4.5 could be made in a smooth running straight six or even straight 5.

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Status and tradition. Americans like their V-8 engine just like baseball, hot dogs, and apple pie.

a largetruck salesman told me god never intended the diesal to be in a V config and pointed out that all the big rigs use an inline engine config

his reason ... a V engine has less mainbearings

XXX_er said:

a largetruck salesman told me god never intended the diesal to be in a V config and pointed out that all the big rigs use an inline engine config

his reason ... a V engine has less mainbearings

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I dunno, there were some pretty substantial industrial boxer and V diesels, and Detroit made 6,8,10, and even V12 2-stroke powerhouse diesels for heavy equipment and industrial applications.

Another possible contributing factor with the inlines for heavy trucks is they are biggest in the direction that such trucks have space to spare. Another possibility is the reduced parts count.

Ski in NC said:

4.5 could be made in a smooth running straight six or even straight 5.

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Inline-5s are not balanced. Then again neither is a 72-degree V8, but I digress. There's mass-balancing (what were talking about here) and gas-force excitations. As you reduce the cylinder count for a given displacement, yes, you reduce friction losses but you increase torque fluctuations requiring heavier flywheels and better torsional vibration dampers. A good read about the subject can be found here.

Split crankpins also tend to weaken crankshafts. All-in-all though this engine is a pretty impressive engineering case-study. Certainly a marvel of packaging and minimizing cost.

A downsized Cummins B59 would be very impressive, though.

There is nothing inherently wrong about a v-block diesel. Like TurbinePower posted, lots of big diesels are v-block. Mostly above 14 liter. Often these share parts with the in line engines to reduce part counts. Cat 34xx, 35xx, 36xx; Cummins 855 & 1710 cid, K 19, 38 & 50 liter; Detroit 71 series. All those have in line and v-blocks. But the base models are usually the straight six.

Nothing wrong with the main bearings on a v-block. Even though there are fewer mains, each one is only loaded by one cylinder firing at a time. It would be a problem if both cylinders paired fired at the same time, but they don't.

The strength of the crank can be a problem. With two rods on each throw, you would like to widen the journal. But this reduces the meat on the web between throw and main bearing. So you increase crankpin diameter, but now that forces longer rods and higher deck height as rods must clear the bottom of cylinders. So you end up with a mess of compromises. And add to it how do you get all the exhaust into one turbine inlet? (Cat 35 &36, Cummins 1710,kta 38&50, emd 567,645, 710 have exhaust manifolds in the valley, which solves that problem..but those are big engines..tricky on little engines)

So much simpler to just do a 4.5 in line 5 or 6.

-Eric

Didnt the older truck engines with V config's run higher RPM whereas the newer trucks use lower engine speeds to get better fuel milage...which is harder on lowerends ?

TDIMeister: Correct about the il 5 not being inherently balanced. But also not balanced are our ALH's with that nasty 2x buzz and their rather rough firing impulses (being 4 bangers). I understand some of the PD's and CR's use balance shafts to cancel the 2x buzz, and the DMF's help on the low rpm firing impulses. They end up being smooth enough to tolerate.

My point is a 4.5 five or six could probably be made sociable in a pickup application. I'm sure GM has their reasons, and I'm not second guessing them. More like thinking aloud.

The first order imbalance on a five (do I have that right?) was made tolerable on a few engines such as Audi, MB, GM. Never drove any of those, but heard they are ok.

-Eric

Ski, it seems you're an engineer.

Yes, I agree that 4-cylinders are also not balanced, but balance shafts go a long way to solving the secondary imbalance. But IMO it's not a panacea: There's a thread in the B5.5 Passat forum about a string of problems with wearing of the hex drive of the oil pump. What does this have to do with balance? Well, in the engine in question it's driven directly off the balance shafts, which are in turn chain-driven off the crank. While I don't know if anyone has authoritatively found the root cause, my belief is that the torsional harmonics of the balance shafts is causing that wear. The balance shafts of the B5.5 Passat 2.0 TDI is a sight to behold because of their hugeness! Blame heavy reciprocating components, a long stroke and low rod L/R ratio for that.



OTOH, the ones installed in the newest BMW 4-banger Diesels are things of beauty in comparison. They are far lighter, helical gear-driven off the flywheel-end, vertically-offset and turn in roller bearings to minimize friction. These little details, and the aluminum crankcase, speak to me as an engineer as to the superiority of BMW engine design to VW's (that's saying a lot because I'm a lifetime VAG fan).



Back to inline-5s: the imbalance mode depends on the firing order and therefore the placement of the crankpins. One layout (1-5-2-3-4) leaves a large primary rocking moment with a small amount of secondary imbalance, which can then be smoothed out with heavy crank counterweights and a 1X balance shaft rotating the other way and putting up with the remaining secondary buzz, while the more common approach (1-2-4-5-3), as done by VAG, Volvo, MB, etc., is to have a small primary rocking moment and a large secondary, but saying to hell with them both and leaving them alone without any balance shafts.

I also believe V8s have a lot of advantages, as do inline-6s and boxer-6s for different reasons and different applications. I think a moment of epiphany happened after seeing the VW balance shafts above, and I'm actively involved in researching better ways to balance engines... One of my biggest banes is the secondary imbalance -- primary is fairly easy to solve -- and I'm working on a potentially patentable design to eliminate the former. If this is the case my dream is Ferrari-sounding flat-crank V8s of any bank angle becoming a lot more commonplace.

I think the in-elegant design of the vag balance shafts probably has its root in being a backfit to a non-balanced engine. The bmw may have had balance shafts from the beginning of the design. Having room to put the 2:1 helical geartrain near the flywheel does not sound like a backfit!! Bless the clean sheet of paper!! A similar situation as the pd cylinder head..forcing narrow cam lobes.

Good luck with your engine design adventures. I too have dabbled in that world, only to be severly humbled by what I found in patent searches. It is not what I specialized in e-school and the gaps in my knowledge were most evident. There are alot of good minds working hard in engine design, and they seem to file patents daily!!

-Eric

pruzink said:

The block is compacted graphite iron, which is stronger than aluminum and lighter than traditional gray cast iron.

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A (very) minor nitpick: CGI is every bit as heavy as traditional gray cast iron, but is indeed stiffer and stronger that both gray cast and aluminum. The weight savings come from the fact that on account of the added specific strength and stiffness, less material (e.g. thinner wall section thicknesses) needs to be used to match the strength of original gray cast iron part.

Aluminum can be designed into highly-loaded engine crankcase designs, as the BMW bi-turbo Diesels (4-cylinder pictured above and 6) demonstrate. But aluminum is still more expensive and energy-intensive.

For a truck application, I agree that CGI is the best material choice, but for small automotive Diesels, aluminum still offers fairly substantial weight advantages (and increasingly porkier passenger vehicles need all the help they can get). I consider it inexcusible that VW is still using gray cast iron in the 4-cylinder engine family; the latest inline-5 and V10 TDI are aluminum and are by far my favourite engines in the entire VAG stable, ahead of the V6, V8 and V12 TDIs (all CGI blocks, but not the only reason for my diminished preference).

Ski in NC said:

I like the idea of the exhaust going into the valley. A vee block turbo diesel has always been a plumbing mess with two manifolds and where the hell to put the turbo? Over the tire like a 6.5 gm?? But this only applies if you are committed to making a vee block. 4.5 liter v8? Why? 4.5 could be made in a smooth running straight six or even straight 5. Parasitic losses go up as you increase number of cylinders and keep displacement the same. I guess in-lines are out the window with pickup truck windshields extending half way over the engine bay. Styling trumps design again. Rats..

-Eric

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Not to mention fact this engine may end up sideways in some GM econobox.

Back when F1 was 3.5l they all decided 350cc was the most efficient cylinder size so all the engines were V10s. Rather think since "reciprocating" means changing directions, changing direction of smaller, lighter parts is the ticket.

Ski in NC said:

I think the in-elegant design of the vag balance shafts probably has its root in being a backfit to a non-balanced engine. The bmw may have had balance shafts from the beginning of the design. Having room to put the 2:1 helical geartrain near the flywheel does not sound like a backfit!! Bless the clean sheet of paper!! A similar situation as the pd cylinder head..forcing narrow cam lobes.

Good luck with your engine design adventures. I too have dabbled in that world, only to be severly humbled by what I found in patent searches. It is not what I specialized in e-school and the gaps in my knowledge were most evident. There are alot of good minds working hard in engine design, and they seem to file patents daily!!

-Eric

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You're completely right about that, Eric. There is something to be said for the VW engine which is still largely recognizable with its ancestors from the 1970s and many parts still bolt-on, but come on, a time comes when one just has to move on. VW still holds to a bit of the Beetle philosophy and syndrome.

My background IS in engine design; been working in the powertrain industry since 2000. Grad school currently, hopeful of a PhD in M.E. Having pored over hundreds of related patents, I believe my proposals stand on pretty solid ground. Stay tuned.

Good luck on the Ph.D!! The best engineers I have ever worked with were also wrench turners. Got to know both the math and the mechanics (the wrench sort of mechanics, that is!!).

Just to fill in a gap in my knowledge..regarding cgi or grey cast iron, isn't the modulus of elasticity essentially the same? So while the strength (however defined..yield, ultimate, fatigue, whatever) may be higher with cgi, if you reduce casting thickness to take advantage of that, won't the casting become more flexible? Alot of beef in an engine casting is not due to material strength limitations, but to limit flexing of the structure under load. Again, thinking aloud.

And how 'bout those tuners that blow the block apart right under the cylinders!! Good way to look at the structure under tension without having to bandsaw a block!!

-Eric

Ski in NC said:

Just to fill in a gap in my knowledge..regarding cgi or grey cast iron, isn't the modulus of elasticity essentially the same? So while the strength (however defined..yield, ultimate, fatigue, whatever) may be higher with cgi, if you reduce casting thickness to take advantage of that, won't the casting become more flexible? Alot of beef in an engine casting is not due to material strength limitations, but to limit flexing of the structure under load. Again, thinking aloud.

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CGI has a Young's Modulus that is about 50% higher than gray flake cast iron. I think I know what you're thinking -- the modulus remains fairly constant by material composition, but this assumes an isotropic material and doesn't consider microstructure. So, a CGI crankcase can be made thinner while still maintaining the stiffness and strength of the thicker-walled gray cast iron part.

For a 5 cylinder engine, isn't it possible to make a V-4 configuration with the 5th piston acting as the balancing weight?

Good explanation on the modulus of elasticity. I didn't know there could be that much variation. Thanks.

MrMopar- That sounds cosmic indeed! I have a hard time visualizing such a beast. A vee with two on one side and one on the other?? Whew...

-Eric

MrMopar said:

For a 5 cylinder engine, isn't it possible to make a V-4 configuration with the 5th piston acting as the balancing weight?

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I seem to recall hearing something about GM trying a "V5" engine design with one of their early diesels, putting the IP in the space that would have gone to a sixth piston and cylinder.

Can't place where I heard it, though. Was a 'net article.

Almost any 5-cylinder layout with equal-firing order can be made to balance for forces in the first order. The problem with an arrangement with an odd-number of cylinder is that with equal firing order, a requirement to resolve the front-to-back rocking moment is that end-to-end piston pairs must be in the same position, and this is not possible with most general layouts.

However, MrMopar, I just sketched on a piece of paper what I think you're getting at. I sketched a V4 with a 72-degree bank angle, and the 5th-cylinder pointed straight down on the center crank pin, so that you have something of a "Y" engine. Without analyzing it much further, I think you have a slight first-order yawing imbalance that could be dealt with using only crankshaft counterweights, and second-order is anyone's guess but pretty small. The resultant firing order should also be analysed for torsional excitations. You should call your patent attorney.

Yes, GM did have a prototype V5 with 3 cylinders on one bank and 2 on the other. It was many years ago that I read this, and I forget what the bank angle was, but spayed-crankpins would have been pretty novel for the time, so 72° might have been likely.

Nah, I was thinking of a 72 degree V engine with one bank of 2 and one bank of 3 with the pistons spaced similar to the VW VR engines. It has the benefit of using only 5 cylinders, but if you're going to have the length of a bank of 3 cylinders you might as well just build a V6 sized for the displacement you want - unless there is some huge design reason that you absolutely need to have 5 cylinders and can't do it in an inline design.

I thought some of you would enjoy this nifty little table that lists mass balance modes for different engine layouts, particularly those less-common ones found in contemporary VAG engines.



Sorry we've come so far off the topic of the Duramax . But if there's any consolation, the imbalance mode for the 72° V8 is similar to the 75° shown.

A 3+2 V5 cannot be made to balance completely due to not being able have symmetry of piston positions about the center of the engine.

TDIMeister said:

A 3+2 V5 cannot be made to balance completely due to not being able have symmetry of piston positions about the center of the engine.

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How does Honda do it with their RC211V motorcycle?

First of all, it's not completely balanced; it might be balanced in the first-order for forces (already stated above that it's not hard to balance a 5-cylinder for first-order forces) but not for moments, and most likely not balanced in the second-order either. If you have a paper that states otherwise, I'm very interested to read it and learn.

And, for racing motorcycles they could pretty much care less about vibration, torsional harmonics and even firing orders if they could come up with something that gave them a perceived advantage on the track (cf. Big Bang firing orders). The axiom in racing is that you only need it to last to the finish.

Dave, I've got a book you might want to read. It's about MotoGP technology (actually, you can probably get it in a book store over there) and it shows really interesting cutaways and parts breakdowns of various engines. Normally this kind of thing never gets seen for public consumption ... but with the displacement reduction to 800cc a couple years ago, it obsoleted the 990cc engines and with it, Honda's RC211V.

Vibration and torsional dynamics are BIG issues with race engines and this is why the Big Bang engines went out, to be replaced with irregular-firing and "long bang" engines. The RC211V engine is claimed to be balanced for first-order forces and moments - but deliberately not balanced for firing order. The Big Bang engines were too hard on driveline components. The RC211V engine has a deliberately irregular firing order to improve rider feel of the amount of grip that the rear tire has. No doubt the irregular firing pattern also avoids setting up harmonics in the drivetrain, although this is something the book doesn't touch upon.

On a street application engine (that has a rev range lower than 17,000 rpm!) an irregular firing order is not a desirable design feature ...

The V4 engine RC212V that replaced the V5 never worked as well. Honda got something right with the RC211V that nobody else figured out for years, and Honda themselves have not been able to top it.

I would figure that as you got way up there in rpms, the effect of an odd firing order would diminish compared to the high amount of inertia in the rotating elements.

What is a big bang and a long bang engine?? Curious..

-Eric