carguy10101010

I suppose I am also curious if the I4 duramax is really benefitting from DOHC instead of SOHC. Its probably redlining at ~4k rpms. Do the DOHC really do much to increase airflow at such low rpms? Are forced induction engines more sensitive to having DOHC for maximal airflow? Does the better control over intake/exhaust valves result in a real performance difference over such a low usable ropm range? Is the extra cam really doing anything for performance here? I'm sure its adding some parasitic friction to the drivetrain even if its not adding to engine performance.

If this is true that is fine, but it would be a solely business decision with no real engineering input into it. That would be disappointing, but its the reality of the world we live in. I was hoping however to generate somewhat of a discussion on the pros/cons of using a similar/same displacement and valvetrain layout but either choosing a small V6 or a large I4. Discussion could probably be expanded into a large V6 vs small V8, etc. Given the performance numbers that Chrysler is getting from a 3.0L V6 diesel and that GM is getting from a 2.8L I4 diesel it seems hard to justify using the I4 given how badly it is lagging its competitor.

Was looking for some feedback on the pros/cons of using differing engine layouts, particularly in regards to the resulting torque curve as well as the peak power/torque numbers. The impetus behind the question are the specs of the new 2.8L I4 duramax diesel at the LA auto show (in the Colorado ZR2 concept). GM is reporting that it will be putting out 181hp at 3400rpm and 369 lb ft at 2000 rpm. Chrysler's current 3.0L V6 diesel puts out 240hp at 3600rpm and 420 lb ft at 2000rpm. What are the advantages to GM choosing to use a 2.8L I4 diesel instead of a 3.0L V6 diesel here? Displacements are very close but the V6 is producing 60 additional peak hp at only 200rpm higher. Its also putting out an extra 50lb of torque at the same rpm. With similar displacements and block materials I am going to assume that engine weight is very similar, with perhaps a slight advantage going to the I4. Does the I4 have substantially less internal friction? If thrown into the same vehicle is the I4 going to be able to return significantly better fuel economy numbers? The only efficiency advantages of an I4 engine that I can think of are easier turbo plumbing, a *tiny* bit less valvetrain friction and a *tiny* bit less piston ring friction. Is there something big I am missing here? I am really curious as to whether there is a good engineering case for GM's engine choice here, or if the choice to the similar displacement, less powerful, less torquey I4 was a business $$$ based decision. As an aside the I4 uses a timing belt instead of a chain, which is an additional turn off. Changing timing belts is a pain (at least for me) and its expensive to pay someone else to do it.

Sounds like the turbo steamer (if it works financially to be mass produced) could net a substantial gain to all vehicles. It could be one of those pieces of technology that everyone begins to use if it really can capture as much waste heat as BMW's claims would have us believe. In conjunction with a mild hybrid system we could potentially see some pretty substantial gains in both city and highway mileage in the future. Definitely good news! The turbosteamer is designed to capture wasteheat from the exhaust and coolant and transform it into usable energy. Water injection is designed to cool the intake charge to prevent detonation and allow for higher compression ratios in the engine. I think someone has proposed an engine that has an extra "water cycle" where water is injected after the exhaust stroke to be turned to steam to convert waste heat into mechanical work, but that would require a decent sized water tank. A lot of guys use water/methanol injection on their diesels to keep their EGTs down, but some of those systems really use an incredible amount of water/methanol. I think some inject over 10% water/methanol mixture v/v with diesel into the air charge. Since most guys use the windshield reservoir for this its a huge pain since it can get emptied pretty darn fast. If diesels had gone the route of water/methanol injection instead of urea injection to control Nox diesels would be more efficient, have more power, and would have cleaner valves. Bummer on that one. If a good set of tuners comes along for Chrysler's ecodiesel that allows the SCR to be shut off and a kit created to use the urea tank for water/methanol injection I would buy one in a heartbeat.

I wonder how much water a system like that would consume? I guess in theory one could make a closed loop system where boiled water was then condensed and boiled again. Heck, if a system like that was not used you could probably do away with the entire cooling system since you could just boil water directly from the engine heat as well as from the exhaust. You would take all of that waste heat that gets dumped into the atmosphere and doing work with it. I wonder if a water injection system, maybe with an extra couple of strokes could suck enough heat out of the engine to reduce or eliminate the cooling system. Shame its so expensive to develop new car tech. Lots of interesting ideas out there.

Also, if its technically too difficult to use exhaust gasses to generate electricity directly, would it be possible to setup some of these hybrids with a smaller engine and small turbo and run a miller cycle? Are the small turbos still too slow to spin up to be of use for a miller cycle engine? With every manufacturer so anxious to turbo everything (allegedly for CAFE reasons) I have wondered why they don't switch to miller cycle engines. They're already spending the money on forced induction and they would get better fuel economy out of the system.

(1) The weight will be significant, but not so much from the motor as from the battery itself. A 70hp motor itself will be in the order of 70~80 lbs, a battery powerful enough and which stores enough charge to support a 70hp motor however will be on the order of 200~400 lbs. Still that is about what the Prius lugs around and it will not offset the gains from regenerative braking and subsequent motor assist. (2) There isn't much "steam" in the exhaust. Certainly not enough to drive anything. However, there is plenty of heat and plenty of pressurized gas. Another source of "free" power is to use half a turbocharger -- just the turbine section without the compressor -- to drive a generator. This way, the normally wasted energy in the exhaust is converted (at least in part) to electricity. The problem with that is that it is much more of an engineering challenge. Turbos run at up to 100,000~150,000 rpm. Generators generally don't work well at such high frequencies, meaning you have to gear it down to maybe 1/10th or 1/20th of that rotation speed. It's a similar challenge as say Pratt & Whintey faces in commercializing the Geared Turbofan except it is actually worse because the reduction ratio is much greater. Alternatively you can simply work with a very high frequency AC source... that's another challenge by itself (efficiencies aside). What kind of duty cycle can these electric motors handle? Would they be capable of putting out max torque output over and over in a short time, say while towing/hauling through a town with a stretch of lights, or would they begin to overheat? Is there a need to liquid cool a large enough electric motor when integrated in with the transmission? I still think a setup like this would seem (at least on paper) to have the biggest benefit in the new mid sized trucks. The electric motor could give a huge boost to the low rpm area of the torque curve, and the mild hybrid setup could essentially use wasted brake energy to remove the parasitic drain of the power steering pump, alternator, water pump, and torque converter - since all of those things would be electrified. Could make stop/start systems work better too I suppose.

Yep, I think of "small" and "mid-size" pickups as two different things. These new trucks are just not quite there for a "mid sized" pickup, a few tweaks I noted above and I think they would be set. These trucks are nowhere near small enough to be a "small" pickup. GM needs to decide what they want. If they want a small pickup they need to shrink the entire thing, if they want a mid sized pickup then there is absolutely no excuse for making a truck of this size that can't fit 4' wide materials between the wheel wells. The Honda Ridgeline can do it with a unique (and highly useful) bed design and that truck is 10 years old. Avalanche could also and there was still a market for them but GM pissed that solid truck away also. I actually think if anything the avalanche type of approach would be ideal for a mid sized truck. It could result in a smaller size with almost no compromises in capability.

Yep, I think of "small" and "mid-size" pickups as two different things. These new trucks are just not quite there for a "mid sized" pickup, a few tweaks I noted above and I think they would be set. These trucks are nowhere near small enough to be a "small" pickup. GM needs to decide what they want. If they want a small pickup they need to shrink the entire thing, if they want a mid sized pickup then there is absolutely no excuse for making a truck of this size that can't fit 4' wide materials between the wheel wells. The Honda Ridgeline can do it with a unique (and highly useful) bed design and that truck is 10 years old.

Their engineers stated in that video that fuel economy was a top priority. If that was the case they failed miserably. If this was to be a real working truck then why on earth did they not add an extra two inches to the width for 4' between the wheel wells? Add a track system to the bed instead of their stupid gear on system? Why did they put a space wasting (but pretty) console shifter in the front instead of a column shifter and bench seat? Why did they mangle the rear seat storage area so badly that its virtually useless? They chose to use the LFX with all of its oil consumption, coked valve, stretching timing chain glory instead of the superior LV3 or L83. Why was GMs in house 8 speed transmission not ready to go at launch for these trucks? Why was the small duramax not ready to go at launch? These trucks are not made for work. They are not made for fuel economy. They're just another half-assed GM attempt at something. Assuming they don't keep having to recall them they will sell well right up until Toyota and Nissan update their mid sized trucks. Without substantial updates at that point these new twins fall right back into the obscurity they came from.

I am very disappointed with this truck. If every decision they made was truly focused on fuel economy then GM employs some pretty terrible engineers. This truck has way too many compromises on it to justify the pathetic fuel economy ratings it currently has.

That shouldn't be too difficult in a truck platform. GM butchered the under seat storage for the back seat so badly in the new canyon/colorado that batteries could be mounted there. Honda put a truck underneath the bed in the Ridgeline, there is no reason the similar void space in a colorado/canyon could not be converted to battery use, instead of empty space or a trunk like the ridgeline has. I would be more concerned about the durability of the electric motors they use in automotive applications and what their duty cycles are. I have never read one way or the other what these motors are capable of putting out before some sort of cooling would be needed.

Even more could you take the current Chevy Colorado scheduled to come out in a month or two and give its 3.6L LFX an atkinson cam grind, then do something a la Acura's RLX sport hybrid with a larger electric motor bolted to the transmission and two smaller electric motors at each rear wheel? This would result in a truck with full AWD functionality that would produce 300 lb ft from 0-6000 rpm. With an ICE running with an atkinson cycle and no more drivetrain losses through a rear diff and transfer case a vehicle like this would be able to do something like 28/28 on the EPA cycle with a very healthy ability to tow and haul. Electric motors would complement truck and sports car applications better than any others, it seems odd that mild hybrid setups like this one have not been implemented in any of them yet.

This seems like a great idea, what kind of cost and weight is associated with a 300 lb ft electric motor? With the fuel economy numbers being released for the mid size truck twins this week and the general underwhelming reaction by the internet at large I wonder what a system like this could do when plugged into trucks like that. Big torque from the get go would work well, and with no torque converter losses and some regenerative braking I would have to think fuel economy would really out do what they're currently going for. Has anyone made a commercial alternator or generator that can run off of the exhaust stream? If possible to implement it would seem like a good fit if the industry is going to keep heading towards electrification of vehicles.

I guess the overarching question would be is there a true performance reason to run an engine line based upon lower displacement boosted engines, or would it be simpler/easier/more effective to stick with an L86 or L83, and either lop off a set of cylinders and/or add boost to hit certain power/performance goals? An I4 would be needed as well I suppose.

Would this approach really net any gains over simply using an IBC design for all of the V6 and V8 engines? It seems to me if one is going to the trouble to make a high compression boosted V6 that you may as well crank everything up more and add methanol/ethanol injection to the whole setup to get much bigger efficiency and/or power gains. I know with diesels they can tie a methanol injection setup directly into the windshield washer fluid. I assume the same could be done on a gasoline engine. Perhaps gasoline could be port/throttle body injected as well as direct injected while the methanol/ethanol could be direct injected only? Keeps things cool and burning efficiently, which should allow somewhat higher boost and/or compression ratios. I suppose you would want more compression ratio with the above proposal since the idea would be to use little boost.

Do you know the weight difference between the 6.2 and the 3.6TT?

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.

Too bad, was really hoping they would put the 4.3L LV3 in the Canyon to differentiate it from the Colorado. Still do not understand the choice of the LFX. With the tune it is running it appears to have nearly identical numbers to the Pentastar V6 in the Ram pickups. That pentastar is still port injected.

This really brings me back to the question I asked on the other thread, of why GM made the decision to put the 3.6L into the new Colorado instead of the 4.3L. Rhetorical question at this point since it does not seem as if there was (is) any engineering rationale behind said decision. I have another question. Does the better ability for DOHC engines to breathe make them more amendable to forced induction, or is that irrelevant since the air has already been compressed before it enters the combustion chambers? Likewise with diesels, do they lend themselves better to a DOHC setup? I understand that the Euro V6 diesels that have made it here in some SUVs (and soon the Ram 1500) are DOHC because they are displacement tax limited to 3.0L, my question is if smaller V shaped diesels became popular in the United States, with no corresponding (and stupid) displacement taxes, would the same general rules hold true - pushrods would offer a smaller / lighter package that would likely offer efficiency advantages for similar power over its DOHC counterparts. I know that diesels are made heavier from the getgo so perhaps the added weight of the cams is fairly miniscule in relation to the overall engine weight?

I don't think that this would give many customers the performance they are looking for. An engine like that would have to go into something like the S10's or rangers of old, that started at ~$12,000. I guess that price point might be $16,000 - $18,000 now, but any more than that price point I think that people will want. How does the NVH of an I3 compare to an I4? Is it noticeably worse? Could they not just make an I4 out of "half" of the 6.2L small block? Would you think it would be easier to produce a "half" 6.2 as a V4 as you mentioned above than as an I4? I think that you're dead on. It certainly makes a lot of sense to base all of the pushrod engines off of the same bore/stroke in order to create the largest carryover of shared parts.

No it wasn't a sales champ, primarily because it was anemic in performance, lacked any significant fuel economy advantage over the half tons, and had a price that was within a stones throw of the half tons. The reveal last month appears as if they are taking some of those mistakes to heart and are really working to keep the new truck from having the same failings as the previous one. There is plenty of interest in a smaller truck, for active types and do it yourselfers, who also commute to the office during the week - and that is exactly who this truck looks to be pitched to. Those that have a lifestyle which is well complimented by a truck - hence the lifestyle truck terminology. But the genesis of the question is why would anyone (from a technical standpoint anyway) choose to put the 3.6L LFX into a new truck (or most vehicles really) over the 4.3L ecotec, when the ecotec has a torque curve shifted to the left producing its peak torque and hp at lower RPMS which is nicer for NVH, and is more fuel efficient to boot. Its not that the LFX is bad - not at all - but if that little bit of additional peak power is not worth additional NVH and lost fuel economy it seems to be a worse choice in the new Colorado, the Traverse, and most places where the LFX is used. I am not convinced that the 2.5L will sell well in the Colorado. The revving that motor will have to do to produce the desired power will neither be pleasant nor fuel efficient. The prospect of the 2.8L duramax is the real interesting engine choice for this truck. The potential fuel economy from said engine along with its ultra low rpm torque curve could turn out to be a real winner if its not too expensively priced.

Which would just smack of "Old GM" thinking if true. It really would be disappointing. The 3.6L LFX seems to be a great engine, but the 4.3L ecotec just really seems to fit the bill better, particularly for a truck application. Based upon Dwight's arguments here it would actually seem that in most V6 vehicles across the lineup the 4.3L ecotec would provide similar or super performance to the LFX while offering better fuel economy as well. I could certainly understand why another automaker -say Hyundai - would choose to not begin developing a line of pushrod engines alongside the DOHC engines they already have, but since GM has already spent the investment it would seem to be common sense to put that investment to use. But maybe there is some other advantage to the LFX over the ecotec that makes it the better choice where it is implemented?

@ Dwight Given the excellent argument for OHV engines you have made here, is there any technical reason that GM chose to put the 3.6L LFX into the 2015 Colorado instead of the 4.3L ecotec? There was an offhand comment made somewhere that "they tested both and the LFX returned better fuel economy". I can't even seem to find where I read that, but given the argument that you are making here that is almost definitely not true. EPA numbers would seem to further validate your thesis considering that a heavier and less aerodynamic silverado with the 4.3L ecotec is rated 17/22 while the lighter and more aerodynamic traverse with the 3.6L LFX is only rated 16/23. Given what you have written and your obvious knowledge of both powerplants and their advantages, is there any good reason to put the LFX in the upcoming colorado instead of the ecotec? Or could this just be a case of GM refusing to use the 4.3L ecotec to ensure differentiation from the Silverado?