Why GM should NOT build a DOHC V8

[dwightlooi]

To illustrate the competitiveness of the pushrod design, let’s compare three V8 engines. All are fielded in high performance production cars, all being of aluminum construction and none having direct injection.

* Chevy Camaro SS

** BMW M3

*** Mercedes-Benz C63 AMG

The pushrod engine offers the highest power and torque density, along with the best fuel economy. It is also the simplest, lightest, smallest and cheapest engine. Why wouldn’t you want a pushrod?

The most common reply to that is “civility”. Well, have you driven a small block lately? If you have, have you also driven the other two engines? I have done all that and here’s my opinion on the civility issue…

The engines have very different characters, but saying that the small block is less civil than the other two is a mischaracterization. The small block is burbly down low and throaty in a throbbing baritone sort of manner when wound out. The BMW V8 quiet and smooth, but also very soft, down low. Get it past 6000 rpm and it wails with a metallic rasp of an engine note. The AMG V8 is (surprising) also rather soft below 4000 rpm, softer in fact than the previous M113 5.5 liter it replaced or the current 5.5 they put in the E550. Wind it out and it responds with vigor and a brash metallic tone from about 4500 rpm to the rev limit of 7200 rpm. Overall, the C63 has the loudest exhaust (I mean this thing is loud enough to wake your neighbors), the M3 has the finest tremble and the Camaro SS is the least edgy and most mellow. I am sure that some of that is how the exhaust and sound insulation in the respective cars are set up, but I didn't get the impression that the pushrod engine is outdated or crude. So, there you go.

This is why I advocate that GM should double down on a good thing and stick to the pushrod V8. With direct injection, variable timing and cylinder deactivation, it’ll be more than up to snuff against anything projected for the next decade. If nobody else is doing it, that’s a good thing they get the monopoly on it!

And, it seems that they are. Currently, there are no plans for a DOHC replacement for the Northstar. There is however a Gen V small block in the works (rumored to be displacing 5.5 liters and sporting direct injection). So, I'll like to offer my congratulations to the General for not losing good judgment despite government ownership.

[Drew Dowdell]

I'll add that the pushrod, whether from GM or Chrysler, has a sound that is distinctly American. This is a characteristic that GM should be proud of an not massage to sound more like the German or Japanese counterparts.

[loki]

i agree, the only thing you have shown to not be very feasible, yet, on a CIB engine is HCCI and ....... is it cam profile changing? when physical cams are no longer needed then the discussion will change/simplify. until then, GM needs to focus on proven tech and keep working on HCCI for the 4 and 6 cylinder engines, move that tech into the smaller more economical 3 cyl that should be for volt 2.0.

although i will always be curious about "what if" all this tech was put into a v6, in the range of high 2L to ~the 3.9L CIB engine.

gm just needs a bigger v8 for HD trucks... and maybe for the corvette.

[smk4565]

If the pushrod was better, everyone else would be copying it. Automakers love to copy and jump on bandwagons. However, no one else, but bankrupt Chrysler has a pushrod. Mercedes has enough money to build any kind of engine they want, yet what do they make. The power similar power/efficiency argument of the LS3 and BMW 4.0 or 4.4Turbo is valid, but all your examples were performance applications. A Luxury car engine has to be refined and whisper quiet in everyday driving and on the highway, that is what the pushrod can't do.

About the cost argument, on a Cadillac, cost cutting should not be an issue. Plastic fake wood costs less than real wood, epsilon would be cheaper than sigma, solid rear axle costs less than independent suspension and magnetic shocks.

If GM had $30 billion sitting in the bank they would have a DOHC V8, the only reason they don't is because they are broke. So they have to justify why it is just as good as what the Germans and Japanese have. GM has lagged behind the imports in engineering for 30+ years, and it shows when they had 40% market share in the 1980s and about 17-18% market share now. They had cheap pushrods for all that time and half of their customers left, mostly going to DOHC imports. (and it goes beyond V8s, to all the 3100, 3400 and 3800 V6 cars that people traded in for Accords and Camrys)

[dwightlooi]

although i will always be curious about "what if" all this tech was put into a v6, in the range of high 2L to ~the 3.9L CIB engine.

gm just needs a bigger v8 for HD trucks... and maybe for the corvette.

Well, a simple way to gauge that will be to assume the same specific output as the LS3 ~69.8bhp/liter.

~272hp 3.9 liter Pushrod V6. And, that's before VVT, DI or AFM. Not bad really and quite competitive with the 3.5~3.6 liter HF V6es. Remember, the 3.9 pushrod is probably a smaller and lighter powerplant.

[Drew Dowdell]

If the pushrod was better, everyone else would be copying it. Automakers love to copy and jump on bandwagons. However, no one else, but bankrupt Chrysler has a pushrod. Mercedes has enough money to build any kind of engine they want, yet what do they make. The power similar power/efficiency argument of the LS3 and BMW 4.0 or 4.4Turbo is valid, but all your examples were performance applications. A Luxury car engine has to be refined and whisper quiet in everyday driving and on the highway, that is what the pushrod can't do.

About the cost argument, on a Cadillac, cost cutting should not be an issue. Plastic fake wood costs less than real wood, epsilon would be cheaper than sigma, solid rear axle costs less than independent suspension and magnetic shocks.

If GM had $30 billion sitting in the bank they would have a DOHC V8, the only reason they don't is because they are broke. So they have to justify why it is just as good as what the Germans and Japanese have. GM has lagged behind the imports in engineering for 30+ years, and it shows when they had 40% market share in the 1980s and about 17-18% market share now. They had cheap pushrods for all that time and half of their customers left, mostly going to DOHC imports. (and it goes beyond V8s, to all the 3100, 3400 and 3800 V6 cars that people traded in for Accords and Camrys)

Try to stay on topic SMK. We're talking pushrod V8s, not V6es, though I personally think the pushrod V6es would have been fully competitive in horsepower and torque given the proper development. The 3800 and the 3900 are very different engines. The 3800 was a 90 degree V6 while the 3900 was a 60 degree V6. Just switching the cylinder angle made a huge difference in "refinement".

Your argument that pushrods can't be whisper quiet and refined on the highway is laughable on it's face. The LT-1 in Buick and Cadillac applications had plenty of balls, was quiet enough for a library, and super smooth to boot. The 3.9 in the Lucerne I had was so smooth and refined that I didn't even realize I had mistakenly put it in 3 instead of drive until I noticed the instant MPG read out was unusually low.

66Stang and I took it for an experiment the next day where I took the Lucerne up to 80mph and dropped it into 3. There was no shudder, no increase in noise, no visceral difference in the feeling of the car.

The Germans like to make things complex. It's kinda what they do. Having DOHC doesn't guarantee refinement.

[dwightlooi]

If the pushrod was better, everyone else would be copying it. Automakers love to copy and jump on bandwagons. However, no one else, but bankrupt Chrysler has a pushrod. Mercedes has enough money to build any kind of engine they want, yet what do they make. The power similar power/efficiency argument of the LS3 and BMW 4.0 or 4.4Turbo is valid, but all your examples were performance applications. A Luxury car engine has to be refined and whisper quiet in everyday driving and on the highway, that is what the pushrod can't do.

Well, maybe it's because they just don't get it... yet.

As far as refinement of an engine is concerned, you can break it into three factors.

• Balance of the Engine
  
• Insulation and engine mounting
  
• Valvetrain slop
  

Of these, you are not going to see a difference between a DOHC V8 and a pushrod V8 when it comes to Balance and Insulation. That's has everything to do with bank angle, counter-weights and sound deadening. It has nothing to do with how the valves are operated.

With Valve train slop, it is really a matter of not allowing poor tolerances and valve float. It also has very little with whether the engine is a pushrod or overhead cam design. The higher valve train mass in a pushrod engine places a limit on how high of a rpm the engine can get to before the valve train becomes a limiting factor both in terms of durability and/or noise becomes an issue. But while this affects the redline of an engine can acheive without compromising durability, the racket the valvetrain makes at a given level of acceptable float or slop is similar. The only difference is that a given threshold for what's acceptable may arrive at 6000 rpm on a pushrod design, but 8000 rpm on a DOHC one.

There are many things when the biggest bandwagon is on the wrong track. People and companies are not immune from the tendency to jump on board with a broad trend even when the underlying facts are highly dubious. Global Warming is one example of what's basically junk science almost becoming a general consenses. The trend towards DOHC Vee type engines, IMHO, is another. The basic Achilles' Heel to the DOHC proposition is that it is a heavier, bulkier, more complicated engine with higher internal friction. It's only advantage is that it provides for better airflow and higher rpm capability. The problem is that a slower turning, bigger displacement engine can be more powerful, lighter, smaller and more fuel efficient. In addition, the airflow potential of a DOHC layout is not realized at the typical 6000~7000 rpm rev limits of a mainstream passenger car engine.

In certain racing applications where the rules limit displacement, and in various countries where the rules of the game or the law makes it highly advantageous to have a higher specific output, lower displacment engine. However, these do not apply to the market for V8 powered cars. This is not a displacement restricted competition event. The luxury/performance market for V8s is also not particularly sensitive to higher displacement taxes even when they do exist. The type of buyers who rank this highly will buy the I4 or V6 variant of the car; they'll buy an Audi 2.0T instead of a V8 S4, they'll buy a BMW 525 or 528 and not the 550. The decision to buy a V8 powered car is a deliberate one.

[smk4565]

The Germans like to make things complex. It's kinda what they do. Having DOHC doesn't guarantee refinement.

The Italians, Swedish, Japanese, South Koreans, and British use DOHC also. Ford, the best performing American auto maker only uses OHC, and is phasing out SOHC for DOHC. Chances are, that massive group is right, and GM and Chrysler (the only 2 to go bankrupt) are doing it wrong.

[Drew Dowdell]

The Italians, Swedish, Japanese, South Koreans, and British use DOHC also. Ford, the best performing American auto maker only uses OHC, and is phasing out SOHC for DOHC. Chances are, that massive group is right, and GM and Chrysler (the only 2 to go bankrupt) are doing it wrong.

OR, chances are, YOU are wrong and there is no single right answer to the valvetrain question.

[dwightlooi]

The Italians, Swedish, Japanese, South Koreans, and British use DOHC also. Ford, the best performing American auto maker only uses OHC, and is phasing out SOHC for DOHC. Chances are, that massive group is right, and GM and Chrysler (the only 2 to go bankrupt) are doing it wrong.

Well, on what technical or factual basis are you making that argument besides everybody is using it so it must be right?

Linking financial performance to engine type is like saying a computer manufacturer is in distress because the CEO wears a red tie instead of white suspenders that the other CEOs wore. Unless you can demonstrate the suspenders affected his performance running the company the connection is quite groundless.

As far as the failures of GM. IMHO, it is a failure of design, failure of quality, failure of product focus and a failure of labor. GM tried to be the value leader while doing most of its manufacturing in a high cost country. That in and of itself is a recipe for failure. To that end, it cut back on quality, technology and put out too many uninteresting vehicles -- which compounded the problem. The Pushrod engine has nothing to do with it.

I put forth an argument that a Pushrod engine is superior to a DOHC engine in cost, performance, packaging, weight and fuel economy. Perhaps you can educate us as to why that argument is flawed or inaccurate?

Edited February 16, 2010 by dwightlooi

[loki]

Well, a simple way to gauge that will be to assume the same specific output as the LS3 ~69.8bhp/liter.

~272hp 3.9 liter Pushrod V6. And, that's before VVT, DI or AFM. Not bad really and quite competitive with the 3.5~3.6 liter HF V6es. Remember, the 3.9 pushrod is probably a smaller and lighter powerplant.

yes, and before those improvements it is roughly 10% bigger than a 3.5L. just like how the new 5.5L will compete very well against ford's 5.0L. that would show how not dead CIB v6's can be. but that's prolly not the future.

Edited February 16, 2010 by loki

[smk4565]

I put forth an argument that a Pushrod engine is superior to a DOHC engine in cost, performance, packaging, weight and fuel economy. Perhaps you can educate us as to why that argument is flawed or inaccurate?

A pushrod is not superior on performance, given equal displacement, the DOHC engine will make more power. For example, 426 hp from an 6.2 liter LS3 and 518 hp from the AMG 6.2 liter. Or 315 hp from the 5.3 V8 and 412 hp from the Ford 5.0 V8. Then you have the 7.0 liter Z06 with 500 hp, but he 4.5 liter Ferrari 458 makes 562 hp. Even take the LS9, the most powerful pushrod with 638 hp and 604 lb-ft. The Koenigsegg 4.7 liter V8 makes 806 hp and 678 lb-ft (on E100 it makes 1,018 hp).

The Jag XFR gets getter mileage than the CTS-V.

[loki]

The Jag XFR gets getter mileage than the CTS-V.

why'd you even put this with out noting curb weight? or actual power too.... the cobalt ss beets the jag xf..... just throwin that out there, like you did. LOL

[Drew Dowdell]

A pushrod is not superior on performance, given equal displacement, the DOHC engine will make more power. For example, 426 hp from an 6.2 liter LS3 and 518 hp from the AMG 6.2 liter. Or 315 hp from the 5.3 V8 and 412 hp from the Ford 5.0 V8. Then you have the 7.0 liter Z06 with 500 hp, but he 4.5 liter Ferrari 458 makes 562 hp. Even take the LS9, the most powerful pushrod with 638 hp and 604 lb-ft. The Koenigsegg 4.7 liter V8 makes 806 hp and 678 lb-ft (on E100 it makes 1,018 hp).

The Jag XFR gets getter mileage than the CTS-V.

A DOHC 6 liter will NOT fit in the space that a Pushrod 6 liter can.

[Drew Dowdell]

SMK, why does this rather simple concept baffle you? Horsepower per litre displacement is stupid. Give me horsepower for overall package dimensions and get back to me.

[regfootball]

a car company needs to consider an engine application for all its global markets, and honestly the US and maybe saudi and AU are about the only places where big displacement motors are marketable now. Euros place tax on high displacement, Japan culture is to make high revving small displacement. Fuel economy pressures lead development money towards smaller displacement.

while the arguments for the pushrod v8 make sense to some degree you also need to consider that if a company is designing a series of modular engines, then they want to develop similar manufacturing processes and capabilities across a wide swath of the products. For example, the combustion chamber design of a cylinder on a DOHC motor can then be used for say, a 2.4 litre four, a 3.6 litre six, and a 4.8 litre v8. The investment in design, manufacturing and tooling can have application and be amotized over many more models and justify the continuous R&D that is needed to keep pace. If you can prove on a balance sheet that you can make enough aluminum block pushrod v8's that will meet epa needs and sell in adequate volume to justify the whole separate program for basically three areas of the world in mostly niche vehicles, then baby play on.

The fuel economy issue is real. We know the large v8 gets great mpg in the corvette, but look at the terrible mpg the G8 GXP got (epa and real world). and that was without the added drag of an AWD system which many buyers consider a requirement these days.

You know too, the rpm issue is a real thing to consider. For example, GM was never capable of making its pushrod v6's feel as eager or smooth as the best v6's from its competition. In v8's they can match better. But large displacement pushrod motors have had the rap deserved for not quite cutting the mustard, mostly in v6's. GM should have applied all it knew to make them better performers in all the facets needed.

Maybe one reason the huge displacement motors can't keep up is the long bore and high piston speeds. I'll also assume longer bore engines generate more rocking forces if their configuration is not inherently balanced. I'd like for you dwight to address this. Cuz if I am revving a small block to 7000 rpm i just want to know how that compared to a smaller motor. More specifically a good turbo four in a lighter vehicle.

If i were developing one vehicle from scratch myself I would probably do a small displacement inline 6 with turbo. v12, if it were a luxury car. a mid engine flat six would be interesting too. I have always been intrigued by a boxer four also.

Edited February 16, 2010 by regfootball

[dwightlooi]

A pushrod is not superior on performance, given equal displacement, the DOHC engine will make more power. For example, 426 hp from an 6.2 liter LS3 and 518 hp from the AMG 6.2 liter. Or 315 hp from the 5.3 V8 and 412 hp from the Ford 5.0 V8. Then you have the 7.0 liter Z06 with 500 hp, but he 4.5 liter Ferrari 458 makes 562 hp. Even take the LS9, the most powerful pushrod with 638 hp and 604 lb-ft. The Koenigsegg 4.7 liter V8 makes 806 hp and 678 lb-ft (on E100 it makes 1,018 hp).

The Jag XFR gets getter mileage than the CTS-V.

Well, let me ask you a question... why does having a greater output for a given displacement matter to you? In otherwords, why is specific output important?

Does it matter if the engine's displacement is larger, when that engine is lighter, smaller, more powerful, more fuel efficient and cheaper to build?

For example, is Ford 5.0 DOHC lighter than a Pushrod 6.2? Doubtful. Does a Ford 5.0 DOHC take up less room in an engine bay? Absolutely not. Does the Ford 5.0 DOHC produce more power? No, it doesn't. Does the Ford 5.0 DOHC cost less to build? No way. Is the Ford 5.0 DOHC more economical on fuel? Again, probably not. So... why is the Ford 5.0 DOHC a better motor?

[balthazar]

dwightlooi ~ >>'LS3 - chain-driven 16v pushrods'<<

Typo, no? Of course the camshaft is chain-driven.. but seems very odd to call a IBC valvetrain 'chain-driven'. Interesting.

DL- you make a strong argument I cannot disagree with on the surface of it. By engineering & business-case parameters, the LS3 in your chart is superior & your point is proven, IMO.

Where I must part ways with your POV is market perception. Cadillac can have a IBC V-8 AS LONG AS it is proprietory and never shared with another division. Too many will bash it for 'using a Chevy motor' (as if there were such a thing anymore).

[dwightlooi]

dwightlooi ~ >>'LS3 - chain-driven 16v pushrods'<<

Typo, no? Of course the camshaft is chain-driven.. but seems very odd to call a IBC valvetrain 'chain-driven'. Interesting.

DL- you make a strong argument I cannot disagree with on the surface of it. By engineering & business-case parameters, the LS3 in your chart is superior & your point is proven, IMO.

Where I must part ways with your POV is market perception. Cadillac can have a IBC V-8 AS LONG AS it is proprietory and never shared with another division. Too many will bash it for 'using a Chevy motor' (as if there were such a thing anymore).

Again, this is a matter of opinion. But, I do not feel that the sharing of the motor(s) between Cadillac and other "less prestigious" GM divisions will have a significant impact on the success of the Cadillac brand. Cadillac can distinguish itself from other GM brands through styling, quality and amenities. It doesn't have to focus on having a unique powertrain. Besides, the same argument for Cadillac possibly receiving a "bashing" for using Chevy motors can be made for Chevy getting an "image boost" for using Cadillac engines. Since Chevy has much greater volume, one can then argue that it works out to GM's overall advantage.

Nissan uses the same 3.5 liter VQ35 on both the Nissans and the Altimas. Toyota uses the 2GR-FE 3.5 liter in the ES350, RX350, Camry, Avalon, RAV4, Highlander and (jeez) Sienna. Audi shares the 2.0T FSI with the Volkswagens. None of the sharing has impeded the success of the respective luxury divisions. In anycase, Cadillac doesn't have powertrain exclusivity today to begin with -- the 3.0 and 3.6 liter V6es -- which account for the the majority of the volume -- are Chevy motors also used in the Equinox, Malibu, Camaro, you name it.

If, for instance, giving Cadillac a "unique" motor will add $1500 to the cost of the vehicle, I feel that this $1500 is better spent on upgrading the grade of leather used in the upholstery, using laminated glass on all side windows and perhaps making a rear view camera standard.

[Carguy]

I think the LS3 could become a premium engine and going further I could see a nice new V6 version of around 4.5L becoming a new base truck engine as well. Remember the V16 Cadillac concept engine was built around two small block V8's and everyone DREAMED about that being built. A premium,smooth and quiet DI AFM OHV Cadillac V8 and even V6 could be something unique and great for them.

[balthazar]

DL- the only difference in your Chevy/Cadillac EX is that for Chevy; that's a positive, for Cadillac, it's a negative.

Chevy has far greater volume, but Cadillac has far higher profit margins. What the exact present #s are, and what will play out down the road is unknown to me.

Again I see merit in your post, but understand I come from the 'first windo' WRT Cadillac- I am as familiar with the dawn of the marque as I am of the present (VERY likely moreso) and the journey from there to here. And for 70-some years, a Cadillac engine was only found in a Cadillac, and (at the risk of making an smk-esque leap of logic) Cadillac grew all during those 70-some years. The perception was buffed to a high luster and proprietory engineering was a major factor in that.

Who can make the stand AGAINST the fact that engineering became the first lynch pin to drop @ Cadillac ??

350 diesels ('78-up, Olds-built), 1.8L/ 2.0L 4-cyls in Cimarron ('81-up, Chevy built), 4.1L V6 in full-size ('82-up, Buick-built).

IMO ^^ the grease at the top of the slide.

Something to always keep in the back of one's mind.

Edited February 16, 2010 by balthazar

[dwightlooi]

I think the LS3 could become a premium engine and going further I could see a nice new V6 version of around 4.5L becoming a new base truck engine as well. Remember the V16 Cadillac concept engine was built around two small block V8's and everyone DREAMED about that being built. A premium,smooth and quiet DI AFM OHV Cadillac V8 and even V6 could be something unique and great for them.

Honestly, I don't see a Pushrod V6 stemming from the Small Block. The reason being:-

• A 60 degree Pushrod V6 will be a brand new design, not a derivative w/o shared tooling
  
• A 90 degree is not a smooth running configuration unless a balance shaft is used.
  
• With less cylinders and (possibly) a 60deg angle the packaging advantages of a Pushrod diminishes.
  
• The HF V6 already exists and there is no good reason for duplicity in the lineup
  

What I do see (and hope to see) is the continued evolution of the Pushrod Small Block. Probably fortification with VVT, Raised Cam, Cylinder Deactivation and Direct Injection in the Fifth generation due in this year or 2011. This will probably be accompanied by a reduction in displacement to 5.5 liters with little or no reduction in output from the 400~436hp of the current 6.2 (LS3).

By 2014~2015, we may see variable valve lift and dual co-axial VVT in the 6th Gen design.

[regfootball]

Well, let me ask you a question... why does having a greater output for a given displacement matter to you? In otherwords, why is specific output important?

Does it matter if the engine's displacement is larger, when that engine is lighter, smaller, more powerful, more fuel efficient and cheaper to build?

For example, is Ford 5.0 DOHC lighter than a Pushrod 6.2? Doubtful. Does a Ford 5.0 DOHC take up less room in an engine bay? Absolutely not. Does the Ford 5.0 DOHC produce more power? No, it doesn't. Does the Ford 5.0 DOHC cost less to build? No way. Is the Ford 5.0 DOHC more economical on fuel? Again, probably not. So... why is the Ford 5.0 DOHC a better motor?

the mustang gt that holds that 5.0 is way lighter, and most likely handles better. ford's pricing is fully in line or cheaper than the camaro. the motor may not cost less to build but the buzz ford will get from this is incredible and its likely that the new GT is quite a bit better than the Camaro.

the camaro has the mustang on exterior styling but its seriously looking like the Mustang GT has whipped Chevy's but on everything else for 2011......

[Drew Dowdell]

None of that answers the question of why go with a DOHC over a pushrod. Vehicle weight, styling, and price all being equal, which is the over all better engine?

[Carguy]

Honestly, I don't see a Pushrod V6 stemming from the Small Block. The reason being:-

• A 60 degree Pushrod V6 will be a brand new design, not a derivative w/o shared tooling
  
• A 90 degree is not a smooth running configuration unless a balance shaft is used.
  
• With less cylinders and (possibly) a 60deg angle the packaging advantages of a Pushrod diminishes.
  
• The HF V6 already exists and there is no good reason for duplicity in the lineup
  

What I do see (and hope to see) is the continued evolution of the Pushrod Small Block. Probably fortification with VVT, Raised Cam, Cylinder Deactivation and Direct Injection in the Fifth generation due in this year or 2011. This will probably be accompanied by a reduction in displacement to 5.5 liters with little or no reduction in output from the 400~436hp of the current 6.2 (LS3).

By 2014~2015, we may see variable valve lift and dual co-axial VVT in the 6th Gen design.

Well the 4.5L V6 based on the bore-stroke of the 6.0L V8 would obviously be 90 degree and would be FAR BETTER then the ancient 4.3L version used in the trucks today. I think properly refined and advanced it could be a wonderful torque advantaged and slower turning and efficent premium V6 over its DOHC high revving competitors. If your stated OHV advantages are true (and I believe they are) whats good for the OHV V8 could be good for a OHV V6 as well.