Clairvoyantwolf

Beautiful.

...Now does it meet GM's requirements for emissions, fuel economy, durability, drivability, and cost? There are multiple factors to consider. In WWII the high performance engines of the day were liquid cooled V12s. The Navy preferred air-cooled radials. Why? Because those engines were shorter thus they could fit more aircraft in the ship.

NY09C6

jefnvk

Who says there has to be a right and wrong? GM does what it does, others do what they do. A boxer engine works spectacularly for Subaru, despite almost no one else using it in any significant numbers. DOHC works for the folks that do it. The Germans still stick to the straight six, even though Americans have abandoned it. GM has hung onto the pushrod, and until there is a clear performance to be had from changing, seemingly has no interest in abandoning it. Manufacturers like doing what they know well in the powertrain world, especially when their goods are competitive as-is.

Tom73

PurpleLion

Correction: Historically they could be found in cars manufactured by companies such as Porsche, Lancia, Benz, Ford, Tatra, Citroen, Alfa Romeo, Jowett, Rover, Volkswagen, Chevrolet, and Ferrari. The most prominent manufacturers currently using a boxer engine as their primary engine configuration are Porsche and Subaru.

Dominic Sorresso

Its actually a $28k motor and the LT5 crate motor starts at 18K. The SB4 demonstrates what is possible w a different valvetrain architecture on a well known engine block, the LS7.

"A two valve engine cannot outperform a four valve engine. The four valve engine has more valve curtain area."
Thank u Michael A. Greater valve area w lighter valves and a more accurate method of transferring cam lobe motion directly to the valves. No pushrods to flex and no ~ 180* change in the direction of motion. In order to get a two valve motor to even breathe close to a 4 valve, u need big lift and duration. And then power still drops off rapidly on a 2 valve motor after peak. Not so for the 4 valve. You can simply get more power out of 4 valves without having radical cam profiles, leading to a smoother idle and greater flexibility implementing variable valve timing technology. Also, before anybody brings up the "oh the weight"or the "the higher CG", just look at the "new" LT5.
GM doesn't give out engine weight or dimensions. But a check at Scoggin-Dickey shows a shipping crate weight for the LT5 of 575lbs. Let's assume the crate weighs 75# of that. The SB4 weighs 498#.
Also, the LT5 crate height is 32". Let's say the crate height is 1.5' more than the motor. The SB4 is 17" tall from crank centerline. Let's not forget what GM had to do to the hood of the C7 just to shoehorn the LT5 into the engine bay.. Any "advantage" the OHV architecture has over DOHC vis-a-vis CG goes right out the window when u slap a huge, heavy twin rotor blower at the VERY TOP of the motor. But GM needed to do that in order to get the 2 valve to breathe enough.
Is GMs OHV architecture a marvel? Yes, a wonderful design maximizing the capabilities off that architecture. But its pretty clear even GM believes it has reached the point of diminishing returns for the implementation
in a vehicle like the Corvette. Other platforms, the OHV may very well be optimal.

Tom73,

GM already uses DOHC architecture in quite a number of their engines. Just a question of how many cylinders u have. All the 4 cylinder powerplants are DOHC as are some 6 cylinders.

Foosh

​​​​​​​Yes, but he was talking today, not historically. Historically, a lot of manufacturers have tried a little of everything before settling into their primary engine specialities they've been using for many years now.

NY09C6

JD_AMG

Weird, cause the LSx's have been doing so for years now. ¯\_(ツ)_/¯

You gave up already huh, well that only took two posts...
Id like to see a street legal version of that engine, and the cost behind it, then we can talk about how much heavier it is too. This is great and all but I doubt that thing would fit in a Corvette's engine bay, would be too wide (height is not the only problem), with the C8 being midengined a fat DOHC V8 could fit, but again would be adding unnecessary weight (and cost).

Zaro Tundov

No reason whatsoever to make it a Hot V since the engine will be in front of the rear axle, and thus width will not be limited. Hot V designs are driven by packaging needs, not performance needs despite the claims by marketing departments.

Functionally the advantage of a Hot V is that it facilitates a cross bank exhaust manifold for even 180˚ exhaust pulses to each turbo, and it concentrates the heat of the two turbos, both advantages leading to more efficient turbo spooling. Yet the cross bank manifold is expensive to develop, and even worse, concentrated heat in the V leads to a cascade of reliability issues with the heads and valvetrains. Google "BMW S63 valve stem seals" to read about the joys of owning such a Hot Vee V8.

Mount the turbos on the sides as shown in the C8 CAD drawings and the result is a lower and wider engine with a lower center of gravity and far higher reliability, all desirable traits for a Corvette.

Dominic Sorresso

JD,

READ THE SPEC. ITS A GM POWERTRAIN LS7 short block w DOHC heads on it for pete sake . IT IS NO TALLER THAN AN LS7. There would be loads of room in the ME for it. But I am not advocating for the SB4 specifically. GM WILL be putting some kind of DOHC in the ME whether u like it or not. And the SB4 shows how u get comparable power at comparable weight.

JD_AMG

Well the SB4 is heavier and will have a higher COG.

So far the engines seem the same weight then, oh but wait the LT5 induces a flywheel(stock is ~65lbs), and exhaust manifolds (~30lbs) and the SB4 does not. Well there goes the weight argument...

Not sure why you keep focusing on height when the width is the problem. The SB4 is significantly wider than an LTx. ~22in wide head to head for the LTx vs 30+in wide head to head with the SB4.

GM did that as its the cheap way for them to get the powerband they want and total power output they want. For whatever reason GM loves lots low end and midrange torque and not just high end power. The easier and cheaper way to get 755hp and over 700lb.ft of torque is through using a blower. If their goal was 755hp and well under 700lb.ft of torque then they could have gone a different route.

Kinda ironic as I would say the Corvette is the perfect platform seeing as its their sports car, that I guess Ill have to remind you again that sports car are about being lightweight handling machines, an OHV V8 suits that much better than a DOHC V8.

JD_AMG

Guess I gotta repeat myself again. Height is not, and never was the real problem, its the WIDTH thats the major problem.

Comparable power with much more weight and size (WIDTH FROM THOSE HUGE HEADS!)

Michael A

Again, the Mustang 5.0L puts out 480 horsepower compared to 460 horsepower for the Corvette's 6.2L.

If you want to go specialty, the GT350 5.0L engine puts out 525 horsepower compared to the discontinued LS7 7.0L 500 horsepower.

Why is this even an argument? Of course, the four valve engine has higher specific output, and, in some cases, more total output depending on displacement and tuning.

For me personally, I would take the 7.0L engine. I love big engines. And I would take a V8 over anything, no matter how many valves it has

I do think Corvette is going the right direction by developing a fairly large (for the times) 5.5L engine, with DOHC and high RPM capability. I think a C8 with that engine is going to be awesome! Whether I can afford it or not may be another matter. We'll see how it is priced.

JD_AMG

Apples to oranges. They are playing the leap frog HP game. The LT1 hasn't done its leap yet and Ford just did theirs, LT1 will do it next and so on. Look at the power output when the LT1 came out: 460hp vs 420hp.

A 2006 engine vs a 2018 engine, again apples to oranges. The C7 LT5 makes 755hp.

All else equal yea a DOHC engine can make more power, but we are not talking about all else equal are we? Its never equal.

Foosh

FWIW, I'd be perfectly happy with an updated LT1 in a base ME for a street car.

Darion

I'm down too, perfect.

PC

bebezote

10000% truth...w twin cam heads .

JoesC5

I can slap an 80 pound Edelbrock E-Force(2.3L) or a Magnusson Heartbeat(2.3L) on the top of my 464 pound(includes the weight of the flywheel) LS7 OHV 7.0L V8 and both superchargers will fit under my stock C6 Z06 hood.

Of course I could also put in a LSX454 720 HP crate engine in myZ06(and not use a supercharger), and since the LSX454 has a 110 pound heavier iron block, the center of gravity will really be low as it won't have either DOHC heavy heads or a heavy supercharger up high, raising the CofG..

Now, take my Mercedes, with it's heavy Roots type twin rotor supercharger. Mercedes mounted it down low, on the side of the engine, and it uses plastic tubing to take the hot pressurized air to the air/air heat exchanger in front of the engine coolant radiator, then back to the intake manifold. Keeps the CofG low even with a "heavy" supercharger. Plus there is no "heat soak".

bebezote

the only ford I own or ever owned is a power stroke... and the mustang is just not a turn on to me...though mad respect for the flat plane... man the sound is amazing...that would push me over the top for a new ME... god I love the flat plane sound... rappppp. rapppppppp