0bbbvettes.com

I agree, and I believe you are likely spot on, I was only throwing out the other ideas to make mention perhaps GM may go there, but I believe it's doubtful for a while.

As far as your insight about closing cam lobes replacing springs, not being practical, can you explain? I would think the perk would be that it could allow for higher revs without floating valves.

Ducati manages with this concept. I would think it would have tremendous perks on centrally located pushrod cams, since the inverse cam forces the other valvetrain back to where it "should" be if it tries to float a valve. Since GM seems to not be a fan of OHC's, I would think this would be a technology that they would be forcing themselves toward if they want to rev beyond 6800rpm reliably.


Above video, except there would be pushrods attached to the rocker instead of the OHC right there. The higher centrally located cam would be the one that closes the valves, and its rockers would be at an angle like 90 degrees, which connect to the near horizontal pushrods.



Back to the original image posted by Jeff about the xv8... the single pushrod for 2 valves and 2 springs would reduce the weight of the pushrod weight vs spring-rate ratio... so technically speaking, that in itself could allow the cars to rev slightly higher with more reliability to avoid floating valves. Not as good as OHC, but a step in the direction of better, not to mention 2 intake valves are used vs only 1, so better air flow.

The other thread they mention that maybe it is a chain to the supercharger. While they were mostly joking, I suppose packaging could force such change, as the belt is thick in width. I do not believe this is the reason, but no need to completely rule out the idea.

GPaTom

Yes, I remember being fascinated with the Ducati system when I first saw it. If you were going that direction it seems cam(S) in head would be much simpler and more package efficient. Just my opinion. I would be shocked if GM would pursue it. We'll know in July!

I remain surprised that that we don't know more through the grapevine. It would seem to be a reach for the LT2 to have any of this valvetrain technology.

0bbbvettes.com

I agree GM won't do it on this engine, it was more of a hope for the future, it would be cool to have a car that could rev to 10k rpm.

Even if valvetrain maintenance has to occur every 15k miles as it does on the Ducati which revs up to 15k at times, I would happily pay a 2 grand service bill even at every 10k miles, if it meant I had a car that revved past 10k, and made the HP numbers that would go along with such an occurrence on our displacements and the turbos which will be attached on the z06 level car....

We wouldn't be needing any hybrid electric front powertrain to break the 1000hp mark with the z06. And then the Zora would be in the 1200hp range with awd and electric up front.

The major downside would be the 50% increase in oil friction per unit of time and thus the heat created, as well as 50% more combustion cycles/gasoline explosions per unit of time ... and that created heat seems to already be a downside which they have trouble solving back down here at 6500rpm.

RapidC84B

So a buddy who worked on the LT1 for Volvo-Penta marine applications looked at the OP picture today. He said the valley looked too close to the primary cam to be twin cam in block. Said it could indeed be chain driven rotary accessory like a water pump or HPFP, but most HPFPs are being directly driven off the cam via a piston and there's little reason to go away from that. He also commented on how the crank case separation and breathing windows were "very nice" and different than the LT1. He postulated the 2nd chain could turn a balance shaft of some kind if the motor was flat plane.

0bbbvettes.com

Ask him his thoughts on the idea that if there were 2 HP fuel pumps, things would be too crowded for the 2nd fuel pump and extra coolant pump, all to run off the original cam, so perhaps GM decided to get away from the single fuel pump, and instead has 2 HP fuel pumps to keep up with volume/flow of fuel needed, but without the port injectors like the zr1 had to use. 2 pumps will be more reliable than 1 very large one... plus the second one can then be activated on the fly perhaps somehow? Perhaps they are doing 2 sets of direct injectors (though unlikely, as those DI HP injectors are expensive)

The reason all of this matters is because fuel does not properly atomize at idle and cruising speeds if the injector is large flow, it has to have extra holes or larger holes, which both harm atomization at lower flows.

Perhaps they figured out a way to split the injector tip into 2 halves/areas, and the 2nd half and its second holes are run by the second pump (a stretch, but just throwing out ideas GM would have to come up with to get away from the port injection patch/method of the zr1) This 2 areas on the direct injector tip would create proper atomization at low fuel flow rates, and then the second set/area of injector tip holes are used when the second fuel pump comes online and slams fuel through those extra holes which are offline when the car is not at WOT.

Also, ask him if there is any possibility that that shaft that runs the pumps, may then have a second sprocket, and a lateral chain goes from head to head, with that sprocket driving the SOHC on each side.

How credible are the leaks that the higher HP versions have OHC setups? If we know those leaks are true or likely true, then this is something to think about.

84 4+3

Never knew volvo started running new stuff. I know they tried some messed up in house thing a while back... panned out about as well as the plastic sterndrives did... it is cool that they're using newer stuff now though. Merc tested it a while back... like 15 or so years ago now but at that point in time it wasn't worth the cost to do so they shelved it. The plot thickens.

BMZR1

https://www.thedrive.com/sheetmetal/...3sK7tajIOeW8dk

Maybe these new style cam/lobes have something to do with it? An oil pump may have to be dedicated to cause the cams to clock, and that oil pump would be located up near the cams maybe?

JerryU

^^
Interesting! Reminded of my old 4 volume book set (>1600 pages) called "Ingenious Mechanisms!"

GM leaked that view AND changed the cid, although modest and therefore not for "Noting Beats Cubic Inches," for a reason! Will be interesting to see just why!

DGXR

I wonder how this compares to the latest Viper design which essentially has a camshaft inside the camshaft (called "concentric"): Mechadyne

BMZR1

http://www.mechadyne-int.com/products/duocam/

I watched this video in the link above. I am not positive how GM's patented idea works exactly, but it seems to me, they may be doing something similar to viper, except there are 2 lobes per valve, and there is a complex rocker maybe? It talks about extending the valve opening duration time, so as the 1 lobe clocks from the 2nd lobe, it creates a longer duration time, as both of the lobes are somehow translated to a single valve it seems.

Dominic Sorresso

Tell me about it. If that drawing is anything close, it looks like a mechanical “cluster...” And the point is what? So u could use pushrods? So GM Powertrain comes up w this while they just finished doing a simpler DOHC design for the Blackwing series which is being built in BG. 🤔🙄

Warp Factor

Maybe the LT2 has some version of the valve train strategy used on their new 2.7 liter truck engine:

"The system’s electro-mechanical variable camshaft effectively allows the engine to operate with three different camshaft profiles, complementing the variable valve timing system to deliver optimized operating modes for different engine speeds and loads:

“It’s like having different engines for low- and high-rpm performance,” said Sutter. “The camshaft profile and valve timing is completely different at low and high speeds, for excellent performance across the board.”

The camshaft design alters the lift of the intake and exhaust valves. As the engine load changes, electromagnetic actuators allow a movable shaft containing different cam lobes to shift imperceptibly between high-lift and low-lift profiles."