Jeff V.

One of the still images that was flashed on screen during the official GM teaser video showed a very weird engine cutaway. It's got two oil pump gerotors, and two timing chains. The positions of some of the other parts are identical to the current 6.6L L8T V8. It's a long shot, but it might be something very old made new again.



Back in 2001, GM had a concept engine they called the XV8. It had two cams in the block, 3 valves per cylinder, direct injection and displacement on demand. It also had two oil pumps. The dual oil pumps were so it could run with deactivated cylinders at idle speeds.

This article has a ton of interesting info. It directly addresses the dual oil pump situation, and the diagrams below explain the 2nd timing chain.

https://www.acarplace.com/brands/gm/xv8-engine.html





I seriously think this is an evolution of the XV8 concept.

skank

Thanks Jeff_V. This is very very interesting!

ltomn

Could this be an indicator of the proposed Advanced Fuel Management?

BEAR-AvHistory

Yeah, noticed that did not look like a standard cam in block engine. Was not aware of the twin in block concept.

ltomn

This is forward thinking stuff!! Displacement on demand, variable valve timing and all for less then $62,000!! I doubt it!

skank

This is from the above linked article on Jeff_V post #1 and it matches the order guide info on the engine that was shown a few weeks ago. Now knowing that Spring Hill is now building the new LT2 it seems plausible that this could be it.

With an aluminum block and head, the 4.3 liter XV8 has three valves per cylinder with an air-assisted direct fuel injection system and two camshafts in the block. Power ratings are 300 horsepower (224 kW) and 295 lb-ft (400 Nm) of torque.

Other features include variable inlet systems (currently the main feature of Chrysler's Magnum engines), cam phasing, and displacement on demand (first seen on the ill-fated Cadillac 4-6-8 engines), variable inlet valve timing (common to Toyota and Honda engines), a narrow 75-degree bank angle, twin oil pumps, and an integrated air compressor. A GM spokesman said this combination was possible, in its best form, because of the engine's clean-sheet design: there was no need to compromise new features to co-exist with existing designs. That was especially important for direct injection.

The XV8's compression ratio of 10.75:1 is achieved with regular gasoline.

Jeff V.

The new truck engines have Dynamic Fuel Management. I found a cutaway of the 6.6L L8T, and it had a normal single stage variable vane oil pump. I don't see anything that says DFM works at idle. This is the L8T truck engine from a similar angle to the engine in the video. Note the single chain and single, variable oil pump.




The suspect C8 engine basically has 3 oil pumps. The variable vane pump, and the two big gerotors. I think that would allow a dry sump, with dual cam in block, and an advanced DFM that works at idle.

Jeff V.

I'm not making any claims about whether or not this is the base engine. For all we know there are two turbos hanging off the sides of this thing.

ltomn

I have a 2019 Silverado and you are absolutely correct! Mine is equiped with the 5.3L EcoTec3 V8 engine with DFM.

• 355 hp [265 kW] @ 5600 rpm
• 383 lb-ft of torque [518 Nm] @ 4100 rpm
• Dynamic Fuel Management technology
• Paired with a 8-speed automatic transmission

Zaro Tundov

They could keep it to two valves per cylinder for low end torque and use the two in-block cams to independently phase intake and exhaust valves. One problem with the dual cam theory is that the visible cam seems to have too many lobes for a twin cam design.





Something that's bugged me in the supposedly leaked order guide info is that the LT2 is described as having AFM instead of DFM. With the later news that the LT2 will be built at the Spring Hill plant, which is tooled for DFM, that makes me think the order guide could either be a troll or maybe just placeholder data.

GPaTom

This is fascinating! I lost sight of this concept as the years have passed. The 75 degree bank angle would reduce the width, an advantage over the conventional 90 degree V8. Packaging for a longitudinal drive mid engine layout would be improved. Three valve combustion chambers and airflow can be very competitive with DOHC 4 valve, and cam(s��)-in-block should allow for a shorter overall height.

If this is in the development plan, it is hard to believe we have not had leaked info before now.

Great work to see it in the video Jeff V .....

Warp Factor

Good catch, Jeff! Would only need two cams instead of four, and the cam drive would be much simpler and shorter than with dual overhead cams.

Zaro Tundov

Yet width isn't a constraint in a mid engine car since the engine isn't between two wheels that need to steer. A 75 degree V would make the engine taller and thus raise the center of gravity and it would also be heavier due to the need of a balance shaft.

Three valve pushrod (2 intake, 1 exhaust) is the worst of both worlds. Lower air velocity at low engine RPM reduces torque output, yet due to valve float the engine cannot rev high to exploit the higher powerband.

Jeff V.

That cam could make sense. In the XV8 example they use one pushrod to drive a dual intake rocker. But maybe they're doing 24 pushrods? Then the intake cam still needs 16 lobes. There would be four on the front section of the cam, between the drive sprocket and the first bearing journal. There's likely a 4th lobe we can't see due to the angle. It's not too surprising the spacing would be different from the LT1-based layout.

I don't know what else that second chain could be for, especially combined with the huge oil pump assembly.

I Fly Low

Wow, great catch! that look exactly like the cutaway. I'm not in the market, but if I was I would stay away from the first year, With something this dramatically different, I would expect quite a few problems. Just my opinion.

Zaro Tundov

Could be, though I can't find any other three valve per cylinder pushrod engines that use two pushrods instead of a dual intake rocker. Probably because the extra pushrods add more reciprocating mass.

Here's a crazy thought: maybe since they're already disabling intake valves for DFM, it was easy to individually disable them so at low rpms the engine can operate on two valves per cylinder, thus preserving high air velocity, high torque characteristics. Once at midrange rpm, both intake valves actuate for increased air volume. Thus, 16 pushrods for 16 intake valves.

Jeff V.

Hmm. Could be. It'd be like VTEC for pushrods.

Zaro Tundov

Wait, the two pushrod for two intake valve theory doesn't work. Look at the lobes - there are no matching pairs for the two intake valves per cylinder.

vndkshn

Well, another way to look at it, two valve springs pressing on one lifter is potentially more load than a 1:1 relationship. Who knows?

Or, the two valves are slightly out of phase of each other to induce a swirl effect?

Overall, definitely interested to hear more about this engine if it is the one in the ME. Could also explain the rumored .1L increase in displacement, a basically entirely new engine. Which now that I "say" that outloud, why would they call it the LT2 and not something different? I'd invision an LT2 to be a derivative of the LT1. But if this has 75 degree banks, all new valve train design, etc... it wouldn't be an evolution of the LT1.

Jeff V.

The RPO for the Blackwing engine is LTA, and it's got even less in common with the LT1/4/5 than this engine allegedly has.

There's also the possibility that this is some mid-range engine rather than the base LT2.