This was over at the Corvette Forums:

"I just got my August 2003 Corvette Fever and there is an article on the LS2. It states that the LS2, which evidently was shown at a North American Auto Show earlier this year (they have a photo of it), is the same size as an LS1 (5.7L, 346ci) and will make 430-440bhp. It goes on to say the main differences between it and the LS1 is new, taller cylinder heads with angled valves, new cam, and DoD. The picture looks just like an LS1, but with an aluminum intake instead of the current black one. Any thoughts -- I thought we had pretty good confirmation that the LS2 would be 6.0L? "

Angled valves = canted valves = "porcupine head" = "semi-hemi" = RAT

Hrumph...

Insight from the more enlightened? Guion, where are you?

It seems logical in a way... the Rat always out-powers the Mouse at equivalent displacements (say, 406 cubic inches) with equivalent cam events because of the flow potential in the heads.

This would be MOST NIFTY, and would certainly point towards higher displacements in my mind.

 

I thought that it was all but confirmed the LS2 was 6.0L?

 

As far as what's happening at GM powertrain, I'm completely useless.

 

I think Corvette Fever is wrong.

LS2 almost has to be 6.0l from everything that has trickled out.

 

Dear friends,

The issue is not the displacement, it's the head design.

The real difference between a small-block Chevrolet and a big-block Chevrolet (apart from the Rat being bigger and heavier) is the cylinder heads.

Now, since the engine is no longer really a small block (which has it's valves all in a row), and not really a big block (bore centers are too close together)... we're gonna get a "medium-block".

Hmmm....

What to call it?

Bigger than a mouse but smaller than a rat....

The Hamster?

 

Not a bad idea. Since the 15-degree angle of the GenIII's heads comes pretty close to optimal as far as parallel valves go, a porcupine or "twisted wedge" design is the next logical progression. With the valves angled towards the center of the cylinder, you get less shrouding from the cylinder wall and chamber. This is the sort of thing that'd allow you to get good flow over a large range of lift from big valves - the size of valves that you might run if you, say, wanted to get 500+ HP in an effort to hunt a couple of particularly nasty snakes.

 

Hmm, nobody's really that interested in this, huh? I guess it'd get a lot more attention if we were talking about something less significant, like a change to SOHC heads or something like that. This is pretty big news, just like the "Mystery Motor" of the early 60s all over again

 

We're surrounded by heathens Eric.

 

It's not that the issue is not important, but for me it is a little over my head so I can not comment with any sort of informed response.................but it all sounds good................

 

Neil,

Nah, it's not over your head.

Take a look at a small block Chevy or LS1 with the valvecovers off.

All of the valves are lined up in a neat little row.

This arrangement is not chosen for maximum power, but because it results in a smaller, lighter head with simpler injector targeting (you want the fuel injector to spray fuel right at the back side of the intake valve), simpler pushrod and lifter geometry, and ease of manufacture.

Now, take a look at a big-block Chevrolet with the valvecovers off.

You'll notice that the valves are poking out of the head in an assortment of interesting directions. For the price of a bigger cylinder head, more weight, and added complexity, you get a higher-flowing head across the board.

Big block Chevys eat big blocks Pontiacs for lunch for a reason (I know, the Pontiac motors really only had one block by the 1970's from 350 to 455 cubic inches) - that reason is a more efficient head design. The big Pontiac blocks all have their valves in a row like the small block Chevrolet. Given equivalent valves, displacement and timing events, a small block Chevrolet and a Pontiac are a good match (say, 400 cubic inches). A big block Chevrolet with 400 cubic inches of displacement will blow a small-block Chevrolet with 400 cubic inches out of the water. It's all in the head design.

Big block Chevrolets were known as "semi-hemi" head designs as the canted valves allow for a semi-hemispherical combustion chamber. Converting the LS1 family motors to this type of arrangement will result in even more power, and that's why we think it's cool.

 

I'm very interested in this. But until a version is tested independently outside of GM powertrain (like the Cobra SC was), I can't add anything interesting or worthwhile.

 

Thanks for the explanation!

Taking the time to spell out some of this stuff helps for me... I will never claim to know tons about internal engine operation and design.... so I enjoy reading tidbits like this!

 

PacerX, excellent explanation of the benefits of angled valve heads. I do have a question though, with better flowing heads and 6 liters, are we looking at potential horsepower in the range of say 500 ponies?

 

Scott,

I think that the LS1/LS6 will have no problems putting down 500hp from the factory with added displacement and canted valves heads as long as the camshaft is designed to do it.

Regular old 346 LS1's routinely put down 500 hp at the flywheel with heads and cam, and some are starting to put down 400 rwhp with JUST A CAM SWAP.

400 rwhp = ~460 flywheel hp with a 15% drivetrain loss.



Here's another way to look at it...

6.4 liters is 390 cubic inches, 44 more than the 5.7 liter LS1 and LS6.

The LS6 makes 1.17 hp per cubic inch (405/346). Take that number (1.17) and multiply it by 390 and you get 456hp. Slap on a better-flowing head and 500hp is a no-brainer.

Now, here's another point - bigger engines like bigger cams with more overlap, lift and duration. More cam = more power, especially if the cylinder heads will let more air through.


The most interesting questions to me, if this happens, are:

1) Can I bolt these things onto an LS1 block?

2) How much do custom headers cost?

3) What's going to happen to the intake manifold design?


It's all speculation, but it's fun and interesting to me.

 

I think I would have liked math class better with examples like that. With bigger engine/cam combos, at what point do emissions requirements begin to get unachievable? Is 500+ hp and emmissions compliance something that could be done?