"Hemi" stands for Hemispherical, refering to the combustion chamber shape, i.e half-sphere. The original Hemi was just that, and used domed pistons to retain a high compression ration. The new "Hemi" has a relatively flat combustion chamber, and flat-top pistons.

It does have a similar valve arrangement to the original, however the "Hemi" name really shouldn't apply anymore. Great marketing idea, though.

If anything, the fact that Chrysler went back to a pushrod design rather than the scaled version of their 4.7 ohc they had planned, demonstrates that GM really knows what they are doing when it comes to large V8's.

16 spark plugs? No thanks. The GenIV looks good to me. D.O.D., cam phaser, and three-valves, all on the finest pushrod engine ever.

 

I read in magazine,they described the new Hemi as a Hemispherical combustion chamber, that then has extra material added in to aid in squish swirl and all those weird important things and Two sparkplugs needed for good flame propagation..



The 3v pushrod design still has the low profile advantage compared to ohc.. which means more cubes in less overall space, to help suck more air thru the heads..

As Xed said, I'm sure GM did their homework.

I think it would be intersting if a version of this 3v head also appears on the C5R engines...


I also remember reading an SAE article a bit ago on GM researching new materials, supplier, manufacturing techniques for valvetrain components, especially springs, to make them stronger, lighter, and affordable..

GM is definatly doing some interesting things...

 

The hemi name originally meant the open chamber hemispherical shape. But that wasn't the genius behind the design, it was the centrally opposed valve layout. All modern DOHC engines take advantage of this with ease, hence they are also referred to as hemi motors. In today's terms a Honda vtech is a hemi motor. The open chamber design is dead precisely because it does not promote air fuel mixing like a closed chamber high squish chamber. I've built 2 motors at near 11:1 compression that won't knock on 87 simply by using closed chamber heads and milling the block to 0 deck. Meaning the gasket is the only thing providing piston to head clearance. This causes squish which jets the air/fuel mixture from the edges back to the center of the bore violently. However, high squish motors tend to blow spark out. Thus to take advantage, it requires a high power ignition system or multispark. Also I believe the high squish chamber in the Hemi head also shrouds the spark in certain areas so Dodge has gone to multicoil waste spark dual plug. Chevy big blocks have been a half *ssed attempt at a hemi head for many years. Only it called a canted valve head.

This new Chevy head is a "hemi head" too based on it's opposed valve layout. It's just a ridiculous way to do it. There is no way you increase the reciprocating mass of a valvetrain by what looks to be about 30% and say it's higher revving without some unusually large bulky spring components. Not to mention all the additional valvetrain bounce at high rpm. It's a hack plain and simple and POS one at that.

The new Hemi is the best pushrod design possible in terms of performance vs simplicity and durability. 330hp 375lb ft in a 5.6 truck motor. That would be with a small round cam in there. Put a half decent car application cam in there and the new Hemi will make 400 without even trying. Want more than 2 valves? OHC simple as that.

 

Well no offense but I'll go with the professionals at GM Powertrain. Why is it that everyone who has ever worked on a motor in their garage feel they know all there is to know. You obviously know a little about engines but to critique a design as a "POS" right off the bat would be jumping the gun.

 

Back when Chrysler introduced the K-car, they called the optional Mitsu engine the "Hemi 2.6". What a joke!

I don't see how GM's 3-valve head is any worse than the new Hemi 2-valve. Looks like it would flow much better. The exhaust rocker/pushrod combo appear to be more massive, however the new Hemi has some fairly long pushrods and big rockers.

Remember, the GenIII block placed the cam higher, and gave it larger base circles, in order to reduce valvtrain mass (pushrod length). Higher ratio rockers also give it lower valvtrain acceleration.

 

You know what? You're right. I am playing a little devil's advocate here. I mean if this setup actually works, it's the coup of decade on valvetrain tech.

But LOOK at it! I mean it really looks like something out of a cartoon. You know where the bowling ball rolls of the shelf, hitting a board, knocking a coconut into a roller rocker pushing a valve open.

I actually should say it's definitely a hack but not a POS. The more I look at it, given that I also believe the engineers have tested the thing to 8000rpm, it would quite a sight seeing that valvetrain in motion.

 

Yes...I'll give you that. It does seem a rather odd way of accomplishing it. And you do have to wonder about how they got it up to 7,000 or 8,000 rpm...safely no less.

Is the 3 valve setup going to be on the Corvette when it releases?

 

I believe there's an old saying in engineering that goes something like, "sometimes a sledge hammer really is the best tool for the job."

You may not think it's pretty, or elegant, but if it gets the job done.....

 

that doesn't mean there isn't a better way to get the job done....

 

I'd be careful about believing everything you read on the internet, especially when it comes to highly protected engine programs.

As an example, for a long time, people were saying the Gen IV would be camless...

 

I think in that instance someone made a mountain out of a mole hill. I'm sure they're working on the concept, but it's obviously years and years out.

 

As far as the camless engine, wasn't it supposed to use the sperical valves from coates engineering?

 

What is the benefit of having an extra Intake valve if they open at the same time? Why not make the one intake valve bigger?

Disclaimer: The below info is provided from my mind as I remember. If somebody knows different please correct me.

I mean in the days of the 305/350, the drawback of the 305 was the limit in intake valve size (besides the lack of cubes). I believe the max intake valve size was 1.94 inches. So people preferred the 350 because putting a head with 2.02-inch intake valves really woke that puppy up if you had a cam that would take advantage of it. If I am not mistaken the LS1 has an intake valve size of 2.00. Can it not be made bigger because the valve shrouding of the cylinder bore? According to Mortec.com the old 305 and the newer 4.8\5.3 have almost the same cylinder bore so just making the intake valve bigger may not be an option for those engines but the ls1\6 5.7 liter and bigger performance engines would benefit from just using a bigger valve.
Bore:
305 = 3.740"
5.3\4.8 = 3.780'

I guess my question in short would be " What is the benefit of a 2nd intake valve other than more flow?" And "If flow is the only benefit then why not just use a bigger intake valve on performance engines?" Is there an engineer or somebody in the know that can answers these questions?

 

I read before that there is a limitation to making a valve too big (can't rev as high maybe ) 2 smaller valves is better for more flow. I don't remember the exact reason for this. maybe someone else can help answer this

 

Velocity.