Dragula

iTrader: (5)

What happened on the plan for 3 valves per cylinder? There was so much talk about it and I haven't seen any specs that say it has 3 valves per cylinder so I assume it's 2.

ddelallata

iTrader: (2)

who cares about the 3 valves per cylinder? Dude, just be happy that GM had the ***** to make it a 7.0L

Dragula

iTrader: (5)

Easy Killer. I just want to know why they backed out?

ChucksZ06

iTrader: (9)

Not needed. Why go to the extra complexity if 2 valves gets the airflow you need? I have been working on my 4 valve cobra motor and it is ridiculous all of the extra moving parts there are...if they improved volumetric efficiency it would be one thing but it seems that less is definitely more with the ls design. GM gets more air in and out with much less weight and complexity and that is a superior machine. I bet ford will come out with an improved pushrod engine in a few years. The new mopar "hemi" is almost a copy of the ls engines.

CSiJason

Less moving parts = less complex = less internal losses = less likely to break = easier to build = easier to work on. Pretty much pick one or all of those answers. Considering how much power they got out of it the way it is, I wouldnt complain.

Another_User

I told everyone it was a gimmick, nobody listened.

PSM

iTrader: (2)

Believe it or not... the three valve heads may have reduced low end torque, maybe something gm did not want. Torque requires high velocity air while high end hp jsut wants a high volume of air. With two intake valves the velocity of the incoming air would be decreased. Two smaller valves would have more area than 1 larger valve. This would cause less of a restriction, therefor the incoming air wouldn't be drawn in as fast. The extra valve would only aid in the high end of the motor because it could draw in more volume. Does this make sense or am i talking outa my ***??

DietCoke

iTrader: (18)

They couldn't keep them together, and they could meet their goals with the two valve heads. Thus, they got the ax.

stik6shift93

My guess is that it came down to reliability issues

Wnts2Go10O

iTrader: (12)

forgot the big one, its also a hell ofa lot cheaper to build.

DavidNJ

Guess it cam down to $$$ issues. Three valves would have flowed better than 2. And 4 would have been better than 3. Note the flow at low lift in 4-valve motors and the max lift. Small valves are light and rev easily.

DOHC with variable cam would have eliminated EGR. And further lightened the valve train. Those Supras have strokes close to the LS1 range, and with stroker kits in the middle (up to 94mm). However many rev past 8k, and some up to 10k.

They could've done that. However, they couldn't for the price at least if the price is in the low 60s.

stik6shift93

The problem with ohc is that if they did indeed use them there's no way the motor would have fit under the stock vette hood, the whole front end would have to be redisgned and i'm sure the dc would be ruined. Not to mention the fact the it would've ruined the weight bias of the car from the extra weight and wouldn't have made the low end torque with the extra valves. Also either the bore would have to be shrunken or the stroke lengthened(which isn't gonna happen) to take advantage of the extra valves, which inturn would've decreased displacement which i'm sure they wouldn't do since they probably wanted a 427 for the nostalgic value. I could go on but i'm sure you get the idea.

PewterWSSicc

This is just speculation and opinion. But I think they decided not to go that route for several reasons.
1. Most LS based engine enthusiasts like our pushrod engines and dont want a OHC engine.
2. They are easier to work on, cheaper to mod, easier to repair and more reliable. Doing an extra valve without an OHC design would have probably been rough on the components. They would have had to do something like split rockers. Unless they had another idea for having a pushrod engine run 3 valves.
3. Simply why change what works. The pushrod engine makes plenty of power. It is cheaper for them to make and for us to maintain.

In the end economically it made more sense not to do it and most of GM's fan base doesnt wanna see it happen. I that we are one CAM and 600-1000 bucks away from making an *** load more power. The pushrod engine is also i think more sought after for racers because of how cheap cams are to do.

52172

iTrader: (2)

427 CI alone acomplishes a lot.

ChucksZ06

iTrader: (9)

It is popular belief that multivalve heads flow better and theoretically they will but in reality they may not...the design of the ports and the physical restrictions placed on putting all that machinery in a limited space makes the theory hard to come by. Go to patriots web site and look at the flow numbers for ford 4 valve heads....they suck compared to ls1 heads...no one ever considers how much the valve stem takes out of the port. GM has 4 valve cadillac motors and they are just like the fords...really hard to get air through. They use a z06 motor to race with...what does that tell you? I think the 4 valve head might be better under high boost but that is about all. The extra weight and complexity of the engine always negates any small hp gains unless you are talking about indycar/formula 1 levels of power which doesn't figure into our level of engine building. I am not being a downer on the multivalve engines but have been watching for 40 years and all the multivalve engines that were supposed to relegate the pushrod to obscurity.... it just isn't happening. View of an old guy.

Another_User

I have two things to add.
1) I was dying to see one of those little pushrods that connected to the second intake rocker go shooting through a valve cover.
2) Two intake valves was a stupid idea. Too much flow. The point behind more than one intake valve is that the second one should not always open. It should open on demand, at higher RPM when air requirements are highest. If I were GM I would fire whoever came up with that idea.

GMCVT

iTrader: (1)

As much as I agree that the 4V is a little overated, if you go to TEA's website and compare say a stg.3 ls6 to a stg.3 4valve, the peak #'s are almost negligable but the #'s under MAX lift are actually significantly better. I dont know what kind of velocity those #'s carry but just speaking of hard flow #'s, they do seem to do very well under the curve. I just dont think there is enough of an advantage to merit the expense of having a 4v ohc engine. Interestingly enough, in the front of 5.0/Super Ford magazine this month, the editor addresses this very topic. Pretty interesting article. Good read if ya get a chance. Its on page 16, entitled, Imagine This.

LTSpeed

I can't speak to the reason they dropped the 3-valve design, but my own experience with that style showed that it increased temps on the head of the piston and led to detonation and, in some cases, damage to the piston itself. This could be overcome by special coating of the pistons, but it is expensive--especially when combined with all of the extra mass/cost of the 3-valve valvetrain might have been the deciding factors.

The net hp gain just isn't worth it when there are a lot more bang-for-the-buck ways to get power.

Another_User

There would be an advantage if they used something similar to VTEC, not whatever poopie stuff Ford is doing.

Anonymous

There are advantages and disadvantages to both two and four valve engines.
A book could be written about it.

Now I believe the 3 valve design was never intended for the LS series engine at all. I read a lot of hype about it in here but never saw proof.

The only 3 valve GM cylinder head I ever saw was in Chevy High Performance in the News section. But if you looked closely it was a new generation Big Block head. The magazine never said it was an LS series head either.
I think that is where the rumor got started.