4-valve v's 2-valve heads

[perthdrivers.txt]

2 valve heads obviously still have a place as they are still very successful in Hemi locations in Top fuel and Nitro funny car applications.

That is more to do with regulations and historical precedence than any mechanical ability

[Dave]

If 2V engines are so good, why are 90% of production engines today 4V?

If the LSx series are so fantastic why was GM even going to produce a DOHC V8 Northstar engine (before the massive $ losses faced recently meant it had to be given the chop)?

If pushrod 2V engines are the equal of DOHC 4V why are only two manufacturers still making them?

Simple answer - because the V8, large capacity blocks on which they are placed masks the inferior design...

Now in the real world no one would argue that the LSx engines arent good, but to say that they wouldnt be better with a DOHC 4v setup is wrong

define better?

[The Pupat]

With no real examples of a big 4V engine we can only guess. I've got a lot of experience with the 4V heads and getting good power from them, someone give me a Nissan VK56DE and I'll build something very scary for you.

Done



Only thing it fits in is a boat... probably won't fit back in the F-Truck it came out of.

[GTSBoy]

Arggh! My eyes! My eyes! That photo!

Curse you again edo!

[TK]

Now in the real world no one would argue that the LSx engines arent good, but to say that they wouldnt be better with a DOHC 4v setup is wrong

They wouldn't be better, they'd cost more, be bulkier & heavier, compromises in In/Ex system design in order to fit them in say, a commodore, would limit any gains.

I'l state again - if a 2V head is able to flow enough air for a 100% cylinder fill at a given rpm, then the higher flow of a 4V head will show no gain, it will in fact show a loss due to lower port velocity & less swirl.

The only benefit will be at higher rpm where the 2V head begins to run out of flow - but higher rpm defeats the purpose of larger capacity & runs into reliability problems.

As an interesting aside, Ford are looking at going back to a 2V design to replance the 32 valve engines - they have found that the added cost, bulk, weight & complexity do not pay off in terms of performance.

No-one will argue that a 4-valve head is superior in many applications, particularly small capacity, high revving engines, but in larger capacity, lower revving engines the advantages are not big enough to offset the disadvantages.

[Nero]

my question is simple enough TK. given open regulations i.e. when the rules do not stipulate 2V can you name any current racing (as opposed to drag) category where a 2V same capacity engine is competitive?
I have no doubt in my mind that the LSx engines are good at what they do, but they are as always designed for their market and to do a 'job', this is what they are 'better' at....i.e. they make more money.

[Sturmovik]

If pushrod 2V engines are the equal of DOHC 4V why are only two manufacturers still making them?

You need to do some more research if you think only two manufacturers make Pushrod engines.

[TK]

The only comparable engines used in most racing classes are smaller capacity - where 4V does have a significant advantage.
I guess something like a VH45/54 nissan would be kinda comparable to an LSx donk, but you wouldn't sqeeze the nissan bugger into as tight a spot as an LSx - which sorta limits it's usefullness.
+ all up weight (including aux systems to run the sods) of the nissan would be a bit more than the LSx - so handling in a front engined car would not be as good, the LSx would be easier to stuff back through the firewall due to it's more compact dimensions.
There really isn't many racing classes that have larger capacity engines (like, 5L+) - the ones that do exist are dominated by 2V engines.

Besides which, we're not talking about race applications, simply viable, cost effective performance engines for the masses.

[Greg Rust]

I started going through here but ended up pissing my self laughing.
http://www.letsmow.com/rulebook.asp

[edo]

The datto V8s are pretty much a 700mm cube, how big are the LS engines?

Oh, You can get the VK56 pretty cheaply out of the states Bill, so get too it

[rj_astra]

The Honda VFR800 runs a VTEC system that shuts off an inlet valve at low speed.

Ford supplies small cars in Europe with 2 and 4 valve versions of the same engine. I assume its based mostly on unit cost and market positioning.

[Sturmovik]

The datto V8s are pretty much a 700mm cube, how big are the LS engines?

Oh, You can get the VK56 pretty cheaply out of the states Bill, so get too it

Just remember this includes front pullys

[GTSBoy]

That is really very comparable. The Datto is slightly wider.

There is no argument that twin cam V engines can be made too big. I was mildly involved in the removal of a 350 Chev from a Corvette and it's replacement with a VG30DET. The VG was bigger in all directions, courtesy of too wide heads, a big exhaust crossover pipe behind the motor etc. The small block looked tiny next to it, was hard to believe that it was twice the internal capacity of the VG.

Of course, it had waaay less power and torque than the VG, but that's another argument (or actually the same argument, but it's not fair comparing a dinosaur era shitter with a modern injected 4 cammer)

[Billzilla]

I'm not interested in all this crap anymore, so I'll let you lot ramble on as you like.
But one thing caught my eye, and it might explain a bit ...

I'l state again - if a 2V head is able to flow enough air for a 100% cylinder fill at a given rpm, then the higher flow of a 4V head will show no gain, it will in fact show a loss due to lower port velocity & less swirl.

... I know how to get something more like 120% cylinder filling, and my heads also have useful swirl.

Since no-one was interested in doing the engine course, I'll keep my secrets to myself.

[Sturmovik]

According to what I found on the net the VH45 is 800mm wide, I doubt the VK56 is narrower?