4-valve v's 2-valve heads

[Nero]

The limitations on the stupidcar donks mean they can't run the best heads - no canted valve/twisted wedge style heads, no offset guides etc - so a 4V probably would show an inprovement.
Different story if you built an 'unrestriced' donk for the same fuel & same capacity & rev limit.

Well there are a few series where things are 'unrestricted' but where is a 2v winning?

[TK]

FFS people, read the damn thread, I ain't arguing it all again.

If you can get as much cylinder fill with a 2V as you can with a 4V on a certain engine in the rpm range that is required then there is no fucking advantage performance wise from running a 4V head - it's pretty fucking simple, the extra flow of a 4V is fucking irrelevant if it is not needed & can't be used.

Get it into your thick fucking skulls - an engine of xx capacity can only injest so much air - fitting it with heads that can flow more than it is capable of consuming is a backwards step in terms of velocity for no benefit whatsoever (in terms of performance).

Christ, it's not that fucking hard to understand, give up on the '4V is always better' religion - yes a 4V head is often a better idea, but under some curcumstances (ie. big fuck off V8's) there is just no benefit.

Fucking pinheads.

Yes I'm annoyed - if Bill can see that 4V's are not the be all & end all under all circumstances (& he is the most dedicated 4V fan that exists methinks) you would think that you lot would be capable of understanding it - or is it just that Bill does actually understand what is going on & you lot don't? -you're too stuck in the 2V is better world to look outside it.

No, I do not believe that 2V heads are better - that is blatantly not true, but I do have enought knowledge & experience to know that they can do a better job than most people think.

Bah, why bother, some people just refuse to think it through - their loss, understanding the thoery could help them better understand engines in general, but nope, easier to just bury yer head in the sand & chant 4V is best, 4V is best, 4V is best....

[Nero]

what?...is this directed at me. I asked a simple question based on your premise of 'unrestricted'. I HAD assumed you would know of a situation where this was the case and you could educate me, not spit the dummy.

[TK]

Sorry Nero, not at you, look at Ze's post - he's argued the same things that have been already covered, some a few times & it shows that he has no understanding of the basic concepts or he can't read.
That's what pissed me off.

But there is not situation I can think of where larger capacity 4V & 2V engines compete in a comparable situation.

If 'unrestriced' means no rpm limit them a 4V of the same capacity is almost always gonna win - at higher rpm the donk can use the extra airflow.

[Nero]

The only situation I can think of is Le Mans, where the Corvettes have done so well...but they are not unrestricted...and have noting in common with road engines.

[Ze]

Sorry Nero, not at you, look at Ze's post - he's argued the same things that have been already covered, some a few times & it shows that he has no understanding of the basic concepts or he can't read.
That's what pissed me off.

I can read and understand the basic concepts :p I just skipped a few pages :p

Mate I'm not one of the people who bash 2-valve engines or say they are a waste of effort. I just like motors , doesn't matter if they are 2-valve , 4-valve , OHV or OHC or side valve.

FFS people, read the damn thread, I ain't arguing it all again.

If you can get as much cylinder fill with a 2V as you can with a 4V on a certain engine in the rpm range that is required then there is no fucking advantage performance wise from running a 4V head - it's pretty fucking simple, the extra flow of a 4V is fucking irrelevant if it is not needed & can't be used.

Get it into your thick fucking skulls - an engine of xx capacity can only injest so much air - fitting it with heads that can flow more than it is capable of consuming is a backwards step in terms of velocity for no benefit whatsoever (in terms of performance).

However there is more to a cylinder head than just the amount of air it flows and the number of valves. I mean fuck you know this you reshape the combustion chambers and do other tricks to improve how it burns.

Alternatively I could be fucking wrong on this count and once you start flowing that much air it's all about flow and nothing about the piston shape , combustion chambers and valve shape. Feel free to tell me I'm completely off base if I am.

No, I do not believe that 2V heads are better - that is blatantly not true, but I do have enought knowledge & experience to know that they can do a better job than most people think.

I wasn't arguing with that TK and I'd be a fucking bigger idiot than I think am if I did :p

[TK]

However there is more to a cylinder head than just the amount of air it flows and the number of valves. I mean fuck you know this you reshape the combustion chambers and do other tricks to improve how it burns.

Go back & read, port velocity, swirl, chamber shape & burn characteristics are all covered back there somewhere.

I've run through the +'s & -'s of both designs, several times I think.

[oldcorollas]

so cliffnotes:

if the engine is spinning slow enough, then both 2 and 4 valve can inhale enough air to get about the same VE.

once the engine is spinning fast enough to take advantage of intake harmonics/pulse tuning (whatever you want to call it), or gets over a certain RPM,then the 2 valve fall behind and can't match the airflow requirements?

[Billzilla]

... or is it just that Bill does actually understand what is going on & you lot don't?

I don't entirely understand why yet, but I'm trying to and accept the evidence so far.
There's still the advantage of variable cam timing available on twin-cam heads, that is not possible on single-cam one - That alone can make quite a difference to to overall torque curve and it quite easy to fit & operate these days.

[GTSBoy]

There's still the advantage of variable cam timing available on twin-cam heads, that is not possible on single-cam one - That alone can make quite a difference to to overall torque curve and it quite easy to fit & operate these days.

Yes, but whilst that advantage is inherent in the head design (in that you can add it because the head design allows you to) it is not inherent in the design.

If you guys can scrape together some more 2 valve engine bore, valve diameter numbers, across a range of bore sizes, I can continue to look at those ratios to see what jumps out.

cheers

[TK]

if the engine is spinning slow enough, then both 2 and 4 valve can inhale enough air to get about the same VE.

once the engine is spinning fast enough to take advantage of intake harmonics/pulse tuning (whatever you want to call it), or gets over a certain RPM,then the 2 valve fall behind and can't match the airflow requirements?

Wouldn't exactly put it as 'spinning slow enough' - I'd guestimate the crossover point to be between 6-7000rpm on average, ie somewhere between 6-7000rpm the 4V will start to show a significant advantage due to superior airflow.
^ that is a very broad statement tho, assumes both a good 4V & good 2V design that is matched well to the motor.

[Billzilla]

Yes, but whilst that advantage is inherent in the head design (in that you can add it because the head design allows you to) it is not inherent in the design.

But it is - How would you move the lobe centre of the inlet cam compared to the exhaust cam on a single-cam engine? True enough it's easy to advance/retard an entire cam, but that has far less effect than being able to drastically change the overlap, etc.

If you guys can scrape together some more 2 valve engine bore, valve diameter numbers, across a range of bore sizes, I can continue to look at those ratios to see what jumps out.

cheers

I'll do that bunch of calculations I mentioned a while back on the single cylinder engines - It'll take a while as I'm really busy this week ..... and really lazy as well.

[goose]

Bill, doesn't the Dodge Viper do exactly that? Found a quick article here.

EDIT: Better article here.

[Billzilla]

Bugger me!
That's clever.

[GTSBoy]

I was going to say, it's not impossible. That is a good trick isn't it?

Even variations on Honda's first VTEC where you have extra lobes locked in by pins would allow you to have crude lobe centre changes between inlet and exhaust, and more lift too even in a dinosaur V8. Would need some differences in follower layout down in the valley.....

And an OHC 2 valver allows you to play with rockers and finger followers and all sorts of toys that can give you some tweakage as well.
It's just dead easy in DOHC by comparison.