4-valve v's 2-valve heads

[Billzilla]

An extract from my site, and yeah it's only a small engine blah blah blah but it's an example.
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This is an extract from a friend of mine, Dave Andrews, about this very subject. He's what he had to say about some dyno runs that he did -
"First off I agree with most of what Bill has said, 4 valve engines simply allow better cylinder filling at all RPM, this translates to improved BMEP and therefore increased torque and BHP throughout the rev range. I would say that a 4 valve engine in aspirated form, developed properly will make about 90ft/lb per litre tops and can sustain most of this for around 50-55% of its rev range, an 8 valve engine developed properly will make no more than 82ft/lb per litre and can sustain most this for no more than 40-45% of its power band. This means that a stonking 4 valve engine will be far more flexible and have a wider torque envelope that an 8 valve.. end of story, where you choose to make that torque is up to you.
Effective cylinder filling at high RPM (and therefore big BHP) comes at a price on an 8 valve engine, the price is wild cams and lots of overlap, these destroy low down torque. 16 valve engines have inherently better cylinder filling because of increased valve curtain area, to extract greater power requires less cam duration and less overlap than with an 8 valve, this allows better retention of the engines low down torque characteristics.
I've run my current engine in 8 valve and 16 valve form, both times running relatively enormous cams (8v 326deg, 16v 302deg) with ultra big valve heads and 48 webers, the 16 valve version produces 70BHP more and comes on cam 1500RPM earlier, at 2500RPM the 16 valve has *twice* the torque of the 8 valve.
Peak torque on the 8 valve was 155ft/lb, on the 16 valve 179ft/lb. From 3500 to 8300 I have over 85% of maximum torque on the 16 valve, on the 8 valve torque hits 85% of maximum at 4400 and drops below again at around 7200. Thats why I changed to 16 valve..
Here is a real example from a big rolling road day at Walkers workshop on Sunday 15th, two engines, one an 8 Valve 'Kent' Crossflow, 1780cc, fully worked big valve head, 296 degree cam 40 Webers and 4->1 exhaust, the other a 16V Rover K series 1788cc, standard head, standard plenum, 268 degree cams, 4-2-1 exhaust.
Both engines made around 146BHP (xflow 145, K series 147)
The following figures are torque in ft/lbsRPM 8v 16v
1500 45 56
2000 68 91
2500 101 130
3000 112 133
3500 112 129
4000 111 132
4500 126 140
5000 129 136
5500 130 134
6000 126 126
6500 112 118
7000 99 108

Speaks for itself... at 1500 RPM the 16v has 24% more torque, at 2500 the 16v has 29% more torque, at 4000 18% more. These are real life engines, no theory here, in order to match the 16 valves output the 8 valve has to use a lot more cam and a big valve head fully reworked. This has worsened its low down torque. The output from the 8 valve is considered very good for a road engine too.
A naturally aspirated 1788 K series 16 valve engine fully reworked (by me) was on the dyno today at Walkers Workshop and made 251BHP and 163ft/lb of torque (90ft/lb per litre). See it in CCC magazine next month, show me an 8 valve aspirated 1800cc engine with those sort of power and torque figures and I'll show you my testicles on a silver salver.
Dave"

[TK]

Work it out Bill, the figures are there.
I'm not gonna give you my data on these heads, I've spent 100's of hours perfecting them.

Saying a 4-valve will give better torque is simply not true, a 4-valve will always have larger port volume than a 2V = less velocity, if a 2V is able to flow the air required for a 100% cylinder fill at a certain rpm then you won't get any more air in with more flow, all you achieve is a slowing of the velocity, resuling in less inertia ramming & LESS cylinder fill.
Your statement does hold true for little 4-bangers where a typical 2V head cannot flow the air for 100% cylinder fill, but it is simply not true when it comes to modern V8's.
Another little point you seem to be twisting is combustion efficiency - older style 2V heads did burn rather poorly, but modern designs offer more swirl than a 4-valve (as a result of the valve being offset over the bore, as compared to the even stagger of a 4-valve), more quench area (coz so much space is not taken up by valves) & faster, or equal burn - the result is, again, better low rpm torque.

[TK]

Your above example is a poor one, the kent 2V engines have a very poor port design & cahmber design, comparing a kent crossflow to a 4V head is stupid & again is a small capacity 4-banger, not a big bore engine which is the basis of this thread.

& yes, I have ported kent heads.

[The Pupat]

If 4v heads give better low down torque, why did honda spend mega bucks developing ways to shut valves off at low rpms.

[Billzilla]

Work it out Bill, the figures are there.
I'm not gonna give you my data on these heads, I've spent 100's of hours perfecting them.

Saying a 4-valve will give better torque is simply not true, a 4-valve will always have larger port volume than a 2V = less velocity

Sorry but that's just plain wrong.
I don't need or want your data, it is clear that I am getting better results out of 4V heads than you are.

Your above example is a poor one, the kent 2V engines have a very poor port design & cahmber design, comparing a kent crossflow to a 4V head is stupid & again is a small capacity 4-banger, not a big bore engine which is the basis of this thread.

& yes, I have ported kent heads.

The chap I quoted has worked on far more than you have, no doubt, and he's corrected all those faults. He knows his stuff - You could do worse than to contact see to see if he will pass on some tips.

[TK]

Sorry but that's just plain wrong.
I don't need or want your data, it is clear that I am getting better results out of 4V heads than you are.

Pft, yeah, right.
You're being an elitist ass Bill, but you're not elite.

Give me any head, even if I've never seen one before & I'll beat your flow figures in 1/2 the development time - do you even port your own heads? - I recall that maybe you don't, not the good ones anyway.

The chap I quoted has worked on far more than you have, no doubt, and he's corrected all those faults. He knows his stuff - You could do worse than to contact see to see if he will pass on some tips.

Anything you do to a kent head is not gonna fix the bastard, they are just not much good - it really is a poor example to base your argument on.
PS - I don't want ay tips on porting kent heads - I have no interest in that crap, haven't touched one for years & probably never will again (if given the choice).

Saying a 4-valve will give better torque is simply not true, a 4-valve will always have larger port volume than a 2V = less velocity, if a 2V is able to flow the air required for a 100% cylinder fill at a certain rpm then you won't get any more air in with more flow, all you achieve is a slowing of the velocity, resuling in less inertia ramming & LESS cylinder fill.
Your statement does hold true for little 4-bangers where a typical 2V head cannot flow the air for 100% cylinder fill, but it is simply not true when it comes to modern V8's.

Maybe use the whole quote next time, not just the bit you think you can disagree with.

[Captain Slow]

sorry but this fits here fucking perfectly.

[Billzilla]

TK rant all you like but I get the results that you can't.
Why not stop the agro and try to learn .... ?

There's people much better than me at building engines and I go out of my way to learn from them, why not do the same?

When I started I thought the 3K was a great thing.
Then I found the 2TG, thought it was wunnerful.
Then I saw the 4AG and thought it was crap, but spent the time to examine it and work it out. Then it was a good thing.
Then I found the 7AFE heads and knew immediately they would kill a G head.
I thought that was about as good as it could ever get really ...
... but the other day I spotted something very interesting in a magazine on a new head design. I don't understand how it works, but the numbers are there so I am going to try to figure it out.

And yes, it's more complex, larger, heavier, and more expensive than a conventional 4V head. But for an n/a engine it looks like it can't be beaten.

Just because I don't understand how it works doesn't mean it's crap - that's one of my main points throughout these threads. There's so many people here that suffer from that.

[psi999]

If 4v heads give better low down torque, why did honda spend mega bucks developing ways to shut valves off at low rpms.

x2

[Billzilla]

If 4v heads give better low down torque, why did honda spend mega bucks developing ways to shut valves off at low rpms.

I'm not familiar with that engine, which one is it?

[The Pupat]

i-VTEC

All latest honda VTEC motors run 3 stage VTEC. Look it up.

[Billzilla]

i-VTEC

All latest honda VTEC motors run 3 stage VTEC. Look it up.

Sorted.
What they're doing there is making the engine work better under a small set of conditions ->

http://asia.vtec.net/article/k20a

Looks like that at low revs and lots of throttle they can get a bit more torque and economy by running just the one valve - and also altering the valve timing.
I'd be curious as to how much more though, and it seems it mainly to run very lean (20:1 in that article) mixtures.

[TK]

In what respect are you getting better results than me Bill?

AFAIK I haven't built any comparable engines to your little 4-bangers.

Resorting to insults & trying to slander my abilities as an engine builder/head porter does not make you right, it simply shows that you are out of your depth and can't refute the key points of my arguments.

I stand by my statement - give me any head, even one you have personal experience with & I will beat any flow figures, velocity & power output you (not someone you know) can get out of it.

So, do you port all your heads yourself Bill?

If not, how can you claim to better me?

[Greg Rust]

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.

4 valve heads are very succesful in small capacity engines in cars and bikes that run high rpm and have their max torque relatively high up the the range,

[perthdrivers.txt]

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