4-valve v's 2-valve heads

[Billzilla]

Tony - FWIW that LS7 32v thing I roughed out on EAN had inlet ports the equivalent of a 2.1" diameter circle. How does that equate to a 500hp - 700hp regular V8?
I've got more measurements if you like.

[TK]

2.1" dia port = 3.46 sq" cross-sectional area.

650hp chev V8, 1.83" av dia = 2.63 sq" cross-sectional area.

3.46 is about 32% bigger than 2.63.

So the ports are 32% bigger for an output of what, 10-15% more?

Those are rather large chev heads, 225cc intakes.

So, yes, 4V ports are bigger.

[TK]

Stick 1.83 dia ports into eap & see if you can beat 650hp at 7000 rpm with 383 cubes.

Then think about this - 32% bigger port will require 32% more airflow to achieve the same port velocity. ie - for the same inertia ram effect that the 2V head will see at 4000rpm the 4V head would need 5300rpm.

[Billzilla]

2.1" dia port = 3.46 sq" cross-sectional area.

650hp chev V8, 1.83" av dia = 2.63 sq" cross-sectional area.

3.46 is about 32% bigger than 2.63.

So the ports are 32% bigger for an output of what, 10-15% more?

Those are rather large chev heads, 225cc intakes.

So, yes, 4V ports are bigger.

About the same power, but still with good bottom-end grunt.
Interesting though ..... !

[Billzilla]

Some other numbers ...

Two inlet valves 1.57" dia
Two exhaust valves 1.45" dia
Exhaust port 1.85" dia

[trent from punchy]

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.

thats 3 stage vtec, which isnt used on any cars in aus afaik

"
Honda also introduced a 3-stage VTEC system in select markets, which combines the features of both SOHC VTEC and SOHC VTEC-E.

At low engine speeds, one intake valve is opened off an economy lift cam lobe, and the second valve is just cracked open a little to help promote better swirl in the combustion chamber. Used in conjunction with a 5-wire, wideband O2 sensor, great fuel ecomomy can be realized.

At medium engine speeds, both intake valves open off the economy cam lobe with equal lift allowing the engine to produce more power, but at the expense of economy.

At high engine speeds, both intake valves are actuated by a high lift cam lobe and produce much higher performance than at the medium speed range, but at an even greater expense of economy.

The 3-stage VTEC system was only offered in the Asian markets and not in the US market at all."


what they are doing now is:

An additional version of i-VTEC was introduced on the 2006 Honda Civic's R-series four cylinder SOHC engines. This implementation uses the so-called "economy cams" on one of the two intake valves of each cylinder. The "economy cams" are designed to delay the closure of the intake valve they act upon, and are activated at low rpms and under light loads. When the "economy cams" are activated, one of the two intake valves in each cylinder closes well after the piston has started moving upwards in the compression stroke. That way, a part of the mixture that has entered the combustion chamber is forced out again, into the intake manifold. That way, the engine "emulates" a lower displacement than its actual one (its operation is also similar to an Atkinson cycle engine, with uneven compression and combustion strokes), which reduces fuel consumption and increases its efficiency. During the operation with the "economy cams", the (by-wire) throttle butterfly is kept fully open, in order to reduce pumping losses. According to Honda, this measure alone can reduce pumping losses by 16%. In higher rpms and under heavier loads, the engine switches back into its "normal cams", and it operates like a regular 4 stroke Otto cycle engine. This implementation of i-VTEC was initially introduced in the R18A1 engine found under the bonnet of the 8th generation Civic, with a displacement of 1.8 L and an output of 140PS. Recently, another variant was released, the 2.0 L R20A2 with an output of 150PS, which powers the EUDM version of the all-new CRV

With the continued introduction of vastly different i-VTEC systems, one may assume that the term is now a catch-all for creative valve control technologies from Honda.

[TK]

I haven't got time to run the sims atm Bill - but it looks like you're starting to see my point.

I'll give you a design brief, I'll run the sims later today & we can compare results:

Circuit racing engine, 6L capacity, 4" bore, 3.63" stroke (common 6L class dimensions), max rpm 6500, peak power around 600hp required. Max area under the curve is the aim.

You can use ITB's & any exhaust system you like, since you'll be using a 4V design you must limit lift to .500", I'll be using up to .700" with a mech roller cam.

[Billzilla]

Okay I'll see what I can come up with.

[TK]

Oh, yeah, must run on pump 98.

I did one quick & rather rough sim - jackpot first try.

593HP at 6000rpm
572ft/lbs at 4500rpm

11.5:1 comp with AFR 215cc ally heads & mech roller cam, 244/248 @ .050", .650" lift & 110 centres, stack injection (efi).
All parts are real and can be bought over the counter, nothing tricky or hand fabricated.

How the fuck do I take a screen shot so I can post the graph?

[Billzilla]

Yep running the numbers on 98 octane fuel.
Got 610ft-lbs and about 630hp so far, trying to flatten out the torque right now.

For a screen shot, get the apporpirate window up on-screen then hit ALT and PRINT SCREEN keys together. Then get a graphics program and paste the grabbed window into it. Then attach it as a file here.

[TK]

Had a weird dip in the torque curve with the last one, fixed by tweaking the intake runner length.

622HP at 6500rpm
609 ft/lbs at 4500rpm.

Plenty more there with more fiddling, I'll spend 10, but then I gotta get some work done.

[TK]

660hp @ 6500rpm
613ft/lbs at 5000rpm

more to come

[GTSBoy]

fight fight fight fight fight!

This is almost as good as the preceding war of words!!

[perthdrivers.txt]

I haven't got time to run the sims atm Bill - but it looks like you're starting to see my point.

And you will conceed the point that 2V has no superiority over 4V, only that for the power outputs required it is "good enough" for large capacity engines?

[Billzilla]

Still roughing it out -
612ft-lbs @ 4800
657hp @ 6000

I'm trying to keep the power down to around 600hp, but spread the torque around.
Got about 440 ft-lbs @ 2700rpm so that's okay.