Welcome, from sunny Australia!
A Comparison of the
Toyota VVT system Vs the Honda V-TEC
On this page I talk about the two
different methods used to increase the power output, and what's good
bad about them.
What the two systems are,
and why they are used
By using a conventional valve system, to
keep a modern multi-valve engine usable for the road, you are limited
about 85hp to 90hp per litre. You can use a bigger camshaft quite
get a lot more power, but only at higher revs, and at the expense of
power at lower revs. So, with a bit of lateral thinking, it is now
becoming more common to be able to change that very cam timing that
limited the engine power while the engine is running. The
VVT system isn't new, however, as similar systems have been in use for
many decades before. But not for a mass production engine and certainly
not with the highly accurate control of the modern engine management
systems. The Honda V-Tec system is a relative new comer, and by using a
system of far greater complexity than that used by Toyota, Honda is now
making an engine that produces as much power as many of the better
So lets have a look at each system, and
how they work ...
Toyota Variable Valve
Timing system, or VVT & VVT-i
The VVT-type system has been around and in
use by various companies for at least 40 years that I know of.
(I can remember seeing a 1960's catalogue
from the US that showed a special cam wheel that bolted onto a small
block Ford engine's cam, and it had a mechanism that worked like a
mechanical advance system in a distributor, so that as the revs picked
up it advanced the cam timing. I also believe that Alfa Romeo or Fiat
used a similar system back around then, or maybe before)
VVT is simple and fairly effective. It
consists of only two main parts; an 'oil control solenoid' and the VVT
This diagram shows a few more bits &
pieces, but you can clearly see the main two - the VVT pulley and the
OCV. (Oil Control Valve, or oil solenoid as it's often called.)
The early VVT system was relatively simple,
ie, at a specific rpm (~4400rpm on the 20 valve 4AGE's) the computer
signals the OCV to open, this lets oil pressure go through a special
gallery in the #1 inlet cam bearing, through the centre of the inlet
to the VVT pulley. There's a small piston in the VVT pulley, and once
gets enough pressure behind it, it starts to move outwards, causing the
outer part of the pulley to turn in relation to the inner part, due to
the helical spline that guides the piston's fore & aft movement.
Closer view & cutaway of the
So, when the computer signals for the VVT
to operate, the OCV opens and thus causes the VVT pulley to advance the
inlet cam timing by 30°, reference the crankshaft. (15° on the
The rpm at which this happens is worked out
by running the engine on a dynamometer with the inlet cam in both the
fully advanced and fully retarded positions. Since the two different
timing's will make different power throughout the rev range, (advanced
inlet give more top end power at the expense of low end power, and
vice-versa) there is a point where the power will be identical for both
cam settings, and this is where the VVT is programmed to operate.
Because the power output is the same with the VVT in either position,
you can't feel anything when it happens. You can, however, hear
a change in engine note, just before there's a big increase in power!
More detail on the the VVT logic - The
VVT comes in three types for the 20 valve. To the best of my
knowledge, silvertop 20v's pre May 1993 have the VVT actuate at
about 4400rpm. Post May 1993 they seem to work on throttle position and
The blacktops seem to work like this, as
described on Club4AG -
1. Starting. When you crank the starter there will be VVT operation
until the engine fires up, obviously to allow more air into the
engine to allow an easier fire up.
2. Coolant temp. There is absolutely NO VVT operation when the
coolant tempt is below 50°C except for that brief moment when you
operate the starter. Reason obvious, who want to stress a cold engine.
3. Engine rpm. VVT will operate in any rpm between the range of
1500 and 7200 when the inlet manifold pressure is right. The min and
max range can be a little out because I was reading from the car
tacho. Trust me they are very close.
4. Engine load/inlet manifold pressure. This seems to be the single
most important parameter controling the system. The VVT will NOT
operate if the inlet manifold has more than about 5 inches of vacuum
(can't get the exact reading because everything happen so fast. It's
very close.). This is very close to zero vacuum which is atmospheric
that is about the maximum load the map sensor will read to tell the
engine in an NA car. As you can figure out the throttle will
usually be in the more than 3/4 position for this to happen.
5. VVT will work without the speed sensor.
Now, back to the above schematic of the VVT.
It shows the second evolution of the VVT system - called VVT-i -
where instead of the simple 'on' or 'off' positions of the earlier VVT
system, this version can make the inlet cam retard/advance to any angle
between the maximum limits, and to do this the camshaft has a position
sensor on the back of the head. This means that the engine is even more
flexible in it's power output than before. The latest version, VVTL-i
is described on this page. It's completely
different to the original VVT system, and is more like the V-TEC in
There are two engines that commonly use
the VVTL-i system, the 1ZZ-FE/2ZZ-GE series and the latest (in 1999
& onwards) 3SGE, as used in the sporty Altezza. The early
generation 'redtop' four 3SGE's have a single inlet VVT-i and the later
'blacktop' generation four 3SGE's have dual VVT-i controllers, one on
the inlet and the other on the exhaust cam, and makes 200hp from 2
So, using VVT technology, it's pretty easy
to get around 100hp per litre.
Toyota has now gone to the third
evolution of the VVT, and it not only alters the cam timing, but it
alters the valve lift as well. The 'old' VVT system simply can't do
this, so Toyota has gone to a system much like the ....
Right. Let's not muck around. For straight
power output, the V-TEC system craps all over the VVT system.
latest Honda V-TEC engine, as used in the S2000 sports car, makes 240hp
odd out of only 2 litres - That's a sparkling 120hp per litre.
The V-TEC system is far more complex than
the VVT, but it allows you to not only alter the cam timing, but to
alter the valve duration and lift at well. It's really like having two
engines in one - A 'sedate' one for grocery-getting, and the other a
red-blooded high revving screamer.
How it does this, however, is with a
multitude of 'fiddly bits'. Here's a picture of the valve gear.
Ok, pay attention - This is where it starts
to get tricky! What happens when the engine computer decides to
make the V-TEC shift to 'grunt' mode is this - Up until that point, the
valves are operated by the pair of cam followers that run directly on
top of each valve. A hydraulic valve opens in the head somewhere,
allowing oil pressure to fill the pivot shaft that the cam followers
swing off. The oil is then directed to a tiny set of pins that live in
the inner follower. These pins push outwards when the valves are shut,
locking the inner cam follower to the two outer followers. The inner
follower runs on a cam lobe that sits between the outer two, and is much
bigger. This is the lobe that has the larger duration and lift, and so
suddenly allows the engine to breath a lot better.
Or if you can't see
enough detail, try this one ->
(121kb pic <-- and
--> 85kb pic)
You can see from the above pictures, and the
one below that there's been a huge amount of effort to make it all
The cam followers all have small rollers, to reduce friction and allow
for a larger cam lobe.
The follower system of valve operation,
believe it or not, is quite similar to the latest developments in
Formula One engine technology. (Though the F1's don't use V-TEC, have
pneumatic valve springs, a smaller included valve angle, and so on ...)
Here's a picture of a head that's been
cross-sectioned. If you look very carefully at the right hand
cam, you can just see the larger of the two sets of cam lobes hiding
behind the smaller ones.
Honda have also made a single cam version of
the V-TEC, (V-Tir system??) though it only operates on the inlet cam
valve timing/duration/lift. As with the twin cam system, it is quite
elegant but has many small parts operating under high loads and speeds.
The point at which the V-TEC system operates
is a purely rpm derived point, as was the VVT system, and is done for
exactly the same reasons. Because of this, you will not gain anything
a standard engine (either type) by using one of the aftermarket
controllers that let you alter the rpm at which the systems operate.
you'll do is create an unpleasant dead spot in the torque curve.
Below is the Nissan version
of V-TEC, the VVL system. It's basically exactly the same as V-TEC in
design and operation and so I assume is used under licence. This engine
is the SR-16-VVL 'bluetop' and they make about 175hp from the factory.
There's a similar N1 version that has a red coloured cam cover and
they're reported to make 197hp. There's only suposed to be about 400
bluetops and 80 redtops made, and they were fitted to the faster
versions of the Nissan Pulsars in Japan. This engine is my own, and
it's going into my Mallock racing car. On
the right is how it looked
when I picked it up in Malaysia.
The VVT and V-TEC in operation
in the real world
The Toyota engines seem to run slightly more
aggressive cams than the Honda's, and so at lower revs they seem to
(anecdotal evidence here ...) be a bit more pleasant to drive and
make a little more power. There's also less of a transition when the
shifting systems operate, but this is obvious due to the Honda system
swapping over to a much more 'racy' cam profile. I think that the
Honda's may seem to be a little 'flat' at lower revs because of this
relatively large contrast, but I'd have to drive one and see a dyno
chart to make verify this.
Pro's - Both systems allow you
to have an engine that's quite a lot more powerful and yet still
driveable than a 'conventional' engine would otherwise possibly be. The
V-TEC is the obvious choice for outright power, and the Honda's
certainly seem to rev a heck of a lot more than the Toyota's do. (The
S2000 red lines at a stratospheric 9,000rpm - stock!)
Con's - You are pretty much
stuck with limited modifications to the engine, eg, air filters,
extractors, etc, to get more power. The reason for this is the very
system that give the engine all that extra power - The cams &
VVT/V-TEC. You can of course use larger cams to get more power,
but this defeats the purpose of having the VVT/V-TEC in the first
You'll most likely lose power at low revs, and not gain a great deal at
high revs. (The VVT will gain proportionally more than the V-TEC,
however, as the V-TEC head is optimised - well, compromised - for the
'big' cam & 'small' cam and so using a larger cam may not help much
So, if you want an engine with power like a
racing engine, then you're better off building a straight race engine
right from the start. Or maybe a turbo engine ...
The other concern I have is the longevity of
these sorts of engines. I believe that the VVT system would be largely
trouble free for the life of the engine provided that you keep the oil
clean and change it regularly. Even more so with the V-TEC, as with all
it's little bits & pieces in close formation in the head I'd hate
think what would happen if some of those little locking pins didn't
engage properly at 6000rpm+. All that being said though, I have it on
reliable advice that Honda have never had a warrantee claim for any
V-TEC engine in the area of the head and/or valve gear. Quite
I think that perhaps the best long term
solution to getting large amounts of power from a relatively small
engine is still by using a turbo, but if you like to hear the engine
scream at high revs then one of these two systems is the way to go.
on with more details on the Honda S2000 engine
the latest Toyota VVTL-i system
For more motorsport links, try the motorsport section on my links page.
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