Answering your performance engine building and tuning questions
Chris has asked, "How do you achieve
VVT tuning for the ghost cam effect
or the lopey idle effect?"
Often that's not actually a tune achieved
through variable valve timing tuning.
Yes, you can get that to a degree
with variable valve timing by creating an overlap effect.
So in this case, we're talking about if the engine
has a variable intake cam,
by advancing the intake cam from its
most retarded position.
what this does is, it creates more overlap
where the intake and exhaust valves
are open at the same time.
And this is one of the aspects
that gives that lope with a large cam profile.
The large cam profile has a lot more duration and overlap.
However, more traditionally, what this is
actually achieved with is really aggressive use
of the ignition idle control tables.
And what this does is advance or retard
the ignition timing at idle
based on whether the engine speed is
above or below the target idle speed.
The theory here is that as we advance
the timing towards MBT, what we're gonna find
is the engine torque increases,
and naturally this results in the engine RPM increasing.
Conversely, if we retard the timing from MBT,
torque is reduced, so our engine RPM drops.
So by using quite large swings
in our ignition timing, perhaps plus or minus
20 or 30 degrees as we swing across our RPM idle target,
what we end up with is quite an aggressive lope
which does sound similar to a cam
with a lot of overlap or a lot of duration.
If you want to know more about EFI tuning,
click the link in the video description
to take our free six part series of lessons
that will show you the fundamentals
behind EFI tuning.
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