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[4 Svo] Porting the Intakes
Sly, Dennis wrote:
> I have an 84 so I would assume that would qualify as an early intake and
> head. Question: if the 85.5 and 86 are much better, why are they, larger
> ports, less restriction?
> 84 SVO, Silver
The differences in the intake manifold are not at all performance
related - in fact the runner length in the early design (83.5-84 ALL and
84-85 SVO) have less variance in the inside vs. outside runner length
than the later manifold design (85+ other and 85.5-86 SVO).
The design change was for clearance and noise. The early manifold was a
very flexible part that had a tendency to generate it's own resonant
vibration inside the same vibration range that the engine did - this is
NOT a good thing - and it made the engines much noisier and louder.
Second, the knock sensor (KS) is mounted in the intake manifold so all
of this "background" noise that wasn't related to detonation had to be
electronically "filtered" and this took up processor time, which limited
the sensitivity of the KS threshold circuitry and therefore the power
output (obviously a much longer story).
When the intake manifold design was changed, the EEC timing profile had
to be changed to match the new location of the KS. Also larger injectors
were installed and straightened in the way they pointed into the intake
ports (hence the new bolt location at the front of cylinder number one)
and then the fuel map had to be modified to work with the larger
injectors. So the later manifild requires a different fuel and spark
Development time being what it is (considering these were the FIRST
engines the EEC-IV was applied to!) and since the SVO wasn't [yet!]
selling well the new development wasn't put into the Phase III engine
profile until MY 1985.5 whereas all other engines in the other chassis
(Mustang Turbo, Capri, Cougar, T-Bird, etc.) served as the development
program. Since they made less power using less boost, there wasn't a
serious chance of lots of warranty returns if something went bad, but
that would never happen in America, Right?
Anyway there's probably no benefit at all to changing manifold designs
FROM AN AIRFLOW standpoint. However from an electronic control point,
it's all the difference in the world. You already know what I think
about after-market "chips" so I won't repeat that here. The problem with
just changing the manifold and keeping the same injectors is the KS
ssytem will be way too under-sensitive and you'll need a louder radio
and rocket fuel to run it or you'll break pistons cause the EEC won't
hear the KS signals.
The cylinder heads and their ports are identical EXCEPT for the one
additional bolt hole at the front of cyl 1 (and this can be added to an
earlier head - use teflon tape cause it's into the valve tray area and
will leak oil). I've done this on several engines with no problems -
certainly cheaper that a replacement head casting and all the new
machining. If you're starting from scratch and doing a head, get the
later one (has 9 bolt holes on the intake side so it will mount either
The later engines made more power cause of a different cam profile
(minor improvement), a smaller blower turbine housing (helped the low
end), a semi-dual exhaust system (helped alot) and electronic
calibration to use the larger injectors (helped a lot). Net result was
about +30HP and +40 Ft-Lbs. They also came with a stronger gearbox.
If you decide to install the later intake manifold, also fit the later
injectors and an SVO PE processor. You'll have to drill and tap the head
for the extra bolt hole (no biggie) and disconnect the Boost Control
Module's connector and manually control boost presssure (which you're
probably doing already).
SVO Owners Association