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Lorenfb Lorenfb is offline
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Join Date: May 2003
Location: Manhattan Beach, CA
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Porsche 3.2 DME Performance Mystery

Issue:

There has been some confusion as to what the basis is for performance
improvements on the Porsche 3.2 from '84 to '89. Some think that Porsche
was very conserative in programming the fuel and ignition maps and didn't
maximize the 3.2's performance. Others think that Porsche lacked the
wherewithal 20 years ago to properly program the DME and left unknown
areas in the maps which could be "harvested" or "hacked" to achieve
dramatic performance gains.

This thinking has lead to the sales of performance chips based on claims
without dynamometer test data and subjective reviews which indicate
a perceived performance increase. As a result, the issue arises as
to whether there truly exists a real performance increase and if so
what is the basis for it. The more key issue is whether Porsche failed
to fully optimize the 3.2 DME for maximum performance.

Published Data:

The Porsche Carrera Workshop Manual page 0.2 (Technical Data) indicates
two U.S./Japan/Aust. models; 930/21 & 930/25. Model 930/21 was produced
for years '84 thru '87 and had a max torque of 185 ft-lbs & a max HP
of 207, requiring an octane of 91. The Model 930/25 was produced in '87
thru '89 and had a max torque of 195 ft-lbs & a max HP of 214, requiring
an octane of 95.

Porsche had three basic DMEs for those years; 911 618 111 05 for '84 thru
'86 which had a 16K EPROM, 911 618 111 14 for '87 which had a 32K EPROM,
and the 911 618 111 20 which had a 64K EPROM. These are all U.S./Japan
type DMEs. These different DMEs are the only major changes Porsche made
which account for the performance difference.

In the Technical Specifications ('84,'85,'86) booklet on page 106,
Porsche indicates an ignition timing change for cars beginning since
11/1986. The timing change (+.5 degrees) increased the idle 80 RPMs.
The max advance remained at 26 degrees at 3800 RPMs, but no in between
values are given.

Test Data:

In an attempt to gather more data, I performed tests on my '88 3.2 using
three different DMEs; a stock 911 618 111 05, a stock 911 618 111 20,
and a 911 618 111 20 with a Hypertech performance chip. The tests
consisted of checking the ignition advance at various RPMs. Each of
the DMEs were tested with and without Pin 10 grounded which retards
the ignition when grounded for NOx reduction.

In doing the test I used a Snap-On MT1261 digital timing light which
provides a digital indication of the ignition advance. Also used was
a digital tach to monitor the RPMs.

The following are the data in degrees:

..........911 618 111 20........... 911 618 111 05..........911 618 111 20 (Hypertech)

RPM.....Adv-W.. Adv-W/O....... Adv-W...Adv-W/O.........ADV-W
900.........2..............2.............-2..........-2....................2
1500.......7..............9...............6....... ....7....................9
2000......15............16..............13........ .14..................14
2500......21............21..............19........ .22..................21
3500......28............28..............25........ .26..................30

W - with Pin 10 jumper connected, W/O - without Pin 10 jumper connected


Conclusion:

One can basically conclude from the Porsche Published data that the
ignition timing maps were changed beginning in '87 as indicated
(TecH Spec - pg 106) and inferred from the octane increase from
91 to 95 on pg 0.2 of the Workshop Manual. One can also arrive at
the same conclusion from a review of the test data. Therefore,
this modified advance curve accounts for the increased torque
(10 ft-lbs) and HP (7) which can account for a perceived increase
in performance of the '87 and later cars compared to the '84-'86
cars.

As a result, it appears that Porsche may have been a little
conservative in the early 3.2 years, i.e. '84 - '86, but decided
to "push" the advance curve with a corresponding increase in the
octane requirement to offset any potential for detonation. So if
Porsche had wanted to, they could have "pushed" the advance curve
further requiring 98 octane as with the 911 Turbo (ROW).

So there is an obvious relationship between torque changes and
small changes to the ignition advance curve and the resulting
octane requirement to avoid pinging. There's no "mystery" to
performance enhancements. Performance tuners have been modifying
the advance curves since "day one". It's also fair to conclude
that Porsche didn't fail to maximize or "harvest" all the potential
performance gain, as there would have been further increases
in octane requirements to levels considered impractical for a
regular "everday" Porsche.

Therefore, performance chip suppliers can always "push" the
advance curves and squeeze that little extra torque that "feels"
better, but what's the cost in potential damage, e.g. broken rings,
from detonation and having to find the next higher level of octane.
These performance chips may "feel" better, e.g. for '84 - '86 cars,
but as can be determined from the Bruce Anderson performance chips
evaluation (Porsche Excellence Magazine), very little if any overall
performance gain really results when checked on a dyno.
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Loren
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'88 911 3.2
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Old 01-27-2004, 09:05 PM
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