WHAT IS A SAUDI SYCLONE ?
In 1991 about 150 Syclone trucks were officially exported by GMC and 113 destined for for resale in the Middle East became known as the 'Saudi Syclones'. In the winter/spring of 1994 100 Saudi's Sy's were withdrawn from Saudi. Only 31 returned to the United States where they were converted at a facility in Pontiac, MI. All of the returned trucks came with a full factory 3/36 warranty (from date of sale) except that any paint problems were specifically not covered as the paint was supposed to not be in the best of conditions - they may have been stored outside in the Saudi sun for quite a while.

All 31 were sold in a lottery to GMC (only) Employees. Apparently not many people knew about the lottery so only about 40 people entered which meant that almost every one who entered got the chance to buy one. The sale price was a mere $12,500 which, it is alledged, upset a lot of GM people in various divisions that they missed out.

To check for one of the returned Sy's, the last four digits of the Vehicle Identification Number (VIN) must be one of the following:

2581, 2590, 2604, 2726, 2734, 2736, 2738, 2739, 2744, 2745, 2746, 2753, 2757, 2759, 2765, 2771, 2781, 2789, 2791, 2792, 2796, 2802, 2804, 2805, 2806, 2807, 2809, 2812, 2814, 2817, 2828

Note: Number 2590 was used as a source for replacement parts for the remaing 30 vehicles.

The remainding 69 trucks were distributed throughout Europe for sale where a small number ended up in a German compound for sometime. GMC, desperate to be rid of them, sold them on a "make us an offer" basis. Lucky purchasers managed to get ahold of one for a few thousand dollars under their market value. At least 4 of the 15 known UK Syclones are Saudis.

WHAT MAKES A SAUDI SYCLONE DIFFERENT ?
Externally the Saudi Sy looks identicle to its American counterpart with no outward changes apparent. The only item to appear different is when you look in the cab and notice the dash.

The Saudi Syclone Dash

The dash used is metricised version of the standard Sonoma/Jimmy one (An example of which can be seen in Figure 8, Section 8C-17 of the 1993 Sonoma And Jimmy Service Manual.) which is normally used for vehicles destined for Canada.

With a maximum registered speed of 200 km/h (124.27 mph) the dash records 4.27 mph more than the standard one and just slightly exceeds the ECM restricted vehicle speed of 124 mph.

Standard Syclone Dash

More differences become apparent as you compare the two. Missing from the Saudi dash are:

• Rev. Counter - Some would argue that for an automatic vehicle this is not necessary but on a performace vehicle full feedback of engine operation is important.
• Turbo Boost Gage - The stock gage is inaccurate but any turbo gage is better than non at all...
• Low Turbo Coolant Warning Lamp - Not a major omission if regular checks of the coolant level are performed. If ever the lamp was instructed by the ECM to light turbo boost would be restricted and the driver would feel a difference in the vehicles performance.

Saudi Arabia has virtually no unleaded fuel available which meant the stock engine configuration couldn't be sent - Leaded fuel in a standard Sy would eventually kill the catalitic convertor and Oxygen sensor leading to a very rough running truck.

GM provided a solution in the form of a NM8 leaded fuel conversion. This is a radically altered chip which has all references to the Oxygen (O2) sensor disabled thus meaning that the sensor can either be removed and the hole in the exhaust capped or, as can be seen from the photograph, 'converted' for leaded use (Ie the wires are snipped off). The wiring harness still exists for the O2 sensor so the conversion appears to be a rather brutal one.

	The O2 sensor is mounted in the top of the exhaust downpipe extending from the turbo charger. The pipe extending horizontally at the bottom of the picture is the turbocharger oil return line and the silver/grey in the top left corner is the air-conditioning condensor.
'Converted' O2 Sensor

Catalitic convertors are damaged by lead in fuel so GM had two alternatives: remove the cat and put a straight pipe in its place or remove the cat and leave an empty box inplace. The first option would seem to be more logical but a quick visual examination under the truck shows what looks like a cat. box. Closer examination shows the box has a part number of 1234567890 which is listed in the ???? parts manual as a 'Resonator Silencer' and is there to provide the same level of noise reduction that a catalitic convertor would.

Shown here are two of the four items forming the Saudi conversion, with the other two being the dash and Resonator box. The O2 sensor (Top) has had its three wires cut within a 1/4" of the sensor making it impossible to reuse by soldering on a new connector. The MEMCAL (Middle) has the NM8 EPROM with a hand written label stuck over the erase window. The meaning of the '6502 DOAC' is, still, unknown. The lid (Bottom) to the MEMCAL has half of a luminous green sticker, again placed there with unknown reasons.

The Saudi Kit

Other rumored differences were:

• The seats had no Syclone embroidery - This is not the case as all the seats were the same
• The trans was calibrated to shift at 4800 Vs. 4300 RPM at WOT - In tests on Saudi vehicles it looks like the shift points are identicle to the regular Sy.
• Able to reach 156 MPH - This is not possible as the NM8 cuts boost off at 116mph and fuel shut-off is at 4714 rpm.

SAUDI TYPHOON
The Typhoon was never bulk exported to Saudi and it was left upto customers to specifically request the import. One such Ty is a 1992 model shown here with the addition of some aftermarket wheels. The Ty was imported by the Riyadh GM dealer Al-Jomaih Co., for HRH Prince Turki.

The prince, son of Mohammed A. A. Al Faisal, also owned a Saudi Syclone that now resides in Australia and is the first Syclone to be imported there.

The interior for the Saudi Typhoon was the same as a standard 1992 Typhoon apart from the exchange of the dash for the metricised one shown. Mechanically the vehicle had the same oxygen sensor and resonator changes as the Saudi Sy.

CHIP DIFFERENCES
With the O2 sensor being physically cut off from the ECM one would expect the NM8 to be different in its operation to a standard chip.

There was always the rumor that the Saudi Sy's were much quicker than the stock Sy's. The spark advance table from an updated standard (aka 'Service Campaign') chip looks like the graph below:

A fairly normal looking advance graph with a relatively smooth incline. Now compare the stock chip against the graph for the NM8:

Similar looking, but noticable differences in two regions: At around 80kPa and 600RPM there's a distinctive dip in timing. This, one assumes is an adjustment for the burn characteristics of leaded fuel at idle. Also, the timing in the 'purple' (20 - 25 degrees) region indicates that there seems to be more timing at higher RPM and manifold pressures.

A more easier way to compare the two tables is to subtract the NM8 values from the Service Campaign values. A figure of zero indicates no difference, negative values shows that the NM8 is less advanced than the Service Campaign and positive values indicate more timing:

It is now clear that low manifold pressures and RPM the NM8 is less advanced but else where, especially at high manifold pressures and RPM, the spark advance is considerably more (Upto 10 degrees). The result from this is that the advanced timing and the burn characteristics of leaded fuel could all contribute to a slight increase in performance.

Error code conditions can be enabled or disabled within a chip and below are the conditions which are different between the two chips:

Code Condition	Standard	NM8
Code 13 - O2 Sensor Open Circuit	enabled	disabled
Code 31 - Turbo Wastegate Overboost	disabled	enabled
Code 33 - MAP Sensor Circuit	disabled	enabled
Code 41 - Unknown	enabled	disabled
Code 43 - Electronic Spark Control (ESC)	enabled	disabled
Code 44 - O2 Sensor, Lean Exhaust	enabled	disabled
Code 45 - O2 Sensor, Rich Exhaust	enabled	disabled

This disabling of codes 13, 44 and 45 are appropriate to the conversion but the others raise questions. The enabling of Code 31 stops overboost conditions (See the Problem Diagnostic Pages for further details on the codes) which could plauge a vehicle with a low restrictive exhaust, such as the Saudi Sy with a Resonator box. The code 31 is not enabled on standard chips which is the reason they can be used with an additional boost controller which sets a higher boost pressure. On a vehicle with an NM8, as soon as the boost went above the sensor limit (Ie, above 14.7psi) for more than XX seconds the vehicle would cut out - Not very safe or good for acceleration...

The Code 43 disabling means that any problems with the knock sensor would not be recognised and therefore destructive detonation could be occuring without the ECM taking corrective action. This alone wouldnt be too bad a problem as the probability of ESC failure is low but delving deeper into the chip reveals a more serious problem. When a knocking event is detected by the ECM a fixed value of retard is applied to the current ignition advance. In standard chips this is 3 degrees but on the NM8 Zero degrees are applied. What this means is that the engine could be knocking worse than a flock of woodpeckers but the ECM is unable to do anything about it... The retarded ignition and the different burn characteristics for leaded fuel could make detonation very much less likely to happen, but...