1991 GMC Sylcone #478Long-time companion

I was backing out of my driveway a few days back and realized I hadn’t taken pictures of the truck in a while.

It’s been stored in the garage for so long that it sort of blends in with all the other stuff. So, I snapped a shot and present it here, with a handful of others.

Out of slumber
1991 GMC Syclone 478 - VIN 0478 11-01-09Some day soon I’d like to write up more details on my truck, a 1991 GMC Syclone, but for now I only have time for this brief introduction. Of only 2,995 made for one year, it is build number 478, as the last three digits on its VIN show.

I am this truck’s second owner. In the early 1990s, I worked for a small family-owned business. In 1991, my truck along with a second were ordered by the company’s owner and his son. The father also owned a Grand National and later an Impala SS (seventh-generation), amongst others really nice vehicles. The son’s truck stayed stock but the father heavily modified all of his cars. His Syclone was even featured in a popular hot-rodding magazine. (The particular magazine escapes me right now, but I have a copy somewhere.)

Anyway, before I had any clue I would own it, I saw my truck almost every day because the son’s wife, who was employed there also, often used it to commute to our office. When the son decided to sell his truck, in 1996, the dad–my boss–came to me with the option to buy, first. He said it was because he knew I would appreciate it. I remember those words. I’m sure he felt that way because he knew how much I was into cars, and was always gawking at his vehicles.

So, I did what any young GM fan would do and jumped at the opportunity. As of May 30, 1996, I was a very, very proud Syclone owner.

1991 GMC Syclone 478 - out of hibernation 09-15-05With that history behind us, I’ll skip way ahead, to 2005. To the left is my truck after having moved it from my parents’ house, where it had been stored for years.

It appears quite dirty but the truth is, under that thick layer of fine dust, the paint has many layers of wax.

1991 GMC Syclone 478 - interior 11-01-09Once at my place, I stored it again for several more years.

Here is a shot of the interior from November of 2009. The truck is in really good condition since it’s been garaged most of its life.

Notice the aftermarket computer and fuel mixture controls (old Kenne Bell equipment, circa late 1990s) strewn into the console’s cup holder. I had them pulled down for some reason. Probably still like that.

The stereo is the same one the first owner had installed in 1991. In fact, right after purchase, he had some high-tech (for 1991) equipment installed that was still in there when I bought it. For instance, a radar detector with its sensor mounted underneath the front bumper, a six-disc CD changer mounted behind the seats, and a hard-wired mobile phone in the console. Despite the curly-corded handset, it could function hands-free using the stereo and its A-pillar-mounted microphone.

I’ve removed most (having saved all) but never replaced the stereo.

1991 GMC Syclone 478 - instrument panel 11-01-09Here is a shot of the dashboard, also in November of 2009.

You can see the boost gauge to the right. The instruments for the Syclone were sourced from a Pontiac Sunbird turbo; the turbo gauge in these trucks is notoriously inaccurate.

Shame on me for never having installed a better one. Not yet, at least.

1991 GMC Syclone 478 - prep work 12-13-09Here’s my truck while I’m prepping for its second awakening, in December of 2009. I’d stored up some money to put into upgrades. You can see many of them piled up next to it, as if it was Christmas morning.

Unfortunately, I got pancreatitis shortly after that and was hospitalized. After recovery, I had lost momentum and it became a chore. The project was completed the following year but I have never felt good about my workmanship. Ever since, the truck has again been stored.

1991 GMC Syclone 478 - impellers 12-28-09To the left is a shot of the turbo’s impellers from when I pulled the turbo apart for cleaning. The left side, that has a reddish color to it, is the drive side that the engine’s exhaust passes over. The right side is the boost side that the cooled intake air is compressed by.

The engine desperately needs an upgraded fuel pump subsequent to other upgrades (including increasing air flow and a chip swap) and especially after my booster pump was inadvertently removed (grr). These trucks had just barely enough fuel pressure from the factory. Any air intake upgrades immediately put the motor at risk of pinging or pre-ignition (that spells doom, expensive doom).

Other than an improved fuel delivery system and an updated computer chip with modern controls, I think the truck is about where I want it. (In the gallery-sized shot of the truck from the driveway, you can see the new low-mounted air-to-air intercooler and the electric fan’s speed selector.)

I leave it on a battery trickle charger and start it every month or two but its registration is expired, once again.

I am in the midst of moving so the truck will again be put on a back, back burner.

1991 GMC Syclone 478 - Pomona strip numbers 04-08-00It did have its heyday though. To the right is a race slip from Pomona Raceway in southern California. It is from April 8/9, 2000. I had a poor reaction time but check out the 1/8-mile time, heh heh. And my 1/4-mile run was over in 12.878 seconds with a trap speed of just over 103 MPH. This was before any significant upgrades.

The slip (provided in its entirety in the gallery) shows it was already noon by my first run and the mercury in the thermostats was higher than turbos like it. Warmer air compresses less, hence a turbo’s performance is reduced as the temperature increases. As it continued to rise, my performance continued to decline. My second run, at 2:30 was a bit slower at 13.072, and my third run, at 3:50 was at 13.382.

My truck was largely stock at the time and it seemed to be one that ran on the quicker end of the spectrum (there was a pretty wide margin between what various Syclones were capable of from the factory).

The pull is phenomenal. I have a high-stall, lock-up torque converter which allows me to rev the engine to a higher RPM, before the system locks up. That means more boost which means more power. To do this, the brakes–including the emergency brake–are fully engaged while the throttle is increased to the point that the engine starts to overpower it all. When it’s time to go and the flood gates are opened (meaning, all brakes off and throttle to full), occupants are immediately thrust a few inches deeper into the seat backs. The all-wheel-drive locks up without fail, every time, even in the rain.

A Syclone may not be able to out perform six-figure exotics on the Nurburgring, but since I’ll likely never take it there, I’m satisfied with its straight-line, light-to-light capabilities. You’d be surprised some of the exotics I’ve shown the GMC’s tailgate to.

Anyway, I put some larger versions of these photos in the gallery. I’ve got more I will add over time. Hope you enjoy looking at them.

Continue below to the photo and video gallery.

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