Those who were lucky enough to get their hands on a 1987 Buick GNX, also known as “The Grand National to end all Grand Nationals” is even luckier if they’re still holding on to one of the original 547 GNXs that Buick produced during the last year of the G-body’s lifespan and the only year that the GNX was in production.
The goal that the crew had in mind when they set out to rework this classic with their own modern rendition was to triple the original horsepower without killing off the drivability. With all of the convenience that modern technology has to offer, we have no issue seeing just how this job could come together flawlessly.
First and foremost, the original 3.8L turbo powerplant was ditched in favor of something that would be a bit easier to coax power out of. To the pleasure of Buick aficionados, the original power source was replaced with another Buick engine. This time, in the form of a 4.1L pulled straight out of a Buick Riviera – 3.965″ cylinders bored .035″ along with a stroker setup brought the engine up to 273ci for a little extra kick. That’s a 42 ci. difference when compared to the 3.8. This increase will go a long way in both helping with power and reducing turbo lag.
Originally, the 4.1L obviously wan’t built to withstand the incredible power that KT Engine Development was looking for . As we all know, the Riviera isn’t exactly a racecar.
Therefore certain modifications needed to be done before even thinking about creating the power that would help the engine meet its eventual potential. First up was a main cap stud girdle would create more anchor points, attaching the caps to the block at over 20 points and helping to reinforce the newly bored and stroked block in order to prevent a potentially disastrous situation.
Completing the bottom end would be Weber forged h-beam rods with custom fit V8 rod bearings. Topping the rods would be JE Pistons forged deep dish pistons with a thermal barrier. The barrier comes in handy with the forced induction setup as it easily pushes the heat out of the chamber and through the exhaust to help with turbo spool. The final piece would be a dry sump oil pan neatly fastened to the bottom.
Even the toughest of setups is nothing without a proper oil cooling system. Piston squirters (top right) were introduced to the build to control heat by sending a steady stream of oil to the underside of the pistons, thus keeping operations at a manageable temperature.
A hydraulic roller cam from COMP Cams and hydraulic roller lifters were up next. The crew selected a cam that isn’t too hefty as to allow the turbo to do the majority of the work. The cam was paired with a decked out set of aluminum Champion GN1R heads with a trick port job.
When we dive inside we even find custom valve guides to accept larger valve stems. This would allow for larger exhaust valves at 5/16″ to withstand higher heat. With new stainless steel valves, these parts would shave off 20 grams from the intake valves and 7 grams off the exhaust valves. This might not seem like much, but with so many moving parts, these savings are a big deal! When the COMP valve springs were put in, the heads were finished being built, they were decked and ready to be reattached to the block. In order to make them withstand the pressure of high boost, external aluminum plates were fastened to the sides of the head.
To wrap things up, the heads were decked to insure proper mating and COMP valvesprings were thrown in. Perhaps the most interesting part of this build comes toward the end when we discover custom made valvespring squirters which are custom fabricated out of a spacer to spray cool oil on to the springs as seen above. As logic would follow, the heads are fastened with head studs and the long block is complete!
We’re cut off before the turbo, engine management, and other accessories are installed, but this series goes a long way toward showing us the work involved in constructing the bottom end of a V6 to be able to handle insane amounts of boost.
If you would like to learn more about this build, we would recommend that you check out the series of videos in the playlist above. The craftsmanship and attention to detail that took place are truly off the charts. You have to see it to believe it.
Jesse is currently a senior at the University of Delaware and has been around cars his entire life. From a GTO and a C5 Corvette, to a CTS-V and a C6 Z06, he’s always seemed to have his fingers in LS performance. He is a student by day and a YouTuber and automotive journalist by night!