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Buick Turbo - Power Trip - TechPart IX: Final Performance Tweaks From the April, 2008 issue of GM High-Tech Performance By Rick Jensen Photography by Rick Jensen
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In the last installment of this turbo V-6's saga, I was able to get my 1987 Turbo-T to the point where I was comfortable making some passes at E-Town. Leaving at 4-psi launch boost, and topping out at 26 psi on the big end, she went 10.83 at 126 mph-not too shabby for the first new-combo track day with no suspension adjustments. Though I was thrilled with a 10, my enthusiasm was tempered somewhat by the fact that there were still several glaring problems that, if fixed, would have resulted in a quicker e.t.-and with a 126-mph trap speed-a safer car. IAT Sensor Relocation
Due to the fact that the intake air temp sensor hadn't been placed in the upper plenum during the engine build, the XFI's tune was a bit off as it was seeing intake air after the filter, not turbocharged and intercooled air in the intake. Tuner Cal Hartline did what he could during the first track day to get that 10.8, but it was more of a band-aid fix and led to a rougher tune than we would like. Downpipe/Wastegate
I was satisfied with every aspect of the Buick's new powertrain-save for the used 3-inch downpipe and stock wastegate left over from my old combo. It was time for a bigger downpipe and external wastegate. As the Cotton's Performance crew up in Agawam, MA, would be doing the final tweaks for me, Jack and Brian suggested one of their 3.5-inch downpipes with a Turbonetics Racegate external wastegate. Both would be more appropriate for this 559-rwhp LC2. Line Lock
I didn't have a line lock at the first track test. This meant that during the burnout, I was unnecessarily heating up the brakes and causing the Eaton posi to unlock. This was compromising boost-holding capacity on the line, causing slippery, sideways launches as only one tire was hot, and abusing the brand-new posi. Brake Service
The swapped-in vacuum brake booster doesn't have the pressure to hold lots of boost on the starting line. However, I love the reliability and pedal feel of the vacuum system-currently, I have no plans to change it. I'll have the Cotton's crew perform some basic stock-brake maintenance on the wrecked front rotors. These things were damn scary when attempting to slow from that 10.83. Between this work and the new line lock, we should be in business. I make the short trip from NYC up to Agawam to see Jack and Brian Cotton, and we get to work. These aren't major mods, but I'm counting on them making a huge difference at the next track day.  To get the XFI zeroed in,...  To get the XFI zeroed in, the IAT sensor had to be moved from the intake pipe to the upper plenum. Here, I've removed the plenum and chosen a place on the passenger side to drill a 9/16-inch hole and tap for the sensor's threads. This location will be away from any cables, etc.  Once the tap is deep enough,...  Once the tap is deep enough, the sensor is installed dry to test the threads. Next, Teflon paste is applied to the sensor's threads and it is installed.  For this 10-second engine...  For this 10-second engine build, I kept my old 3-inch downpipe, and used the stock-style heavy-duty wastegate that came with my Precision Turbo 67GTQ turbocharger. However, I was never able to get the boost below 20 psi with the HD 'gate. This wasn't going to work with a 17-psi pump gas tune, but if I went with a "street" stock-style wastegate I might run out of adjustment when it came time to hit the track with race gas and turn up the boost.  I'll be utilizing Turbonetics'...  I'll be utilizing Turbonetics' Racegate external wastegate (PN 10307, $496). This 'gate is superior to a stock-style 'gate in several ways: it is a 1.80-inch, stainless steel valve compared to a "puck"-style wastegate with a hole of less than an inch; the Racegate is fully closed until it is actuated; the stock-type is open a little, which affects spoolup. Finally, one spring in the Racegate will give 9-30 psi boost, offering a much wider range of adjustment than a stock-style wastegate.  My current 3-inch, Houston-style...  My current 3-inch, Houston-style downpipe with dump pipe has been a great upgrade, but at 550-plus rwhp and 25-plus psi of boost, I'm now leaving power on the table. Brian Cotton lifts the T up and removes my current 3-inch downpipe by unbolting it from the exhaust system down below, unbolting it from the turbo, and pulling it out.  Cotton also removes the shield...  Cotton also removes the shield by the heater box. This extra clearance isn't needed for a 3-inch downpipe, but it is necessary for a 3.5.  We'll be swapping that 3-inch...  We'll be swapping that 3-inch pipe for a custom stainless 3.5-inch Cotton's Performance downpipe ($699). Cotton's Performance offers standard external wastegate 3-, 3.5-, and 4-inch downpipes, and is also in the process of creating a production 3.5-inch downpipe to fit most every header out there, and use whatever flange is needed for the customer's turbo. Contact Jack for more details.  For this story I get to sit...  For this story I get to sit back and watch as Brian fabricates a 3.5-inch 'pipe to work with my TA Performance headers...  ...Jack says, "Hey Scott Scrivner-sorry!...  ...Jack says, "Hey Scott Scrivner-sorry! We ran into a fitment issue but were able to make easy mods to this downpipe for Jensen's TA Performance header'd car." Nothing like stealing some poor guy's parts for the sake of editorial.  A hole is cut into the TA...  A hole is cut into the TA header to mount the wastegate tubing.  Brian cuts and welds the pipes...  Brian cuts and welds the pipes needed to mount the external wastegate. He tacks the pipes in place first, and verifies that the angle will work in my engine bay.  Here's the engine bay, all...  Here's the engine bay, all ready for the new downpipe. Note the relocated IAT sensor in the upper plenum.  Brian drops the new downpipe...  Brian drops the new downpipe into the engine bay, twisting it as he lowers it.  Some high-temp RTV is placed...  Some high-temp RTV is placed on the downpipe's flange, and Brian bolts the downpipe up to the exhaust housing with Allen bolts and one hex-head.  Cotton installs one of the...  Cotton installs one of the Racegate's gaskets.  Next comes the other gask...  Next comes the other gasket.  The Racegate is lowered down...  The Racegate is lowered down ...  And bolted up. There are two...  And bolted up. There are two fittings that screw into the Racegate-one on the side at the boost port, one on the top at the vacuum port. Rubber hoses attach to these fittings; the side connection goes to a T, sensing boost (from the turbo) and leading to one side of the variable boost controller. The top connection goes directly to the controller.  The two lines are run through...  The two lines are run through the firewall and under the center console. They are connected to the controller via screw-in fittings. The controller will be mounted in the center, a good spot where I can easily reach it from the driver seat to adjust boost.  Final installation of the...  Final installation of the new downpipe happens when Brian mates it up to the exhaust system. There isn't much room where the 3.5-inch pipe snakes down, but it does not hit anywhere-a testament to Cotton's fabrication work.  A Cotton's Performance Deluxe...  A Cotton's Performance Deluxe Line Lock Kit (PN BR107, $109) will be going in next.  To install the line lock,...  To install the line lock, Brian disconnects the brake line going into the brake reservoir, and attaches the hard line from the line lock into this spot. The line that originally went into the reservoir is gently bent, then run into the line lock itself. There are two wires: one goes to ground, and the other goes to the switch in the ashtray. Cotton connects the other end of the switch to a wire tapped into an ignition power source in the fuse box.  Turbo Buick owners know just...  Turbo Buick owners know just how important it is to keep the mediocre-at-best braking system in top form; not just for stopping power after a 120-plus mph quarter-mile run, but also because an optimized rear drum setup is key for holding boost on the line. Cotton's Performance stocks Durastop front rotors (PN 19171304, $280), high-performance ceramic front pads (PN PGD154C, $50), and rear drums (PN 18028393, $110), as well as Rear Brake Shoes Sets (PN 6722-Buick, $42). However, my front brakes were the ones that needed love, and as the rears were in decent shape with fairly new soft brake shoes, recently turned drums, and S-10 wheel-cylinders, we left 'em alone for now.  Two 3/8 Allen-head bolts retain...  Two 3/8 Allen-head bolts retain the caliper. Brian removes them and lifts the caliper out. The old pads are removed and tossed.  The dust cover is removed,...  The dust cover is removed, and he pulls the cotter pin out before removing the nut.  He pulls the first bearing...  He pulls the first bearing out, replaces the nut, and pulls out on the rotor, which dislodges the second bearing.  After cleaning the bearings...  After cleaning the bearings out with a parts cleaner and spraying with brake clean, an air-powered bearing packer is used.  The large bearing goes in...  The large bearing goes in first on the back of the rotor, then the seal goes on and is tapped into place with a hammer.  Then the smaller bearing on...  Then the smaller bearing on the front goes on. The rotor is slipped onto the spindle, a washer is placed, and the nut is screwed down. Cotton tightens the nut down until he feels tension; then the cotter pin is replaced.  The cap is tapped into place,...  The cap is tapped into place, and then he replaces the other front rotor. Afterwards, Brian uses soapy water and a Scotch-Brite pad to remove oil from the rotors.  He then turned his attention...  He then turned his attention to the caliper pins and sliders; they were in bad shape and needed some wire-wheel love. Here's the before and after.  Any contact point of the pins,...  Any contact point of the pins, sliders, and the backs of the brake pads are lubed with GM silicone brake lubricant. The pads are installed, the sliders and pins go in next, and they are tightened down. The wheels go back on and I'm ready to roll.  Track test No. 2 went off...  Track test No. 2 went off without a hitch, and the bad black Buick didn't disappoint. Grab the July issue of GMHTP to see how quick it went.
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