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.