Precision Turbo Upgrade On A 1987 Buick Grand National - Turbo Buick Basics, Part 3

We mounted (in-line between the boost source and wastegate actuator) the RJC Racing Hybrid Boost Controller on top of the new Precision Turbo. RJC developed this boost controller so you can run a larger turbo and experience less lag as well as eliminating boost creep. We installed it according to the instructions (adjusting the wastegate actuator and bypassing the factory boost solenoid). On our testdrive the boost came in noticeably sooner, smoother, and at a lower rpm as advertised. $55 well spent!

Our next step to reduce turbo lag was a G Body Parts 3-inch downpipe. It features an internal wastegate flange (5/8-inch) assembly. The new downpipe is polished 304 stainless steel, and it will certainly outflow the stock elbow housing and 2.5-inch downpipe. With less restriction the new turbo should be able to spool up more easily, and the 3.8L will not have to work quite as hard to dispel the exhaust.

The new downpipe goes in from the top. The stock exhaust elbow/wastegate housing was unbolted and removed from the turbo. The catalyst also needed to be unbolted from the exhaust to make room for the new downpipe and testpipe.

Better appearance is apparent with the new G Body Parts downpipe in place of the stock piece. It fits quite nicely with plenty of clearance (1/2-inch minimum). We felt a big increase in acceleration with less turbo lag. It was much easier for the turbo to spool up with a less restrictive exhaust (downpipe) hanging on its side outlet.

Bottoms-up, there's plenty of clearance room. It's obvious the size difference in downpipes when comparing the old (2.5-inch) to the new (3-inch) by looking at the crusty crossover pipe (2.25-inch) next to the downpipe.

We connected the new 3-inch testpipe to the downpipe using a 3-inch stainless band clamp from a local parts jobber.

We were back at TTP to find out what the boost controller and bigger downpipe was worth. Once again George strapped down the GN securely. We were expecting more (felt like 20-25 hp), but picked up 10 lb-ft of torque without any hp gains. The best thing about our gains was our peak torque was lowered by 500 rpm (now at 3,000 rpm, from quicker spool-up) and our powerband (peak tq to peak hp) was broadened by 500 rpm (previously 3,500 to 4,500, now 3,000 to 4,500 rpm). With more bottom-end power and a broader power curve, Tim's TR will get down the track quicker.

Matt Hauffe (supertuner extraordinaire) kept track of the motor for a safe state of tune via this wideband O2 sensor and a Soltus (Snap On) scanner to detect knock retard. There was knock retard even if we programmed it pig rich (10.0 to 11.0:1 A/F). All along testing has been at 19 psi of boost, and at high-boost (over 17 psi) the knock sensor has been detecting knock over 200 times on each pull causing knock retard resulting in a power loss not allowing us to show our actual gains.

The '86-87 Turbo Buick, with its forced induction, pushes most of the airflow through the plenum to the rear intake ports (cylinders) causing the front cylinders to go lean and have knock (detonation). We placed the RJC Racing Airflow Distribution Power Plate (ADPP) between the upper plenum "hat" and the lower intake manifold.

The ADPP will evenly distribute and maximize airflow to all the intake ports to prevent knock in the front cylinders. Typical users of the RJC ADPP report lower e.t.'s and an increase in power. By simply eliminating the knock retard issues in the front cylinders-it helps allow for more boost (3-5 psi) without detonation. This piece is designed for the stock plenum (different designs are available for Precision, Kenne Bell, Accufab, etc., plenums), and costs only $65.

We exchanged our stock throttle body for a ported and polished unit from Jose Motor Sports. The stocker sports ridges before and after the throttle blade. Also notice the throttle shaft/blade screws sticking out. The Jose unit shows no ridges and screws sticking into the airflow for less turbulence. A ported and polished stock unit will increase throttle response, and though Jose remarked none of his customers have seen lower e.t.'s from a ported throttle body, all have reported better driveability.

It was easy for us to install the ported TB along with the ADPP while working on the induction. Our testdrive confirmed a noticeable increase in power and driveability from bolting on the TB and the ADPP.

Since third gear was still intact, we still managed to dyno test the RJC power plate. which proved to eliminate our knock retard issues and we gained 17 rwhp with a slight loss of torque (6 lb-ft). Now, we could safely tune-in the proper amount of fuel (10 percent enrichment) and 4 degrees more timing (with a safe 50/50 mix of 110 race gas/93 pump gas). This resulted in another 5 rwhp and 2 lb-ft of torque! We could have safely cranked up the boost (22-24 psi) without knock issues, but stayed at 19 psi for fair dyno and e.t. results. We left our new tune alone having a perfect 11.8 to 11.9 A/F. We were very satisfied gaining 22 rwhp from the RJC Power Plate. We'll make it to the track in our next episode after the transmission is rebuilt and teamed up with the right stall-speed converter matched to our combination.