Precision Turbo Upgrade On A 1987 Buick Grand National - Turbo Buick Basics, Part 3
Replacing A Tired Turbo And Adding A Handful Of Bolt-Ons For An Easy And Safe 49 HP
From the March, 2010 issue of GM High-Tech Performance
By Dan Foley
Photography by Dan Foley
In the last installment we left off installing and dyno testing Pypes hi-flow exhaust system on our buddy Tim Cairone's '87 Buick Grand National. We realized gains of 38 hp and 35 lb-ft by ditching the stock, restrictive exhaust. Issues with the tired, stock turbo (leaking oil, smoking intermittently at idle and while driving) prevented us from risking a strip test on the Pypes exhaust. We called the folks at Precision Turbo for their advice-should we go with a stock-rebuild or upgrade to a stock-appearing type turbo? Precision offers a large assortment of different size, direct bolt-on turbos for the Turbo Buick, and for our intended build-up Precision recommended we upgrade to its PTB-5758 turbocharger. It's the latest midsized unit for the GN, using the most recent in turbo technology (compressor and turbine housing shape, billet compressor wheel), which will bolt right in place of the original, tired-out turbo.
It was easy to remove and replace (R&R) the tired turbo for the new Precision Turbo, and we chose to bolt on the stock wastegate/exhaust elbow housing and downpipe to the new turbo for a fair test (stock 34mm vs. Precision's 58mm compressor wheel). A testdrive told us the larger turbo was slower to spool, but hitting harder at full boost (19 psi). To find out how much more power the new turbo developed, we visited our friends at Tune Time Performance for dyno testing. After Matt Hauffe (Tune Time's tune-master) put the hammer down on TT's Mustang chassis dyno we realized 25 more hp (from 278 to 303 rwhp) with the same torque output (440 lb-ft). While the larger turbo made more power, its added turbo lag showed both torque and horsepower peak at 500 rpm higher. This is a natural occurrence-the larger the turbo, the longer it takes to spool.
We hoped the added turbo lag wouldn't hurt the e.t.'s as much as the added power should help, but at the track we could only launch at 0-1 psi of boost. Our 60-foot times worsened from the previous 2.1 to 2.3 (full boost wasn't until 100 feet down track). Also working against us was a bad-air summer day (85 degrees, 55 percent humidity, 29.74 barometer, 3,000 feet altitude corrected). Even under these conditions we saw gains in trap speed of over 4 mph, but only dropping a tenth (best e.t. of 13.50 at 104.68 mph) due to the excessive turbo lag.
However, we heard RJC Racing's new hybrid boost controller would help the boost come in quicker, and we were equally as quick to dial them up to give it a try. Meanwhile we also wanted to test out a couple bolt-ons to better take advantage of our new turbo, which might also aid spool-up. A 3-inch downpipe from G Body Parts was first on the list, replacing the stock 2.5-inch piece should in theory reduce backpressure and (hopefully) turbo lag. A testdrive after first installing the RJC Racing boost controller confirmed its effectiveness, as did the G Body Parts 3-inch downpipe. The bigger downpipe added a tangible increase in power as well as responsiveness, and after installing these two products we felt there should be a big reduction in e.t.'s (hopefully into the 12s).
In the meantime, of course, we had to quantify these improvements on Tune Time's chassis dyno, and to see just where peak power occurred. Our seat-of-the-pants feel was confirmed as the the power curve did in fact come in sooner and last longer. Peak torque (450 lb-ft, 10 lb-ft gain) was now 500 rpm lower and horsepower (303 hp, 0 hp gain) occurred at the same 4,500 rpm. With the power curve broadened by 500 rpm (previous 3500 to 4500 rpm, now 3,000 to 4,500 rpm), it helped make Tim's GN feel faster and deliver better all-around driveability.
Here's the power brute from...
Here's the power brute from Precision Turbo (PN PTB305-5857). It's a true bolt-on to replace the worn-out, oil-leaking original.
It features larger housings...
It features larger housings and wheels (compressor and turbine). It's actually a mid-sized unit (58mm billet compressor wheel) when compared to the typical 10-second TB that usually runs a size 67- to 76mm turbo.
The stock turbo performed...
The stock turbo performed well for over 20 years and over 100K until we turned up the boost. Notice the stock 2.5-inch downpipe and the stock exhaust elbow / internal wastegate housing-both turned out to be a major restriction for the new, larger turbo.
It's a simple task for anybody...
It's a simple task for anybody with the right handtools to remove the stock turbo. The turbo's bracket has two bolts holding it to the passenger side cylinder head. The three bolts to the exhaust inlet are a little difficult to get at. A couple of universal sockets (14- and 15mm), extensions (6, 8, and 12 inch), a good ratchet, and a few wrenches make the job easy.
After removing the stocker...
After removing the stocker and placing it next to the new unit, there's a noticeable size difference. Here's looking at the compressor housings and wheels of the new and old turbo. Larger turbos might have more lag (take longer to spool), but make more power. Using today's technology we'll try a few fixes to help reduce turbo lag.
The old and the new turbo...
The old and the new turbo both have 3-inch inlet bells. On the stocker the inlet bell tapers down with sharp edges (causing turbulence) leading to a 34mm compressor wheel.
Notice on the new turbo how...
Notice on the new turbo how the bell gently tapers without any sharp edges leading to the 58mm billet compressor wheel. The original turbo is said to flow about 550 cfm while the new Precision Turbo is reported to flow well over 800+ cfm.
Next up on our test quest was to exchange our throttle body for a ported stock unit from Jose Motor Sports. While working on the induction we would remove the plenum "hat'' (aka doghouse) and install an RJC Racing Airflow Distribution Power Plate. The RJC ADPP has proven, after extensive research and testing, to evenly distribute and maximize airflow to all the cylinders through the lower intake manifold. This enables the Power Plate to eliminate low airflow to the front cylinders, which notably cause lean knock timing retard conditions. It's a well-proven performer used by many of the fastest Turbo Buicks. Jose Torres (Jose Motor Sports) has high regards for the RJC Racing ADPP-he uses one on his 9-second ride (March '08) and mentioned we'll love the results. And we did. On our test loop, after installing the ADPP and ported throttle body, we felt better throttle response and a noticeable power increase.
Unfortunately, the next day on our ride to Tune Time we felt slippage in First and Second gear. Good thing dyno testing is done in the gear with a 1:1 ratio (Third gear in a 200-4R). The RJC ADPP lived up to its reputation, and we were impressed to learn that we picked up 15 hp (without any knock retard issues). This enabled us to add more timing (4 degrees) and fuel (10 percent) to gain another 7 rwhp. Now the A/F was at a safe 11.8 to 11.9:1 This was great considering our previously lean A/F conditions. At that point we left the new tune alone, thanked the Tune Time guys for all the dyno testing, and drove home.
In a perfect world we could have strip-tested the results from the new turbo, boost controller, bigger downpipe, and power plate, but in this real world the transmission went south, slipping away. We missed our track test day, but felt the Buick could have dipped into the 12s. Once the transmission is rebuilt and teamed-up with the right stall speed converter, we'll get to see what a gain of 117 rwhp and 190 lb-ft of torque is worth from the bone stock baseline (14.25 at 94.53 mph). Hopefully, the over-100,000-mile Buick V-6 motor continues to survive the added boost and the host of bolt-ons. Stay tuned.
|DYNO AND STRIP TEST RESULTS
|Stock 13 psi
|Valvesprings, fuel pump
|42-lb injectors, chip, 19 psi
|High-flow exhaust, 19 psi
|3" downpipe, boost controller
|ADPP, ported TB
||No strip test, bad trans
|TOTAL GAINS FROM STOCK: 117 RWHP, 190 LB-FT
In all fairness to dyno testing...
In all fairness to dyno testing these turbos-we removed the stock exhaust elbow / internal wastegate housing and installed it on the new turbo.
Don't do this when stepping...
Don't do this when stepping up to a larger turbo. A larger turbo will need a larger downpipe to perform properly.
Our new Precision Turbo easily...
Our new Precision Turbo easily bolted right in place where the original turbo once resided. The exhaust elbow housing and 2.5-inch downpipe proved restrictive towards spool-up. On our testdrive we felt more power from the new, larger turbo. It definitely hit harder, but was taking longer to spool up-a problem we intend to fix soon enough.
At Tune Time Performance we...
At Tune Time Performance we learned the larger turbo developed 25 more rwhp. Both peak torque and horsepower occurred at 500 rpm higher due to the added turbo lag. Since we began dyno testing this Buick, we've had 3-6 degrees of knock retard on every pull. It didn't matter if we adjusted the air/fuel mixture ratio to be safe (11.3 to 12.0) and if there was 110 octane race fuel in the tank.
For these pulls we started...
For these pulls we started out with a dangerous 12.6:1 mixture. Before the next couple of pulls Matt Hauffe (Tune Time's owner) programmed more fuel into the mix for a safe 11.8:1. We should have seen more power, but the knock retard was working against us. We'll also address the knock issue.
With total gains of 35 lb-ft...
With total gains of 35 lb-ft of torque and 63 rwhp from the new Precision Turbo and Pypes exhaust (Part 2) we expected e.t.'s to drop by roughly a half a second. Unfortunately, bad summer air slowed us by a few tenths and turbo lag didn't mix with the stock torque converter. Due to disappointing 2.3-sec. 60-foot times (previously 2.1), the e.t. only dropped by a tenth (13.60s to 13.50s). Again, we could only launch with 0-1 psi of boost even with our go pedal to the floor while power-braking (TR's launch better at 4-5 psi). With gains of over 4 mph in trap speed, we needed to reduce turbo lag for lower e.t.'s and support our power gains for the next test day at Englishtown.
We mounted (in-line between...
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...
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 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...
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...
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...
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...
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)...
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...
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...
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...
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...
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...
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.