Buick Grand National Precision Turbo Upgrades - The Sultans of Spin

Here are the combatants: Precision...        read full caption Here are the combatants: Precision Turbo's LT-70 with standard wheels (left), Limit Engineering's hybrid LT-70 with a standard compressor wheel and a GTQ exhaust wheel (middle), and Precision Turbo's full GT TSM-70 (right).

Anyone who questions the GT's...        read full caption Anyone who questions the GT's superior power potential can check out the dyno chart: all else being equal, just going from the standard to a GT exhaust wheel netted 6.4 horses and 22.7 foot-pounds at the rollers. The full-on GT turbo added an additional 14.5 horses and 7.6 foot-pounds at the wheels over the hybrid. And overall, the difference between a T-series 70 and a GT-series 70 is 20.9 horsepower and 30.3 foot-pounds at the wheels! Also, Hartline says that at higher boost levels, the GT would have widened its lead on the other turbos. As an aside, a high-boost run in the GN pushed the GT-series 70 to 29 pounds--and recorded 642 horses and 584.3 foot-pounds at the wheels!

Cal Hartline would be running...        read full caption Cal Hartline would be running our turbo shootout; here Cal (left) and car owner Louie Lopez tie up loose ends before the testing begins.

To precisely regulate the...        read full caption To precisely regulate the boost pressure, an Innovative Turbo Systems' multi-stage boost controller with a CO2 setup is used. The bottle contains CO2 and has a gas regulator. The controller uses the gas to provide an artificial reference signal to the wastegate solenoids. The electronic controller pulses the wastegate solenoids (one in, one out), either purging the gas or holding pressure to maintain the target boost setting.

The best part about it is...        read full caption The best part about it is that weather conditions do not affect its performance and boost control will remains consistent. With the appropriate sized wastegate it will control boost creep also.

The 3-bolt 70-series turbocharger for the 3.8-liter Buick--track-proven to run easy 10.50s--has enjoyed lasting popularity with Turbo Regal racers. A couple of years ago, 10.50 was good enough to win a lot of races, including the GSCA's red-hot Turbo Street Modified class--created for Buick racers who fit between the GSCA's Turbo Street Stock and the Turbo Street Eliminator groups.

But if there's one trend with the aging Turbo Buicks its that technology just keeps coming, and these days in TSM, you'd better be running 10.20s to high 9s if you want a chance in Hell of seeing the winner's circle. TSM is wildly popular due to its rule structure, which requires racers to utilize stock components like the block and crank and limits the maximum turbocharger size to a 70mm compressor wheel. While it is true that ultimately, the tune is the most important aspect of a TR's setup, occasionally a new component comes along that raises the bar--enter the Garrett GT turbocharger.

Garrett's GTs were developed in the 1990s to be superior replacements of the older T-series turbos. Initially released overseas, they were around for a few years before filtering into the American turbocharger market. Only a few U.S. companies--including Lake Havasu City, Arizona's Limit Engineering and Hebron, Indiana's Precision Turbo & Engine--are licensed to distribute them.

While many of the GT's features were a vast improvement over the old T-series (45 percent fewer components, improved shaft stability, increased thrust bearing capacity), the radical fin technology is what got the racers' attention. These wicked-looking wheels were said to spool much faster--swapping a similarly sized GT in place of your old turbo could get you into boost quicker, and upgrading to a much larger GT turbo could make gobs of extra power without the lag. But the question remained: in an apples-to-apples comparison, would the GT wheels make any more power than the old T-series wheels? We wanted to know, so we set up a test with Cal Hartline of Hartline Performance. Cal is known for having the magic touch when it comes to building and tuning forced-induction cars. The proof is in his 8-second, 1,200-horse '87 GN that rules over Turbo Street Outlaw--and stalks Central Florida's streets in full sleeper mode ("Hardline", March 2004). Hartline was eager to compare the new GT technology to the older-style T-series units where it counts--on the dyno and at the track.

The guinea pig was Louie Lopez's TSM '87 GN. The Hartline-built LC2 has 160,000 miles and features a girdled 109 block displacing 234 cubic inches and retaining the stock rods, crank, and rod bolts. The buildup goes like this: JE forged pistons, a 214o/214o Comp roller cam, ported Champion aluminum heads, and 1.65 T&D roller rockers are the hard parts. Feeding that mill is a ported stock intake, a Precision plenum with a 70mm throttle body and a RJC Power Plate. RJC pulleys and a V2 front-mount intercooler free up power, as do the ATR headers and 3.5-inch downpipe. A TurboSmart wastegate, in conjunction with an Innovative boost controller, keeps the pressure in check, and 72-pound injectors, fed from a 2015 Weldon pump, take orders from a F.A.S.T. system. With this setup, Lopez has won Bradenton's 2004 TSM and TSM Outlaw events, and he's run a best of 9.98 at 134 at Orlando using a Limit 70 turbo.

Three turbos were procured for this test: a Precision LT-70 with a standard P-trim compressor/exhaust wheel with .85 housing (around $995), a Limit Engineering LT-70 with a standard compressor and a GTQ exhaust with .85 housing (around $1195), and a Precision TSM-70 with a GT compressor wheel and GTQ exhaust with .85 housing (around $1295). (Note that calling the TSM-70 a "true" GT turbo would be inaccurate; Garrett's new GTs have redesigned housings, which won't fit on turbo Buicks. Instead, GT components are used inside Buick-compatible turbo housings. Also, the brand of each turbo was not important for this test; we required a full T-series, a hybrid T/GT series, and a full GT series to determine power differences, and it so happened that we used two Precision turbos and one Limit Engineering turbo.)

Mike Norris of Norris Motorsports in Ocoee, Florida was generous enough to lend us his DynoJet for an afternoon, so the GN was strapped down and warmed up. Since the timing would be set at 22 degrees and the target boost pressure would be 23.5 pounds, the GN would be drinking straight VP C16 (motor octane 117) during testing. The coolant temp was to be kept between 159 and 160 for every run, and we planned to record three important variables: rear-wheel horsepower, rear-wheel torque, and the amount of time it took each turbo to spool from 8.5 to 23.5 pounds of boost. Since there is not a huge difference in price between the three, it was put-up or shut-up time for the GT.

Hartline got a laptop connected...        read full caption Hartline got a laptop connected to the GN's F.A.S.T. system to keep digital tabs on the LC2's boost, rpm, injector pulse width, and the air/fuel ratio.	Mike Norris (right, seen bringing...        read full caption Mike Norris (right, seen bringing the DynoJet software online) ran the dyno for our shootout. Cal was to bring the GN to full boost before the TH400 shifted to third gear, and Mike was to start the pull after the shift to ensure no dyno spikes.
		Quality GM performance shops...        read full caption Quality GM performance shops can be hard to find in Florida, it's nice to have Norris Motorsports in the Orlando area. Proprietor Mike Norris sees lots of Vette business here but also caters to F-body and Impala SS customers; from bolt-ons through twin-turbo setups, Norris has you covered.