Buick Grand National Precision Turbo Upgrades - The Sultans of Spin

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.