Old-timers who were around back during the original muscle car era will look back longingly on the engines that ruled the streets then: the 290hp 302, the 350hp 350, and the 375hp 327. Those of us cutting our performance teeth at the start of the second muscle car era will look back at a decidedly different set of muscle motors. To combat the Ford H.O. 302 in the Mustang, GM introduced a powerful 5.0L of its own. First available in L69 carbureted form, GM soon introduced the LB9 TPI 305 with Tuned Port Injection. Sure, they offered the L98 350 in the Corvette (and Camaro with an automatic), but the stick shift LB9 was the hot setup in an F-body back in the day. Despite an epic battle with the Blue Oval boys, the 305 never gained the respect it deserved. Lest we forget, the LB9 305 (or any 305 for that matter) is still a small-block Chevy, and that is one heck of a starting point.
OK sure, most 305 owners would gladly trade up to the larger 350, but rather than go the swap route, let’s take a look at some performance possibilities with the standard displacement. For those new to the small-block world, the difference between the 305 and the 350 is bore size. Both small-blocks share the same 3.480-inch stroke, but where the larger 350 runs a 4.000-inch bore, the 305 was saddled with a smaller 3.736-inch bore. The argument against the 305 is that the smaller bore size limits the breathing potential of the cylinder heads by shrouding the valves or outright limiting valve size. Both of these are true, but the real question for 305 owners is at what power level does this truly become limiting? If you are building a simple 375-400hp street/strip small-block, the 305 can get you there even with the limitations imposed by the bore size. If you want to take things beyond that level things get more difficult. That is, unless you add the great equalizer: boost!
To illustrate the potential of a boosted 305, we took an original LB9 TPI 305 small-block and added positive pressure from a TorqStorm supercharger. Prior to the pressurization, the small-block was treated to some performance mods: a performance cam, aluminum heads, and a much-improved induction system. The cam offered a 0.570/0.565-inch lift split, a 218/224-degree duration split, and 113-degree LSA. The cam was teamed with a set of Trick Flow Specialties (TFS) Super 23 175 aluminum cylinder heads. Designed specifically for the small-bore size, the Super 23 heads featured 175cc intake ports, a 1.94/1.50 valve package, and 56cc combustion chambers. Compared to their stock iron counterparts, the Super 23 heads from TFS offered sizable flow gains and were capable of supporting nearly 500 hp on the right combination. The final mod was to replace the long-runner, factory TPI intake with a Holley Stealth Ram intake and 58mm throttle body. Run with a Holley HP ECU, the modified LB9 305 produced 372 hp at 5,900 rpm and 353 lb-ft of torque at 5,000 rpm. The 305 was already off to a good start.
Boost for the modified TPI 305 engine came courtesy of the gang at TorqStorm. The centrifugal supercharger offered a number of desirable features, including billet aluminum construction, a proprietary ceramic bearing system, and coating of the internal components for temperature and wear control. While other blower manufacturers offer superchargers capable of exceeding 1,000, 2,000, or even 3,000 hp, TorqStorm designed their blower for real-world, daily driven applications. Capable of supporting over 700 hp on the right application, the TorqStorm supercharger was perfectly sized for our modified 305. The kit supplied by TorqStorm included the supercharger (with pulley), mounting bracket, and crank pulley assembly (including the hub-centric spacer). The kit also featured the belt and tensioner, which allowed us to successfully run over 10 psi of boost with no belt slippage. Also included were couplers, tubing, and a blow-off valve (BOV) to eliminate the pressure spike that occurs when lifting off the throttle at high rpm/boost. The BOV also eliminates boost buildup under cruise conditions. Installation was beyond simple, with no need to supply oil to the self-contained blower or drill and tap the oil pan to serve as an oil return.
Because the kit was originally designed for use with a carburetor (we ran it carbureted for John McGann and the boys over at our sister publication Car Craft), we had to improvise the discharge tube connecting the supercharger to the throttle body. Since we were going the DIY route, we decided to include intercooling into the mix. We happened to have an air-to-water intercooler from a test we did on a big-block. Since the core was capable of supporting the needs of 1,200+ hp, it had no trouble cooling roughly half that amount. After installation of the revised 3.5-inch discharge tube to match the inlet and outlet of the intercooler, we were nearly ready. We connected a vacuum/boost line to the Turbosmart BOV (already installed on the aluminum tubing) from the Holley manifold. Water for the cooler was supplied by the dyno, but additional power could be made available with ice water. After tuning on 100-octane race fuel, the supercharged 305 belted out some impressive numbers. Running a peak boost pressure of 10.2 psi at 6,000 rpm, the blown, Tuned Port Injection small-block produced 612 hp and 546 lb-ft of torque. Who says you can’t make power with a 305? CHP
1. How do you make power with a 305? Easy. Just add boost!
2. Our test mule started life as a simple LB9 TPI 305. Though taking a back seat to the larger 350, it was primarily the 305 that could be found slugging it out in the streets against the 5.0L Mustangs of the day.
3.The stock hydraulic roller stick was upgraded with a performance cam that offered a 0.570/0.565-inch lift split, a 218/224-degree duration split, and 113-degree LSA. This was a perfect little street cam for the 5.0L.
4. The stock, iron TPI heads were replaced by a set of as-cast TFS Super 23 175 alloy heads. The 175cc heads flowed amazingly well and were sized perfectly for the little 305.
5. Topping the TFS aluminum heads was a two-piece Holley Stealth Ram intake. The lower intake resembled a tunnel-ram equipped with injector bungs to allow the use of electronic fuel injection.
6. The box plenum bolted to the lower manifold using the supplied hardware and gaskets. The polished system was both visually impressive and considerably more powerful than the factory TPI.
7. Feeding the upper intake was a dual 58mm throttle body from Holley. The Stealth Ram and 58mm throttle body allowed us to keep the TPI look of the LB9.
8. Run with the new heads, cam, and intake, the modified 305 produced 372 hp at 5,900 rpm and 353 lb-ft of torque at 5,000 rpm.
9. After running the 305 in naturally aspirated trim, we installed the aluminum blower mounting bracket and tensioner assembly.
10. Next came the TorqStorm supercharger head unit. The blower bolted in place to the bracket using the supplied hardware. Note the use of a V-band clamp to allow easy orientation of the volute.
11. The TorqStorm kit featured a 3.25-inch (eight-rib) blower pulley. The eight-rib system combined with an efficient tensioner design eliminated any belt slippage during our testing.
12. Thanks to an efficient impeller design, the TorqStorm supercharger was able to support as much as 700 hp on the right application. This was more than enough for our street-oriented 305.
13. The kit also included this adapter hub/spacer to properly locate the crank pulley. The pulley was bolted to the stock damper using a combination of the center damper and three pulley mounting bolts.
14. With the hub in position, we bolted on the 8-inch aluminum crank pulley. Installation of the kit was very simple and straightforward.
15.After installation of the eight-rib belt, it was secured in place using the two-bolt tensioner system. This combination provided a repeatable boost curve run after run.
16. To spice things up we added this air-to-water intercooler. Since we had to design our own discharge tube anyway, we figured an intercooler was a good idea.
17. Though TorqStorm supplied a blow-off valve with their kit, our custom discharge tube was already equipped with a Race Port blow-off valve from Turbosmart.
18. Run on the dyno, the modified small-block showed just how well a 305 responds to boost. Equipped with the TorqStorm supercharger pumping out a peak of 10.2 psi, the 5.0L produced 612 hp at 6,000 rpm and 546 lb-ft of torque at 5,500 rpm.
19. Every engine responds to boost, even the 305. After the top-end modifications, the small-block produced 372 hp and 353 lb-ft of torque. Adding the TorqStorm centrifugal supercharger to the mix upped the ante to 612 hp and 546 lb-ft of torque. This thing would be seriously fun in a street/strip IROC.
Photography by Richard Holdener