In the grand scheme of small-block Chevy performance engines, there's a ton of information on the first-gen engines, and every month there seems to be more on the new Gen III and now Gen IV small-blocks, but the LT1 engine-the Gen II if you will-seems to have been overlooked.
Our pal Tim Moore got the call to build a solid-performing LT1 small-block that would occupy the engine compartment of a certain Impala SS owned by Joe Freeman. Since the Impala SS is a hefty sedan, torque is the name of the game if you want good street performance, so this demanded an infusion of cubes.
Moore's first step was to contact Scat for one of its performance cast cranks along with a set of 4340 forged-steel I-beam rods to add stroke to the 4.030-inch bore. He filled the cylinders with forged flat-top SRP pistons and a 11/416-inch ring package. The stroker package required some careful block clearancing near the oil-pan rail to clear the rods. The minimum clearance here is 0.050 inch, but even more is advisable. The problem is you must remain conservative in order to avoid hitting the factory water jacket located nearby, so don't get carried away with the die grinder. This combo also required internal balancing because we were running the stock front damper, which doubles as the front accessory drive pulley.
Moore had already decided to invest in a set of Airflow Research 180cc aluminum heads, figuring that the smaller ports would create enough airflow to help build torque, since the LT1 intake offers extremely short intake runners that tend to hurt low-speed torque. These smaller AFR LT1 180cc heads produce more airflow than many larger competitors, which will tend to improve the midrange torque. As you can see from the power curve, the torque curve is amazingly flat, which just makes the Impala SS that much more fun to drive.
With a solid 11:1 compression ratio dialed in with the AFR 64cc chamber size and flat-top pistons, Moore knew he would have to add some camshaft duration to the mix to avoid detonation problems on California's marginal 91-octane pump gas. Looking through the Crane catalog, Moore ran across a single-pattern hydraulic roller with excellent cam lift-218 degrees at 0.050 inch-combined with 0.498-inch valve lift. The best part is that Crane went to the effort to establish an Executive Order that makes this cam 50-state legal with the smog police, which in California is a must-have option for a '90s daily driver. Moore spec'd the rest of the valvetrain all from the Crane catalog, including 1.5:1 narrow-body roller rockers to clear the stock LT1 valve covers, springs, retainers, keepers, and pushrods to create a durable valvetrain.
While an LT4 intake would probably have improved peak horsepower, Moore chose to have the stock intake port-matched to the new AFR heads. Slover's Porting in North Hollywood, California, did the work and also trimmed the step formed just behind the larger 58mm Holley LT1 throttle-body. Without the mild porting, there is probably little to gain from using the larger throttle-body. Because this stroker would easily exceed the stock fuel injectors' capacity, Moore also stepped up to a set of 30-lb/hr ACCEL fuel injectors, which even at the stock fuel pressure are capable of supplying sufficient fuel to make almost 500 hp.
There's also little reason to invest in a good set of heads and a more aggressive cam if you don't give the engine every opportunity to breathe. This meant bolting on a set of Borla stainless steel headers matched up with stock converters and a stainless Borla 211/42-inch exhaust system complete with an H-pipe.
Once Moore had assembled the engine, he trundled it over to Duttweiler Performance where dyno-man Ed Taylor bolted it up to the Digalog dyno and gently broke in the engine before abusing it all in the name of horsepower. While peak horsepower reached a solid 437 at 5,600 rpm, what impressed us most was the amazing torque curve that averaged a stout 439 lb-ft from 2,400 to 5,800 rpm. Peak torque came in at 460 lb-ft. Combine these two achievements and you have exactly the kind of power curve necessary for a heavy vehicle with an automatic.
A typical '96 Impala SS weighs in at around 4,000 pounds, which means the stock 3.08 gear is aimed more at highway cruising than moving off a stoplight. So Moore stepped up the Impala's acceleration prowess with a set of 3.73 gears from Randy's Ring & Pinion. This, combined with the 4L60-E transmission's 3.07 First-gear ratio and the 400 lb-ft of torque at the stock converter's 1,900-rpm stall speed, gives the big B-body plenty of grunt when it comes time to bury the throttle from a stoplight.
The final step was to have Steve Cole, owner of The Turbo Shop in Compton, California, do a part-throttle tweak on the factory computer to smooth out a few rough edges that resulted from adding the bigger camshaft and fuel injectors. Magazine deadlines and an early wet California winter have prevented us from a drag test, but all indicators point to high 13s at 100 mph, and our intrepid owner Joe Freeman has already had the Impala up over 140 mph "and it was still pulling."
The key to this impressive package is the combination of a mild cam, excellent heads, a little added compression, and some electronic goodies like an active factory detonation sensor that can work in concert to make great power without sacrificing the street manners of a big road car.
The Numbers GameWe tested the LT1 383 with a few exceptions to the way the engine is configured in the car. We omitted the catalytic converters, the Impala SS air-cleaner system, and the LT1's front accessory drive. The test did include spinning the water pump and using the stainless Borla headers and exhaust system.
RPM TQ HP 2,400 425 194 2,600 426 211 2,800 425 227 3,000 429 245 3,{{{200}}} 436 266 3,400 447 289 3,600 454 311 3,800 458 331 4,000 459 349 4,200 460 368 4,400 459 384 4,600 457 400 4,800 453 414 5,000 445 424 5,200 436 431 5,400 424 436 5,600 410 437 5,800 393 434 Avg. 439 342 Peak 460 437 Cam Specs Adv. Dur. @ Lift Camshaft Dur. 0.050 (in) Crane Hyd. Roller, Int. 280° 218° 0.498 2050, PN 104241 Exh. 280° 218° 0.498Lobe Separation Angle: -116 degrees50-state-legal E.O. camshaft
Parts List Component Mfr. PN Price Crank, cast, 1pc. Scat 9-350-3750-5700L $289 Rods, forged 4340 I-beam Scat 2-350-5700-2100 {{{300}}} Head bolts ARP 134-3601 50 Oil pump drive ARP 134-7901 14 Piston, flat-top, forged SRP 138089 468 Main bearings Federal-Mogul 139M 47 Rod bearings Federal-Mogul 8-7100CH 50 Cam bearings Federal-Mogul 2100M 34 Gasket set, head set Fel-Pro HS 9966PT 145 Gasket set Fel-Pro CS 9966 {{{62}}} Oil pump Melling {{{M}}}-55 17 Cam, hyd. roller Crane 104241 270 Lifter, hyd. roller Crane 10530-16 188 Pushrods Crane 10621-16 110 Rocker arms, 1.5 Crane 10751-16 320 Cylinder heads, aluminum AFR 0908 1,824 Throttle-body, 58 mm Holley 112-{{{505}}} 400 Injectors, 30 lb/hr ACCEL 150830 250 Headers Borla 17089 1,103 Exhaust system Borla 14504 893 Spark plug wires, LT1 MSD 32143 70All prices from www.summitracing.com except for the Scat and SRP parts, which were obtained from the specific manufacturers.
