Whether it's from a desire to maintain a traditional underhood appearance or an aversion to the perceived expense and complexity of dealing with a modified electronic engine management system, there remain some die-hards out there who'd rather stick with their tried-and-true carburetor, yet still want to upgrade to a modern engine design like GM's Gen III/IV small-blocks. The roadblock is that this high-tech engine was never factory-available with a conventional carb and distributor. Fortunately, aftermarket carbureted intakes that accept standard-flange four-barrel carbs have become available from both GM Performance Parts and Edelbrock. However, without a factory computer, some sort of electrical device is required to both fire the individual factory coil packs as well as provide an ignition advance curve. One simple solution is a standalone aftermarket controller, available from both Edelbrock and MSD.
Manufactured for Edelbrock by MSD, Big E's controller is included in the box when you buy one of Edelbrock's carbureted LS1 intake manifolds. The analog unit is tuned by changing one of the six provided plug-in timing-curve "pills." Each pill contains what amounts to different engine-rpm-based and vacuum-based advance curves of varying aggressiveness. The rpm-based curves equate to an old-school engine's initial timing plus centrifugal advance. The vacuum-advance curves are just like vacuum advance, but the signal is generated by a MAP sensor referenced to either manifold or spark-ported vacuum.
MSD also directly markets its own branded controller. It includes the six timing-curve pills, plus adds the capability for the end user to digitally input any desired timing curve through MSD's supplied Pro-Data+ software installed on a Windows-based PC. The end user can program the minimum and maximum timing, any amount of "centrifugal" advance and retard, "vacuum" advance and retard, and low and high rev limits. An additional step retard can provide a user-defined fixed amount of retard via a separate switched 12-volt circuit-especially useful when using nitrous oxide. An idle-timing-control option can be enabled that permits the controller to alter the ignition timing constantly to search for the best idle quality. Finally, the MSD unit can be piggybacked with a stock EFI controller by using accessory harness PN 8886, which allows the MSD controller to tap into the sensor signals without interrupting the OEM ECU. The ECU and coils in this scenario would operate as normal while the MSD unit controls the timing and rpm.
Basic hookup for both the MSD and Edelbrock units is similar. Most of the wiring is contained in a preassembled harness with factory-style connectors that make hooking the unit into the existing factory (or aftermarket equivalent) coils and sensors easy. There are only two mandatory separate "nonfactory" hookups-switched 12-volt power and ground. An extra yellow wire is provided for an optional tachometer signal. Edelbrock's unit additionally includes an optional idle-compensator hookup that in conjunction with an available Edelbrock idle compensator (PN 8059) increases idle speed when running an A/C compressor and/or a wild cam. The MSD box has two extra wires for its step-retard and rev-limit functions.
To check the units' functionality and effectiveness we had Westech Engineering throw an LS1 on its SuperFlow engine dyno for a two-day thrash. The engine was internally stock except for a fairly healthy Comp Cams XR275HR Xtreme RPM High Lift hydraulic roller cam (see "Cam Specs" chart). We evaluated all six curves included with Edelbrock's analog controller using the Edelbrock LS1 Victor Jr. single-plane intake, then installed the MSD controller and compared Edelbrock's Victor Jr. against its Performer RPM dual-plane intake. Finally, a mild ZEX nitrous-oxide kit was installed to evaluate MSD's stepped-retard function.
Each combination was run three times, and the reported data reflects the average of the three runs. The test range was from 3,000 to 6,300 rpm, the typical full-throttle street-car operating envelope. Idle, off-idle, low-rpm, and part-throttle driveability were not evaluated.
Ignition-Curve TestThe engine was set up and run using the Victor Jr. intake, a Mighty Demon 750-cfm carb, and the Edelbrock controller with a Comp XR275HR cam (specs on page 122). Preliminary runs were made to dial in the carb, then each separate plug-in pill was tested. According to Edelbrock, pill curves 1 through 3 are intended for stock or mildly modified vehicles, while 4 through 6 are for modified vehicles. Depending on the curve, "initial" timing starts out anywhere from 12 to 22 degrees BTDC, peaking out around 36 degrees on top (see graph). Much of the difference in the curves occurs below 3,000 rpm; although important for evaluating driveability in an actual vehicle, it makes much less of a difference under full-throttle over 3,000 rpm. Because a real-world vehicle's driveability and detonation thresholds are influenced by the car's overall weight, transmission type, and final-drive ratio, what worked best for us on the dyno may not be directly applicable to any specific car even if it's running the same cam. But it's a lot easier to change pills than mess with a distributor's weights and springs.
Bearing these caveats in mind, although Curve 4 made the most peak torque (429.9 lb-ft at 5,000 rpm) and Curve 5 the most peak power (456.8 hp at 6,100), Curve 6 proved to be the best overall in terms of average power and torque production numbers, or "area under the curve" (see table below).
Intake-Manifold TestTo evaluate the differences between Edelbrock's two available LS series-engine intakes, Westech re-baselined the engine on the second day of testing. The MSD controller was installed in place of the Edelbrock controller with a PC-generated curve similar to the "pill-generated" Curve 6 that had produced the best overall numbers the previous day. Still using the single-plane Edelbrock Victor Jr. intake, Westech's dyno showed repeatability within approximately two numbers compared to the previous day's test, with the engine now producing 454.6 hp at 6,000 rpm and 430.9 lb-ft at 5,000 rpm.
Traditional wisdom holds that compared to a single-plane intake on a street engine, a dual-plane configuration offers better low-end and midrange power, with some sacrifices on top. The tests bore that out, with the Edelbrock Performer RPM making slightly more peak torque (433.5 lb-ft at 3,900 and 4,000 rpm, a gain of 2.6 lb-ft) but slightly less peak power (451.7 hp at 6,100 rpm, a loss of 2.9 hp). These peaks were spread over a wider band: Where the Victor Jr. single-plane's torque and power peaks were separated by 1,000 rpm, the dual-band spread was 2,100 rpm. Not surprisingly, due to the greater spread the dual-plane had the most area under the curve. The dual-plane would have demonstrated even more gains under 3,000 rpm. Unless you have a light car with steep gears and a stick-shift trans, the RPM dual-plane is clearly the better choice with Comp's XR275HR cam.
Cam SpecsAll lift figures are in linear inches. All duration and timing events are in crankshaft degrees at 0.006-inch tappet lift, unless otherwise noted.Manufacturer: Comp CamsType: Hydraulic rollerSeries: Xtreme RPM High LiftGrind: XR275HR-12PN: 54-426-11Lobe lift: 0.333/0.334Valve lift (1.7:1 rockers): 0.566/0.568Duration at 0.006 tappet lift: 275/277Duration at 0.050 tappet lift: 222/224Lobe centerline: 110/114 degreesLobe separation: 112 degreesIntake opens/closes: 28 BTDC/68 ABDCExhaust opens/closes: 73 BBDC/25 ATDC
Nitrous-Retard TestMost nitrous oxide-savvy racers retard the timing several degrees per each additional 100 hp added by the spray over the engine's normal baseline output without any N2O. Nitrous develops better, more efficient combustion characteristics, and the resulting quicker burn requires less advance-both to reduce detonation and to prevent the engine "working against itself" as the piston is still rising on the compression stroke. Generally, each 50hp increase in nitrous boost needs about 1.5 to 2 degrees less total advance.
MSD's controller makes it easy to dial in ignition retard, thanks to its optional switched 12-volt user-reprogrammable retard function. To demonstrate this function, Westech installed a Zex perimeter-plate nitrous system under the carb. This system has the potential to deliver up to a 300hp boost, but for this conservative test with a stock bottom-end, we jetted it for a 100hp increase. Once again the engine was re-baselined over three average runs, then the kit was actuated at 4,300 rpm with the retard function enabled. Not surprisingly, the engine churned out 539.8 hp at 535.9 lb-ft, a gain of 85.2 hp and 105 lb-ft over the non-nitrous numbers. Averages were up across the board by over 50 numbers overall and by over 80 numbers over 4,700 rpm.
ConclusionFor die-hards who just don't want to run an engine computer and miles of wiring, the Edelbrock and MSD controllers in conjunction with an old-school carburetor and intake are an available and effective solution. If a conventionally shaped advance curve with easy plug-in modules is all you need, the Edelbrock controller is more than adequate. Otherwise, step up to the MSD box, which lets the user program any desired advance curve.
TIMING-CURVE TEST CURVE 1 CURVE 2 CURVE 3 CURVE 4 CURVE 5 CURVE 6 RPM LB-FT HP LB-FT HP LB-FT HP LB-FT HP LB-FT HP LB-FT HP 3,000 364.0 207.9 367.8 210.1 367.0 209.6 372.9 213.0 371.9 212.4 375.0 214.2 3,{{{100}}} 368.1 217.3 368.0 217.2 368.0 217.2 373.9 220.7 374.0 220.8 377.9 223.1 3,{{{200}}} 370.2 225.6 368.9 224.8 370.2 225.6 378.5 230.6 377.1 229.8 381.5 232.4 3,{{{300}}} 375.3 235.8 373.4 234.6 374.8 235.5 382.1 {{{240}}}.1 380.2 238.9 386.2 242.7 3,400 382.1 247.4 381.4 246.9 382.2 247.4 386.3 250.1 388.6 251.6 391.7 253.6 3,500 389.5 259.6 391.4 260.8 390.9 260.5 395.0 263.2 396.2 264.0 396.7 264.4 3,{{{600}}} 397.0 272.1 397.6 272.5 395.9 271.4 402.7 276.0 402.0 275.6 402.5 275.9 3,700 402.0 283.2 401.4 282.8 400.1 281.9 404.3 284.8 409.2 288.3 406.6 286.4 3,800 404.6 292.7 403.8 292.2 402.9 291.5 407.9 295.1 410.3 296.9 409.4 296.2 3,{{{900}}} 406.9 302.2 406.3 301.7 406.6 301.9 412.0 305.9 412.3 306.2 413.0 306.7 4,000 410.8 312.9 412.3 314.0 410.8 312.9 415.1 316.1 415.0 316.1 416.6 317.3 4,100 415.0 324.0 415.3 324.2 414.8 {{{323}}}.8 418.2 326.5 417.1 325.6 419.9 327.8 4,200 415.4 332.2 417.4 333.8 416.3 332.9 417.3 333.7 418.2 334.4 420.7 336.4 4,300 415.5 340.2 416.6 341.1 416.8 341.2 417.8 342.1 420.2 344.0 420.5 344.3 4,400 416.0 348.5 416.3 348.8 416.7 349.1 419.4 351.4 421.3 353.0 419.7 351.6 4,500 415.6 356.1 418.2 358.3 416.3 356.7 420.0 359.9 419.4 359.3 420.6 360.4 4,{{{600}}} 415.1 363.6 417.1 365.3 416.9 365.1 419.0 367.0 421.5 369.2 419.3 367.2 4,700 416.3 372.5 417.8 373.9 419.4 375.3 424.7 380.1 422.0 377.6 422.3 377.9 4,800 417.6 381.7 421.8 385.5 421.1 384.9 424.7 388.1 422.6 386.2 425.2 388.6 4,{{{900}}} 422.0 393.7 424.5 396.0 423.4 395.0 426.3 397.7 424.8 396.3 427.0 398.4 5,000 424.3 403.9 425.4 {{{405}}}.0 426.3 405.8 429.9 409.3 427.9 407.4 428.8 408.2 5,{{{100}}} 423.0 410.8 425.5 413.2 426.5 414.2 429.5 417.1 425.9 413.6 427.3 414.9 5,{{{200}}} 423.0 418.8 423.6 419.4 424.3 420.1 426.5 422.3 423.9 419.7 425.6 421.4 5,{{{300}}} 420.9 424.7 421.9 425.8 421.8 425.7 425.0 428.9 421.4 425.3 425.4 429.3 5,400 417.7 429.5 419.6 431.4 420.4 432.2 421.0 432.9 419.4 431.2 421.2 433.1 5,500 413.7 433.2 416.6 436.3 417.6 437.3 415.4 435.0 416.9 436.6 419.5 439.3 5,600 410.0 437.2 413.6 441.0 414.9 442.4 411.9 439.2 413.9 441.3 415.3 442.8 5,700 407.1 441.8 408.9 443.8 410.6 445.6 409.5 444.4 412.9 448.1 412.6 447.8 5,800 402.2 444.2 405.1 447.4 406.9 449.4 404.9 447.1 409.9 452.7 408.3 450.9 5,900 396.4 445.3 400.9 450.4 402.1 451.7 400.9 450.4 405.9 456.0 404.1 454.0 6,000 390.8 446.5 395.4 451.7 395.1 451.4 395.9 452.3 399.3 456.2 398.9 455.7 6,100 384.6 446.7 388.4 451.1 387.0 449.5 388.8 451.6 393.3 456.8 392.7 456.1 6,200 377.2 445.3 382.3 451.3 380.7 449.4 380.7 449.4 385.8 455.4 383.1 452.3 6,300 371.0 445.0 375.8 450.8 374.3 449.0 374.3 449.0 379.2 454.9 376.9 452.1 Max 424.3 446.7 425.5 451.7 426.5 451.7 429.9 452.3 427.9 456.8 428.8 456.1 Gain 0.0 0.0 1.2 5.0 2.2 5.0 5.6 5.6 3.6 10.1 4.5 9.4 Avg. 402.4 357.1 404.1 358.9 404.1 358.9 406.8 360.9 407.6 361.8 408.6 362.5 INTAKE TEST PERFORMER RPM VICTOR JR. RPM LB-FT HP LB-FT HP 3,000 399.3 228.1 376.4 215.0 3,{{{100}}} 398.8 235.4 377.0 222.5 3,{{{200}}} 399.9 243.7 380.1 231.6 3,{{{300}}} 403.5 253.5 384.7 241.7 3,400 407.7 263.9 389.4 252.1 3,500 415.4 276.8 398.1 265.3 3,{{{600}}} 424.6 291.0 401.1 274.9 3,700 429.8 302.8 403.3 284.1 3,800 430.4 311.4 406.9 294.4 3,{{{900}}} 433.5 321.9 410.5 304.8 4,000 433.5 330.2 414.1 315.4 4,100 432.5 337.6 417.7 326.1 4,200 431.1 344.7 421.8 337.3 4,300 430.1 352.1 420.9 344.6 4,400 428.1 358.7 422.9 354.3 4,500 426.7 365.6 421.9 361.5 4,600 425.7 372.9 422.5 370.0 4,700 425.3 380.6 426.6 381.8 4,800 423.3 386.9 426.2 389.5 4,900 422.3 394.0 428.3 399.6 5,000 422.4 402.1 430.9 410.2 5,100 421.4 409.2 429.4 417.0 5,200 423.0 418.8 427.9 423.7 5,300 419.0 422.8 424.5 428.4 5,400 417.5 429.3 418.9 430.7 5,500 414.5 434.1 415.4 435.0 5,600 408.9 436.0 413.5 440.9 5,700 {{{405}}}.4 440.0 412.0 447.1 5,800 401.9 443.8 408.0 450.6 5,900 398.4 447.6 403.0 452.7 6,000 393.9 450.0 397.9 454.6 6,100 388.9 451.7 390.4 453.4 6,200 381.3 450.1 382.5 451.5 6,300 373.8 448.4 375.3 450.2 Max 433.5 451.7 430.9 454.6 Max gain 0.0 0.0 –2.6 2.9 Avg. overall 414.5 365.8 408.2 362.1 Avg. gain 0.0 0.0 –6.2 –3.6 Avg. low 420.6 305.3 404.1 293.9 Avg. high 408.3 426.2 412.4 430.4