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Small Block Chevy Engine LS Conversion - Coil Conversion Therapy

DIS for SBCS

A Basic LS Conversion

This is a somewhat complex story because of all the components necessary to convert a small-block Chevy to LS EFI control with DIS. But the job can be simplified by using factory parts from an ’02 Vortec engine in a fullsize truck. The ECMs for these engines required crank and cam position signals from a 4x trigger wheel on the front of the crank and via the crab-cap–style distributor. While the 4x trigger wheel will not work for an LS engine PCM (which requires at least a 24x wheel), you can use the Vortec’s distributor and plastic timing cover, which was molded to accept a crank sensor. Combine these parts with EFI Connection’s 24x wheel wiring harness, LS coil package, and a few assorted small parts, and you can easily convert an ’80s vintage TPI engine to LS control. We’ve called out all the essential parts in the Parts List with an asterisk (*), or you could try saving money by piecing a portion of this system using boneyard parts like the LS engine coils, the Vortec distributor, and possibly the LS computer. We won’t get into the details here, but it’s also possible to build an LS computer-controlled, big-block Chevy using similar, late- ’90s-era, L-29 Rat motor components.

Inductive vs. Capacitive Discharge

There are two basic types of ignition systems used in gasoline engines. The most common is inductive, which is found in all stock production vehicles. In its simplest form, battery voltage is fed to a step-up transformer (the coil) on the secondary side. When a switch on the primary side closes, it feeds a voltage across the primary side of the coil. When the switch opens, the field energy created by the primary windings collapses across the larger number of windings in the secondary side of the coil. This increases the voltage that is then fed via the coil wire to the distributor and finally to the plugs.

The advantage of inductive ignition is its long spark duration and good spark energy. Its weak point is that at higher engine speeds, there is less time to adequately charge the single coil to fire eight cylinders at speeds above 5,000 rpm. As a result, spark energy diminishes at higher engines speeds. This is the main reason OEs have converted to using a coil per cylinder inductive ignition, since even at very high engine speeds, the coil has plenty of time to build sufficient spark energy.

Before multiple coil technology, the racing world embraced the capacitive discharge ignition system in which a voltage amplifier charges a large capacitor that stores 480 volts. When the ignition system is triggered, 480 volts are blasted through the primary side of the coil. This massive amount of voltage is then stepped up to extremely high voltage across the secondary side, which is sent to the spark plug. One advantage to a CD system is that this process can happen very quickly, but the downside is that the spark duration is very short compared with that of the inductive system. This allows the CD system to fire up to three times at engine speeds below 3,000 rpm. This is the reason for the MSD’s name—multiple spark discharge. Unfortunately, at above 3,000 rpm, there is insufficient time to multistrike, and the spark reverts back to a single spark of very short duration.

While CD ignitions work, there are advantages to the inductive system, especially when individual coils are employed per cylinder. By using individual coils per cylinder, the amount of time necessary to completely recharge the coil is increased, as a single coil on a V8 engine must fire 50 times per second at 6,000 rpm. On that same V8 with eight individual coils, the number of spark firings per coil reduces down to 6.25 times per second at 6,000 rpm. This allows the coil to supply near maximum spark energy, which has the potential to improve power at higher engine speeds.

Dyno Chart

RPM LT1 TQ LT1 HP 24XTQ 24XHP TQ Gain
2,500 373 177 406 193 +33
2,700 383 197 414 213 +31
2,900 411 227 424 234 +13
3,100 411 242 424 250 +13
3,300 413 259 431 270 +18
3,500 419 279 430 286 +11
3,700 418 295 441 311 +13
3,900 423 314 446 331 +23
4,100 425 331 443 346 +18
4,300 427 349 454 372 +27
4,500 443 379 461 395 +18
4,700 454 406 480 430 +26
4,900 467 436 489 456 +22
5,100 482 468 493 479 +11
5,300 484 488 507* 511 +23
5,500 485* 508 502 526 +17
5,700 483 525 496 539 +13
5,900 468 525 494 556 +26
6,100 463 537 480 558 +17
6,300 456 547 466 559 +10
6,500 444 550 454 562 +10
6,700 433 552* 443 565* +10
Peak 485 552 507 565 33
Avg.* 439.7 394.6 458.4 410.7 18.7

Parts List

Description PN Source Price
EFI Conn. 24x basic kit 120-00022 EFI Connection $515.00*
EFI Conn. 24x crank wheel 120-00001 EFI Connection 275.00
EFI Conn. LT1 billet cover 120-00014 EFI Connection 345.00
EFI Conn. SBC billet cover 120-00013 EFI Connection 310.00
EFI Conn. 24x TPI engine harness 100-00472 EFI Connection 650.00
EFI Conn. Vortec dist. 120-00003 EFI Connection 125.00*
EFI Conn. Vortec timing cover 120-00007 EFI Connection 50.00*
EFI Conn. LS2 coil 110-00002 EFI Connection 40.00 ea*
EFI Conn. coil pigtail 110-00510 EFI Connection 10.50*
EFI Conn. LS1 PCM used 110-00003 EFI Connection 100.00*
EFI Conn. 24x crank sensor 110-00001 EFI Connection 92.50*
EFI Conn. sealed alum distributor cap 110-00005 EFI Connection 25.00*

* Individual items for a basic conversion

SOURCES
EFI Connection
814-566-0946
http://www.eficonnection.com
Tuned Port Induction Specialties (TPIS)
952-448-6021
http://www.TPIS.com
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