VT Commodore LS1-to-LS3 engine swap

Dropping an LS3 into an LS1 Commodore isn’t as easy as it sounds

Photographers: Julius Goboly

With the introduction of the VT Series II Commodore in 1999, Holden killed off the long-lived Aussie V8 and began plonking the US-sourced, 5.7-litre LS1 (Gen III) between the front rails. This was the first of the all-new LS family of engines that has proven to be hugely popular and seem to be taking over the world. But many LS1s are getting long in the tooth and owners are looking to add some neddies under the hood. Enter the LS crate engine – or the more powerful 6.0-litre engines fitted to the VE.

First published in the January 2014 issue of Street Machine

Virtually all the GM crate engines are based on LS3 architecture (like the VE’s L98, 6.0-litre), and along with other changes they feature rectangular-port cylinder heads and a better flowing intake. Overall they’re a superior performance platform. While the LS1 and LS3 look similar, there are enough differences to prevent them from being a direct swap. The main differences are the reluctor wheel, cam angle sensor, MAP sensor, knock sensor and injector plugs. At a glance it may seem easier to upgrade your early Commodore to the later ECU, but that only creates a world of pain because you also have to integrate the later BCM, gauges, electronic drive-by-wire throttle, etc. Luckily the industry has developed straightforward solutions to address the LS1 and LS3’s incompatibilities.

Marcus and the crew from Gen-Tech Performance offered to run us through these changes as they fitted a Chevrolet Performance LSX 376 (an LS3 based crate engine sourced from Eagle Auto Spares) into a LS1-powered VT Commodore.


Here are the major differences all laid out: LS3 on the left, LS1 on the right. LS1; cam sensor goes in the back of the block (triggered off the back of the cam). Knock sensors screw into the valley cover.

Crank sensor is in the same location as LS3, however, LS1 sensor is only compatible with LS1’s 24-tooth reluctor (chopper) wheel. MAP sensor goes into back of manifold. LS3; cam sensor fits into timing case cover (triggered by the ‘lumps’ on the face of the cam gear).

Knock sensors are different and mount into side of block. It features a 58-tooth reluctor wheel and the MAP sensor is fitted into the front of the inlet manifold.


1. Leave the engine harness intact on the engine. It’s easier to swap it to the new engine once the old engine is out. Unplug loom at the computer and feed it through the large rubber grommet (firewall right – main image). There are also a few ancillary plugs (firewall left – inset) and although they can be a bugger.

  1. 2. After dropping the gearbox, disconnecting the battery cables, A/C lines, heater hoses and fuel lines – as well as lowering the steering rack – the old LS1 will slide straight out. To disconnect the fuel lines, you’ll need the special collar-like tool to release the factory push-fit.

3. Although it uses a different plug, the front-mounted LS3 cam sensor is compatible, but it needs to send the right signal to the LS1 ECU. The best option is to install a new cam and timing chain (opt for a double-roller). Use a three-bolt cam and a two-window (2x) cam gear (see Step No. 4). VCM Performance offers a patch lead to extend the LS1 loom to the LS3 sensor.

4. The cam gear window reference relates to the ‘lumps’ on its face. On the left is a four-window, on the right is a two window. The half-moon lump results in only two transitions for the pickup to register per revolution. Whereas the multiple lumps on the left gear results in four transitions.

5. Although fitting a double-row chain is a good idea, you’ll need to clearance (i.e. grind) the timing case to clear the thicker assembly. Note the boss (upper right) along with the material that’s been removed from around the front seal area. If the donor engine is an L98-style out of a late VE, it will be fitted with AFM/DOD lifters.

6. LS1 engines use a 24-tooth chopper (reluctor) wheel, while LS3 uses a 58-tooth. You can buy interrupter boxes, but the preferred method is to fit a new wheel – which requires a special alignment tool. Before removing, Marcus checks the alignment and marks the crank with a pen. Judicious.

7. To fit the new wheel, it needs to be heated to 230-degrees Celsius; Gen-Tech has found that a pie-oven works a treat. Alternatively, you can use oxy to bring it up to temperature, but be careful not to overheat it. Either way you’ve got to be damn quick during installation and ensure it’s properly aligned (with no run-out) before it cools and rigidly affixes itself to the crank.

8. While externally alike, VY-VZ sumps (middle) are the optimum choice as they feature effective internal baffling. The VT-VX (right) version has a metal plate but no baffling. The VE sump (left) and most LS3 crate motor sumps are completely wrong and cannot be used. *Note: the early VT-VX pick-up can be used.

9. LS3 knock sensors are compatible with the LS1 ECU. However, LS1 sensors were mounted in the valley and the LS3 sensors screw into the side of the block; LS1 versions cannot be substituted. A patch loom is available to plug the side-mounted knock sensors into the LS1 engine harness. Most incorporate.

10. Late injectors are completely different but compatible with the LS1 ECU – patch looms allow connection to LS1 harness, but you have to use an LS1 MAP sensor. Fitting the LS1 MAP into the larger LS3 hole (front of manifold), requires a special adaptor. However, VCM told us it can be fitted via a fat OD O-ring and secured in place with fabricated.

11. Later factory engines use drive-by-wire throttle, which cannot be made to work with the LS1 ECU, and the three-bolt LS1 throttle body doesn’t fit. The solution is to use an aftermarket four-bolt throttle body that will accommodate the factory LS1 throttle position. LS3 positions the purge solenoid at front.

12. LS3 harmonic balancers and water pumps must be swapped for LS1 versions. All the mounting bolt holes are the same so standard LS1 accessories bolt straight up. The LS3 dipstick goes through the block, while the LS1 goes through the sump. You must block off this hole.

13. All buttoned up and ready to install. The LS3 uses identical engine mounts and bellhousing pattern, and even though LS3 engines have different exhaust ports, the LS1 extractors bolt straight up. LS1 coil packs will also fit, however, LS3 coils are bigger – although many feel they offer no advantage. All this compatibility makes the nuts and bolts.

  1. 14. Due to the Harrop blower being mounted prior to installation, Gen-Tech decided to drop the cradle out, mount up the engine and install it from the bottom (i.e. lower the car onto it). When installed in this fashion, care must be taken with the wiring harness, brake.


Regardless of what configuration LS2 or LS3 or L98 engine you use, it will need a custom engine tune. So once it was all fired up and the Gen-Tech crew had checked all the vitals were within spec, they backed it up onto their Dyno Dynamics dyno and went about developing a new set of engine maps. When finished, the combo proved very healthy, churning out a stout 419rwkW, despite the less than ideal cam (the blower was a late inclusion) with plenty of boost in reserve.

When undertaking such a conversion, some prefer to cut and splice the wiring to create the various loom extensions (the terminals and connectors can be sourced on the net). However, the patch looms have proven extremely reliable and they make retrofitting the original LS1 a very simple undertaking – you never know, maybe you’d like to keep your good engine when selling the car. We thank Gen-Tech Performance and VCM Performance for their help in putting this feature together.