When it comes to the electronic intricacies of GM’s modern powerplants, the folks at Speartech have been at the forefront since the very beginning. The Anderson, Indiana-based outfit was founded by John Spears in 1997, an electrical engineer who had spent more than two decades at General Motors, largely focused on engine controls and ignition system development.

“We’ve been at it for a while now,” Spears says. “I started with the earlier tuned port injection (TPI) stuff – initially, this was kind of a hobby on the side, but as this work started to get busier and busier for me, I finally decided to take this up full-time in 2001. And those were the early days of the LS engine platform, which I’d worked on in engineering at GM. So, I had a lot of first-hand knowledge of the LS stuff even before it went into production. Early on, and through the years that we’ve been doing this, we’ve kind of focused on building the harnesses and programming the computers – setting it all up for the specification of the customer.”

Speartech originally got underway right around the time that the 345 horsepower LS1 was making its debut under the hood of the then-new C5 Corvette. Who would have guessed that, in just two generations time, we’d have mills like this 755 horsepower LT5 making more than twice the power right from the factory? Given its status as the most powerful production V8 in GM’s history (a title formerly held by the LT4), it was the obvious choice for Speartech’s latest build.

Spears notes that custom length harnesses and specialized programming are common requests from customers, and Speartech’s development and testing rigs are designed with that in mind. 

“We do all the harness building and layout on actual engines here,” he says. “We’ve got probably 15 or 16 live engine stands with transmissions in our shop, with the radiator, battery, key switch – the whole bit on each one. And building the harness in that environment allows us to test it right there for proper engine operation, transmission shifting, and everything else before it ever leaves our facility.”

Over the years, Speartech has put together a number of restomod combinations to showcase its latest offerings, first starting with an LS1/4L60-E swap into ’91 Camaro Z28, which later moved to an LS2 before eventually stepping up to an LS9 and 4L60-E combination. “It ended up running somewhere in the 9.70s in the ¼-mile,” Spears says. “Now it’s currently powered by an LS7 that’s paired up with another 4L60.”

Speartech also developed an L99 and 6L80-motivated 2001 Silverado as a shop truck that doubled as a rolling showcase of its accessory line. “We make so many supporting parts now,” he explains. “Gear indicators, cruise control, tap-shift options, and more. Doing these swaps really helps us evaluate all the different hardware that can go with it. And that’s what led to the C10.”

Speartech’s latest restomod machine is a ’69 C10 pickup, which the team originally saw fit to install an LT4 and an 8L90 gearbox. “That was a few years ago, back when the Gen V craze was just getting started,” Spears tells us. “So it required some specialized mounts, which we worked with BRP Hot Rods on, along with a custom driveshaft, and then all the usual electronics needed to make it all work the way we wanted it to. In many ways, that build was sort of a proof of concept for the LT stuff.”

Although Speartech offers packages to support manual transmissions like the Tremec TR6060, Spears explains that the company specializes in swaps that involve automatic transmissions — not only because they require more expertise to tune, but also due to their popularity, making the new 10L90 10-speed a good match for the LT5 going into the C10. “You don’t have a separate module for the transmission in a manual setup,” he explains. “So it’s a little bit simpler of a system because you’re changing gears on your own. But the popularity of the automatic has just soared in recent years, and this 10-speed has earned a good reputation for quick shifts and overall durability.”

And in keeping with company tradition, its latest endeavor sees the C10 scoring GM’s latest and greatest powertrain. 

“We pulled that out to move to the LT5 with the 10-speed,” Spears says. “This is the highest horsepower engine that GM has ever offered, and over the years we’ve found that whenever an engine comes out that tops all the rest, that’s where everyone wants to go. I’ve always been a big fan of the C10 trucks, and they seem to have gotten so popular over recent years – I just think it’s a great platform to showcase some of this stuff.”

Gen V Considerations

Although the LT engine family is ostensibly an evolution of the LS platform, Spears notes that there are some unique factors involved that are worth keeping in mind when tackling a project like this.

“The main thing is the fuel system,” Spears points out. “While the extremely high-pressure direct injection element is handled by a separate mechanical fuel pump in the engine, all of these engines now also use pulse-width-modulated fuel pumps, so that adds another module, an in-line sensor, and a few other bits and pieces. The computer needs to always see what the fuel pressure is in the line, and then turn the pump on and off at a high rate of speed in order to maintain the correct pressure.”

Speartech also offers turn-key powertrain packages, an option that allows the customer to request an engine and transmission combination and tells the company what vehicle it’s going to be installed in. The company then sources the hardware, assembles everything, and fits the necessary components and programming to that specific application to make the package as plug-and-play as possible from the crate. Spears also notes that by ordering this way, it allows Speartech to test the fully assembled powertrain before shipping to ensure that every element of the package is up to snuff before the customer gets it.

And while the LS and LT are dimensionally similar, there are important changes there, too. “The mounts – the ‘pad’ on the side of the block – for a Gen V engine differs from that of a Gen IV engine,” he says.

And beyond that, the electronics have evolved significantly, as well. 

“The LTs run on the E92 ECM and use a separate transmission control module,” he adds. “Back in the LS1 days, that was all combined into one box. But ever since the LS3, if you’re using an automatic transmission, that uses an ECM and separate TCM. And on the Gen Vs, there’s also a fuel pump control module – FPCM, which controls the pulse-width modulation (PWM) pump.”

Harness and Control Module Package

So it’s clear that when you’re tackling a swap like this, getting everything to work together is more than just some engine mounts and wire splices. And to that end, Speartech offers packages that provide builders with everything they need to see the project through from start to finish, which includes the LT5 and 10L90 transmission combination that the C10 is now outfitted with.

“The main goal was to make sure our package addresses each element and controls each component properly,” Spears points out. “So we started with the base LT4 package and added to that to make it all functional with the LT5 – with the LT5 you now have 16 injectors, for instance, so there are some additional things involved when you move up to the next level of horsepower. We’ve addressed all of that from the component standpoint, and for the tune, we sent it down to a dyno shop in Texas to get that aspect dialed in, and they did a fabulous job.”

Spears offers a bird’s eye view of the harness and control module installation process. “Of course it will vary a bit from application to application, but typically you’d take the harness and plug it into all the sensors on the engine, feed the hookup in through the firewall, and plug your modules in. From there you’d start your hookups – a wire going to the ignition switch, another for fan relays, your speedometer and tach, and so on. After that’s all hooked up you’ll want to find a place to mount the diagnostic port and the check engine light. If you’re doing this install on an assembled vehicle, I’d recommend allotting about 6-8 hours from start to finish, including integrating it under your dash, etc.”

Speartech provides what it calls a “start-up” tune with its kits. 

“There are so many outside variables, especially in terms of bolt-ons, exhaust setups, and air inlet configurations, that we found it was best to establish a good baseline to start from. You can probably get a bit more out of it with a dyno tune. But our tunes are pretty much spot-on for stock engines.”

Weighing Your Options

While the basic package includes the harness with the programmed computer and transmission modules as well as the throttle pedal, fuse block, and diagnostic port, Speartech also offers a number of additional components that can help builders round out their projects.

“Cruise control is a really popular option,” Spears says. “Back-up lights are done through a special module now – there’s no switch coming out of the transmission for that anymore, so we offer that, as well. There’s also a neutral safety switch module available, and all these little things can be added to complete the package for you.”

For those looking to simplify the process as much as possible, Speartech offers options there, as well.

“We’re doing full powertrain packages now, where we source the engine and transmission for you, put it together with the correct bolts and fasteners, the starter – the whole deal. We also include the factory exhaust manifolds, mass air flow sensor, the air tube, a K&N filter, the inlet elbow, the driveshaft yoke for the transmission, and while it’s optional, we typically end up putting a front drive kit on there, too – there are some choices you can make there, as well. And once we know from the customer what they’re putting it in, we wire it up for that specific application.

“Buying the complete powertrain package allows us to do all the testing here, so we know the entire package is good to go before it’s crated up and shipped,” Spears continues. “It’s as complete as we can make it before shipping – it’s ready to be installed. And we ship worldwide. These days we’re seeing a lot of activity going on in Australia, England, and of course the Middle East.”

And as you’d expect, Speartech is always developing accessories to make swaps like these as seamless as possible. 

“Right now we offer a standalone gear indicator for up to eight-speed transmissions,” Spears says. “The Dakota Digital dash option is the way we support the 10-speed automatic, but expect to see our standalone gear indicator option for that in the near future.”