Tuff Mounts Gen V test bed: 6.2L L87

This may not be the kind of fire-breathing monster with four-digit power figures you’re used to seeing in Mill of the Month, but with stocks of a long-standing street-machining staple (the GM Gen III and Gen IV small-block commonly referred to as ‘LS’) rapidly drying up, it’s important that we look at the newer Gen V ‘LT’ series.

First published in the November 2024 issue of Street Machine

This particular Gen V mill, a 6.2-litre L87, now powers the Tuff Mounts HQ Holden wagon, and you can read all about the installation process here. While it has little more than a cam kit, lightly fettled heads, an inlet manifold and an aftermarket ECU in terms of performance-focused mods, it should still spit out around 650hp at the crank. Importantly, it also features a number of clever tweaks to make retrofitting it into an older car a lot easier.

MORE Gen V: GM’s LT engine family

Take-up of the LT-series engines for conversions here in Australia has been painfully slow, largely due to Aussies shying away from the complexity and expense surrounding the direct-injection (DI) fuelling, variable valve timing (VVT), and variable-pressure oiling system. Fortunately, Jason Waye of Tuff Mounts has already done the hard work and hopes to make these mills a viable option for Aussie street machiners. “We set out to simplify everything, and that meant converting to port injection and ditching the VVT and variable oil pump so that running this engine was a lot like running an LS – even though they are actually very different,” he explains.

The L87 is essentially the truck version of the LT1, and the two are fundamentally very similar. This ex-Silverado donk came to Jason with a spun bearing, so it was pulled down and treated to a freshen-up. The crank was machined 30thou and the pistons and connecting rods were reused, with new rings sufficiently gapped for nitrous so Jason has that option down the track.

MORE World’s first LT1-swapped Holden

“We gave it a quick dingle-ball hone and everything came up mint,” Jason says. “The heads went to Peter Schaefer for a clean and tickle; he faced them, tidied up the ports a bit, and fitted the BTR locks, springs, collets and retainers.”

The engine was assembled by Cory at Read’s Mechanical, with a BTR 225 camshaft kit that included the cam, lifters, pushrods and all the associated valvetrain components matched to suit.

“The cam kit comes with a VVT delete, so you can choose to either retain VVT or get rid of it,” Jason explains. “Deleting it made the most sense for our application, so we fitted the billet blanking plate. It makes it more like an LS; it just simplifies everything.”

To that end, Jason also ordered a BTR Trinity port-injection inlet manifold, as well as a DI delete kit from ICT Billet. “The DI delete comes with injector plugs and brackets,” he says. “A lot of people just leave the original DI injectors in place, which is fine, but we went this way just to make it look a bit nicer.”

A Katech billet oil pump was used in place of the factory variable-pressure pump, which is controlled by the factory ECU in a standard application. The Katech pump is also a stronger and more reliable item.

Seeking to further simplify the LT-based donk, Jason also had it 3D-scanned and has developed CNC-machined adapters to fit a more widely available VE water pump. “It looks a lot nicer and centralises the water pump, making more room for other engine ancillaries. Importantly, it still lines up with the standard LT crank pulley,” he says.

For the ECU, Jason went to Aussie engine management gurus Haltech, and with the switch to port injection and the deletion of the VVT and variable-pressure oil pump, the Haltech crew advised that their popular Rebel LS would do the job, so it got the nod.

With a few carefully prescribed mods, it turns out swapping a Gen V Chevy small-block into your street machine isn’t such a scary proposition after all. “These engines are cheap and plentiful out of the States, and they’re fast becoming more popular here in Australia, too,” Jason says. “We’re looking forward to helping people with their LT swaps and will be developing plenty more conversion parts in the future.”

IS IT QUICK?

The Tuff Mounts HQ hasn’t seen the dyno as yet, but Jason is hoping for an honest 500hp at the tyres from the cam-only combo. With plenty of cubes and an impressive 11.5:1 static compression ratio from the factory, it’s not hard to see the performance potential of these engines. At Drag Challenge, the wagon ran a best of 12.6 at 112mph, with both the ECU and the trans still in self-learn mode. Jason is hopeful that with some more fettling, the wagon will crack the 11s normally aspirated. Stout!