THE DIRECT APPROACH

> GM’S NEW-AGE GEN V SMALL-BLOCKS SHUN CONVENTIONAL EFI IN FAVOUR OF DIRECT INJECTION. SO HOW DOES IT WORK, AND WILL WE MAKE MORE POWER FROM IT?

IN EARLY 2013, the world got its first look at General Motors’ high-tech V8 that would soon take over from the LS series, and bring with it some cool new, horsepower-rich tech. Dubbed the LT1, the fifth-generation Chevy small-block carries many familiar features over from the Gen III and IV LS engines, but is a whole new design that will throw a couple of curveballs at punters hoping to apply their LS knowledge to the new donk.

Offered in a 6.2-litre capacity, the naturally aspirated LT1 (335kw) and LT2 (365kw), and the supercharged LT4 (484kw) and LT5 (563kw) all feature variable valve timing and variable-pressure oil and cooling systems. Some features like Active Fuel Management (AFM) will be familiar to LS experts, but the biggest change is the switch from traditional port-style fuelinjection to direct injection (DI) as a way of improving power and efficiency.

Direct injection moves the fuel injectors from the intake manifold to directly into the combustion chamber, providing a more efficient air/fuel mix and combustion process. The end result is more power and fewer emissions.

The high pressure that DI runs at (up to 2900psi in the LT4!) atomises the fuel, which cools the combustion charge. This allows GM to push compression ratios higher, improving power. On top of this, DI’S precision-timed fuelling events mean every skerrick of fuel is combusted, and this means the engine’s tune can be made absolutely perfect.

This is why the LT1 rocks a compression ratio of 11.5:1, up from the LS3’S 10.7:1, as it has tighter control on the combustion process. And the GM boffins reportedly would have pushed it higher were it not for the fact that they wanted the Gen V to be able to run on non-premium fuels.

Having to jam a sparkplug, six-hole fuel injector, 54mm intake valve and 40.4mm exhaust valve inside a 103mm bore caused a bunch of headaches for GM engineers, so the direct-injection equipment (including fuel lines, mechanical high-pressure pump, pressure regulator and injectors) was moved to the valley of the V8. Because the high-pressure pump is mounted on the engine, the rest of your fuel system

SWAPSIES

THE big question is whether you can drop in an LT V8 where an LS was, connect up a few plugs and skid into the distance. The answer to that, unfortunately, is no.

All the Gen V shares with the Gen IV is its bore, stroke, displacement, cam location, deck height and five minor fittings (including starter bolts and piston pins). None of the sumps, valley covers, engine covers or front drive components – let alone internals – interchange between LS and LT.

The engine mounting positions have been updated, so existing engine fastening systems for LS mills won’t fly with the new-gen motors, and neither will headers. LT engines aren’t offered by GM with a hydraulic power steering pump, but there are aftermarket accessory brackets available to adapt Corvette hydraulic pumps, or you can switch to a hydro-electric pump like the popular TS Astra unit.

The LT also steps up to continuous variable valve timing, adding complexity to the tune. There are 62 degrees of adjustment in the cam gear-mounted phaser, which improves low-end torque, but many people swapping cams will likely just bin this technology in favour of fitting higher-lift and duration bumpsticks.

DIRECT INJECTION PROVIDES A MORE EFFICIENT AIR/FUEL MIX AND COMBUSTION PROCESS, RESULTING IN MORE POWER

ALL THE RANGE

THERE are four basic types of alloyblock LTS. After the front-enginefitment 455hp LT1 and the 490hp LT2 found in the mid-engined C8 Corvette, the next step up is the supercharged, 485kw/650hp (640hp in the Cadillac CTS-V) LT4. Dropping the compression to 10:1 and adding a new-generation, intercooled TVS

R1740 blower in the valley, the LT4 runs forged steel crank and rods, and stainlesssteel exhaust manifolds.

Topping the range is the

755hp (563kw)

LT5. Retaining the

6.2L sweep, the LT5 runs a 2.65L blower that is 52 per cent larger than the LT4’S pump and apparently out-flows a 2.9L twin-screw blower by 10 per cent. The big boost-box runs 14psi over the LT4’S 9.4psi and features a 30 per cent larger intercooler system. GM also pumped up the drive-by-wire throttlebody from the LT4’S 87mm unit to 95mm on the LT5.

While the LT1 and LT4 siblings run new-age direct-injection, the LT5 has such voracious appetite for go-juice that Chevrolet engineers had to back up the DI with an extra traditional port-injection set-up. This means there are 16 fuel injectors – eight large DI units spraying straight into the motor, and eight smaller injectors spraying the intake ports under the blower. The smaller injectors only kick in once the duty cycle of the larger squirters gets near its capacity.

GM had to engineer a secondary electronic control system to fire the port injectors, meaning the LT5 uses two systems for fuel control.

The passenger-car

LTS have been joined by a revised range of truck motors. The two of interest to street machiners are the 5.3L, 355-376hp (265-280kw), 11.0:1 L83; and the 6.2L, 420hp (313kw), 11.5:1 L86. Both V8s feature all-aluminium construction and the same technologies as the LT1.

shouldn’t require massive re-engineering if it is already set up for EFI.

Tuning DI engines will require far tighter controls of the actual point of injection; this can only happen when both the intake and exhaust valves are closed, because fuel is being squirted directly into the cylinder. On port-injection engines, tuners can start pulsing injectors before the valve opens, but doing this on a DI engine can lead to fuel pooling on the piston or being blown out an open valve.

Many American LT swaps use the ECU and transmission controller from the same vehicle the engine and gearbox was plucked from, to avoid tuning issues around vehicle security systems and body control modules.

Thankfully, there is tuning software from companies like Hptuners that can adjust settings in the factory computers.

For those wanting brand new parts, GM sells a stand-alone wiring harness, driveby-wire accelerator pedal, ECM (Engine Control Module) and TCM (Transmission Control Module) to control the Gen V engines. The company also offers several LT engines as ‘Connect & Cruise’ packages that include all wiring, computers, transmissions and more, though they’re not cheap.

Aftermarket stand-alone ECUS are another option, but it is important to check with the ECU manufacturer and your tuner to see if the electronic brain box has enough inputs and outputs to control all the functions and features of the late-model small-block. With functions like Pwm-controlled fuel and oil systems and CAN communication for the dash, the LT will need a top-spec ECU, and that will add a level of expense to your project.

All this new tech may seem unnecessary and over-the-top, but General Motors hasn’t been making new cars with LS engines for several years now, and the LT series arguably offers a better base for a hot donk for your project car. We learned how to control EFI and overhead-cam engines, and the aftermarket is already well on the way to cracking all the high-tech secrets of the LT V8.

The 755hp LT5 is the top dog of the LT family, boasting a 2650 blower sat atop the 6.2L Gen V mill. It runs both port and direct injection, so you’ll need a powerful ECU to control the fuelling, two-stage oil pump, variable cam phasing and all the other new tech features Here is the LT4’S injection system in all its glory. While the Gen IV LS mills ran up to 54psi fuel pressure, the Gen V LT4 requires 2900psi – enough to cut your hand off on pressure alone!

Some late-model LS engines had variable valve actuation, but the LT1 brings it across the board. Similar to Japanese and European multi-cam engines, the LT system works off multiple cam lobes and fattens the bottom-end torque without making the 6.2L V8 feel like a low-revving tractor Gen V engines use a wholly new cylinder head, with intake and exhaust valves swapping places in the casting and the sparkplugs moved for better combustion. Even the head bolts have been increased to 12mm from 11mm in the LS mills, while the cam core is larger on the LT donks to reduce stress on the valvetrain

The injector bosses on the LT4 have moved from the intake manifold down into the cylinder-head castings, with the valves splayed out at a five-degree angle to allow for the fuel system. Everything for the direct injection either lives in the valley or works off the accessory drive on the front

Making 650hp with a 1.7L supercharger, the LT4 highlights the efficiency of the base 6.2L long motor, as the 2009 LS9 needed a 2.3L blower to make 638hp. Still an Eaton four-lobe TVS unit, the new pump reportedly rocks Teflon rotors and other exotic touches for better thermal efficiency