Ask Away! with Jeff Smith: Some Good, Mild Performance Upgrades to a Direct-Injection Chevy Gen. V 5.3L LT Engine

I am rebuilding a 2014 L83 5.3L engine for my Silverado pickup and I’m considering making some changes to improve the performance slightly. I have looked into adding larger fuel injectors and perhaps other parts. I’m not going racing or anything but I thought since the engine is apart, this would be a good time to change a couple of things to improve the power. Thanks.

T.P.

The 5.3L (325ci) engine used in your 2014 Chevy Silverado is a member of the Gen. V engine family which GM debuted in your model year of 2014. The significant difference for the Gen. V engines is direct injection (DI), which replaced port injection used in the Gen. III and IV LS engines. Another major upgrade for this engine family is that the truck blocks are now aluminum instead of cast iron and compression for DI has increased from the older truck engines at 10:1 to a much more efficient and powerful 11:1.

Benefits of E85 & Higher Octane Fuels

Speaking of power, your engine makes an impressive 355 hp and 383 lb.-ft. of torque on gasoline. Since most of these engines can run E85 as Flex Fuel engines, the power goes up to 376 and 416 lb.-ft. of torque! These are huge increases over a 2003 5.3L port injected engine that was rated at 285 hp and 325 lb.-ft. of torque.

This power increase is really aimed at taking full advantage of the octane rating of the E85 fuel, since otherwise the engines are intended to run on 87 octane gasoline. But right out of the gate, you have the potential to make over 400 hp. If E85 is not available in your area, you can still run a higher octane 91 gasoline and as long as the detonation sensors don’t pull the timing back, it might make at least 350 hp.

Keep in mind that these ratings are net horsepower numbers. When compared to typical “hot rod” power numbers, all shops use the traditional correction factor that is worth roughly another five percent more power. So on a normal SuperFlow dyno, your bone stock 5.3L engine would probably make somewhere around 370 hp and 400 lb.-ft. of torque.

These are great numbers.

Variable Valve Timing

Beyond just running E85 or mixing your own fuel to run something like E50 that offers most of the octane benefits while still retaining 50 percent gasoline, there are a couple of other ideas you might consider.

The first is to retain the benefits of variable valve timing (VVT).

A few years ago, we put a direct injected Gen. V LT1 on the dyno and spent half a day trying to improve power by changing the cam position with VVT. We could not find any power anywhere, which means the factory has done a great job of optimizing the power these engines make—so don’t eliminate the VVT.

It helps make torque at low rpm and also improves power at the top end.

Deleting Active Fuel Management (AFM)?

AFM or Active Fuel Management is GM’s version of displacement on demand, which deletes four of the eight cylinders when the engine is under mild load (like cruising on the highway). There have been countless documented problems with AFM that relate to poor engine oil maintenance where the screens that keep junk out of the lifter eventually plug up with debris and the AFM system fails. There are also issues with the lifters themselves failing.

With the engine apart, this is a perfect time to delete the entire AFM package. Scoggin Dickey offers a complete AFM delete package that replaces the eight lifters and the camshaft with an identical non-AFM cam that is actually the same cam using the 6.6L truck engine that does not have AFM. This is important because the AFM cam employs different timing specs for the AFM lobes vs. the other four cylinders.

The kit includes the cam, lifters, head gaskets, new trays, new head bolts, and a new crank bolt, plus the plugs to block off the AFM ports in the block. Separately, you can also buy the small plugs necessary to block off the hydraulic circuits which will allow you to re-use the original lifter valley cover. It can be replaced with a non-AFM cover, but that’s a bit more expensive than the press-in plugs. Of course, this will still require custom tuning to disable the AFM software in the ECU. This will have to be accomplished with help from a knowledgeable LS/LT engine tuner.

A Basic Cam Swap

Another option is to retain the VVT and AFM but still change the cam. Several companies offer AFM-compatible cams. We found a COMP XFI cam (CCA-624-500-13) that looks interesting. It’s a very short duration cam, but still adds roughly 17 degrees of added duration to improve low-speed torque and overall power. We’ve included the cam specs below. COMP also says this cam requires the use of a COMP phase limiter which reduces the total movement of the VVT phaser to prevent piston-to-valve contact.

While the original small block Chevy would always respond to a better cylinder head, the direct injection engines are already equipped with outstanding flowing cylinder heads—so all these engines really need is a little more cam to wake them up even more. It would be very easy to make 450 hp or more with just a simple cam change and perhaps some mild tuning.  

There are plenty of options in terms of mild increases in power that should not require massive changes to the software. The Gen. V engines offer impressive cylinder head flow right off the factory floor.

All it needs is a little more cam timing to create a really powerful engine.

COMP XFI AFM Hydraulic Roller Cam for Gen V LT Specs

5.3L Gen. V LT Camshaft & AFM Delete Parts List

• COMP Cams XFI AFM GM Gen V Camshaft, CCA-624-500-13
• COMP Cams Cam Phaser Limiter Kit, CCA-5456
• Scoggin Dickey AFM delete kit, 5.3L, SDAF53