I have a 2014 Camaro with the L99 and a bent push rod. Can I disable the AFM and use LS3 lifters without changing anything else? Thank you.
T.K.
***
The short answer is no—you have much more to do than just replace the lifters. But that doesn’t fully answer the question so let’s expand our answer to cover the details.
How AFM Works in a GM LS Engine
First we need to define AFM. This is what GM calls Active Fuel Management or displacement on demand. This process uses specific lifters that can be disabled on four cylinders to turn that 6.2L L99 V8 into essentially a V4 for light duty cruising on the highway to improve fuel economy.
GM accomplishes this by using special lifters to disable the intake and exhaust valves. The engine employs a special lifter valley cover called a Valve Lifter Oil Manifold (VLOM). This lifter valley cover uses solenoids to direct oil to the lifters to disable them. The lifters are designed so that when oil pressure is applied to the lifter, it still move up and down with the cam lobe, but the internal piston is deactivated which means the pushrods do not move up and down.
Think of these lifters as lost motion devices.
When eliminating the AFM, it’s best to replace the VLOM with a standard LS3 style lifter valley cover and to plug the stands in the lifter valley that were used to direct oil to the AFM lifters. This can be accomplished by tapping the holes to install small pipe plugs which can be done with the engine in the car if the tapping operation is done very carefully to prevent aluminum chips from entering the oil circuit. Ideally, you would remove the engine and tap the plugs with the engine upside down to catch all the chips.
AFM engines also use a different camshaft so if you are considering disabling the AFM by removing the lifters this also means you will need to remove the cylinder heads since swapping lifters requires pulling the cylinder heads.
The Relationship Between VVT and AFM
This L99 engine also uses variable valve timing (VVT) and we would highly recommend retaining this feature because it adds torque down low by advancing the camshaft especially when adding duration. If you consider using a more aggressive camshaft, pick one that allows you to retain the VVT system. There are many aftermarket cams designed to be used in conjunction with VVT.
You might also consider using a VVT limiter which is a kit to reduce the amount of cam movement the VVT can employ. This allows you to use a cam with more lift and duration while still retaining the benefits of VVT.
This is important because too much VVT movement combined with a longer duration camshaft can create valve-to-piston interference which must be avoided. For example, Comp offers a Stage 1 cam for the L99 with 218/232 degrees of duration at 0.050 with valve lift of 0.563 inch for the intake and 0.575 inch lift for the exhaust. This cam will offer better overall power while still creating decent idle quality. I don’t believe this cam requires a VVT limiter which will save some money. A longer duration cam like the Stage 2 at 232 degrees of intake duration will require the VVT limiter.
Other Things to Consider
If your intention is to upgrade the cam, 16 new hydraulic roller lifters will be necessary along with pushrods and better valvesprings in order to take full advantage of the camshaft since it will raise the rpm curve. We’d also recommend converting your factory rocker arms over with more durable aftermarket roller trunnion bearings. Summit Racing offers a nice conversion along with an excellent tool to allow you to do the conversion yourself.
Read more on the trunnion conversion here: A Smart LS Roller Bearing Trunnion Upgrade
Of course you will also have to re-flash or re-tune the ECU to disable the AFM software. The easiest way to do this is to give your ECU a competent tuner where he can make the necessary changes. Or, it’s also an option to invest in a suite purchase from HP Tuners or EFI Live to make your own changes. This is not our first choice only because it generally is more expensive and you need to know how to make the necessary changes. That’s why paying a professional tuner to make the changes is both easier and less expensive.
***
As you can see, this conversion is certainly a major exercise and also more pricey than just changing lifters. There are other steps involved with this AFM delete process but these are the main points. This is certainly worth the investment since your L99 will instantly make more power with a better cam and valvetrain.
MUST also change to a non-DOD camshaft if using non-DOD lifters, it is not optional. The DOD lifters have a lot of internal lash at the retractable locking pins and to compensate the 1-4-6-7 cam lobes have super long lash ramps. If you put conventional lifters on those lobes, it will have misfires on 1-4-6-7 at idle.