LS cam swap, step by step: Gen III and Gen IV, any chassis

How we put this guide together

Of the 2,012 LS swap questions we pulled from forum threads, 134 were about cams, springs, pushrods, lifters, AFM or VVT. Our 1998–2002 F-body cam swap walks one car through it bolt by bolt. This guide is the general version: any Gen III or Gen IV LS, car or truck, in the chassis or on a stand. The job is the same on every LS. What changes is the parts list, and that's where most of the questions (and most of the mistakes) are.

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Step 1: Know which engine you have

Before you buy a cam, know four things about the engine: generation, cam gear, AFM and VVT. Each one changes what you order. Look the engine up in the engine and donor finder if you're not sure.

	Gen III (24x crank)	Gen IV (58x crank)
Cam sensor	Back of the block, reads the cam once per turn	In the front cover, reads a 4x wheel on the cam gear
Cam gear	3-bolt	3-bolt on early non-VVT engines; single-bolt on AFM and VVT engines
AFM	Never	Many 2005+ truck and SUV engines
VVT	Never	Some truck and car engines (cam phaser behind the gear)

AFM (Active Fuel Management) shuts off four cylinders with special lifters fed by an oil manifold in the valley cover. An aftermarket cam means deleting it, and a proper delete takes the heads off: a non-AFM cam, all 16 lifters (not just the 8 AFM ones), new lifter trays, a non-AFM valley cover or the correct plugs, head gaskets and head bolts, plus GM's 12639759 cap over the oil pan's pressure-relief valve. More: what is AFM, and should I delete it?

VVT engines have two routes. Keep the phaser: the stock one swings the cam through 52–62° depending on year, which a bigger cam can't live with, so it needs a cam made for VVT plus a phaser limiter (limiters cut the range to around 20°, or a few degrees, or lock it out). Or delete it: a non-VVT Gen IV front cover with the cam sensor, a non-VVT 4x cam gear, cam bolts, a new balancer bolt and a tune that turns VVT off. Only the Gen IV truck pump and the LS3/L99 Camaro pump clear a VVT front cover, so the choice also decides your water pump.

Step 2: Buy the parts, and know why each one is on the list

• The cam. Pick it in the cam finder. Each cam page lists its springs, converter and idle needs, and owner dyno numbers.
• Cam bolts that match the gear. A 3-bolt cam needs a 3-bolt gear; a single-bolt cam needs the single bolt. Putting a 3-bolt aftermarket cam in a single-bolt Gen IV means a 3-bolt gear with the 4x reluctor wheel, or the cam sensor has nothing to read.
• Valve springs matched to the cam. Stock springs aren't made for big lift: LS6-style beehives are good to about 0.550 in, and past that you plan on springs (duals handle 0.575–0.600 in) unless the cam maker says stock is fine. Too weak and the valves float at rpm; too little travel and the coils bind, which takes out the cam and lifters. Check installed height on your heads, especially if they've been milled, and keep at least 0.060 in between the coils at full lift. More: how to pick valve springs for a cam
• Hardened pushrods. 7.400 in is stock length. Measure with a checker if the heads or block were machined or the cam has a smaller base circle, because the wrong length changes lifter preload.
• Timing chain. Replace it on a high-mileage engine or with a big cam. Some double-roller sets need front-cover work, and some high-volume oil pumps are drawn for single-roller chains, so check the pair.
• Front cover gasket and front crank seal. The cover comes off to get the cam out; reuse neither.
• A new balancer bolt. The factory bolt is torque-to-yield and used once. A reusable ARP bolt (234-2503) is the alternative.
• Water pump gaskets, and a pickup O-ring if the oil pump or pan is disturbed. A pinched or dry O-ring is the first suspect for low oil pressure after a cam swap.
• Lifters only if they're tired or it's an AFM engine. They sit in trays under the heads, so new lifters mean the heads come off.

Tools: an on-head valve spring compressor, a lifter holding tool (or 16 pen magnets), a spark-plug air adapter and compressor, a balancer puller and installer, a torque wrench to 240 ft-lb and a torque-angle gauge. A degree wheel is worth it on bigger cams.

Step 3: Decide engine in or out

On a swap, do it before the engine goes in. If the LS is on a stand waiting for mounts, the cam is a few hours of work with nothing in the way. Once it's in the chassis, everything in front of the engine has to move.

In the car, the heads stay on and the springs change with shop air in the cylinder (or the piston at top dead center). You need room in front of the engine to slide the cam out: the radiator and fans come out, the A/C condenser lifts or drops without opening the lines, and on some trucks the grille or front panel comes off too. Budget 8–12 hours the first time with the right tools.

Step 4: The swap, in order

1. Disconnect the battery, drain the coolant, remove the intake tube, coils and valve covers.
2. Remove the rockers and pushrods, keeping every part in order.
3. Remove the belt, water pump, radiator and fans.
4. Lock the crank, break the balancer bolt loose and pull the balancer with a puller that pushes on a protector, never on bare crank threads.
5. Remove the front cover. On a Gen IV, unplug the cam sensor in the cover first.
6. Line up the timing marks dot to dot, then remove the cam gear and chain.
7. Turn the engine at least four full turns to push the lifters up into their trays, then hold them there (a lifter tool, 5/16 in dowels down the pushrod holes, or magnets). The trays alone aren't enough. Spin the cam; any lifter that moves isn't held.
8. Remove the retainer plate and slide the cam out with two long bolts as a handle, turning it so the lobes don't nick the bearings.
9. Change the springs one cylinder at a time with air or top dead center.
10. Install the new cam with fresh oil or the maker's lube, then the retainer plate (18 ft-lb).
11. Set the timing dot to dot, torque the gear (3-bolt: 26 ft-lb; single-bolt: see the torque table) and turn the crank two full turns to recheck the marks.
12. Pushrods and rockers, each lifter on its base circle before torquing (22 ft-lb). Turn the engine two turns by hand; if it binds, stop.
13. New front seal, cover centered on the crank (18 ft-lb), balancer pressed fully on, new bolt (37 ft-lb plus 140°).
14. Water pump in two passes (11 then 22 ft-lb), then everything else back on.

For photos of each step on one car, follow the F-body guide; the order is the same on every LS.

Step 5: First start, then the tune

1. Build oil pressure first. Leave the coils unplugged and crank in short bursts until you see pressure.
2. Start it and expect lifter noise for a few seconds. Check for leaks, bring it up to temperature and bleed the cooling system through the steam line.
3. No flat-tappet break-in. A hydraulic roller cam doesn't need the 2,000–2,500 rpm run-in an old flat-tappet does. Drive it at varying loads for the first 30 miles or so with no wide-open throttle, and keep stiff springs out of high rpm until the engine is warm.

A cam always needs a tune. It changes how much air the engine takes in at every rpm, so idle airflow, fueling, spark and torque modeling all have to change, plus AFM or VVT turned off if you deleted them. Build the start-up file with the turn-on tune builder: it gives idle and spark starting values for your cam from real tunes. Then log it and always finish on a dyno before any hard pulls. More: cam tuning.

Rather have us do it? Send us your read and we'll build the start-up file for your cam, or send the tune you're running and get a Tune Report on what to fix first.

Common mistakes

• Timing one tooth off. Recheck dot to dot after two turns. On an interference engine one tooth can put valves into pistons.
• A 3-bolt cam with no 4x gear in a Gen IV. The engine has no cam signal and won't run right.
• Plugging AFM instead of deleting it. The collapsible lifters stay, and oil can collapse them later.
• Stock springs on a big cam. Valve float at best, a wiped cam at worst.
• A dropped lifter from trusting friction to hold it up. Fixing it means pulling the heads.
• Driving it hard on the old tune. Tune it, log it, and finish on a dyno.