LS engine mounts and swap kits: how mount position decides everything else

How we put this guide together

Of the 2,012 LS swap questions we pulled from forum threads, 105 were about mounts, swap kits, adapter plates or engine position. Most of them are really one question asked from the far end: the header hits the steering shaft, the pan sits on the crossmember, the driveshaft is the wrong length, the hood won't close. Each of those traces back to where the mounts put the engine. Below is how we pick a mount, what to measure before money changes hands, and what the common kits do on each of our 36 vehicles.

Step 1: Understand what the mounts decide

An LS is about the same size as the small-block Chevy it usually replaces (28 in tall, 29.5 in long, 24 in wide for an LS1 vs 28 x 30 x 26 for a 350). Its mount bosses sit roughly where the small-block's did, so on a GM car or truck the engine can go back close to the old spot. On everything else, and on a lot of GM swaps too, the kit maker picks a new spot. That spot sets six things at once:

• Oil pan clearance. Move the engine forward and the sump slides toward or over the crossmember; move it back and it clears. The same truck pan that fits with one kit hangs on the crossmember with another. More: oil pan guide.
• Header fit. Swap headers are bent around one engine position. Hooker's BlackHeart brackets for the 1967–69 Camaro come in four positions (stock, 0.5 in, 1.25 in and 3 in forward), and the BlackHeart headers only fit the position they were drawn for.
• Steering clearance. The driver-side primaries and the steering shaft fight for the same few inches on most swaps. An inch of engine position, or an offset to one side, decides whether the shaft clears or needs U-joints and a new route.
• Hood and cowl. Mounts that raise the engine (flat adapter plates lift the crank centerline about 0.18 in; some truck plates sit the engine "forward and high") eat hood clearance, and a tall truck intake makes it worse.
• Driveline angle. The crank centerline normally runs about 3° down toward the back, with the pinion set the same amount the other way so both U-joints work at matching angles. Raise or lower the front of the engine and that angle changes.
• Transmission tunnel and crossmember. Move the engine back and the transmission goes with it, into the tunnel and onto a different crossmember location. That changes driveshaft length too.

So pick the mount position first, then the pan, headers and crossmember that were built for it. Buying them in the other order is how people end up with three sets of headers.

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Step 2: Know the four kinds of mount

1. Adapter plates on the factory frame stands. Plates bolt to the LS block and give it the small-block Chevy three-bolt pattern, so the stock frame stands and rubber mounts carry over. Cheapest route on GM cars and trucks: ICT Billet 551628 plates run about $35–60 and give four positions (0.100, 0.600, 1.86 and 2.36 in forward of stock). The catch is stack-up: plate plus old mount can change height and angle, so check pan and hood clearance before you call it done.
2. Chassis-specific bolt-in brackets. Brackets drawn for one vehicle, often with clamshell or F-body style mounts. They put the engine in one known spot so the maker's headers, pan and crossmember line up. Examples: Hooker BlackHeart brackets for GM classics, Speedway's C4 kit, Novak's Jeep mounts.
3. Complete swap kits. Mounts plus transmission mount or crossmember, and sometimes pan, headers and steering shaft. Typical on imports and BMWs (Sikky, CX Racing, ISR, LSE9x), where the factory chassis gives you nothing to bolt to.
4. Adjustable sliders and weld-in universals. Slotted plates (Dirty Dingo's slider mounts, CPP FitRite) or weld-on brackets that let you choose the spot. Good when no kit exists or you're running a non-standard pan, but now you own every clearance and the driveline angle yourself.

Rubber, poly or solid: rubber isolates the most and suits a street car; poly is the usual middle ground; solid mounts don't deflect at all and pass every vibration into the chassis, which makes sense on a track car and gets tiring on the street. Most bracket kits take any of the three, so you can change your mind later. More: solid vs polyurethane mounts.

Step 3: Measure before you order

Do this with the old engine out and the bay clean. A tape, an angle finder and a straightedge are enough.

1. Firewall to the front of the frame stands or crossmember. Compare it to the kit's engine position. On an 86/BRZ the kits differ by 60 mm (48–110 mm from firewall to head), which is the difference between a header that clears the steering and one that doesn't.
2. Top of the crossmember to where the pan rail will sit. Then compare to the depth of the pan the kit calls for. A pan has to clear by more than zero: allow for the engine moving on its mounts under load.
3. Crank centerline height to the hood. Measure from the frame stand to the underside of the hood at the intake, and add the height of the intake you plan to run. Truck intakes are the tallest.
4. Steering shaft location. Note where the shaft passes the engine on the driver side and how far the box or rack sits from the block. If the kit's headers need a different shaft, budget for it now.
5. Transmission tunnel and crossmember holes. Check the kit's crossmember for your transmission. Many kits list separate crossmembers or adapters for the 4L60E, 4L80E, T56 and TH350/700R4.
6. Ride height. Lowered cars and trucks lose pan and header clearance to the road. Measure at the height you'll actually drive.

Then mock it up before the engine gets plumbed: bolt the mounts on, set the engine (an old block works), put the transmission on its crossmember and check every item above again. Shim the transmission mount upward to fix angle if you need to, never downward.

Step 4: Kit or parts?

A kit costs more up front and saves money when the parts only work as a system. A piece-together build saves money when the chassis already has a well-known layout.

• Buy the kit when the headers, pan and steering shaft are drawn around one mount (Fox and SN95 Mustangs, BMWs, 350Z/G35, 240SX, Miata, 86/BRZ). Sikky, Vorshlag, CX Racing and ISR all build their headers around their own mounts, and mixing brands is where the cutting and re-buying starts. Matched kits run from about $670 (LSE9x E9x kit: mounts, crossmember, CAN module, accessory drive, driveshaft adapter) to about $5,500 (G Force 944 kit with headers and exhaust).
• Piece it together on GM trucks and muscle cars, where adapter plates on the factory stands work, a Holley 302-series pan is the known fix and plenty of headers exist for each position. A squarebody can go in on $60 plates, the stock truck pan and junkyard parts; a full bolt-in kit like Pro Performance's for the same truck is about $2,295 with mounts, poly mounts and mid-length headers.
• Watch for kits that aren't complete. Hawks' "The Basics" 3rd-gen kit ($899) includes the mount pads but not the clamshells; Hooker's Nova brackets don't include the clamshell mounts or long bolts; some import kits list the trans mount separately. Read what's in the box before you compare prices.

Common mistakes

• Buying headers before mounts. The header fixes the engine position; the mount has to match it.
• Mixing brands in a matched system. Hooker lists its brackets, crossmembers and headers as one geometry; other brands' parts in the mix change clearance, ground clearance and engine angle.
• Ignoring the A/C and accessories. Low-mount A/C compressors don't clear on several kits (2nd-gen F-body with Hooker brackets, C4 Corvette, 3rd-gen F-body without a frame notch), and a GTO alternator can hit the pitman arm. Pick the accessory drive with the mounts. More: accessory drive guide.
• Setting the engine too far back for the tunnel. It helps weight balance and header room, until the bellhousing hits the tunnel or the shifter lands in the wrong hole (CX's 350Z kit doesn't line up with the factory shifter hole).
• Forgetting the driveshaft. New engine position plus a new transmission means a new length. Measure after the engine and crossmember are final. More: driveshaft and driveline angles

Not sure which kit fits your plan? The swap planner builds a shopping list for your vehicle, and "Just tell me what to buy" picks the parts for you.

Find your vehicle in the table below for the common mounts and what each one pairs with.