How much heavier and bigger is an LS than a small-block Chevy when swapping into older GM cars?

The LS is lighter, and about the same size.

Weight: Speedway puts a dressed small block at about 575 lb and an aluminum LS at about 430–470 lb. Our dimensions chart lists a Chevy 350 at 550-600 lb and a 5.3 at 440-460 lb. Iron-block truck LS engines weigh more than the aluminum ones.

Size (chart figures, in):

	Height	Length	Width
Chevy 350	28	30	26
LS1/LS3	28	29.5	24
5.3 LS (truck)	34	30	24

Truck LS engines use a taller truck-style intake manifold, so check hood clearance with the intake you plan to run. If the truck or car already had a small block, the LS drops in with a handful of swap parts: LS-specific motor mounts (the bolt pattern is different), an oil pan that clears the crossmember, and either your GM transmission with an adapter or an LS-pattern transmission — the bellhousing patterns differ slightly. EFI also needs a harness, a computer and a high-pressure fuel system.