Everything you ever wanted to know about LS belt offsets
We get quite a lot of questions about belt offsets, so we figured we should put all the info that we have gathered in the last 20 years on the LS platform in one place, with a nice picture to go along with it. This will cover every belt offset that the GM LS/Vortec family used, other than the LS4, which is not very common, and isn't really suited for use for the products that we make.
GM used 3 main belt offsets, we generally call them Vette, Fbody, and Truck. Obviously there are a few others in the mix, but we will cover that as well. Lets start with the common ones first.
GM Truck. This belt offset was used on EVERY LS/Vortec V8 platform that came in a truck or SUV from 1999 Silverados up to 2018+ LS powered HD trucks. All the SUVs got the same offset as well, Tahoes, Suburbans, and TBSS as long as it was an LS based V8 (not a 4200 I6 or an 8.1L). This is the farthest from the block spacing that GM made. There are aftermarket offsets that are farther, but we will cover that later. Another GM belt drive uses the same offset as truck, the 5th Gen Camaro, but the water outlet is swapped to the driver side, and the routing is quite different. The blower drive for the LSA is also Truck offset, with 1 rib added forward and 1 rib added backwards. Some ATI/Innovators West balancers in this offset will be an 8 rib version, but they are 2 ribs forward only, so different spacers may be needed for brackets.
GM Fbody/GTO and most export/Aussie cars. This is the middle ground for the belt drives. 98-02 Fbody, and 04-06 GTO used this offset, as well as most of the Holden stuff that was made and sold in Australia. Unlike the Vette and truck, you cannot "stack" the Fbody offset drive with anything else, as it is basically overlapped with Vette on one side and truck on the other (see the picture below). This offset is common for swaps since the package is quite compact, the parts are cheap, and they are a well performing setup. All 8 rib upgrades for this offset are 2 rib forward design.
GM Vette. This covers all Vettes other than the LS9 (yes it covers the LS7 and LS3-GS as well). This also covers the CTS-V1, the Pontiac G8 and the new SS Sedans, as well as the accessory drive (not blower drive) of the V2 and the ZL1 Camaro. The Vette LS7 and LS3 Grand Sport use a dry sump oil pump, and a special balancer that is thinner in the hub area, but the offset at the belt itself is the same. The routing and placement is different between the Vettes and other models in the same offset family, but some of it can be mixed and matched. All 8 rib upgrades for this offset are 2 rib forward design.
Most DOUBLE BELT swaps, as well as the OEM drive from GM, stack the Vette offset belt drive in a 6 rib for the accessory drive, and place an 8 rib Truck offset drive belt in front of it for the blower, since they dont overlap and interfere with each other. Most customers that want a dedicated drive for the blower have to go this route, and convert the entire front drive to some combination of vette/factory LSA, V1, G8, SS and use the OEM or other parts to drive the blower.
The oddball of the group are the LS9 drive, since it is 2 ribs (and change) farther back than the LS Vette offset, and doesnt line up accurately with any of the other belt drives. This uses an single 11 rib belt to drive the entire front drive, and is normally VERY hard to find parts for.
The Holley Mid Mount drive is the other oddball, which spaces the ribs even farhter forward than the Truck offset, to get the alternator and PS pump to sit in front of the block, rather than off to the side. Nothing else will interchange with the Holley offset, and the balancer is made specifically for the Holley drive. There is no option for 8 rib upgrades here without a LOT of custom parts.
If you have specific questions feel free to contact us and ask!!!