When GM introduced the LS engine in 1997, it featured many design changes from the Gen 1 Small Block Chevy (SBC) engine that improved engine durability and efficiency. One of those changes was the evolution of the cylinder firing order from the well-known 1-8-4-3-6-5-7-2 to 1-8-7-2-6-5-4-3.
In a four-stroke engine, the crankshaft spins twice (720 degrees) to the camshaft’s single revolution (360 degrees) for the engine to complete one full engine rotation of an eight-cylinder firing.
Typical V8 engine crankshafts phase the connecting rod journals at 90 degree intervals, meaning that two of the eight pistons will share the same position in the bore at any given time; these are considered “paired pistons.” Chevy engines share paired pistons on cylinders 1-6, 5-8, 4-7, and 2-3.
As the crankshaft rotates, the paired pistons will simultaneously arrive at top dead center (TDC). One piston will be at the top of the compression stroke, and the other will be at the start of the intake stroke. After the crankshaft spins 360 degrees from this position (one-half of a complete engine rotation cycle), the order of those two cylinders will trade off. Swapping the firing order between any of the paired pistons can be done within reason but requires a special camshaft to change the order of valve actuation; this will also change the overall engine firing order, including the ignition order. Additionally, paired pistons firing order sequences will always be 180 degrees from each other.
In the 1990s, Pro Stock and other racing classes began dyno testing 4-7 cylinder swap cams based on the theory of reduced intake reversion and better heat management in the two left-rear cylinders (5 and 7), which fired back-to-back and tended to run hotter. Moving these sequentially firing cylinders from the back of the block to the front (now firing cylinders 4 and 2 in order) placed them in a fresher coolant path. Engineers also observed reduced crankshaft torsional loads and improved induction tuning from more uniform cylinder temperatures.
Reduced crankshaft torsional vibration was the main reason GM adopted the LS engine’s 1-8-7-2-6-5-4-3 firing order (4-7/2-3 swap for SBC). According to GM engineers, computer modeling showed that the new firing order improved reluctor wheel accuracy and eased bearing loads. Using a 4-7/2-3 LS swap camshaft for SBC still moves the pair of adjacent firing cylinders from the back to the front of the block, but to cylinders 3 and 1 instead of cylinders 4 and 2 like the 4 -7 swap cam. It also swaps the firing order of paired cylinders 2 and 3. While many variables come into play with the benefits of swapping engine firing orders, the 1-8-7-2-6-5-4-3 firing order is a clear advantage for the LS and potentially beneficial in SBC engines, as well.
Until now, if you wanted to run your SBC with an LS firing order, it meant purchasing a custom-ground cam—if a core was available. However, the team at Summit Racing has stepped up with a new line of American-made SBC hydraulic roller cams with the LS firing order without the custom cam price—click here to see the Summit Racing Pro SBC LS Firing Order Hydraulic Roller Camshafts.
Summit Racing also offers hydraulic flat tappet Pro SBC 4-7 Swap Camshafts as well.
Will i get better fuel economy with this swap and how about more hirse power
Hello Jose,
The smallest of the cams can increase gas mileage and power because the increase in torque often allows a higher gear when going up a hill. Power increases of one or two percent are common even over other hydraulic cam conversions and some of this may be due to an entirely new lobe series design for these cams that’s designed to take advantage of newer beehive springs.
Will you be making the step nose cams for the factory roller cam sbc’s? Thanks.
Hello, Summit Racing currently has the standard firing order SUM-8800 Stage 1 , SUM-8801 Stage 2, and SUM-8802 Stage 3 cams in stock. These are step nose for the 1986-02 factory roller blocks. Summit Racing may introduce LS Firing order versions in the future.
What changes to the engine must I make in order to make the cam swap?
Hi Eddie, Summit Racing currently makes 4/7 swap flat tappets and LS firing order Hydraulic Rollers for the Gen. 1 SBC. If it’s the 4/7 swap, you would just switch those two wires on the distributor cap. If it’s the LS firing order, then the wires would be switched to the 1 8 7 2 6 5 4 3 order.
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It’s a good idea to tag the distributor with a notification that states the revised firing order in case someone is doing a cap/rotor or wire change in the future.
In regards to heat what is the difference if you have two rear cylinders or two front cylinders fire back to back?
Hey Ken, here’s another article that covers some advantages of a firing order swap, but here’s an excerpt that addresses heat:
“By moving the adjacent firing cylinders nearer to the water pump, it means the combustion chamber stays relatively cooler, allowing you to run slightly more timing without detonation.”
Hey guys how much horsepower gang with just the cam swap do you think it will be making?
Hey Cary, here’s an earlier response from Brian Nutter on potential power gains:
“Power increases of one or two percent are common even over other hydraulic cam conversions and some of this may be due to an entirely new lobe series design for these cams that’s designed to take advantage of newer beehive springs.”
My complaint has always been the routing of the spark plug wires for the small blocks. The distributor/cap for the early Vortec seemed to solve that problem. Why can’t a cap be made with similarities so the plug wires can be orderly?
I HAVE A GROUP OF 9 OF US 2ND GEN CAMAROS RUNNING BOWTIE 415CI ENGINES WE HAVE BEEN WAITING FOR SUMMIT TO MAKE THE LS FIRING ORDER IN A STEPNOSE FOR OUR ENGINES , THEY WOULD OF SOLD MORE CAMS IF THEY MADE THE STEPNOSE STYLE SINCE THERE ARE LOTS MORE OF THAT STYLE ON THE STREET INSTEAD OF THE RETRO CRAP.