Saw an article in the past year but cant find it now. The article talked about switching the 4 and 7 cylinder firing order and cam gamgrind for 12 or so horse power more? Does anyone remember the issue that this might have been in?
thanks  

For a street car this doesn't really give you anything. The 4&7 cylinder switch is nothing new, circle track racers have been doing it since the 60s. because a street engine doesn't see the consistent high rpms a circle track or drag motor does, this swap for the street really doesn't do anything.

As for problems with the swap, there aren't any. You can take a stock small block with the stock cam, switch the No. 4 and 7 cylinder spark plug wires on the distributor, and won't notice anything on the surface until you rev the motor. The timing is so close on these cylinders it's common for people doing tune ups to swap the plug wires, not realize it, and then wonder why their engines don't run quite right later on.  

Yes it's good for about 10,15 horsepower as it corrects to some extent number 7's problems. But cams and manifolds to support this change tend to be expensive and unless you're a competitive racer are usually not worth the pursuit when considering cost against the power gained as there's many more effective and less expensive things to do.


7 and 8 tend to run hot as they see coolant that's passed over 3 cylinders before getting to them, unless you install external plumbing to take coolant off the pump and put in into the block often at the soft plugs. However, some guys drill and tap the block for fittings. The flow from the back of the heads isn’t the best either, 7 and 8 tend to suffer from flow stacking or stalling above the combustion chamber where steam pockets form, more on that in a bit. Number 7 has the additional problem of exhausting into number 5's slightly earlier exhaust, as a result, has some pressure and temperature problems. It also, tends to get the short end of the mixture stick, especially with a 2 plane manifold and carb. Injection gets around this problem, as does ram designs with 2-4's typical of drag engines. But with a circle track configuration of one carb, there's lots of mixture issues, especially with 7. Attempts to solve this have included cross jetting to richen one side, twisting the carb to move the left rear barrel closer, or the Duntov/Holley "Z" that connects 7 and 8 with a balance pipe have been tried with varying success.

Headers tend to reduce the 5 to 7 exhaust issues but if your stuck with factory manifolds you’ve got a big problem that short of Rams Horn manifolds really doesn’t have any sort of a solution.

Coolant flow off the back of the engine is poor causing 8 and especially 7 to run hot. A cheapo/weepo cooling solution for the average guy with a street/strip machine, who isn't running air conditioning but just has an old fashion heater, is to put a return fitting on both sides of the rear of the intake where the heater sources hot coolant. Remember to remove any plugs from the manifold to head gasket. "Y" or "T" the two sides together and run them into the heater core and then back to the pump or radiator connection, which ever configuration your vehicle has. This provides an extra flow path off the back of the heads and helps eliminate "pressure stacking" within the back of the heads that leads to 7 and 8 running too hot. You can also do this without the heater core and just run back to the intake side of the cooling system. The problem with air-conditioning is that these systems usually have a shut off valve for the heater, so unless you’re running the heater there’s no coolant flow present.

Another trick used in years gone by was to "retard" 7's timing by filing off the leading edge of the contact inside the distributor cap, resulting in the rotor having to move a few degrees further before sparking that cylinder. That seems self defeating, but if you're loosing power to detonation, that technique can help squelch detonation thus increasing power.

Bogie