Firing Order, Small Block & SVO
This is one of the most common questions asked by our Ford customers. The firing order for the early 221-302 engines and the early 5.0 engines is 1-5-4-2-6-3-7-8. This is the firing order for all prefix “31” cams and is the standard replacement cam for all early engines. The later 5.0 engine and all 351 engines are designed to use the 1-3-7-2-6-5-4-8 firing order. This is the firing order for all prefix “35” cams, and cams ordered for these engines should use this prefix. Other than the firing order, the cams are identical. By changing the spark plug wiring at the distributor these cams can be interchanged.
My cam grind is a # "31".
I just have had some recent discussions with a friend about this as well. Does it change, enhance, dampen anything using the new order vs. the old one ?
I used the '351' cam build on my Reed. It helps even distribution and better 'balance' through the core of the engine.
There is definitely a benefit to the different firing order for higher revving/HP/Torque engines. I think newer 302 Builds use it because the technology proved it to be a better firing order than the original 60s specs.
The reason for this difference in the 1:1 STD-vs-HO is all in the camshaft timing, lift, and duration. Cylinders 5 and 4 , and cylinders 3 and 7 fire really close together as matched pairs. When the H.O. version was cooked up, a number of customers complained of a rough idle. Even in the heyday of factory hot-rods, a lot of folks wanted smooth idle.
Ford engineers quickly worked this out, and found that swapping cylinders 5-4 with 3-7 got rid of this, thus eliminating a customer satisfaction problem.
No overall performance difference can be felt with either wiring order. No kidding.
edit: oh by the way, if you look at V-8 firing orders overall you will find that Ford's cylinders physically fire in the same order as GM and Chrysler's, Ford just numbers the cylinders differently that's all."
BTW, my cam has the 351 F.O., Dema Elgin suggested it for a "race" engine.
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