Looking for a plug wire diagram for the 455 Olds 4/7 swap. I’ve installed a Howard’s hydraulic roller cam with a
firing order 1-8-7-3-6-5-4-2

 

1-8-4-3-6-5-7-2 is the stock firing order, your new firing order is 1-8-7-3-6-5-4-2 which swaps the 4 and 7 plug wire positions at the cap, your wiring diagram changes accordingly.

 

I've never heard of this kind of swap. Inquiring minds want to learn more.........

 

Olds "invented" the 4&7 swap in 1949.
All first generation Olds (303,324,371,& 394) engines had a 18736542 firing order.
The second generation (330 in 1964 and 425 in 1965) had a more conventional 18436572 order.
Personally, I can't see any advantage to it. Other than to sell camshafts to rubes who would believe in it.
You would have to show me on a dyno that there was any advantage.

 

It's supposed help head temperatures, better fuel distribution, smooths out idle, some power gain.

 

But it really doesn’t. I know a few that have done back to back tests, maybe 4-5hp on a 550hp SBC Spec engine. And that could be Dyno error as well.
Next it was supposed to spread crank loading. But on a cross plane crank, which is what 99.999999% of V-8s have, you’ll always have two cylinders next to each other that’ll fire in succession, always.

 

 

Very informative, Thank You!

 

No problem. If you have MotorTrend On Demand, the Engine Masters show did a 4/7 cam swap test on a big block Chevy.

 

Make sure your Howards cam is actually a 4/7 swap.

I got a Howards Hydraulic roller cam that was supposed to be a 4/7 swap, and I didn't check the compression stroke on 4/7 before starting it up the first time, and that was off.....

It ended up being a standard firing order cam.

We had Howards grind a Lunati austempered iron core, so that may have been where the confusion started.


Just saying.... check your valve events on each cylinder to confirm the cam

 

The only ROLLER core they currently stock for an Olds is the 4/7 swap, maybe they had an old one laying around? Same with Erson. They both jumped on the band wagon years ago when some claimed they made “more power”. They don’t really.

 

The storey behind GM originally doing the 4/7 swap was to spread out the main bearing loads more evenly when they designed the G3 engine.

the #4 main had more peak loading than the others. They found moving the double firing hit to the front of the crank, it evened out the peak loading..which makes sense since the rear end of the crank is seeing all the loading…why would also want the 5/7 double hit there too?

the Big block Olds does load #4 main more without a doubt..when a main bearing goes out from making to much power..its #4. Just like when the factory crank breaks..it’s right at #4 main.

That’s the only reason GM did it in the first place. Engine builders were finding slight gains when used with single plane intakes. Nobody seems to know why but it’s generally thought that it’s the intake / exhaust tuning..even though the firing order doesn’t change the side by side runner robbing …but it’s never actually identical because of header design and Intake minor differences.

Reher Morrison believes it’s a benefit enough that all their bigger inch engines get the 4/7

some think it’s the crank not twisting or less peak load difference front to back that helps . Daren Morgan said they tried every firing order possible, the only one that made more power was the 4/7 swap.. he doesn’t know why , but it did. It’s not negligible..it’s throughout the power band..maybe 5 on the low end and 10 plus mid range and then drops to a couple on the top end, both HP and TQ

I think anytime you can reduce the peak loading on the Olds #4 main..it’s worth it

Ive done the 4/7 just because.. if someone wants to crowd fund some testing. I’ll do it. I already have a solid roller small block with the 4/7 swap in it now.

 

How many cubic inches is it?
You're already most of the way there. Whoever ground the 4/7 just have them grind you the same on a std core. I’m sure you’ll be able to get someone to take one of the shafts for a reasonable price.

 

From the 1958 issue of Motor's Auto Repair Manual.

 

yep, bullet did it..they’ve always ground whatever I wanted and fast turnaround

 

There you go!!