big block firing order swap

[THE BOSTON SIDEWINDER]

ok it's opinion/fact time. who out there is running a bbc with the 4 and 7 firing order reversed? isn't this the way all new gm crate engines are? i heard it balances out lean spots it the intake so the cylinders get more even fuel/air, and that there is less crank stress at high rpm. my boss thought he read in hotrod mag that it is bu***hit? any comments?...thanks, bill.

[cstraub]

On a 500 CID Pro Stock motor it is worth around 15 to 20HP. On a mildly modified BBC, you won't see anything.
Chris

[Infomaniac]

The new GM firing order is not the 4 - 7 swap.
I made this chart for myself some time back for a visual on the different firing orders. The new GM is basically a mirror image of the original. The new firing order claims less stress because the successive firings of cylinders across a crank pin are at the rear of the block vs the front. Closer to the oil pump.
http://marineassault.net/2113-med.jpg

[NAMarine]

Summit offers a cam to do that made by Comp Cams on pg. 144 of their new catalog. Says Roller cam dyno tests show exceptionally smooth torque curve and a decrease in crankshaft deflection, means more HP and cooler temps and less wear and tear on motor. Smallest lift is .714/.680 for BBC.

[THE BOSTON SIDEWINDER]

I Thought There Must Be Something To It If Gm Is Researching And Changing It's Engines. That Stuff Costs A Ton Of Money. Can't Get The Investers Too Pissed Off.

[BrendellaJet]

what does this change to for fuel distribution in a carbed motor?

[Infomaniac]

The 4&7 swap was done to prevent 5&7 from competing for a fuel air charge. If you look at all 3 they each have adjacent cylinders competing for a charge. I guess 2&4 do not compete as much as 5&7 did.

[Jet City]

The 4&7 swap was done to prevent 5&7 from competing for a fuel air charge. If you look at all 3 they each have adjacent cylinders competing for a charge. I guess 2&4 do not compete as much as 5&7 did.
Thats what I was wondering after studying the chart, the original has 5-7 firing adjacent, new GM has 3-1 and 4-7 swap still has 4-2 firing adjacent. I guess for my power level it just doesn't matter either way, but it's a great marketing tool.

[PC Rat]

Here's my $.01, the builder that custom ground my cam said that the swap was worth about 5-7hp.
I'll save the other $.01 for when I actually have the facts first hand.
Brian