Re: [Chevelle-list] Changing Firing Order On Cam

[Emil Dusek]

Primarily the 4/7 swap is to help eliminate crankshaft harmonics at high rpm's.

 Standard firing order:     18436572

If you pair the rods on the crankshaft journals you get these pairings:

1-2, 3-4, 5-6 and 7-8.

On the standard cam, there are three instances that you have successive

firings on the same journal, 2-1, 4-3 and 6-5

By swapping the 4/7 you eliminate one of the successive pairings on the

same journal thereby eliminating some of the harmonics.

-----Original Message-----
From: Bill Lessenberry <[EMAIL PROTECTED]>
Sent: May 4, 2007 1:47 PM
To: The Chevelle Mailing List
Subject: Re: [Chevelle-list] Changing Firing Order On Cam

The idea behind the 4/7 swap is to eliminate the 5/7 firing sequence which can lead to cross-firing and detonation between those 2 cylinders.  It's a problem only on high-revving motors, but it wouldn't hurt anything to have it on a street motor if you have $$$ to burn.  BTW, it's an old idea, I've seen stuff from the late 1960's that was written about it.  Seems to me that you're just swapping the problem from the 5/7 sequence to a 4/2 sequence, but I ain't an engineer or high $$ race engine builder.
BillL


At 01:28 PM 5/4/2007, you wrote:

INFO I HAVE BEEN TOLD ABOUT THE  4/7 SWAP  IS IT WORKS BEST ON RACE CARS AND YOU HAVE TO HAVE A CAM MADE FOR A 4 / 7 SWAP, LITTLE PRICEY ALSO.
SS427