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4,7 swap

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    Short and stout nunes792003's Avatar
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    Question 4,7 swap

    I was wondering what the advantages of the 4,7 swap cams are? Also does this give the motor that awesome lop sound as well. Thanks for the info.

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    Quote Originally Posted by nunes792003 View Post
    I was wondering what the advantages of the 4,7 swap cams are? Also does this give the motor that awesome lop sound as well. Thanks for the info.
    What gives it the "lop" sound is the overlap of the cam. In the overlap region you have the intake and exhaust valves both open at the same time for a certain amount of crank rotation, basically creating an internal vacuum leak of sorts if you will. Some of the intake charge is scavenged as the exhaust is still flowing out of the cylinder. Hence, making the motor sound like it has somewhat of a vacuum leak, or a "miss", at idle.

    According to an article in "The Horsepower Handbook - Big Block Chevy", the idea behind the 4/7 swap cam was to increase overall engine smoothness. Bill Compton, who was the crank engineer for the GenIII LS series project, has this to say about the 4/7 swap cam -

    "Since the G3 engine was a clean slate project, each group looked at things that they could change to optimze the performance of the small block. Although we did not have an issue with crankshaft loading on the older V8s, there was room for improvement in the area of distributing the peak firing loads among the 5 crankshaft journals. Analysis showed that main 4 had peak loads significantly higher than main 2. By changing the firing order, the peak loading on main 4 was reduced and the peak loading on main 2 went up. Overall, the loading through the mains was much better balanced. By improving the load balance across the crank, we created a better balanced oil film interface across the crank. The valvetrain group simply changed the cam lobe timing to work with the new crank firing order."



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    In high HP applications and big rpm it's usually good for some power as well. maybe 15-25hp.

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    Quote Originally Posted by cjordan View Post
    In high HP applications and big rpm it's usually good for some power as well. maybe 15-25hp.
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    Quote Originally Posted by gn7 View Post
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    Quote Originally Posted by cjordan View Post
    In high HP applications and big rpm it's usually good for some power as well. maybe 15-25hp.
    That's generally the result of a better cam profile on the new cam, but I imagine has little to do with the firing order change.

    I'd like to see some back to back Dyno runs with 2 of the same cams, switching only the firing order. I doubt much more than the exhaust tone will change.

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    And if you make it the full ford firing order you increase to a total of 30-50hp!

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    Quote Originally Posted by MikeF View Post
    And if you make it the full ford firing order you increase to a total of 30-50hp!
    If you were to number a Ford's cylinders the same as a Chevy's, you'd see that they both have the same firing order.



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    Quote Originally Posted by Jetaholic View Post
    If you were to number a Ford's cylinders the same as a Chevy's, you'd see that they both have the same firing order.
    Yes they are.

    Jon Kaase does the swap on/in his mountain motors ( 700-817" engines) the crankshafts live a multiple of times longer. No extra power just easier on the cranks in the mountain motors spinning over 7,500 rpms.

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    Thats the real reason GM made the change on the LS. Not power. One of about 3 things Ford got right before GM. The other 2 are the 9" and the Top Loader.



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    Quote Originally Posted by Jetaholic View Post
    What gives it the "lop" sound is the overlap of the cam. In the overlap region you have the intake and exhaust valves both open at the same time for a certain amount of crank rotation, basically creating an internal vacuum leak of sorts if you will. Some of the intake charge is scavenged as the exhaust is still flowing out of the cylinder. Hence, making the motor sound like it has somewhat of a vacuum leak, or a "miss", at idle.

    According to an article in "The Horsepower Handbook - Big Block Chevy", the idea behind the 4/7 swap cam was to increase overall engine smoothness. Bill Compton, who was the crank engineer for the GenIII LS series project, has this to say about the 4/7 swap cam -

    "Since the G3 engine was a clean slate project, each group looked at things that they could change to optimze the performance of the small block. Although we did not have an issue with crankshaft loading on the older V8s, there was room for improvement in the area of distributing the peak firing loads among the 5 crankshaft journals. Analysis showed that main 4 had peak loads significantly higher than main 2. By changing the firing order, the peak loading on main 4 was reduced and the peak loading on main 2 went up. Overall, the loading through the mains was much better balanced. By improving the load balance across the crank, we created a better balanced oil film interface across the crank. The valvetrain group simply changed the cam lobe timing to work with the new crank firing order."


    the "LS" firing order isn't simply a swap of cylinders 4 and 7 but also includes numbers 3 and 2

    old gm: 1-8-4-3-6-5-7-2
    LS: 1-8-7-2-6-5-4-3

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    I put this thing together a number of years ago. I'm a visul kind of guy so it helped me understand the differences.

    And the striking thing was plotting the firing order and then connecting it as a continuation.

    In all 3 two adjacent cylinders compete for an intake charge and 3 mains are successively fired across. Just different ones.


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    Thanks Info,

    I did that same thing many many moons ago when I was told the 460 Ford and BB Chevy had the same firing order they just have the cyl numbered differently.

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