Connecting rod lengths??
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Connecting rod lengths??

  1. #1
    Senior Member carreradude's Avatar
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    Default Connecting rod lengths??

    I have built some small chevys and one big block. I have a question for the engine builders out there. I know there are quite a few here with way more smarts than me. I have done a 406ci small block with the 6" rods in it. I have seen some 454's with the long rods in them. I guess my question is what are all of the benefits of longer conn rods? And is there a reason not to use a longer conn rod for certain builds?? I was told it makes the engine turn over easier, not laying the rod over as much and helping the piston to travel downward without pushing it into the cylinder wall. Does a longer conn rod change piston speed as well?? If this has been hashed over already, I have been here for a few months.
    Thanks for any thoughts!! Mike

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    Just another Wannabe Wannabe's Avatar
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    It makes the same power. Chevy invited just about everyone to be part of a testing program. Reher and Darrin Morgan spoke to me about the results. 1" difference in rod length and same power to the number!!!
    Longer rods can lessen the side loading of the piston against the cylinder wall. Also keep the piston at and around TDC a touch longer. Then you get into lighter pistons with the pin higher up in the piston, etc.
    I like them. But it is not a manditory thing like some say.

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    Senior Member APOLLO's Avatar
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    You guy's know more about this then I do but the longer rod has more of a chance to detonate.

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    There's a great theard around here somewhere (David519) that discussed long/short rod. I'll see if I can find a link:


    Sleeper CP

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    steelcomp was here
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    I have no opinion on rod lenght.

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    steelcomp was here
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    Quote Originally Posted by Wannabe View Post
    It makes the same power. Chevy invited just about everyone to be part of a testing program. Reher and Darrin Morgan spoke to me about the results. 1" difference in rod length and same power to the number!!!
    Longer rods can lessen the side loading of the piston against the cylinder wall. Also keep the piston at and around TDC a touch longer. Then you get into lighter pistons with the pin higher up in the piston, etc.
    I like them. But it is not a manditory thing like some say.
    That's just so wrong as a general statement. Ther are others in the industry IMO that are smarter and more experienced that will argue against that and with good reason, but the bottom line is like everything else, it depends on the application. IMO rod ratio isn't something that can be generalized about. Taking one engine and simply changing rod ratio proves nothing. Change the rod ratio in an F1 engine and see what happens....or a cup engine...there are reasons to use or not to use different rod ratios, all based on application.
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    Cantard 71hallett's Avatar
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    Quote Originally Posted by steelcomp View Post
    I have no opinion on rod lenght.

    Back in the can, worms!
    LMFAO. ahhh comon just one post.
    Quote Originally Posted by gn7 View Post
    It would be a balmy 85* in Steel's shop if he would move a little faster

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    steelcomp was here
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    Quote Originally Posted by 71hallett View Post
    LMFAO. ahhh comon just one post.
    LOL...you be quiet!
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    i see a lot of thrust load on my 496 w/short rod 6.135. and my t/d 496 w/.400 long rod shows very little, as far as power there just seems to be no power differance between the two engines (seat of the pants power)

    i think the only reason to use the longer rod is to shorten up the comp/ht of the piston to make it as lite as possible.

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    steelcomp was here
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    Quote Originally Posted by flat601 View Post
    i see a lot of thrust load on my 496 w/short rod 6.135. and my t/d 496 w/.400 long rod shows very little, as far as power there just seems to be no power differance between the two engines (seat of the pants power)

    i think the only reason to use the longer rod is to shorten up the comp/ht of the piston to make it as lite as possible.
    The arguement against that is you'll add more weight to the rod than you'll save in the piston. (not my arguement...the weight savings on the piston to me is more critical than the rod)
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    Quote Originally Posted by steelcomp View Post
    That's just so wrong as a general statement.

    there are reasons to use or not to use different rod ratios, all based on application.
    I know a couple of guys who built a few stroker Smblk Fords for some desert pre-runners same builds but 2 with the long rod ( I think a Ford 400 or was that the 6.800 six cly rod) Which ever it was all else being equal their long rod engines had a much better trq curve I think approx 30 lbs ft at some rpms. Max power was the same but the trq curve building up to peak was much broader with the long rod.

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    Quote Originally Posted by Sleeper CP View Post
    I know a couple of guys who built a few stroker Smblk Fords for some desert pre-runners same builds but 2 with the long rod ( I think a Ford 400 or was that the 6.800 six cly rod) Which ever it was all else being equal their long rod engines had a much better trq curve I think approx 30 lbs ft at some rpms. Max power was the same but the trq curve building up to peak was much broader with the long rod.

    S CP
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    gn7
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    Steel, I thought you were banned from discussing rod lengths on this forum



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  16. #14
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    Quote Originally Posted by steelcomp View Post
    Ding-ding!
    I should have added that the guys with the trucks said the long rod trucks were much easier to drive and felt like they had a B Block under the hood with the added mid-range trq.

    It's all about application I guess

    S CP

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