Engine size vs reversion.
06-08-2003, 07:23 PM
#1
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Engine size vs reversion.
Is there a relationship? Example my 498" BBC is running a 272/280 duration @ .050" cam on a 112+4 installation. My exhaust pipes exit completely underwater which makes it very quiet which I personally like especially with BS noise laws. Anyway with my 498 there is no problem with reversion with the exhaust I am currently running. Would the same or basically the same cam be reversion free in say a 540" or 572" using the same exhaust? Does the larger motor pull more back on overlap and does the extra flow leaving the exhaust basically keep the reversion away? I hope I am stating what I am thinking clearly.
Thanks,
Craig
Thanks,
Craig
06-09-2003, 12:45 PM
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Dang, no answers! Well with a larger motor the vacuum signal to the carb will be better than a smaller motor running the same cam. Does this also mean there is more vacuum during overlap to pull back the exhaust, or will the added exhaust flow / velocity offset the increased "exhaust vacuum"?? I guess it is one of those things you won't know until you try it out.
06-09-2003, 03:25 PM
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Bobby,
That is good to know and kinda what I thought. I try thinking things through and sometimes come up with some off the wall thoughts about what may happen. Thanks for the response.
That is good to know and kinda what I thought. I try thinking things through and sometimes come up with some off the wall thoughts about what may happen. Thanks for the response.
06-10-2003, 04:45 AM
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On your cam specs; Did you mean that the cam is 272/280 minus 50* or 272/280 @ 50*? If it is the latter then that is a LOT of duration! I didn't know you could run a cam with those specs in a boat WITHOUT getting reversion. Just curious.
06-10-2003, 11:43 AM
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The duration I mentioned is not a misprint. The specs are @ .050" lift and I currently do not have any reversion problems with the 498" motor and and the CMI exhaust I am currently running. They exit about 6" below the water so they are real quiet at idle and at the same time because of the drop there is a lot of dry pipe which keeps the reveresion at bay. The reason I ask about the larger motor is because my 498" is running 13.2:1 compression and $3.00 gas. If I go to a 572 or 598 I can run 10:1 comp and use basically the same cam on pump gas and make close to the same amount of HP as the 498 is now running 110 octane.
06-10-2003, 06:30 PM
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Duration @ .020" lift is 308/316, and the duration @ .050" lift is 272/280. Advertised duration isn't even listed on the cam card. Lift is .714" and valve lash is .024" hot.
