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Author Topic: Top end advice  (Read 2965 times)

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Schwabie

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Re: Top end advice
« Reply #15 on: March 31, 2017, 08:24:10 PM »

Picked up a shiny pair of SE II slip ons.  :) The last thing that I'm still not sure about is milling the heads. Is .060" too much to take off combined with the .030" head gaskets? Will there be enough valve clearance if I keep the stock lifters and push rods? And if it all the milling comes off of the heads and not the cylinders could it create a pre-ignition problem?
Thanks again for the input,
Gary
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Schwabie

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Re: Top end advice
« Reply #16 on: March 31, 2017, 08:27:21 PM »

OK, thanks Ridgerunr. I've got to settle down and do some investigating before loosening the heads.
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Schwabie

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Re: Top end advice
« Reply #17 on: July 13, 2017, 06:01:33 PM »

Rolling again!
It seems to run and sound great. I did go ahead and mill the heads .050". That combined with .030" head gaskets made the compression jump up from 110 to 150, but that also resulted in the push rods being a touch too long, so I got adjustables. Feels good to have it on the road again. Thanks for all of the advice!
Gary
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MCE

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Re: Top end advice
« Reply #18 on: May 18, 2018, 03:06:33 PM »

Good analogy.  I'd suggest you make sure it is not a straight-through design and has some back pressure in the baffle design.  Then it's just what sounds good to you.

A little late to the party here, but:
"Back pressure" is an old wives tale. The only thing back pressure does is increase pumping losses, which is
counter-productive to making power.
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2002FXDWG3

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Re: Top end advice
« Reply #19 on: May 18, 2018, 03:10:19 PM »

Whatever the explanation, mufflers with some sort of baffle typically make more power, at least lower end torque, than straight-through "drag pipes" on a typical Harley.  YMMV.
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MCE

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Re: Top end advice
« Reply #20 on: May 18, 2018, 07:19:29 PM »

It has more to do with dampening the sound waves (acoustic pulses) that get reflected back toward the port if left unchecked.
(Ideally, you don't want any back pressure) If the reflected wave arrives at the wrong time (like they do at low speed) it upsets the
gas flow during overlap. That's what kills the low end TQ.

Baffles will dampen these waves and circumvent some of their detrimental affects. Back pressure will only increase pumping losses and
rob power.  2 cents...
« Last Edit: May 23, 2018, 11:04:22 PM by MCE Performance »
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