Which is better
Tourer
Joined: Jun 2013
Posts: 272
Likes: 5
From: pomgolia
milling heads is a cheap and easy way to get more power with very few if any negative side effects
the possible downside of not being able to add metal back can be negated by replacement heads / low compression pistons / stroker plates under the barrels
have had to resort to the stroker plate solution on my panhead that has had heads milled a few too many times and ended up poping head gaskets as compression was too high
the possible downside of not being able to add metal back can be negated by replacement heads / low compression pistons / stroker plates under the barrels
have had to resort to the stroker plate solution on my panhead that has had heads milled a few too many times and ended up poping head gaskets as compression was too high
Road Warrior
Joined: Jul 2013
Posts: 1,476
Likes: 5
From: Florida
THC, I laboured over this when building my engine as well. I went w/ pistons and here's why:
1) you more than likely will have to use adjustable PRs (I know you already have them), and I'm just not a fan of anything "adustable" in the valvetrain geometry, just me.
2) as you said, once you mill them you can't go back.
3) as said in another post, it changes the spatial relationship of the intake to the cylinders, maybe not enough to matter, but it just seems "hack" to me.
4) it is true that combustion chamber volume can vary from head to head, but your not building a drag bike, and chances are if it runs smooth now it will be the same when you add the domed pistons.
5) if you go with a piston brand like Wiseco or JE you will have a much more durable forged piston.
6) I paid just over $200 for my Wiseco piston kit, so it would have cost me as much or more to have the heads cc'ed and milled. I didn't have to bore my cylinders, so that is one factor to consider.
In the end, either way works. I was just giving you my reasoning for the route I chose
1) you more than likely will have to use adjustable PRs (I know you already have them), and I'm just not a fan of anything "adustable" in the valvetrain geometry, just me.
2) as you said, once you mill them you can't go back.
3) as said in another post, it changes the spatial relationship of the intake to the cylinders, maybe not enough to matter, but it just seems "hack" to me.
4) it is true that combustion chamber volume can vary from head to head, but your not building a drag bike, and chances are if it runs smooth now it will be the same when you add the domed pistons.
5) if you go with a piston brand like Wiseco or JE you will have a much more durable forged piston.
6) I paid just over $200 for my Wiseco piston kit, so it would have cost me as much or more to have the heads cc'ed and milled. I didn't have to bore my cylinders, so that is one factor to consider.
In the end, either way works. I was just giving you my reasoning for the route I chose
Road Warrior
Joined: Apr 2007
Posts: 1,952
Likes: 15
From: Senoia, Ga., by way of Miami, Fl..
Most of our performance engines got the heads milled for two reasons. First and most obvious more compression. Secondly to balance the combustion chambers. Harley heads can and do vary from head to head more than we like to see. This can make for more vibrations than there should be. So in closing if you are going to have the heads CC'ed then go ahead.
John
John
Thread Starter
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Dirt don't hurt
Joined: Jan 2011
Posts: 21,065
Likes: 4,561
From: Haslet Texas
Thank you for all your replies.
I think I'm going to go with the pistons because of what a friend said (and was mentioned above).
Basically if I don't like it I can go back with some lower compression pistons (the only reason would be if I can't get the spark knock out).
From what I've read I should be safe at 9.5-1 but I know my luck (all bad) and I don't want to have to buy new heads if I don't have to. Kinda a CYA thing.
I think I'm going to go with the pistons because of what a friend said (and was mentioned above).
Basically if I don't like it I can go back with some lower compression pistons (the only reason would be if I can't get the spark knock out).
From what I've read I should be safe at 9.5-1 but I know my luck (all bad) and I don't want to have to buy new heads if I don't have to. Kinda a CYA thing.
Seasoned HDF Member
Joined: Sep 2012
Posts: 6,570
Likes: 590
From: almost there
I haven't had any problems with my build. My Indy has his own prescription for his builds and he is hell bent to change from it. He wanted to go 10.5 weisco's but I said not over 10.1 and that's what went in. So Mine starts very easy with no pings. This is the build,
Heads Built & shaved .030, 10.1 weiscos .30 over, cometic gaskets. Also Ev27, HD lifters,
Adj pushrods, roller rockers, Dyna igniter. Only problem is don't WOT out the hole.
Heads Built & shaved .030, 10.1 weiscos .30 over, cometic gaskets. Also Ev27, HD lifters,
Adj pushrods, roller rockers, Dyna igniter. Only problem is don't WOT out the hole.
Last edited by aces&8s; Jan 17, 2014 at 08:48 PM.
Road Master
Joined: Jan 2008
Posts: 1,187
Likes: 8
From: Montgomery, AL
I have a spare set of heads I'm going to send off for port & polish along with shaving for compression bump. Since it is apart from what I've read adj pushrods aren't necessary. How many miles on your bike?
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Seasoned HDF Member
Joined: Aug 2008
Posts: 5,078
Likes: 2,150
From: Ohio
In proven theory, a flat top piston with a smaller combustion chamber is better for engines, flame travel hot spots are eliminated that can cause detonation, domed pistons increase weight that affects rotating mass, efficient combustion.
Since you are building a everyday motor and not out to attack Twinkies, a new piston with a good bore is always peace of mind and will fit your needs. You can put a .030 head gasket with those pistons to help out but make sure your pistons have designed valve clearance.
Since you are building a everyday motor and not out to attack Twinkies, a new piston with a good bore is always peace of mind and will fit your needs. You can put a .030 head gasket with those pistons to help out but make sure your pistons have designed valve clearance.
Thread Starter
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Dirt don't hurt
Joined: Jan 2011
Posts: 21,065
Likes: 4,561
From: Haslet Texas
I will probably go back with stock pushrods.
I have 35k on a reman motor.