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[roadking53]

Without getting really deep....... what are the basic advantages of going one way or the other.
Looking to increase usable street performance.

[Ed Ramberger - One_Screamin_Eagle]

Without getting really deep....... what are the basic advantages of going one way or the other.
Looking to increase usable street performance.

Your question is very vague because your goal is unclear.  In the simplest of terms, once you mill a head it can't be undone.  Thinner head gaskets and different pistons can always be changed.  Also, heads do not have to be disassembled for pistons or gaskets. 

Some pistons will require additional clearance on milled heads, some are designed for them. 

Do you have a specific budget, goal, vision?

What is the bike going to be used for 99% of the time?

[HILLSIDECYCLE.COM]

Without getting really deep....... what are the basic advantages of going one way or the other.
Looking to increase usable street performance.

Useable street compression can be readily increased via re-surfacing the heads, and is a very cost effective way to establish the needs of many cams.
Scott

[roadking53]

Is there a down side to just doing pistons. for example...If your cam specs say 9.1 - 10.0 and you put in a 10.5 pistons are you more prone to have pinging or problems running lower octain gas when you can't get the good stuff ?

[naitram]

Tmans CVO street performance headwork. He also milled them to give me 9.9 comp to use with stock piston I also used his SM600 cam. V&H power duals with fulsac 2.25 SD cores, GREAT POWER  and good fuel mileage 40mpg in city & 47mpg on highway   Dyno final pull was in 4th gear, 5th gear would probably show just a little higher numbers. My tuner does final pulls in 4th only.

had to remove your orginal post, it was causing an error. did you have a large attachment?

[HD Street Performance]

Is there a down side to just doing pistons

Sometimes, depends on the dome shape.
A flat top piston and a smaller compact chamber will win the race dyno or street.

[lilcoot]

A flat top piston and a smaller compact chamber will win the race dyno or street.

Could you elaborate?  Why will a flat top piston and a smaller compact chamber get better numbers?

TIA

[HD Street Performance]

My answer relates to the 110 family of heads specifically as good candidates because the chamber is deep and there is not a lot of squish area. Milling them improves that. Plus there isn't a dome in the way to trap and cause dead spots for either air/fuel or exhaust. Same holds true for the 120r. This concept is not unique to the 110 just a little more exaggerated than some of the other head castings. There is one downside however, the builder needs to check piston to valve clearance, which they should be doing anyway, and be prepared to correct if needed. The heads have big valves.

[prodrag1320]

agree`d,try to keep the piston flat and the combustion chamber small as possible to achive the cc`s needed,you`ll have a quicker burning,more efficiant chamber.so mill if the desired compression ratio can be had by milling (sometimes theres no choice but to replace pistons)

[HILLSIDECYCLE.COM]

.................and to achieve certain results, a combination of both a piston, and chamber volume reduction may be needed.
Scott