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  #1  
Old 11-11-2012, 09:17 AM
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Default What pistons should I use in my build

Currently the bike has the 103" big bore with the flat top cast pistons and the builder is trying to talk me into putting in the "SE Pro Twin Cam High Compression Forged Pistons". The compression on the bike right now is 168 lbs in both the front and back cylinders so the current pistons and rings are in good shape but I am going to do a Cylinder Head upgrade to the "SE Pro CNC Ported Factory Cylinder Heads with Valve Upgrade" so would it be better to upgrade the pistons or should I keep what is already in the bike. Right at this time I am going to use the SE255 cam that is already in the bike but I am having the adjustable push rods installed just in case I want a different cam put in later on.
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  #2  
Old 11-11-2012, 11:03 AM
Deweys Deweys is offline
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No need to change and there are good reasons not to, the stock cast piston works well and for a very long time in stock to mild performance builds. Going to a 107" the story changes.
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Old 11-11-2012, 11:07 AM
akjeff akjeff is offline
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If you plan to keep your 103" displacement, I think the builder is trying to take you for a ride. Not a damn thing wrong with the SE cast flat tops, for what you're doing. If you really want your bike to come alive, for what you'd spend on the SE Pro heads, you could send your own heads to a reputable head porter, who can tailor your heads to a specific cam.

Are the heads on your bike bone stock? 168psi seems a little on the low side, for an early closing cam like the 255. Compression releases maybe not disabled? Throttle butterfly held wide open?

Jeff
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Old 11-11-2012, 11:11 AM
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Quote:
Originally Posted by Deweys View Post
No need to change and there are good reasons not to, the stock cast piston works well and for a very long time in stock to mild performance builds. Going to a 107" the story changes.
You beat me to it, Don!

Jeff
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Old 11-11-2012, 11:18 AM
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Agree with the previous posts, unless you are going to be over 6000rpm on a regular basis, or running extreme conditions like a turbo or supercharger, there are alot of good to NOT change your pistons.
For the same reason, I think the CNC SE heads are overkill for what I suspect is your style of riding. If you're happy with the power band the 255 cams produce you'd be better served to do upgraded stock heads. Ported and shaved stock heads and the right head gaskets to get you no more than about 190-195psi compression is what you want for a reliable highway ride.

IMO........
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Old 11-11-2012, 12:52 PM
Deweys Deweys is offline
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Guys get sold HP when they really want torque. Yours is really cranking 193 when you close the ACRs and open the throttle, Jeff is right there.
I see the heads as a waste of money. Just Blueprinting the stock head with stock valves is appropriate if that cam is kept and higher HP is not the goal.
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Old 11-11-2012, 03:55 PM
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Quote:
Originally Posted by akjeff View Post
If you plan to keep your 103" displacement, I think the builder is trying to take you for a ride. Not a damn thing wrong with the SE cast flat tops, for what you're doing. If you really want your bike to come alive, for what you'd spend on the SE Pro heads, you could send your own heads to a reputable head porter, who can tailor your heads to a specific cam.

Are the heads on your bike bone stock? 168psi seems a little on the low side, for an early closing cam like the 255. Compression releases maybe not disabled? Throttle butterfly held wide open?

Jeff
The heads are stock and I don't know what conditions that the compression test was done under because I wasn't present. This shop is a machine shop but the builder want to sell me the SE heads instead of doing my heads, part of the reason is that he claims not to have the ACR jig and that the SE heads come ready for the ACR's but what I am reading the heads that he is recommending are not ACR ready. Here is the builders web site www.kellysperformancespecialists.com The shop is very very clean and he has been in business for quite sometime and I haven't heard anything bad about his work
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Old 11-11-2012, 04:11 PM
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I have to agree with the masses here, your stock pistons are fine for what you want to do. Same for the heads, a good performance valve job with street type porting will work exceptionally well with the RPM band your looking for. It"s easy to get caught up in over-kill hype.
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  #9  
Old 11-11-2012, 05:21 PM
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Just like everyone else said. Use your flat top pistons and have your heads reworked. That has been the ticket for two of my bikes. Seen too many spend the extra when not needed.
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  #10  
Old 11-11-2012, 05:32 PM
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The guy who did the bore out on my bike said I did not need fancy pistons. Cast, flat top 10:1 pistons. I never even asked who's they were.

Last edited by OldNerdGuy; 11-11-2012 at 05:45 PM.
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