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Sportster Motorcycle Engine Conversions Advice, questions, and tips for 1200, 1250, 1340, 1450 etc... for Sportster and Buell motorcycle engine conversions

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  #1  
Old 3rd December 2006
XLFREAK XLFREAK is offline
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Default reverse dome....or flat top

so are flat tops better than reverse dome...are they louder??? and what would be a good reccomendation
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Old 3rd December 2006
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Seeing that this is in the conversion section I am guessing that you are referring to pistons. If you are indeed talking about pistons then I will try to clear something up for you. You use reverse dome pistons when you use the stock 883 heads. This will give you compression that your engine can live with. Flat tops are used when you have a set of 1200 heads on your bike. If you try to use flat tops in an engine with 883 heads you will have to much compression. There is an alternative though, HD sells a templete so you can grind a section out of your 883 heads to give the combustion vhamber more CC's. This will lower your compresion. Which one is louder? I can't really tell you because it is mostly up to the exhaust on how loud the bike is. My reconmendation would be to use the reverse dome pistons if you plan on using the 883 heads so you won't have to do any modification to your heads. I have the 9.5-1 pistons in mine and I still have to run 93 octane so it won't ping.
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Old 3rd December 2006
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The main difference is that the flat top will require chamber work to get the compression down to something streetable. The reverse dome conversion piston is designed to go under an unmodified head.

Neither is louder than the other one. Piston slap type noises are primarily a function of piston to cylinder wall fit.

Go with the flat top and do the chamber mod if you're looking for say 10.5:1 or more. It's tough to get it much lower than that with the flat top unless you start compromising squish clearance or cutting away part of the squish band, neither of which is a desirable thing to do.

If you're looking for a lower compression motor, go with reverse domes.
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Old 3rd December 2006
XLFREAK XLFREAK is offline
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i undersdstand al the cumbustion stuff with the heads and everything....my only concern was i heard that flat tops are heavier than say wiseco reverse dome pistons.....also im not sure if i plan on keeping this bike FOREVER....maybe a few more years i bouth it used and i can offord to finance a new bike....so i want more power BUT not looking to race....just streetable reliable.....if i do reverse should i with 9! or 10:1,,,
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Old 3rd December 2006
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Boh of those are very steetable compression ratios. You should not have a problem with either.
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Old 4th December 2006
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didnt really understand where the LOUDER came from. Hmm.. I went with reverse domes. Not really bummed either because there are a ton of things I could with headwork down the line.

my question, why even spend the near 1k if you're gonna sell her. I do not think you get your full value back when you sell a conversion bike. Just my opinion, but who know... i may be correct. just enjoy your 883 - you likely have not even used the full potential.
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Old 4th December 2006
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let me correct this LOUD thing,....i meant more vibrations....someone said they vibrate more then reverse.....and i wont send near a grand if i want to sell her eventually...but it wont be for a couple of years prob....so i was thinking to just do a little minimal stuff to get mreo power for the mean time
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Old 4th December 2006
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Quote:
Originally Posted by chrism84
let me correct this LOUD thing,....i meant more vibrations....someone said they vibrate more then reverse.....and i wont send near a grand if i want to sell her eventually...but it wont be for a couple of years prob....so i was thinking to just do a little minimal stuff to get mreo power for the mean time

the piston shape would not affect vibrations...it would affect compression ratios...
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Old 4th December 2006
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Do the work yourself and use the money saved on the NRHS headwork and piston kit. Add mild cams for street use and you MIGHT NOT WANT to sell it. It will have a serious increase in power.
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Old 4th December 2006
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I installed flat top pistons and 1200 heads on my 04 883. If it vibrates any more than before, it's so little that I can't tell the difference. There are good reasons to choose either flat-tops or domed pistons, but I wouldn't decide based on vibration.
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