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Discussion Starter #1
I am basically building up my 86 750 to 830 cc by putting an 89 top in on. I might be able to get a set of overbore pistons but they are 13-1 compression. Is this too high for a bike primarly used on street. I have heard that if compression is too high I would need lots of mods to complement the compression and it could cause problems with the head. Anyone know?
Thanks.
 
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You could always use a thicker base gasket to lower the compression.
 

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Go with a thicker gasket unless you complelty want to make a new motor, I personally would,t go over 12:1 on the street with an oiler motor, when I build my 1340, I am going to keep compression right around 12-12.5:1 and I should still kick out 175+rwhp
-Karl
 

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Discussion Starter #4
So should I get the pistons and go with a thicker gasket or just keep it stock. The pistons are wisco 1mm overbore.
 

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No repalcement for displacement

-Karl
 

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I had a set of weisco 1mm over 13.5:1 pistons in a 90 750. The displacement turned out to be 771cc. The bike ran great on 93. It didn't like race gas. I lost 4hp just by switching to race gas from premium. In the real big oil cooled bikes 1200+ I would definitly keep the compression around 12:1, but in a 750 you can run more
 

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Discussion Starter #8
Yep, I will be getting a spacer plate. I have been talking to a guy in Pennsylvania that did this mod years ago. Right now I am just trying to get all the pieces.
 
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<blockquote><font size="1" face="Verdana, Arial">quote:</font><hr>Originally posted by suzukiltd:
Yep, I will be getting a spacer plate. I have been talking to a guy in Pennsylvania that did this mod years ago. Right now I am just trying to get all the pieces.<hr></blockquote>

Yeah.....if it's the guy I'm thinking about then there was an article in Sport Rider about his bike. In fact that article was scaned and posted here in this forum a few months ago.
 

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<blockquote><font size="1" face="Verdana, Arial">quote:</font><hr>Originally posted by GixxerRacer371:


Yeah.....if it's the guy I'm thinking about then there was an article in Sport Rider about his bike. In fact that article was scaned and posted here in this forum a few months ago.
<hr></blockquote>


This is the phobia I spoke of earlier.
 

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Discussion Starter #11
Thats the article I was talking about. I was outbidded on ebay for the pistons. I might still go with some aftermarket pistons, I will just need to wait and see.
 
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<blockquote><font size="1" face="Verdana, Arial">quote:</font><hr>Originally posted by Simon Orttan:
What's the difference in the piston heights? I'd be worried with that short stroke block.<hr></blockquote>

Well, I don't know if you know this but you can't just stick the 89 pistons and cylinders on your 86 and be done with it. I believe you have to use a spacer plate to compensate for the shorter stroke cylinders.
 

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Agree with the overall concensus here - 13:1 is just too much of a pain in the ass for the street. I'd say the absolute practical limit should be 12.5:1 (only if you trust your local premium blend!)
 

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Discussion Starter #14
Thanks for the input. I will probally keep the compression down. I don't need any more problems
 
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