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Low compression banshee


Sjk545545

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I bought a 2006 banshee, It came with cool heads on it the guy said he didn’t know a whole lot about it except he had wisco pistons put in in October 2016 It ran good and showed 135 pounds of compression so I bought it now a year later I have 130psi I took the coolheads off to put 19 cc domes in  and come to find out it had 19s already,  The internals of the motors are all stock except the pistons and they are stock size so how can I be running 130 psi with 19 cc domes?  I should be up around 175 or 180, I am at 3500 elevation which could bring me down to 160 PSI but that still means I’m 30 pounds short the motor has not been ported do I need to just put new rings a I am at 3500 elevation which could bring me down 260 PSI but that still means I’m 30 pounds short the motor has not been ported do I need to just put the rings in it? Any insight is appreciated

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40 minutes ago, SKEETER said:

Besides what you "think" it should have,  how does it run ? Are you happy with it?  

Runs really well fires up good, and it has always done me right but no the last 3 bikes I had  all  dyno out between 70-90 hp so this bike is lacking compared to what I’ve had in the past, 

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42 minutes ago, 375hp banshees said:

If wall clearance looks good & it runs OK send it , unless you just want more . which I assume you do , or you wouldn't have wanted to change dome sizes 

 Yeah it runs great,  I just advanced the timing And I was hoping to get the compression up with the new domes so I could run 108 octane have a big dune trip planned in March and want it to be screaming by then 

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You can't compare a 70-90 HP to a bolt on stock bore banshee, no matter what the compression is. As far as current compression the fact that it has new pistons in a stock bore & 19 domes seems odd to me, could be squish due to dome or gasket mismatch? But i would lean towards side clearance

Sent from my XT1080 using Tapatalk
 

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3 minutes ago, 375hp banshees said:

You can't compare a 70-90 HP to a bolt on stock bore banshee, no matter what the compression is. As far as current compression the fact that it has new pistons in a stock bore & 19 domes seems odd to me, could be squish due to dome or gasket mismatch? But i would lean towards side clearance

Sent from my XT1080 using Tapatalk
 

I’m not comparing it to the other banshees  he just asked if I was happy with it and I said it ran great but I am trying to get a little more horsepower that’s why I wanted to raise the compression,  but I found that it already had the 19cc domes in it  and it had compression of 130 pounds ,  everything I have read says that with those domes you should be around 180 pounds of compression and you have to run high octane,  I am simply asking for everybody’s opinion on why my compression is low despite the 19 cc domes 

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9 minutes ago, SKEETER said:

Waste of time and $ IMO.  For what minor gains you'll get from more compression and race fuel on that engine.   

 

10 minutes ago, SKEETER said:

Waste of time and $ IMO.  For what minor gains you'll get from more compression and race fuel on that engine.   

Well I was also going to have it ported to really wake it up but not till this summer, so you think I should check cylinder wall clearance? And what do you say the clearance should be? 

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Get another compression tester. Ive seen testers straight out of the box be completely inaccurate. Also you need the correct length nipple(same length as plugs) to get accurate reading. My favorite compressor tester ive ran across for the money is a craftsman. It comes as a kit with everything you’d need.

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12 hours ago, special06shee said:

Get another compression tester. Ive seen testers straight out of the box be completely inaccurate. Also you need the correct length nipple(same length as plugs) to get accurate reading. My favorite compressor tester ive ran across for the money is a craftsman. It comes as a kit with everything you’d need.

this right here. 

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