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Discussion Starter · #1 ·
I was checking compression on a buddies banshee last night so since i had my gauge out i thought i would check my 700. the best i could get it to read was around 80 psi. That seems low to me but i dont really know what its suppose to be. The bike is all stock except for the 3 mods. It also only has 25 hours or so on it.
 

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That seems low to me....what type of gauge did you check it with and did you have the correct adapter on there. Remember that it must be the same as the plug profile when screwing into the head.

M
 

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Discussion Starter · #5 ·
oh yeah i know, I was checking it right. I used my mac tool comp tester. I thought maybe since it was gettin a little old it wasnt as accurate as it used to be so i went out and bought a $60 actron gauge and come up with the same readings. Do you think maybe the rings havent quite seated yet? They should be with 20 hrs on it but i dont know to much about single cylinder 4 strokes
 

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This is for the Banshee or Raptor? If it's for the raptor...then that's actually pretty high. Ideal and normal is around 64 and high is like 71 with lowest being 56. I didn't see until now your talkign about the rappy sorry.

M
 

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Discussion Starter · #9 ·
yeah im talkin about the 700. My buddies banshee is crankin out about 165 psi. Which after lookin at that 80 psi seems low but then again his banshee has 18 cc domes in it.
 

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These 700's only have a 9.2:1 Piston in them, they're already low compression.
 

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yeah 80ish does seem low compared to a 2 stroker. my blaster with .80 over bore wiseco piston and high comp head gasket gets 145psi. i read the shop manual for the rappy and 60-70 is about right..
 

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80 psi might not be low for the 700R, but most 4 and 6 cylinder engines in cars today run around 200psi. And just think all those cars run on 87 octane :eek:

Im guessing the 700 has lower compression to make the motor rev faster and higher vs higher compression 4 strokes that normally run under 5000rpm and take longer to get there.
 

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There is more to the required gas octane then compression. Factors like squish angle, compression, camber layout etc. all play a factor when the engine is designed. Also the compression is not why it takes longer or shorter to rev....that's due to the stroke of the engine.

M
 

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Would the auto decrompression not come into play?
 

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Compression pressure (at sea
level)
Minimum
392 kPa (3.92 kg/cm2, 55.8 psi)
Standard
450 kPa (4.5 kg/cm2, 64.0 psi)
Maximum
504 kPa (5.04 kg/cm2, 71.7 psi)

a. Set the main switch to “ON”.
b. With the throttle wide open, crank the
engine until the reading on the compression
gauge stabilizes.
WARNING
_
To prevent sparking, ground the spark plug
lead before cranking the engine.

I know there is a compression release valve on the raptor
so I guess this it what it should read if it's all good
I believe the actual compression is higher tho.
but no way to read it with the compression release
I guess they have it all figured out so the manual shows the above to be normal
 
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