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i did a compression test on my mxz 700 it has about 2200 miles on it and it tested at 130 lbs. is that good or bad? just wondein if anyone else had any numbers on this? and if so can i boost compression by changin gaskets to thinner ones or what are other ways to accomplish this. the last thing is how much can i safely raise the compression to without having to worry about losin the bottom end of the motor? i use the sled for trail ridin not drag racin or anything.
 

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Compression should be 150psi both cylinders.

Before you start freaking 130 is still ok but is low and its probably just your gauge or method. Make sure you hold your throttle wide open as you pulling it or cranking it over. If your still getting 130 try another gauge.

If its low you need new rings.
 

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well i tested my friends 2002 polaris 800 edge and his was just a tick under 150. so my gauge is good i didnt hold the throttle open howver and i already have it all apart why do u need to hold it wide open? if i put in new rings will that put it back up to 150 and can i go more than 150 like maybe 160 170?
 

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130 is not too low. The 2000 MXZ's came with the decompression slots, and mine was always 125lbs. before tinkering. Our local dealer tested 14 new 700's and found only one to be over 125lbs. don't worry, if it bothers you, rings are not cheap but will give you piece of mind.
 

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I am with kid rocker on this 100%.but then again what do I know about '00 700's
 

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Wow. Guess my 800 was wore out the day I brought it home with 135lbs!

The bigger the bore, typically the less the compression. A 809 has a 68mm bore, a 700 series3 has eith 74mm or 76mm (I think) and the 800 has 81mm.

809s should be 145sh to 150. But most of the twins are in the 125-130-135 range. (At least Doo twins)
 

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SOrry if I miss informed anyone. I just though it was 150 becasue my Mach is 150, My 1998 500 mxz is 150 and my departed 2000 600 grand touring was also 150. I thought this was a trend.
 

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Be still my beating heart, machzzzz was wrong & admitted it. Holy sh** :yee:
 

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Good thing the year is almost over, because your only allowed one mistake per year. :p
 

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after the piston update on my 01-800 i had 147lbs on each cylinder,then added the rkt head and was reading 172 lbs
 

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WOW 172psi hope you don't get a bad load of fuel.
 

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Originally posted by mkfasttoys@Oct 7 2002, 05:26 AM
well i tested my friends 2002 polaris 800 edge and his was just a tick under 150. so my gauge is good i didnt hold the throttle open howver and i already have it all apart why do u need to hold it wide open? if i put in new rings will that put it back up to 150 and can i go more than 150 like maybe 160 170?
You want to hold the throttle open as to allow for the engine to pull in the maximum amount of air, making for a more accurate reading. A closed throttle can drop your readings substantially.
 

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mxz900 i used the same gauge for both readings,i know some read different,and not sure if the gauge was psig or psia (15lbs difference in reading)
 

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I am guessing that unless it actually says psia on the face of the guage that it is reading in psig. psig is what you want to measure cylinder pressure in anyways.

You want it to measure in psig because psig (g is for guage) measures the difference between the inside of your cylinder at full compression and the ambient atmospheric pressure.

psia (a for absolute) measures the absolute pressure (in this case, the pressure of your cylinder) and this is against the reference point of 0psi or perfect vacuum.

Since you do not run your sled in a vacuum (which is good, because it would be tough to breathe) and in fact your sled is sucking in air from the surroundings, you want the pressure reading to use atmospheric pressure as the reference point or baseline. :)
 

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172 psi WOW,I think that would be in the c-14 fuel range. :)
 

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i run 91 octane,only problem i had was when i had a frozen carb(took my piston out)other than that its been great,i do worry about bad gas as i live up north,so i keep a little rich on the jetting :D
 

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Remember that the proper method of testing is to test when the motor is warm, about 5 good strong pulls should be about right. The two cylinders should not be more than about 10-15% different, and I would not be worried until they drop below 115-118 or so. Compression is different on every sled and I have seen 5 psi difference in gauges testing the same sled at the same time. Use a GOOD gauge, not the el cheapo $20 special.

The compression on my 02 MXZ 700 was about 133-135. The compression on my 99 MXZX 440 with the low compression domes was about 150-152, and the high compression domes was over 170.
 
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