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Monsoon 350 Cylinder Compression

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2009 VLX - Monsoon 350 - approx. 450 hours.

What compression should I be reading?

Engine has been running poor, cylinder misfire issues, decided to do a tuneup (and appears to really need it).

While i had the plugs out, i decided to check the compression.

All cylinders came in at 210-220 psi. Is this too high?

What is the standard compression new? With 400-500 hours?



1 - 210 psi

2 - 210 psi

3 - 212 psi

4 - 220 psi

5 - 215 psi

6 - 215 psi

7 - 212 psi

8 - 215 psi

Edited by LSU

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This is not too high. It's kinda impressive. Compression creates horsepower. As long as it was fairly consistent as you indicated it was, then I consider this a good thing.

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Those results are good, misfires are usually fuel or spark related.

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Thanks for the feedback guys.

I called and spoke with the service department at the local Malibu dealership.

The rep confirmed that 150-180 psi was the general range. He couldn't really speak any more to the higher compression without seeing/ digging into the engine.

As far as i know, its just the stock 350. Is this really uncommon? Could some kind of motor work have been done to the boat before i bought it ('09 I bought in '12).

Should i start running a higher grade fuel because of the higher compression?

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Could be the accuracy of your gauge. What's important (and good, in your case) is that all cylinders are so close.

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What RTS said.

Gauges aren't always accurate, pressure wise, so the thing to look for is consistency. You typically want within 10% of each other all across the board.

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