Compression on DI motor

[1goofball]

hello!

I just heard that the compression on a DI motor is different than a carbed motor. By that I'm meaning - while a 2002 Seadoo GTX 951cc motor might have 150psi in each cylinder - a 951cc DI motor might have could compression at 120psi. Does anyone know if this is true?

OR does it matter? If its a 2 cylinder motor, it should have 140 - 150psi or so - no matter if its carbed or DI?

 

[seadoosnipe]

compression....

The compression on most Sea-Doos is 140 psi. If you get a compression reading of anywhere between 100 to 140 or 150, then your in good shape. The idea of a compression test is to identify the age or time the pistons and cylinders were last worked. One of the most aspects is to see that both cylinders are within a few pounds of each other. If you have one cylinder at 110 psi and the other come in at 140 psi, then this isn't good. The difference of compression will make the engine run unevenly. Like one piston doing most of the work and in some cases will cause overheating.
The DI motor uses a compressor to inject the combustion chamber with fuel and air at a higher pressure to overcome the pressure present. I'll pop into a manual and see if I can get some specific info on those pressures. I do know, there have been issues with the compressors of the DI motor. The RFI (rotax fuel injection) uses a different principle, so the air compressor system isn't needed.

 

[kustomkarl]

To add to Seadoosnipe's input, the compression is a reading of compression of the cylinders reguardless of it being asperiated or injected.( how fuel enters the engine)

Karl

 

[1goofball]

<<< The idea of a compression test is to identify the age or time the pistons and cylinders were last worked.>>>

never heard that before. The reason I was wondering, is that I have a 2002 RX DI with 115psi in each cylinder, which I thought was time for a top end rebuild. Another reason is that it would only run 6500rpms. Then I heard that DI ran lower psi so maybe there is something else wrong instead of top end.

seadoosnipe - i see you are in Mobile? I'm over in Gulfport, Ms