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Author Topic:   HDPI or DFI?
Lars Simonsen posted 02-01-2003 06:18 PM ET (US)   Profile for Lars Simonsen   Send Email to Lars Simonsen  
I thought my 1998 Mercury 135 Optimax had High Pressure Direct Injection (HPDI). The January edition of Sportfishing Magazine says the 2003 135 Optimax has Direct Fuel Injection (DFI). Have they changed the injection system on the new Optimaxes? If not, am I wrong about the injection system or is the magazine?
PMUCCIOLO posted 02-01-2003 06:35 PM ET (US)     Profile for PMUCCIOLO    
Direct Fuel Injection ("DFI") includes Optimax (Mercury), HPDI (Yamaha), and FICHT (Bombardier) systems. They all inject fuel with pressurized air when the piston is PAST the exhaust port on it's way up toward the spark plug.

The differences lie in the type of plunger used with the injector and the pressure at which the fuel is injected for atomization.

Nissan also has a system branded "TLDI," which is very similar to Optimax technology.

I hope that this helps clarify things! Enjoy your motor!


Lars Simonsen posted 02-01-2003 09:32 PM ET (US)     Profile for Lars Simonsen  Send Email to Lars Simonsen     
Yes, that clarifies things. Thanks. I really like the motor, but I haven't yet developed a great deal of trust in it (the powerhead blew last summer, but Mercury replaced it even after the expiration of the warranty with a "factory remanufactured" powerhead) I'm impressed they did that, but it will stll take me a while to trust the motor. Do you think a factory remanufactured powerhead installed in 2002 would have the improvements made to the Optimaxes since they first came out?


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