Plenum & Injector Housing Porting

[Marc Haibeck]

Mercury Marine corrected the port mismatch problem in '93. It was part of the 405 hp upgrade. They CNC blended the injector housing ports 1.5" down the port. They also increased the plenum port diameter from 33 to 34 mm. That's why porting an early engine well will add 35 hp. Only 20 hp can be gained on the '93 and up engines.

[jss06c6]

Here's a couple of pictures to illustrate.. note that using the gasket as a reference, the head ports are concentric, while the injector housing ports are shifted, dramatically on the primary runners..[ATTACH][ATTACH]

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[jss06c6]

As point of reference, these are the original injector housings from this engine..

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[XfireZ51]

Steve,

One thing I did when I first ported the top end is to use a double fluted burr (I think that’s what its called) and then I finished things off by bolting everything together and using a 38mm ball hone to smooth out the transition.

[jss06c6]

Thanks Dominic.. I'm using three different burrs depending on where I am in the runner.

I need to know if this is sufficient removal of the primary injector boss.. hesitant to get deeper, but certainly still have room..

Yes, I touched the face with a burr! Very, very minor..

[ATTACH][ATTACH]

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[jss06c6]

Took a bit more off.. better transition now..

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[jss06c6]

Moving on to next primary..[ATTACH]

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[tiegsd]

Just had my original injectors replaced, 4 of them are no good. Happy to donate a couple to the cause.

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[Paul Workman]

Originally Posted by tiegsd

Just had my original injectors replaced, 4 of them are no good. Happy to donate a couple to the cause.

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The 90 injector housing is the only one that you can eliminate the primary injector boss entirely as the injector seal is @ the top of the injector. Maybe you realize that, IDK.

More later...

[XfireZ51]

Originally Posted by jss06c6

Thanks Dominic.. I'm using three different burrs depending on where I am in the runner.

I need to know if this is sufficient removal of the primary injector boss.. hesitant to get deeper, but certainly still have room..

Yes, I touched the face with a burr! Very, very minor..

[ATTACH][ATTACH]

Sent from my XT1585 using ZR-1 Net Registry mobile app

If u don’t punch thru, ur not trying. 🤣🤣🤣