Yamaha HPDI gearcase mod..

allstock · **Joined:** August 30th, 2012, 11:21 am **Posts:** 325

wildcatt wrote:

I don't know about the HDPI cases, but the last few cones I've done, I've left the side intakes stock. One was a Yamaha, and the other an OMC. Both cases had no problem keeping water pressure when surfacing. I had the backup intake on the sides in case I ran into weeds etc.
My other plan was to just block off the side intake screens, then I could pull them off for draining etc. I never needed to do it though.

Just my 2 cents

My thoughts exactly Tom. My theory is at speed there will be enough volume coming threw the drilled bullet holes that it will have lots to feed the pump and any "extra" will exit out the stock inlets. I'll let ya know the verdict on Saturday but you have done it that way and it works so I have faith!

DoktorC · **Posted:** June 4th, 2014, 8:00 pm

This will be interesting. One difference is that the bobs feeds the cavity that the water pump draws from whereas the HPDI mod feeds directly to the back of the screens.

I'm surprised you had pressure Tom with the screens open but I guess if you're not crazy high any pressure at the screens would keep it from bleeding off more than the LWP generates.

allstock · **Joined:** August 30th, 2012, 11:21 am **Posts:** 325

Yes Doc it will be a hydraulic balancing act. We will see how it works with two holes and the screens half shut. Perhaps Jordon was overheating at idle because the two holes were too restrictive at idle but fine at speed. What size did you drill the holes?

allstock · **Joined:** August 30th, 2012, 11:21 am **Posts:** 325

allstock wrote:

Yes Doc it will be a hydraulic balancing act. We will see how it works with two holes and the screens half shut. Perhaps Jordon was overheating at idle because the two holes were too restrictive at idle but fine at speed. What size did you drill the holes?

Sorry I meant the holes in yours, I was little unclear ^.

DoktorC · **Posted:** June 4th, 2014, 10:50 pm

Mine were 1/4 I believe...I matched my bobs lol.

allstock · **Joined:** August 30th, 2012, 11:21 am **Posts:** 325

DoktorC wrote:

Mine were 1/4 I believe...I matched my bobs lol.

Ya I was thinking 1/4" as well, will be an interesting experiment in any event!

wildcatt · **Joined:** April 29th, 2012, 7:26 pm **Posts:** 503

allstock wrote:

Yes Doc it will be a hydraulic balancing act. We will see how it works with two holes and the screens half shut. Perhaps Jordon was overheating at idle because the two holes were too restrictive at idle but fine at speed. What size did you drill the holes?

I know the OMC pumps are like sewage pumps, but I'm still getting over 40 psi at speed, with the shaft 1" below the pad. Can't say for sure how much pressure, 'cause the needle is so far past the pin, it reads 15, on the other side. LOL Temp is solid on both temp gauges at just under 140 F.

The yammie was not quite so high, and I had one of those damn metric gauges. But I was pretty consistently at 1.2 kilo something or other. Which I think equates to about 15 psi.
It was the same with or without the LWP.

beavertonae-21 · **Posted:** June 5th, 2014, 2:57 pm

40 psi on an omc???? wow thats the highest I have ever seen Tom. My old 225 would be just over 20lbs that wa about it, I always assumed it was the massive volume that cooled it as it never ran hot.

Steve

DoktorC · **Posted:** June 5th, 2014, 8:24 pm

wildcatt wrote:

allstock wrote:

Yes Doc it will be a hydraulic balancing act. We will see how it works with two holes and the screens half shut. Perhaps Jordon was overheating at idle because the two holes were too restrictive at idle but fine at speed. What size did you drill the holes?

I know the OMC pumps are like sewage pumps, but I'm still getting over 40 psi at speed, with the shaft 1" below the pad. Can't say for sure how much pressure, 'cause the needle is so far past the pin, it reads 15, on the other side. LOL Temp is solid on both temp gauges at just under 140 F.

The yammie was not quite so high, and I had one of those damn metric gauges. But I was pretty consistently at 1.2 kilo something or other. Which I think equates to about 15 psi.
It was the same with or without the LWP.

1" below is why it works. The side inlets are still in the lake lol...or close enough to be fed.

allstock · **Joined:** August 30th, 2012, 11:21 am **Posts:** 325

Alright now that I'm there I'm going to do the four holes, it's on the bench with the tools out so why eff around. I'm going to leave the half-shut screens the way they are and try it. I can pull them off and epoxy them shut easily if need be.

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Yamaha HPDI gearcase mod..

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