Yanmar 75hp to 100 hp upgrade

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boathead
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Yanmar 75hp to 100 hp upgrade

Post by boathead »

Just a quick question regarding 34 power plants, obviously the 75 hp is adequate but the 100 hp is a bit more desired. We are looking for a 34s and the models we are looking at have the 75hp. The 4JH4-TE engines share the same engine block. Has anyone looked at the bolt on differences to increase hp without a full engine transplant? I'm thinking the differences are likely size of turbo, heads, cooling etc. Has anyone dug into this regarding costs etc?

Cheers Carl & Joan (hope to be new owners in the near future)
2003 Hull 28 75 hp Belmar (soon to be renamed KARMA)
home port Queens Creek Mathews Va.(Chesapeake Bay)
AlanH
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Re: Yanmar 75hp to 100 hp upgrade

Post by AlanH »

Carl and Joan,

I have a 2006 with 75's. My thinking was a little like yours, that it was probably a doable upgrade. After checking I decided to leave well enough alone. If my memory serves me right it would require a turbo, an after cooler, fuel injectors, and maybe a camshaft. Seems like there were some other items as well. Dick Tuschick set up a two day Yanmar diesel maintenance course specific to our engines that I attended. I talked to the Yanmar guys teaching the course about modifying the 75's and they were pretty clear, forget it.

My recommendation is don't buy a boat with 75's if you want the 100's.

When it comes to performance with the 75's we are satisfied except when we travel with someone that has the 100's. Our boat with full fuel, water a rib with 10hp engine and our stuff cruises at 13-13.5 knots and 3400 RPM. By they way, I used to cruise at 3200 max and the Yanmar guys said you can cruise the 75's at 3400 all day long.

Good luck in your boat search.

Alan
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75hp engines
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Re: Yanmar 75hp to 100 hp upgrade

Post by duetto »

i agree with alan. we cruise our 75s at 3400 all the time. many days it's 10-12 hrs straight. we've done that for 13 years.
john & diane cummings
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boathead
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Re: Yanmar 75hp to 100 hp upgrade

Post by boathead »

Thanks to everyone , its great to get real world info. when you are in search of something new. Much appreciated. I have been digging around gathering my info, found a really in depth article on performance by Sno dog some years back. My guess is somebody perhaps in Aus or NZ has done some mods to increase HP as discussed. I'm sure the Yanmar folks would sooner sell new 100 hp engine packages that the knowledge and parts to upgrade a 75hp. Just sayin.
Thanks again all,
Carl
2003 Hull 28 75 hp Belmar (soon to be renamed KARMA)
home port Queens Creek Mathews Va.(Chesapeake Bay)
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Re: Yanmar 75hp to 100 hp upgrade

Post by duetto »

if you're truly thinking about modifying the 75s you might want to think about swapping for the newer 110s
john & diane cummings
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Re: Yanmar 75hp to 100 hp upgrade

Post by deising »

Gregg Burdick, former owner of Stuart Yachts in Stuart, FL, was heavily involved in repairing and modifying our PDQs for a number of years. I recall he often fantasized about removing the diesels, transmissions, shafts, props, and rudders, and adding appropriate structure to mount outboards - maybe 150HP each side.

Obviously, that would save a bit of weight, but change the trim noticeably. If you added the outboards at the stern steps, you have lost easy access to the water. If you move them inboard, you have lost the ability to use the current davit system for the dinghy. I am sure you could fabricate a pivoting davit system to swing the dink astern of the engines, if needed.

Another important factor is overall speed. How much will the boat take? Just interesting to think about.
Duane Ising
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2006 PDQ MV 34 - hull 91, 75HP, 3-blade
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Re: Yanmar 75hp to 100 hp upgrade

Post by dstrecker1 »

I don't think the 100s are available from Yanmar. Probably would need to go to the 110s which I heard are slower rev engine.

Dennis and Cindy Strecker
Hull 95 w/100s
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Re: Yanmar 75hp to 100 hp upgrade

Post by dstrecker1 »

I thought about the same thing, changing to 150 Hp outboards. Wouldn't do it until I would have to. Certainly would be easier to work on and replace, if needed, and would probably cruise at 20+ knots. It seems like once the boat starts to plain it doesn't take much more Hp to push it faster. Draw backs is gas versus diesel safety and mounting. If they were fixed mounted you could use the same rudder system for steering. I wounder if it would be possible to mount them thru the hull in the vicinity of the existing engines. Looking at the depth of the hull sides below the beds it might be possible with a seal to keep water from penetrating from wave action.

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Re: Yanmar 75hp to 100 hp upgrade

Post by deising »

Here are the specs for the 2 Yanmar choices at 110HP. There was no 100 listed anymore. Double-click the image to make it easy to read.

yanmar 110HP.jpg
Duane Ising
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2006 PDQ MV 34 - hull 91, 75HP, 3-blade
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Re: Yanmar 75hp to 100 hp upgrade

Post by deising »

Dennis, I am far from an expert on these matters, but placing an outboard where the existing diesel sits seems problematic. For one thing, how would you get it in there? Part of the "charm" of an outboard is the ability to pull it off the boat with a lift/crane and replace/repair it quickly, if needed.

I have seen outboards in "wells" before, but you usually need a really good reason to use a well. They create a lot of drag moving through the water and I can't see that working out well for a 20 knot, either.

As far as the rudders, I would opt for having the engines pivot as usual and removing the extra drag of the rudders. I think it would likely be a big deal to move to outboards, but it is interesting to think about the possibilities.
Duane Ising
m/v Diva Di
Punta Gorda, FL
2006 PDQ MV 34 - hull 91, 75HP, 3-blade
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