Yamaha Jet Drive Lower Unit similarity

[ZeeCapitan]

Is the Yamaha Jet Drive Lower Unit with a short shaft assembly the same for all Yamaha short shaft motors?
I did a stare and compare on the Yamaha website and the impeller assembly and housing are the same.
Zee

Ref: Yamaha Jetdrive 90 and 40

[150aintenuff]

different pumps.. the 90 hp model uses a 7.25" impeller the 40 uses a 6.625 inch impeller.. the 40 hp is a true short shaft that bolts on a 22.5" transom height.. the 90 is a 27.5" transom motor.. long shaft prop mid.. the "look" of all OB jet pumps are identical just sized according to impeller diameter and water flow requirements to hold the motor to the RPM..

ALL jet drive units for outboards REGARDLESS of manufacture are built by Specialty manufacturing out of SanLeandro CA.. so if XYZ HP is present it doesnt matter what manufacture of motor you use the boat will run identical..

what are you looking to put a jet on... I recommend to MAX your HP cert plate rated power... IE if your boat is rated for 80 hp... use a 115/80 jet for your motor choice... shallow water is not a place to sit and dig a hole gettin on plane and a underpowered jet propelled hull will do just that.. dig a big hole..


here is a break down of prop to jet hp conversion...
prop hp/jet hp
250/175
225/150
200/140
150/105
115/80
90/65
75/50
60/40
50/35
40/30
25/20

good luck and if you need any more info i have alot jet drives are VERY popular in my area... i probably fix 20+ per year.. also if you get a jet and dont go in shallow water all the time spend the extra $$$ and buy a standard prop drive in the shaft length 5 " shorter than what your height of transom is so you can mount your jet pump and be set up height wise, and then when in deaper water use a 5" bay kit and the prop to gain the lost HP and fuel economy in deaper water.. that way you get the best of both worlds.. effeciency of the prop in dealer wter and the shallow draft of the jet in the ripples

[ZeeCapitan]

Thanks for the reply 150aintenuff. The info you provided answers alot of questions that I was having.
It would appear that the parts manuals on the Yamaha website are being shared amongst many models.
So if the housings are the same then do you change out the impeller for the different horse powers? For example if I have a stock 40hp and change out the carbs to make it a 50hp, would I just change the impeller? or if I had a 40 hp motor and sold it could I use a 60hp motor with the jet drive if I changed the impeller? If this is the case what are the different size of impellers that are available? Your chart is great!! Could you indicate what the size of impellers are used for the appropriate Jet Drive horsepower, if that is available? Would be goooood information.
I would be interested in what jet drives you have available or can get your hands on. Please let me know. You can pm me with your contact info. Thanks.
Zee

PS Can you put a jet drive on a Yamaha 70CES?
Now that would give the boat a little zoooom down the creek




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[150aintenuff]

there are several variations of the mounting flange on the same basic housing so in reality there is a different pump housing for each different midsection.. as long as your midsection mounting patern and adapter plate for the pump match up you can swap the jet unit on to another engine of higher or lower hp... the switch in impeller diameter is between the 50 and 60 prop hp motors.. 60 prop horse power and up use the larger impeller diameter and adjust impeller pitch to hold RPM to recommeded rpm.. to adjust rpm if you swap power heads all you do is order next size up.. but personally i would rather have a slightly smaller impeller as most setups from OBJ only rev to about 5200 or so and most of the new motors like to run to around 6K..

and inreallity the difference between 40 and 70 hp going into a jet is really not that much.. maybe not more than 5 to 10 mph..

and yes you can pump ANY outboard above 25 hp.. and no more than 250 hp... they tried 300's but couldnt hold down the RPM below the rev limiter regardless of the impeller pitch..

regarding 40 to 50 hp carb swap you do nothing to the pump or impeller its the same the added hp gives you another 3-400 RPM

[150aintenuff]

look here.... www.outboardjets.com

heres the yamaha page

http://www.outboardjets.com/Yamaha.htm

[ZeeCapitan]

Sounds good, thanks for the lesson and all the info.
Where would I purchase used. Are there any lower units that come up For Sale or is it better to buy new from OBJ?
Thanks again,
Zee

[ZeeCapitan]

The next step to more push, I guess, is to get away from the outboard and go inboard, and to use turbines?
www.americanturbine.com have some rich gear that would push the boat along just a little faster.

Zee

[150aintenuff]

Sounds good, thanks for the lesson and all the info.
Where would I purchase used. Are there any lower units that come up For Sale or is it better to buy new from OBJ?
Thanks again,
Zee

used take off units are available and are basically priced along the lines of a same year lower unit so expect to spend around 600- or more for 1..new from OBJ isnt cheap.. and to buy them you have to be a dealer or have an in with one... i have an in but the break is only 10%.. not worth it .. plus they sell new for around 2500 atleast in my area any how.. how big of boat are you talking.... 16 or 18' with 60" bottom a 115/80 will push near high 40's and may touch 50 a fast OB jet runs at around 55 even going to say a 250 opti sportjet will give you more speed than a ob of same HP.. an inboard is really only choice if you want to run big ### speed.

[rockdamage]

a jet pump will easily handle A 300XS