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Author Topic:   Prop Question - 1985 Montauk w/ 90 hp 2003 Yamaha 4s
mnwhaler posted 09-08-2002 11:03 PM ET (US)   Profile for mnwhaler   Send Email to mnwhaler  
Just repowered my 1985 Montauk with a 90 hp 2003 Yamaha 4 stroke.

Dealer was able to connect my original tach to the new motor and recommended I start with a 13.25" x 17" standard aluminum Yamaha prop. WOT got me 6300 rpms.

Returned 13.25" x 17" for 13" x 19" standard aluminum Yamaha prop. WOT now is at 6100 rpms.

I am thinking I need to move up to a 13" x 21" standard aluminum or stainless. Looks like "newt" had success with a high end stainless for his 2s Merc 90. Any suggestions for me, I think the same logic would hold true for my 4s Yamaha 90.

newt posted 09-09-2002 08:07 AM ET (US)     Profile for newt  Send Email to newt     

Actually, I put on a Merc aluminum prop - definitely not high end, just a better match than the other one. It's 12.75 x 21 pitch. It cost $150.

I think the motor could swing a bigger prop, since WOT will climb above 5500 rpms. I may experiment next year, but for now I am quite happy with the setup. Top speed so far is 44 mph, and I literally jump up and out of the hole.

I am not sure how relevant this is to your motor, as the gear ratios may be different. Good luck!

mnwhaler posted 09-09-2002 10:16 AM ET (US)     Profile for mnwhaler  Send Email to mnwhaler     

Gear ratio is 2.31:1.

Bigshot posted 09-09-2002 11:27 AM ET (US)     Profile for Bigshot  Send Email to Bigshot     
Ratios screw up the whole thing. You can not compare the Merc to the Yamaha unless ratios are alike and both 4s. Try the 21. You want the rpms to be under 6k(redline right) and even 55-5700 would be fine at WOT.
ratherwhalering posted 09-09-2002 08:16 PM ET (US)     Profile for ratherwhalering  Send Email to ratherwhalering     
Are you sure that old tach is working properly with the new motor? That RPM reading sounds a little high. Nice engine btw.
lhg posted 09-09-2002 08:54 PM ET (US)     Profile for lhg    
If you want the ultimate in performance for your rig, get one of the Mercury 20" pitch vented Laser II or High Five performance props. The vents (which are adjustable & closeable with plug sets) will allow the 4-stroke quicker acceleration, and these props hold like crazy, allowing 1 1/2" high mounting height, and great bow lift resulting in a MUCH smoother ride. I run them on both of my Whalers.

If top speed is your interest, you want the Laser II. If ultra smooth pulling power, as in water skiing, is your interest, get the High Five. These come with a Yamaha hub option (at no additional coast), and bought right will cost you about $380 (I can refer you if necessary). Worth every penny of it, and you'll be thanking me for a long time. One of these props will give you about 45-47 MPH if you're set up correctly. They should not be run completely submerged (engine all the way down on the transom), since that increases the effective pitch by 2", and they don't make it an 18" pitch.

Forget an aluminum prop. They are worthless for any rig that will do over 30mph, except as a spare.

You could also use the Mercury Prop selector for the 2-stroke 90, which has the almost identical gear ratio of 2.33 (yours is 2.31), and is similar in power.

Your Yamaha dealer may advise against a Mercury prop, since that means no sale for him, but don't listen to him. Keep the Yamaha aluminum prop as a spare. In outboard and stern drive props, Mercury rules the water with the most advanced prop technology and research and testing. They have a huge selection of designs and really know their stuff.

Bigshot posted 09-10-2002 09:58 AM ET (US)     Profile for Bigshot  Send Email to Bigshot     
True...I also thought merc and Yammie were interchangeable. Are they or is it like OMC and Zuki where different back shim is needed.
mnwhaler posted 09-10-2002 04:26 PM ET (US)     Profile for mnwhaler  Send Email to mnwhaler     

Guys, thanks for all of the advice. After lengthy discussion and thought decided to try a Yamaha Stainless SST 13" x 19".

WOT put me at 5800 rpms. This prop seemed to do the trick.

Cost on new SST was a little high, but am looking forward to comparing speed/performance of Laser II vs. SST next spring.

Thanks again, greatly appreciated.

Bigshot posted 09-10-2002 04:36 PM ET (US)     Profile for Bigshot  Send Email to Bigshot     
lhg posted 09-10-2002 07:37 PM ET (US)     Profile for lhg    
Nick - Mercury's line of props are now designed without a hub, so any propeller can be used on ANY brand engine simply by purchasing (also from Mercury) the engine specific hub assembly which slides into the prop splines. A very clever idea to make their props universally useable. When you buy a new Mercury prop, you now have to specify engine brand so that the right hub is included in the box.

So if one has a Mercury engine, and switches to an Evinrude, just by purchasing the hub for Evinrude, the prop can be used. I have noticed recently that Michigan wheel has now adapted this system also, propably under license from Mercury. It's a great system for re-selling a prop, since only a $50 hub has to be purchased for a different engine brand.

So now you can get a Mercury prop for your Suzuki and really make it run! Take a look at the 4 bladed Trophy models if you need something less than 20" in pitch.

Bigshot posted 09-11-2002 11:39 AM ET (US)     Profile for Bigshot  Send Email to Bigshot     
My Merc inline rpop fit my 90 Yamaha like a glove.

I bought a SS OMC prop on e-bay last fall and it was changed to fit a merc. I had it rehubed at general prop for $40.

With OMC and Zuki they are interchangeable except that you have to slightly shim either the back washer or front nut depending on which way you swap.

I find all OEM props work very well. Merc definately has the most invested in racing props, etc. I will not buy aftermarket like Ballistic, etc. Those props are garbage compared to OEM. I also can not get good results. If you have a 17" OEM SS and you are running 5800. You pretty much know a 19" will bring you down about 400 rpms. Throw a Ballistic or Michigan, etc on there and I have seen some crazy stuff like really bad holeshots, slipping or rpm staying the same, etc.

Moral.....stay with an OEM prop. They cost more but are quality. Does not mean only keep a Yamaha on a yamaha but run a factory prop.

tomol posted 09-11-2002 01:34 PM ET (US)     Profile for tomol  Send Email to tomol     
Are you sure that Yammi is 90 hp? I thought the 4-stroke4 came at 80, 100 and 115.

For the record, I made the switch from the 100 on my Montauk and initially went from 13 x 17.75 to 13 x 19 and was underpropped. It would go over red line, if I let it, when I had a light load.

I replaced it with a 13 x 21. It's great. I posted the comparitive numbers on the 4-stroke vs. 2-stroke dead horse -- I mean thread. However, in the above mentioned light load situation. WOT gets just under 40 knots at 5500 rpm.


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