does anyone know of a web site that will list the reccomended WOT for Mariner motors?

Or, if you happen to have the same motor could you share?

I tried calling a few local dealers and one actually wouldnt tell me, unless i bought his prop. then he hung up when i asked again, nicely i might add.

Specifically I'm looking for info on an 86 Mariner, 4cyl, 2-stroke, 75hp.

thanks

From what I can find, it looks like the rpm range is 5000 to 5500 rpms.

Take a look at this link, not exactly definitive proof but it's a start.

http://groups.google.com/group/rec.boats/browse_thread/thread/94feeba96367f5cb/27a635617c5e7fc1?lnk=st&q=mercury+75+hp+rpm+range&rnum=1&hl=en#27a635617c5e7fc1

I've done two prop changes this year, one just recently on a Mercury 45hp and another on a Johnson 15hp, both with excellent results. The calculator I linked to below was a big help.

http://www.rbbi.com/folders/prop/propcalc.htm

Also, here is Michigan wheels propeller application chart. It lists both original equipment part numbers and their numbers. Once I figured out what pitch prop I needed I was able to go to Michigans listings and find the part number I needed. Then I went on to Ebay and found a used prop in good condition for next to nothing.

http://www.miwheel.com/MIWheel/pdf/obsd_03.pdf

Let me know if you need any help.

No such thing as an WOT RPM calculator, way too many variables go into what determines the Max recommended rpm of a motor.  Bore, stroke and porting are main determing factors but other variables do apply.

Based on the bore and stroke, total  CC displacement, the engineers determine what type application they intend for that motor and port it to most meet that application.   If they want it to have maximum bottom end and mid range power, they port is so the peak power band is low in the rpm range.  If they want it so it will have max horse power in a safe rpm range, they port it so the peak power band is up higher in the rpm range.   That's why you can see two motors from the same manufactor and looking at the spec sheet, they look identical in bore, stroke, and cc's but one's rated for 100 hp and 6,000 rpm and  the other rated for 75 hp and 5,500 rpm.  Look at the 2.5 merc, same bore and stroke but they vari in hp from 150 - 300+ and rpm range from 5,500 - 8,000.

Almost any two stroke motor can turn over well over 6,000 rpm and not bother it but if it's not ported to turn that many rpm you are so far over the peak power band you are just burning more fuel and running slower than if proped to run in it's designed rpm range.

For those that know car motors, changing port heights, sizes, angles etc is just like changing the cam in your car motor.    The bigger the cam, the more hp and top end power but you have to use more rpm and ride the clutch to get it moving.  Low lift cams get you moving real quick but quit pulling when you try to turn them any rpm.

Way2Slow

I don't believe he's asking how high he can spin that outboard. What he's asking is the recommended wot rpm range, which looks to be 5000 to 5500rpms.

Car engines is what I know. I won't disagree with you about the port size, height, shape, valve sizes and their affect on power. But, the lift of a camshaft has little to do with where an engine makes it's power. The cam duration is what determines how high or low in the rpm range it makes power, like the port timing on a 2 cycle engine.

For example, you could have two cams with identical duration. One has .500 lift and the other with .750 lift, the cam with more lift will have nearly the same powerband but will make more power across the board than the lower lift cam.

sorry, my question really wasnt worded right. i was looking for some type of documention on the wot range for my particular motor. i wanted to say 4750-5250 but needed to make sure. i can turn 54-5500 right now wot but thought it was a bit high.

i thumped my prop this weekend so now is the perfect time to replace the prop and make sure i get the correct size. right now i have a 17 pitch.

thanks to the both of you. i'll continue to call around and make sure i get the correct figure.

60 Big Foot -  2.3 5000-5500

60 Big Foot -  2.3 5500-6000

75 4-Stroke -  2.3 5000-6000

75 Classic -  2.3 4750-5250

90 4-Stroke -  2.3 5000-6000

this what i found on line.  i need to confirm mine is the classic listed.  mine is a 2 stroke.

Jb

the 75hp classic you listed is a different animal than yours. The classic is much newer and a 3 cylinder!!

Why not plug into the Mercury/Mariner's web site and ask them your question?

maybe i missed it but i couldnt find that info.  just a list of local dealers and info on more current motors

jb,

I plugged Mercury Marine into Yahoo. Then picked the site re outboards. There is a, "Contact Us" in the upper right with  phone numbers, email and fax info.