Logo
FULL SITE MENU

1992 75hp Mercury vs 90hp?

P

pismo10

Contributing Member
I have a 1992 75hp 3 cyl Mercury outboard. I know the 90hp was based on the same block/basic setup.

Does anybody know exactly what the difference's are between these two models? What did they change to get the extra 15hp? Carbs?

I think they made a 115hp as well off this model.

Thanks very much
SL
 
Torque (ie: displacement) is what moves a boat, not raw horsepower, so if you increase the carb sizes you won't see much speed difference.

Your wallet will notice it, however.

Jeff
 
I disagree on the "improved" hole shot. Torque is what gets 'em out of the hole, and bigger carbs will not improve that.

Jeff
 
Just got a 1992 Mercury catalog. 75 and 90 were certainly the same base motor. Top rpm is 4750/5250 to 5000/5500 so not much there. 71.1 cuin, 3 cyl, 288lbs each. Well, if I find 3 carbs for 50 bucks some place maybe I will try it. It is on a 15' Whaler so doing well already. Steering is the weak link in my setup.
 
Hope I'm not going to look too stupid here, but my opinion is that if the carbs are the only difference between these motors, you will see some worth while gains. Yes you will spend more on fuel, but that's always still worth it if the fun increases for me. Power = torque x speed. So if the horsepower increases to 90 from 75, that's big. The speed on the crank is still similar, so the torque WILL increase. This means better hole shot by far with the current prop, or more speed with a larger prop and probably the same hole shot. Get the prop right to reach the right RPMs and use other methods if the hole shot is bad. Like drilling holes in the prop or getting a hydrofoil. Not sure if the latter works!

Please please, try it and put us out of our misery. We can only learn from experience, sell the stuff again (carbs and prop) if it's not worth it for you, boats and parts are timeless, someone will buy the parts!
 
Torque will increase about 22% which equal bigger prop equals speed and use less fuel. If you ran 45 mph at 5000rpm you should be able to run 45 mph at 4200-4500 with 90, less rpm =less fuel
 
General rule of thumb.

To get a 15% increase in top speed for a given hull you need to increase the horsepower by 50%.

75 to 90 horse is an increase of 15 horses which represent a 20% increase in horsepower which might translate into 6% more "top end".

So if you are getting 35 mph now you might see 37 mph.

Your hole shot and time to plane will NOT improve because your torque curve is exactly the same - you need more displacement to improve the torque.

You need 3 carbs to make the change. They are discontinued for that model but when they were available, they sold for $300 each.

The 90 was maybe the most prolific Merc of all time so you may be able to find them used without much trouble.

You would be looking for Walbro WME-19's or whatever superseded them.

I see carbs currently listed on Ebay for between 175-200 bucks each.

So you really got to ask yourself - HOW MUCH IS 2 MPH WORTH TO YOU??? upwards of 600 bucks?
 
Your hole shot and time to plane will NOT improve because your torque curve is exactly the same - you need more displacement to improve the torque.
Click to expand...
4 stroke yes 2 stroke no.....The torque is improved and raised as engine makes more hp. Anytime you increase airflow, hp will increase whether it be from larger carbs, reed block mod's, airbox mod's. The torque curve will increase with rpm as the larger carbs increased hp and torque. The 75 has 71.5 ft lbs of torque @5500rpm and the 90 will have 85.9 ft lbs which is a 20% increase. This will allow motor to go up 1prop pitch which will add right at about 5 mph to top speed not 2 mph. Take the 4 cyl 100/115/125 motor, same exact block, electronics only difference is carbs.
 
Also since you mess with small engines, the Merc 18/20/25 are the same engine just carb the changed and a 25hp will get out of hole quicker and be faster at WOT than the 18hp. Being the same displacement engine the large carb moved the hp and torque curve up.....
 
It is on a 15 whaler, old style. Might try it if I can find cheap carbs. Cruising below 3000 all day forever is the goal, not top end. It goes 45 with a 21" already which is fine. 22" or 23" would be great. The best benefit of Overpowered boats is cruising. All anyone ever thinks about is top end. Silly.
 
Not really. The 2 stroke has better low end torque to get the boat on plane, and a wider power band in general. To make the hp needed for outboards 4 stroke engines need to be high performance with long duration (wild) cams. (Think truck engines vs. race car engines.) If you have any experience with hot rods using high performance cams on the street, you know they tend to have lousy low end performance but go like stink at full song.

Jeff
 
Not sure if you ever swapped but I swapped the carbs on my 75 today with carbs off a junk 90 I bought(thrown rod) and it made a HUGE difference in my boat! I have a 17 ft Spectrum aluminum vee hull and it was running 23 mph at about 4500 rpms. After changing carbs, I now have to back out of the throttle a little to keep it under 6000 rpms and now runs 43 mph. Would take forever to get on plane before but now will jerk a knot in your neck starting off. I know my prop was an inch more pitch than I should have before but now I need to go up an inch in pitch instead of down.
 
A gain of 20 mph takes more than 15 HP.----I say there was an issue with the 75 HP carburetors that was limiting you to 23 MPH.
 
racerone said:
A gain of 20 mph takes more than 15 HP.----I say there was an issue with the 75 HP carburetors that was limiting you to 23 MPH.
Click to expand...

My carbs were fine but I think it had a lot to do with my prop being too big for the 75. With the 90 hp carbs, it gave it enough extra to get the prop spinning.
 
Howdy, How did you recognize the difference between 75hp and 90hp carburetors? Do 90hp carbies have different wme bodies (and numbers) or it it just the internals that are different? I can't get a fix on the part number differences.


Davidbolen said:
Not sure if you ever swapped but I swapped the carbs on my 75 today with carbs off a junk 90 I bought(thrown rod) and it made a HUGE difference in my boat! I have a 17 ft Spectrum aluminum vee hull and it was running 23 mph at about 4500 rpms. After changing carbs, I now have to back out of the throttle a little to keep it under 6000 rpms and now runs 43 mph. Would take forever to get on plane before but now will jerk a knot in your neck starting off. I know my prop was an inch more pitch than I should have before but now I need to go up an inch in pitch instead of down.
Click to expand...
 
I'm thinking those old 75 hp carbs were not working properly for you to see that much of a gain.

Jeff (AKA Mr. Cynic)
 
The WME numbers are different and so is venture bore and jets...Need as set of WME-19s as you have the small bore L3. When Merc in 1994 went to big bore L3 there are several sets of WME numbers but they wont work.
 
So is that WME 3301 9012C or WME 3301 - 90126 ? Or some other numbers? It seems to me you could get 75hp carbies and update the jets...as the bodies look identical. Very confusing... I really need the specific part number for 90hp to make sure.


faztbullet said:
The WME numbers are different and so is venture bore and jets...Need as set of WME-19s as you have the small bore L3. When Merc in 1994 went to big bore L3 there are several sets of WME numbers but they wont work.
Click to expand...
 
Norgen14 said:
??? 5yrs or 50yrs - same topic. If you don't have the information I need - then don't comment. Simples.
Next time dont be lazy start your own post. Why does the.person who started this post give a sh@t about your question. He has been gone for 5 yrs.
Click to expand...
 
Last edited:
flyingscott said:
Norgen14 said:
??? 5yrs or 50yrs - same topic. If you don't have the information I need - then don't comment. Simples.
Next time dont be lazy start your own post. Why does the.person who started this post give a sh@t about your question. He has been gone for 5 yrs.
Click to expand...

Lazy...ha.

Here's the rub... There is only one person on this WHOLE site who has revealed themselves as having done a carby swap as per my requested information. Now, if you had observed, that person doesn't reside within any other topic with this particular issue. And if you look at the DATE - it really wasn't that long ago.

I'm not sure you are adding or aiding the request by your pragmatic, and bombastic comments.

As for Hyjacking - well that's you showing a lack of respect for that particular word and the English language. I dare say that if you were ever actually 'Hyjacked' - then the flippant use of such a word would not enter your vocabulary...Hyjacking is a very traumatic experience, and a crime.

Now, if you have specific information (as per my request) or you know the person whom did the 'swap' in question, or know their contact details, then please pass that along.

Otherwise.... well you know!
Click to expand...
 
Back
Top