Real answers about converting f75-f90 please?

[Sfcahrusaret]

Iv read numerous sort of kind of aswers about restrictor plate removal to increase f75-f90. Is it true?

[boscoe99]

It may be an internet truism. As in, anything published on the internet becomes true by the very nature of it being posted. Thousands become believers and rush to pass thst truth along to their fellow internetites.

In the real world the answer is no.

[madharchod]

mate i have done it so the answer is true ,iam sorry broscoe ,the real life situation is it has been done and proven ,its not only i have done F75 to F90 band also F80 to F100 detl models as they both the same engine except f75 and F80 come with air restrictor plates which when removed will give you extra 400to 550rpm extra ,and once the battery terminal is removed and replaced the ECU automatically adjust the new air to fuel mixture
cheers

[almetelo]

Hi!

I have already leaved my opinion in previous posts about this subject and in this particular case of just remove the air flow restrictor to increase 75hp to 90hp my opinion is NO! You may have a little gain but not that much.

I did this on my cousin F50 and the results were just more 100rpm and around 1kts, for sure did not become on a F60 like many people say.

Try it and let us know the results...

Good luck

[rodbolt17]

mate
I gotta disagree.
the ECU does not and cannot measure airflow.
Yamaha uses speed density not mass airflow.
the ECU will not and cannot and has NO reset function.
the only way to gain 25 HP is by burning about 2.5gallons of gas per hour more at its rated HP.
to increase the injector on time that much would require an ECU remap.

but its on the internet and everyone knows if its not true you cant post it on the internet.

[robert graham]

Just curious, but how would one prove/establish any increase in HP except with some type of dynamometer?....

[ausnoelm]

To Prove it as being 100% true, a dyno is the only way, under con*****ed conditions, lots of things have been done to outboards over the years to make a certain model into a greater HP by just replacing jets, removing restrictors, bending timing linkages and all sorts of weird and wonderful things, some might increase performance a bit, but most of the extra HP is in the mind of the owner.

[boscoe99]

To Prove it as being 100% true, a dyno is the only way, under con*****ed conditions, lots of things have been done to outboards over the years to make a certain model into a greater HP by just replacing jets, removing restrictors, bending timing linkages and all sorts of weird and wonderful things, some might increase performance a bit, but most of the extra HP is in the mind of the owner.

And the mind is made up. Don't go confusing it with facts or the truth.

I can feel that extra power in the seat of my pants. Right before the motor done blowed up because of the overly lean air/fuel mixture and maybe too much timing.

[bajakeith]

adding HP

As always Sir ROLDBOLT is correct !! but you don't want to confuse him with the FACTS !! next he will be telling us hp gains of even more with running AV gas... LOL,,LOL

[muskydope]

It really depends on the year and model your motor is..... I have a 2003 F75 that runs a little "hotter" than your fathers F75.... 5+ mph to be exact. Meaning on my boat (a deep V 17' Crestliner) I went from 32 - 33 best mph (gps) to 37 - 39 mph with the same load ( 2 fat guys + gear). Alone I can hit 41+..... with my speed prop. More info about your motor and boat would help.... if its a fuel injected motor... your probably looking at remapping or replacing your ECU, if carbed as is mine... pullout your wallet and order some F90 carbs.... install them... balance them.... and find the right prop.

[rodbolt17]

don't bust my chops .

however the 1 gallon per hour per 10 HP runs pretty much acrossed the board.

at its rated HP and load gasoline fueled engines tend to burn 1 gallon per hour per 10 HP.
means that pair of F350 V8 yamahas will smoke 68.5 GPH at 5900 RPM.
just ran it yesterday.
that F75 will smoke about 7 GPH at 5900 RPM.
that F90 will smoke about 9GPH at 5900 RPM.

on to the AV gas.
would make a Yamaha F90 about an F60 at 5900 RPM if it actually could spin that fast on AV gas.

the higher the octane the slower the fuel burns.

with no other mechanical changes AV gas runs slower and dirtier that 87 octane.

but its on the internet and nothing not true can be posted on the internet.

what I would like is the part number to this mythical air restrictor.

[bajakeith]

HP

To be clear,,I was referring to mad orchard about AV gas and hp gains...LOL,, most folks out there do not study about the gas we put into are motors...strange,, when I was younger the gas in Baja mex had to be filterd and was low octane...Today its much better than the gas in calif.. sad state of affairs !!

[rodbolt17]

with most EFI motors in the same engine family the HP difference is typically simply the ECU mapping.
occasionally on the 4 stokes there will also be a camshaft change.

on carbureted engines we can do everything from mechanically stopping the throttle shutters as the old Nissan/tohatsu 115/140 to adding exhaust restrictors to changing intake and ex port timing.
some of the 2 stroke Yamaha 9.9 to 15 simply required a reed box change.

but with most EFI Yamaha 4 strokes the difference will be in the ECU mapping.
from a manufacturing standpoint its the simplest cheapest way to fly.

chatting with a merc tech buddy he told me the only difference from the 200 verado to the 300 verado was the 6000 dollar ECM.

[bajakeith]

HP changes

my main boat is a 18.5 Livingston...a 1400 lb caterman with twin 2004 merc 75's 2 strokers (rocket) exact motor as the 90 hp but with smaller ports and carbs...sooo....almost bullet proof...catching AIR for a smooth offshore ride !!

[madharchod]

hey guys retirement is fun and so is changing motors from different hp to higher ones was once my specialty as i was in Mexico for long when most of the US market motors were made then i moved to Japan and then to China so i basically
lived and breathed the parts that went in this motors and i checked all these motors as they were basically all the same except few parts that were added and some were removed to make different hp ,it was a trade secret so i couldn't reveal as i was under contract with these companies i worked for ,but then when ever i flew to the islands in the pacific i would try changing these motors by removing the parts and it worked and since the inception of the 4 stroke me being a veteran in 2 stroke technology i had to put in some hard yaka to learn so i spe******ed in yamaha F100 detl model which is basically the same motor as the F80 so i couldnt stop the urge to change this motor to a highe hp i finally tried removing the air restrictor plate from F80 and gained some about 400to500rpm extra as i ran 19 pitch prop ,the overall rpm i acheieved at WOT was 5800rpm but the speed was increased by about 10 to 15mph and the fuel savings increased ,i wouldnt recommend a novice to try this as you will end up damaging the motor ,this motor i switched from F80 to F100 to date has clocked 4800hrs with no fault
A note to all out there dont try this if you are not an expert as it will end up being a costly mistake which you will regret.