F75 to F90.... a new angle

[skidooguymxz]

I removed the plug from the intake this a picture off of google but it is near identical. It necks down the joint between the throttle body and air from 2" to 1.25" removal and installation is a 5 minute job.

I went for a test run and achieved 37mph at 5250 rpms. after ten minutes of blasting around I stopped and reinstalled the plug back down to 5000 rpms and 34 mph. I also had a passenger aboard where as my previous top speed of 35 was set by myself.

now onto the next part of the equation, tricking the ecu. From what I can figure this is the IAT/MAP?BAP? sensor. 68F-83688-00-00 four wires run into it. Could anybody confirm if this part actually reads Air intake temperature?

[rodbolt17]

are the ECU part numbers the same?
are the injectors the same?

if you add more air you also need to use the correct injectors and injector on times.

[boscoe99]

68F-83688-00-00 is a combination air pressure (MAP) and intake air temperature sensor.

[boscoe99]

are the ECU part numbers the same?
are the injectors the same?

if you add more air you also need to use the correct injectors and injector on times.

With respect to the ECU, of course not.

Injectors are the same.

Free horse power will be found when the fountain of youth is found. I am in more need of youth than I am HP.

[skidooguymxz]

are the ECU part numbers the same?
are the injectors the same?

if you add more air you also need to use the correct injectors and injector on times.

injectors are the same, ecu's are not. I do not know if ignition timing is the same or if the pulse timing of the injectors are the same. I'm on the lookout for a used 90 ecu but I would really like to do it without, either using a purchased or assembled fuel tuner.

I'll be happy with my extra 250rpms and 2 mph if I can make the plugs look nice and brown. hell going down to a 15 or a 3 blade 17 would put me close to 40 with the little extra power. I don't care If it's not truly a 90

[skidooguymxz]

With respect to the ECU, of course not.

Injectors are the same.

Free horse power will be found when the fountain of youth is found. I am in more need of youth than I am HP.

luckily I NEED neither. I'm curious what you mean by free horsepower not existing. Can the same block, Rotating assemblies, and fuel controls not make a wide range of power depending on how it's tuned? Do fast pwc's not have multiple settings of power? do they change physical equipment to neuter the power when you slip the beginner key in or is it the same motor running on a different tune?

Don't worry, I didn't vote for obama and think you can get something for nothing but one motor making a wide range of power is not a fountain of youth.

[rodbolt17]

goes back tpo some basic laws that have affected articulkated rod normally aspirated internal combustion motors since before the wright brothers.

if you add air you MUST add fuel
if you add fuel you MUST add air.

the ECU is programmed to do just that based on engine throttle angle and load.
throttle angle is a function of the TPS.
load is a function of intake air pressure vs baro pressure.
density of the air is a function of the IAT.

if the engineers that mapped the F75 used a restrictor to limit air at WOT and used the same throttle bore if said restrictor is removed the ECU does not know it has way more air than fuel now.
now if the F75 and the F90 use the same rail pressure and the same injectors the F75 running with the restrictor removed now runs lean at WOT.
\lean is never good.
the F90 ECU will have a longer on time than the F75.
google speed density open loop EFI systems.
they all work the same.

[Steveflynn]

- heres the truth

I turned an F75 into an F90. Simply remove the intake restrictor - a small aluminum restrictor in the intake near the throttle body. Then buy the 90hp ECU off an EFI motor ( $250 on ebay ) . Sold my F75 ecu for $100

I had a 15 pitch prop running at 32 mph as an F75
then as an F90 I turn a 19 pitch prop running 40mph

still gets a great hole shot - I know I could go to 20 or 21 pitch.

Simple way to add 15hp - cost me $150

I use a lot less fuel now

My motor is a 2005 75hp 4 stroke EFI.

[Steveflynn]

be careful

the ECU on an F75 and F90 are different. You could burn down a motor. Spend the money and buy the ECU from an F90.

I pulled the restrictor and put in the new ECU from an F90 - now I get 8 mph faster and it has been running perfectly for a month without any problems.

I also had to go up from a 15 pitch to a 19 pitch because a 15 and a 17 would over - rev the motor.

[boscoe99]

I turned an F75 into an F90. Simply remove the intake restrictor - a small aluminum restrictor in the intake near the throttle body. Then buy the 90hp ECU off an EFI motor ( $250 on ebay ) . Sold my F75 ecu for $100

I had a 15 pitch prop running at 32 mph as an F75
then as an F90 I turn a 19 pitch prop running 40mph

still gets a great hole shot - I know I could go to 20 or 21 pitch.

Simple way to add 15hp - cost me $150

I use a lot less fuel now

My motor is a 2005 75hp 4 stroke EFI.

That'd be the key.

That I don't understand.

[99yam40]

yep, how do you get more HP without burning more fuel.

now you can put more HP on a boat, and never run it up to the rated HP, but you could do that with the lower HP motor also