New tohatsu EFI 9.9/15/20 - conversion 9.9 to 20?

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Mcboatface

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Hello all,

I’m looking to get a new 4 stroke for my ole’ 12 ft aluminum vee (Lowe 1256, about 120lb, rated for ten hp). I’d like to get the tohatsu efi tiller manual start, and this series is all the same weight and size up to 20hp. Upgrading to the 20 isn’t terribly much more $ than the 9.9 as they are mostly the exact same motor. Long term I expect to keep this motor a LONG time, and future plans would probably have me put the motor on a small whaler, rib, or Carolina skiff rated up to 20.

I’m tempted to get the 20 now and drive carefully, maybe even adjust the throttle cable so it won’t get WOT. Still seems a little sketchy though.

So, my question is, if I get the 9.9 now what will it take to convert it to a 15 or 20 in a year or two?
 

Scott Danforth

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Hello all,

So, my question is, if I get the 9.9 now what will it take to convert it to a 15 or 20 in a year or two?

welcome aboard

sell the 9.9 and buy a 15 or 20. will be cheaper than trying to buy all the parts

or buy a 15 or 20 now and buy stickers
 

Mcboatface

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I've found parts diagrams online up to 2017 efi’s (not sure that’s a valid comparison as I thought the efi’s came out in 2018) , and at least the ecu is different between the 9.9 and 15, but they don’t have a price on it. I do wonder what other parts might be different. If the parts total is under 500 bucks it’s probably worth it to me to get the 9.9 now, and convert later (as the price difference from new 9.9 to new 20 is about that much anyway.
 
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Scott Danforth

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call a dealer and ask them how much an ECU would be... BTW, you need a serial number

$500 will be cheaper
 

raczekp1

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uppgrade 9.9 to 15 is just take out a restrictor located at the carb inlet
to 20 hp needs to be changed ECU and camshaft
 

Sea Rider

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uppgrade 9.9 to 15 is just take out a restrictor located at the carb inlet
to 20 hp needs to be changed ECU and camshaft

Don't think that Tohatsu will make a 15 HP-OB in which by getting rid of the internal carb air restriction can pass it directly to a 15 HP for peanuts cost. All 3 OB's 9.9-15 and 20 HP being 333 CC should be powered by different ECU's. A matter to check all 3 ECU's part numbers. Tohatsu Guru and Paul will surely have a proper tech answer for that.

Happy Boating
 

pvanv

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uppgrade 9.9 to 15 is just take out a restrictor located at the carb inlet
to 20 hp needs to be changed ECU and camshaft

NO.

Each ECU is different. The 9.9 restrictor and the 15 restrictor are also unique to each other. The cams are already identical. You must match the restrictor and the ECU for it to work properly. If you just pull out the restrictor, you will run way too lean.
 
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pvanv

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Hello all,

I’m looking to get a new 4 stroke for my ole’ 12 ft aluminum vee (Lowe 1256, about 120lb, rated for ten hp). I’d like to get the tohatsu efi tiller manual start, and this series is all the same weight and size up to 20hp. Upgrading to the 20 isn’t terribly much more $ than the 9.9 as they are mostly the exact same motor. Long term I expect to keep this motor a LONG time, and future plans would probably have me put the motor on a small whaler, rib, or Carolina skiff rated up to 20.

I’m tempted to get the 20 now and drive carefully, maybe even adjust the throttle cable so it won’t get WOT. Still seems a little sketchy though.

So, my question is, if I get the 9.9 now what will it take to convert it to a 15 or 20 in a year or two?

To convert the MFS9.9E to a 15 or a 20 requires changing both the air restrictor at the throttle body and changing the ECU. If you just pull the restrictor, you will be way too lean. Each ECU has the correct spark advance curves to produce the appropriate power. The ECU costs $900, so the only way it would be cost effective would be to re-sell the old one, and since they almost never fail, there really isn't a market for a used one.
 
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pvanv

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Don't think that Tohatsu will make a 15 HP-OB in which by getting rid of the internal carb air restriction can pass it directly to a 15 HP for peanuts cost. All 3 OB's 9.9-15 and 20 HP being 333 CC should be powered by different ECU's. A matter to check all 3 ECU's part numbers. Tohatsu Guru and Paul will surely have a proper tech answer for that.

Happy Boating

100% correct. Need to match the restrictor with the ECU.

Since the cost of the ECU is more than the difference in cost between motors, it is cheaper to just buy the size you want. If 20 is too much for your current boat, and you expect to upgrade boats (won't your current boat still need a motor?), then you could just buy the 20, and don't run it WOT on the smaller boat.
 

Mcboatface

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Interesting info, thanks, that answers my question.

I wonder if an aftermarket will develop to tune/reflash the ECU eventually, or if there isn’t a market for that. For example, it’s now supposedly cheaper to buy the detuned 60 hp sea doo spark jet ski, and get an aftermarket re-flash, than to buy the 90 hp right out of the box.
 

Scott Danforth

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there is no market for re-tuning/re-flashing outboards like there are cars. there are literally about a hundred people that would want to buy it, so the cost would be 10,000 where on cars, there are literally 100,000 people who want to buy something like that so the cost is in the few hundred dolars.
 

Sea Rider

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For an ECU upgrade will need to find a skilled software engineer to spot the parts difference needed between all 3 ECU'S if happens that the electrical harness remains same on all 3, but that won't happen any time soon. LOL!!

appy Boating
 

pvanv

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The 3RU (9.9), 3RT (15), and 3RS (20) are NOT the same ECUs. Duh.
If you remove the restrictor on the 9.9, it will run horribly lean.

The 15 also uses a (different) restrictor (3RT035360M) from the 9.9.
To convert from 9.9 to 15, you change restrictors, and change ECUs.
To convert to 20, you remove any restrictor, and change the ECU ($900 in parts plus labor).
 
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jimmbo

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Come on people, everybody knows you can DOUBLE an engine power by simply changing the jets in carb, and turning a screw on the block...

Even changing a ECM and removing a restrictor plate can't be all of it. Other differences like Heads, Valves, Camshafts, Intake Manifold, WOT RPM range, would be needed to Double the HP of a given displacement.
 

pvanv

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Come on people, everybody knows you can DOUBLE an engine power by simply changing the jets in carb, and turning a screw on the block...

Even changing a ECM and removing a restrictor plate can't be all of it. Other differences like Heads, Valves, Camshafts, Intake Manifold, WOT RPM range, would be needed to Double the HP of a given displacement.

As with all outboards from all manufacturers, they are built in families. The MFS9.9/15/20E is one such family. The ECU is the detuning factor. The motor is designed and built as a 20, and then detuned. The air restrictor is needed to match the ECU. So, YES, changing the ECU and restrictor DOES make the change. No change to head, valves, cam, intake manifold. Just as the carb is the determining factor for the MFS2.5/3.5, and also for the MFS4/5/6, as well as the MFS8/9.8. Yes, it DOES make the change.
 

Sea Ray 320

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Pvanv - how hard is it to change the ECU and pull the air restrictor out. It appears the ECU slide out and then unplugging a wire harness or two. I bought a 3 month old zodiac with a 2019 9.9 efi but would like to bump it up to 20 hp. I’m debating if it’s worth doing this instead of selling my 9.9 efi to then buy the 20 efi. I would think I’ll pay at least $900 more after selling my 9.9 and then buying a 20 efi.
 

pvanv

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Should be under an hour. No big deal.
3RS064011MECU ASSY (20)$864.93
 
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