Outboard advice

[KTW]

Can someone tell me what the optimal outboard motor will be for my Honwave T35 AE? (3.5 meters with aluminum base)

I currently have a Honda BF6 SHU, but find it lacks a lot of power, especially when carrying either a lot of equipment or just an extra person.
And then I really struggle to cope with the exhaust gas that comes out in the middle of the shaft.

I have looked at these Mercury 4 stroke models:

• F 9.9 MH - 38 kg - 2852 EUR
• F 15 MH EFI - 45 kg - 3074 EUR
• F 20 MH EFI - 45 kg - 3468 EUR

The 9.9 hp model is almost not worth it because of the price, but can be found more easily on the second-hand market.
But is there much advantage with the 20 hp over the 15 hp model?
I also love the idea of EFI.

[Steve509926]

Hope this thread helps. IMO if the weight isn't a problem and your sib is rated for it go for the 20hp. The difference is very noticable.

https://www.rib.net/forum/f36/merc-1...nce-88972.html

[KTW]

Thanks Steve. 🙂
I will get the 20 hp model then. 👍
The sib is rated for 20 hp max.

[Blankton]

I wonder what the difference is between the 15hp and 20hp, possibly just a microchip on an efi engine.

[Steve509926]

Originally Posted by Blankton

I wonder what the difference is between the 15hp and 20hp, possibly just a microchip on an efi engine.

I assume all the important electronics are in the ECU, and both the 15 and 20 have the same ECU part number 8M0135817, so will that make the difference something other than a microchip?

[Blankton]

Originally Posted by Steve509926

I assume all the important electronics are in the ECU, and both the 15 and 20 have the same ECU part number 8M0135817, so will that make the difference something other than a microchip?

I was going off the weight. Both the same weight, so the same block etc. If it was an old school engine I'd say different carb, or jets or a restrictor plate etc, but I don't think they'd bother with an electronic engine, it's easier to change a map. That's what car manufacturers would do anyway.

Either way, if the same weight, I think I'd go for the 20hp. Is it the same engine as the tohatsu efi? That is quoted as a similar weight.

[chipko]

Originally Posted by Steve509926

I assume all the important electronics are in the ECU, and both the 15 and 20 have the same ECU part number 8M0135817, so will that make the difference something other than a microchip?

That’s interesting, as Mercury reckon that the ECU triggers limp mode if the air intake restricter is removed from the 15. Perhaps they’re telling porkies!
From the manual:

“A restrictor in the air intake induction system restricts the amount of air that can enter the induction system. The restrictor cannot be removed to gain more horsepower. If the restrictor is removed, the computer controlled CDI will limit the engine RPM to 2800, the warning light will flash, and the warning horn will beep six times every five minutes.”

Regarding weight just be aware the Merc/Mariners are plated at 47.5kg despite the claimed 45kg. If weight an issue the Tohatsu (same motor different hood & tiller) comes in at 43kg and the Suzuki 44kg.

[Blankton]

Originally Posted by chipko

That’s interesting, as Mercury reckon that the ECU triggers limp mode if the air intake restricter is removed from the 15. Perhaps they’re telling porkies!
From the manual:

“A restrictor in the air intake induction system restricts the amount of air that can enter the induction system. The restrictor cannot be removed to gain more horsepower. If the restrictor is removed, the computer controlled CDI will limit the engine RPM to 2800, the warning light will flash, and the warning horn will beep six times every five minutes.”

Regarding weight just be aware the Merc/Mariners are plated at 47.5kg despite the claimed 45kg. If weight an issue the Tohatsu (same motor different hood & tiller) comes in at 43kg and the Suzuki 44kg.

Does it have a MAF? The ecu could be looking for different values depending on whether this plate is there or not, so it could be a 15hp map and a 20hp map in the ECU with different acceptable ranges for MAF sensor. If outside of these ranges the alarm occurs. I suspect you could prove it by unplugging MAF (if it has one).
If this was a car there would almost certainly be a YouTube to explain how to re programme your ecu. I guess not as much interest for ob's.

[Steve509926]

Originally Posted by chipko

That’s interesting, as Mercury reckon that the ECU triggers limp mode if the air intake restricter is removed from the 15. Perhaps they’re telling porkies!
From the manual:

“A restrictor in the air intake induction system restricts the amount of air that can enter the induction system. The restrictor cannot be removed to gain more horsepower. If the restrictor is removed, the computer controlled CDI will limit the engine RPM to 2800, the warning light will flash, and the warning horn will beep six times every five minutes.”

This is starting to get beyond my paygrade, but does this sound feasible?
Remove the restrictor to increase airflow and gain more hp, then reprogram (remap?) the standard ECU to take into account the increased airflow.

[Limecc]

Originally Posted by Steve509926

This is starting to get beyond my paygrade, but does this sound feasible?
Remove the restrictor to increase airflow and gain more hp, then reprogram (remap?) the standard ECU to take into account the increased airflow.

Currently no tuner in the world has managed to crack security on Mercury ECU's. One solution will be to use a custom programmable ECU (didn't they do that for a while with Sky Movie cards?) and that is under development.

Meanwhile it's also getting harder with Suzuki. DF40/50/60a models have an ID chipped main harness so the ECU knows if it's mismatched, it throws a 4-1 error and goes into limp mode. The workaround is to copy individual maps from the 60 rather than cloning the entire ECU.

Situation is better with DF9.9/15/20 models. West Wales Tuning can clone the 20 ECU and optionally give a boost to say 25hp. No idea where they get the images from but they are certainly available and exportable so any tuning is easy and fully reversible.

[Blankton]

Originally Posted by Limecc

Currently no tuner in the world has managed to crack security on Mercury ECU's. One solution will be to use a custom programmable ECU (didn't they do that for a while with Sky Movie cards?) and that is under development.

Meanwhile it's also getting harder with Suzuki. DF40/50/60a models have an ID chipped main harness so the ECU knows if it's mismatched, it throws a 4-1 error and goes into limp mode. The workaround is to copy individual maps from the 60 rather than cloning the entire ECU.

Situation is better with DF9.9/15/20 models. West Wales Tuning can clone the 20 ECU and optionally give a boost to say 25hp. No idea where they get the images from but they are certainly available and exportable so any tuning is easy and fully reversible.

That is interesting stuff. I guess it comes down to a lack of market for cracking the software. I can get a hookey map for my vw car for a few quid and the lead and software to install it for 15 quid. I'm sure vw have a much bigger budget for their ecu / software department than Mercury Marine, but there are also a lot more people interested in cracking it!

In the automotive world standalone ecus are generally reserved for high end modified builds, due to the costs involved and the time required to setup. I guess it would be the same with ob's it might pay on a 150hp engine used for racing or skiing, but it's not going to be a realistic option for. 15hp tiller motor. It's looking like biting the bullet and paying the extra money is the best option to get the extra horses.

[KTW]

I have just been offered a brand new 20 hp for 3294 EUR, at the local dealer.
(24500 DKK)

[Steve509926]

If that's including all taxes, pre delivery inspection, it would be considered cheap in the UK.
See if you can push it a bit further and ask for the first 20hr service to be included.

[Fenlander]

Bit late to the party here but having owned a T35 I'd say yes a 20hp if you can. We ran several SIBs over a few years with the same 15hp motor and the T35 had the most sluggish performance. It is a very roomy and stable SIB but not the easiest for an outboard to push along.