Honda 115hp and 150hp weigh the same

[willy13]

Anyone else notice that Honda uses the same engine block in both there 115hp and 150hp models? Which means there is no weight saving in going with the 115hp motor. Being that weight is important on a boat I find this odd. It seems like the 115hp is simply a detuned 150hp motor. Both engines are 2354cc (2.35 litre) and both models weigh 478lbs. Yamaha on the other hand has a smaller and lighter block for there 115hp model than there 150hp model. The Yamaha has a 1741cc engine block and only weights 401lbs.
http://marine.honda.com/outboards/motor-detail/BF115
http://marine.honda.com/outboards/motor-detail/BF150
http://www.yamahaoutboards.com/outboard ... ection-nav
I just thought I would share these observations. Do you guys think 75lbs is no big deal on a pontoon boat? If I decide to go with a 115hp motor, it seems to me the Yamaha is the choice since it is 75 lbs lighter. If I went with a 150 hp motor, the Yamaha and Honda are basically the same weight.

[Bamaman]

The Hondas are never the lightest motors on any transom.

The Yamaha 115 shares the same basic weight/engine as the 90 hp and 75 hp motors. Yamaha's 75 hp motor is substantially more gutsy than their 70 hp motor based on the 50 hp motor.

With modern CAN/BUS boat engines, the difference in engines is often just reprogramming of the ECU, and possibly a little baffle in the intake system/air cleaner. You can now purchase a 200 hp motor and have the ECU remapped to produce 310 horsepower--and save substantially on the cost.

[Bamby]

You've stumbled into what seems to be a common conspiracy of outboard motor manufactures. They all pretty much just offer a few block sizes in given in a few horsepower ranges or motor classes. They then de-tune the best in class motor down to offer other various horsepower motors.

And yes weight does matter in any boat but maybe it's especially true with pontoon boats. Let's say you did get the 115 Honda over the Yamaha. It ain't just the seventy five pounds of the motor in extra weight it's another seventy five pounds it's Battery which is a lot hanging on the very tail end of your boat. Seventy five pounds is also close to maybe a half a tank of additional fuel on board.

But all in all if you can swing it a 150 is they way to go. From my observation though conservative of most folks here the 150 may offer the best in class for overall pontoon boat performance if actual fuel burn in use is any consideration.

[The_Hellbilly]

Interesting. I knew my 135 was the same as the 150, but didn't know about the 115. I wonder if someone could buy a 115 and just mod it?

[willy13]

I tried finding further specs on the Honda outboards but could not. I was specifically looking for compression ratio. Internally that would be the easiest way to de-tune a 150hp motor to 115hp. If the compression ratio is the same then it would most likely be de-tuned the way Bamaman mentioned. Hellbilly makes a good point, and if Bamaman is correct a 115hp Honda could easily be tuned to 150hp. One could buy the cheaper 115HP Honda and mod it to 150hp for less than the price difference.

[cwag911]

Here's the specs you were looking for: BF115 ------------------------------------BF150
Bore and Stroke/ in mm ---------------- 86x97 --------------------------------------87x99
Compression/psi --------------------------199-228------------------------------------222-250

[Bamaman]

A Verado 200 hp ECU can be reprogrammed to 310 hp, but there are few mechanics with the programming skills or experience to re-map the fuel injection system.

They charge $650 to do the programming.

I got my diesel truck reprogrammed for $75-- +80 horsepower. I guess it's supply and demand.

The mainly fishermen that have had their ECU's reprogrammed appear to be very satisfied with their performance, and are glad to only pay $650. They just have to run 93 octane fuel in the engines.

[ROLAND]

So based on what I've just read here on this thread, does this mean I could have my yamaha 75 "retuned" so that it was actually performing like a yamaha 90 or even yamaha 115, since all three apparantley share the same size block... and can it be retuned without causing me other issues?

[Bamby]

So based on what I've just read here on this thread, does this mean I could have my Yamaha 75 "re-tuned" so that it was actually performing like a Yamaha 90 or even Yamaha 115, since all three apparently share the same size block... and can it be re-tuned without causing me other issues?

Roland this has been discussed before and all I can say is "Maybe". For my satisfaction at least I need a lot more fairly substantial technological facts on the topic. But that said I've dug up some references as to where it's feasible with Yamaha's but the larger part of the horsepower increase seems to be circled around the removal of a restriction in front of the throttle-body itself. Here's a couple of quotes from this source.

For those worried about a change of ECU this is not really an issue, there may be some slight fuel and timing map differences however all modern EFI ECU's are designed to notice and adapt to changed conditions, they have an AFM, TPS and an O2 sensor to give feedback to the ECU to control spark retardation and fuel map positions. The ECU will adapt to the higher airflow by pushing the fuel load higher in the map table to suit but still try to maintain AFR at stoic. The only exception to this is at WOT (wide open throttle) at this point the fuel map is at peak, if there is a difference between the two ECU's then this is where it will have the most effect by running the engine lean, for me this is no issue as I almost never run my engine at WOT mostly its about 1000rpm below the limiter and for me thats only 4500rpm at around 21Kn

Anyway some useful information for reference as I have just removed the restrictor in my engine....

The restrictor in the F80 reduces the intake port diameter to 24mm. Without the restrictor the diameter is 41mm, thats a significant difference. The restrictor is actually really well designed with good fluting on each side. What this means is that on removal there may be some change in the airflow characteristics toward the intake port. When looking at the length and design of the runners they seem to be a tuned length. fortunately they are quite long runners so most turbulence will be settled before they hit the intake and IMHO any flow distortion and fuel droplet issue at the injector will be negligable compared to HP gain.

Just a quick one on flow rate for those technically minded, these are not hugely accurate as there are too many variables but...
assuming 3cm length and 0.1bar pressure drop

40mm flows 678cc
24mm flows 238cc

I wont get the boat on the water for a couple of weeks but once I do ill let you know how much difference it will make. If someone can host them I have plenty of photos of the removal and dimensions that could be posted up.

Followup below from same poster....

Ok so I had the boat in the water a few weeks ago and it all ran fine, the most noticeable difference is in the rev range and I really didn't push it too hard, however where the engine used to stop breathing at 5500rpm it will now easily rev to 5800rpm and beyond, I held it back at 5800rpm until I get a real feel for the changes and feel confident to push it beyond that. The engine should be able to rev to about 6500rpm now in theory at least.

Without throwing the throttle control to WOT but using about 3/4 throttle from standing start there is a noticeable difference in acceleration. I didn't have the GPS fine logging on this time out but I can tell from the speed/rpm ratio there is an overall improvement, on average I have gained around about a 1Kn speed improvement vs rpm across the top of the rev range. For example previously at about 4500rpm I would get about 21Kn, now its closer to 23Kn as my cruising speed. This is consistent across the whole rev range. The engine is obviously delivering slightly more power per stroke to achieve this through a better AFR.

With regard to top end previously I would get to about 29-30Kn at 5500rpm, 31Kn on a good day into a head wind (air lifting the boat out of the water assists in drag reduction), now that I can rev higher in the range I got to 33Kn @ 5800rpm and there's still a little more in the legs from the engine after that but for what I do I am not likely to need those sort of speeds.

Fuel economy has changed, where I used to get around 8L/Hr its now about 9.5L/Hr but it was pretty flat when we went out and so we were cruising a bit faster than we would normally out the front and you could probably take off about 0.5L/hr to take this in to account based on my previous logs.

Ive put photos up of the restrictor here.... http://s323.beta.photobucket.com/user/ira11y/library/

Like I said I've encountered this topic before but real hard facts on the conversion are real difficult to dig up, but with Yamaha's it always somehow involves a restrictor just like NASCAR. But with other engines others may very well be right, maybe all they do need is re flashed. But this is an interesting topic that would benefit the time of looking deeper into to find the real resourceful facts.

[willy13]

Originally posted by Roland
So based on what I've just read here on this thread, does this mean I could have my yamaha 75 "retuned" so that it was actually performing like a yamaha 90 or even yamaha 115, since all three apparantley share the same size block... and can it be retuned without causing me other issues?

The Yamaha 115 is actually a bigger engine block than the 75 and 90. The Yamaha 115 has a 1741cc engine, while the Yamaha 75 and 90 have a 1596cc engine. From an earlier post it looks like the Honda 115 and 150 have a different compression ratio, but the Yamaha may simply be a restrictor plate or ECU change as discussed above. If it was simply a restrictor plate, that would be an easy mod.

[ROLAND]

bama & willy....thanks for the info.. I asked because I'll be taking my boat to a local guy who runs a boat / motor repair shop from his home... comes highly recommended.... thought I'd run this by him and see what he thinks.... now that I know that the 75 is not the same size block as the 115, not sure theres much reason to try to bump up from 75 to 90 and running the risk of causing a problem somewhere else... btw, the mechanic that is going to service my boat said that one thing he usually does that often times get's overlooked is adjust the valves.....not sure what all that entails, but I come from the school of " if it aint broke don't fix it". so should I let this valve adjustment take place or just tell him not to worry with that?

[Bamby]

Sometime preventive maintenance really does matter. And checking the valves on four stroke Yamaha's is suggested. You can review the Yamaha maintenance schedule here. Now that is said it's highly unlikely you've got enough hours on your motor yet to justify it. I know I don't I'm still more than a hundred hours away with probably more use in the last four years. But I do intend to check or have them checked on or around the 500 hour mark that is suggested.

[Bamaman]

If you read on the internet, you'll find most people using the guy that reflashed Bryden's new Verado to 310 hp. But it doesn't mean he has taken the time to reflash every outboard motor. I imagine most of his work is done on 200 hp and larger Verados and SHO's.

There's a boat repair shop in Southern California also doing some electronic tuning.

I have read of other people that had the programs and hardware to work on their laptop that. Reprogramming is very technical, and few boat mechanics have the knowledge to do it. It's just doubtful that many local mechanics have the skill or working knowledge of modern electronics to do the job.

[BoatCop]

One other note to remember is that HP is measured at the prop (or other drive) and not solely based on the engine size, compression, etc.

As an example, we have 2 16' rescue boats with 40HP EFI 4 stroke Mercury jet drive OBs.

The specs for them is:

60.8" displacement
2.56 x 2.95" bore/stroke
278 lb weight

This is the same block used for the 60HP prop model.

While the 40HP prop model is:

45.6" displacement
2.56 x 2.95" bore/stroke
204 LB weight

Since we all know that jets have a significant drive loss over similar powered prop models, Mercury has to have a larger engine to produce the same 40 HP at the jet than they need to produce 40 HP at the prop.

[willy13]

Roland, if Yamaha simply used some sort of restricter plate, that would restrict the air intake, you may still need to reprogram the ECU, unless there was an air/fuel ratio sensor that could compensate for the additional air getting to the engine.

All of our modern outboards could benefit from reprogramming but at the cost of needing 93 octane gas. From the factory they normally are tuned for 87 octane gas.