Gas consumption comparison

[Btuvi]

18 foot boat bowrider style-

two different engines

one engine is a 115 4 stroke - the other is a 150 2 stroke - same year

At 30 miles per hour what will be the difference in gas consumption

Though it may seem obvious I'll ask anyway - which will have faster hole shot and how dramatic is that difference

Which will have greater top speed and by how much

what other differences might there be regarding operating cost, repair, and maintenance

I understand that there are variable but I'm not looking for a definitive answer - just a good educated guess

Thanks

 

[Kev144]

Re: Gas consumption comparison

18 foot boat bowrider style-

two different engines

one engine is a 115 4 stroke - the other is a 150 2 stroke - same year

At 30 miles per hour what will be the difference in gas consumption

Though it may seem obvious I'll ask anyway - which will have faster hole shot and how dramatic is that difference

Which will have greater top speed and by how much

what other differences might there be regarding operating cost, repair, and maintenance

I understand that there are variable but I'm not looking for a definitive answer - just a good educated guess

Thanks

It is quite obvious the faster hole shot and top end will be the 150 2 stroker. I dont know why you are comparing a 115 4 strk to a 150 2 strk. PRobably weight around the same and the 2 strk has an extra 35 hp. The 4 stroke will probably be easier on fuel depending what year we are talking as the new 2 strks have DFI which is close if not better than some 4's.


Really need more info like make/model and year.

 

[Btuvi]

Re: Gas consumption comparison

My primary interest (though I had other questions) is in trying to determine which would use more gas at 30mph. One engine has more hp so does not have to work as hard to produce the 30mph speed. The other has less hp so has to work harder to produce the same speed. So, if you were constantly operating at 30mph, which would be more fuel efficient and by how much.

 

[JRJ]

Re: Gas consumption comparison

The 115 will use less fuel.

 

[jay_merrill]

Re: Gas consumption comparison

I would surf the net for boat and/or engine reviews that come close to matching the setups that you are contemplating. The information might not be an exact match, but it might come pretty close.

BTW - if the 2-stroke is an ETEC, you might be very surprised at the numbers involved.

 

[kenmyfam]

Re: Gas consumption comparison

What boat are we putting this on and what is the max rated HP for it ????
That should be the first question before any comparisons take place.

 

[JB]

Re: Gas consumption comparison

There are too many different 2 stroke 150s to give anything like an intelligent answer.

Is the 2 stroke carbed, DFI or etec? If carbed, is it a crossflow or looper? The differences in efficiency are huge.

 

[Silvertip]

Re: Gas consumption comparison

I suggest you visit the Yamaha web site and look at performance bulletins. You can select virtually any boat and look at test reports for that boat with both 2-stroke and 4-stroke motors. What you really need to be careful of is how you interpret fuel economy numbers. At any given RPM a two-stroke motor will almost always be pushing a boat faster than the equivalent 4-stroke because of gearing and prop selection. Therefore MPG and GPH numbers need to be analyzed at MPH rather than RPM for an objective comparison. The two-stroke (of the same HP) will almost always provide the better hole shot as well as top end.

 

[Rancherlee]

Re: Gas consumption comparison

at anything less than WOT a 4 stroke with drink ALOT less gas then an equavilent carbed/efi 2 stroke. DFI 2 strokes are pretty close or even with 4 stroke engines. The extra power of the 150 might be nice in your case but the 115 will definitely use less gas in every situation. The down side is that most 115 4 strokes are the highest HP rating of a shared engine block thats used on lower HP ratings also so they will probibly not be as "snappy" as a 2 stroke out of the hole.

 

[Btuvi]

Re: Gas consumption comparison

JB, you and Tashasdaddy have both reminded me on occasion that unless things are exactly the same in every respect there is a likelihood that they will be different. Good advice and I appreciate it. You've taught me that not only can one not compare apples and oranges one cannot compare apples and apples unless one is talking about the same kind of apple.

I'd like a chance to restate my question in an effort to make it more clear. I'm not hopeful but I'd like to take a shot.

You have two outboard motors that are exactly alike in every respect except for horsepower - one being 115 and the other being 150. Place them each (at separate times) on, let's say, an 18 foot Searay bowrider. Run them both at 30mph. What will be the noticeable differences in gas consumption, hole shot, WOT, etc.?

Thing I'm trying to get at is - if one engine has to operate at 60% capacity (for instance) to maintain 30mph and the other has to operate at 80% capacity - which will provide better gas milage and by how much.

Is the 150, simply because it has more hp, going to use more gas even though it is operating at lower levels of its capacity? If so, how much more gas will it use?

I know that this is a difficult question to answer given the fact that I didn't mention whether or not one boat was carrying two passengers and the other four or one boat pulling a skier and the other not but I'm trying not to muddy the waters anymore than I already have.

All comments appreciated. Thanks.

 

[jevery]

Re: Gas consumption comparison

Here?s efficiency and speed differences on this hull

From these,
http://www.yamaha-motor.com/assets/...ke_midthrustjetport_al_wlc-195bay-f115txr.pdf
http://www.evinrude.com/NR/rdonlyres/23C6CF3D-280E-4B55-AAE1-AAEBBA6910FB/0/PE434.pdf

 

[Btuvi]

Re: Gas consumption comparison

jevery, that is about as definitive an answer as I could imagine. Gave me a lot of insight. Thanks a lot. Really worthwhile to me.