What happened to the study??

[Silvertip]

I posted a fuel economy study on this forum yesterday and it's now gone. I surmise I did a "no-no" but I'd like to know what the problem was so I don't waste my time again.

 

[wbeaton]

Re: What happened to the study??

I was wondering the same thing this morning. I perused it yesterday and was excited to read it this morning on my day off. I thought I dreamt it when I couldn't find it. I sure don't know why it would have been deleted. It seemed to me to be a very good and useful post. Exactly the sort of post we should be encouraging here.

 

[mrfixitman40]

Re: What happened to the study??

engine faqs page just read it thanks for the info

 

[cougar1985]

Re: What happened to the study??

hey! no complaining,you,ve made it to the top!

 

[wbeaton]

Re: What happened to the study??

It was worth the wait to read it. Great post Silvertip. You can't argue with numbers. You definately cleared up any questions I had about 2 vs 4 strokes.

I'm with you - carbed 2 strokes forever.

 

[rickdb1boat]

Re: What happened to the study??

Thanks Silvertip for the informative post...

 

[tashasdaddy]

Re: What happened to the study??

some how it ended in the faq forum. i think it would get more reading as a sticky here. http://forums.iboats.com/showthread.php?t=219751

 

[dajohnson53]

Re: What happened to the study??

Yes, I really enjoyed that page. It answered a question I was actually trying to "research" on the web recently: do newer technology engines actually burn less gas than older carb'd engines. It's pretty clear that they do not at WOT - new or old, the "10% of HP" in gal/hour still applies.

From the info you posted, I was looking at mileage, because that's what interests me the most since I use my boat mostly for recreational transportation. It's clear that some engines get better mileage, but the speed at which the various engines are most efficient does vary quite a bit. Some may find it at 20, some at 30 mph. For my purposes, I would tend to look at the speed I'd like to go (e.g. 25 to 30) and find the engine that is most efficient at that speed. I don't care if another engine gets better gas mileage if that improvement is achieved at a speed that is much slower - because I'm not willing to take longer to get there!

If that makes sense.

But that info that was posted was very interesting because it seemed to make a reasonably controlled look at those sort of factors.

Thanks!

 

[Bass Man Bruce]

Re: What happened to the study??

I saw it last nite and posted a "Good on ya" for your work. Went to find it this morning and saw it in the engine faq's. I knew i wasn't crazy cause I printed it for a buddy and still had the hard copy.
Thanks again for the info.

 

[External Combustion]

Re: What happened to the study??

This was a good study and good information, yet I have a different conclusion as far as the data is concerned. I re-ran the numbers and found that there is even more of an advantage to the 2 strokers at 1000 rpm and under. I calculated 22 mpg at 650 rpm and 12.2 mpg at 1000 rpm. There is no data for the 4 stroker at 650 rpm.

I do find that from 1500 to 4000 rpm the milage definately favors the 4 stroker in the chart that compares the same hull and horsepower. At 4500 rpm and up the two banger gets the prize. I had to extrapolate the mileage at 5370 and came up with 4.96 mpg for the 4 stroke as compared to the 5.1 mpg of the 2 stroke.

As an engineer that worked for one of the major marine engine manufactures, I know that statistics can be easily manipulated to bolster whatever argument that you believe in. As Simon and Garfunkel said in the song "a man hears what he wants to hear, and disregards the rest."

At 75% power down to idle, the charts shows the 4 bangers gets the better milage. Most operators do not run their engines at WOT all of the time, most of those I know run WOT less than 10 % of the time.

What I really would like to see is a comparison of both types of engine at the same horsepower, with props that are tuned to maximize the economy, in the same hull at the same weight. Unfortunately what has been presented leaves some questions unanswered.

This research is the best that I have seen on the subject though!

Thanks Silvertip for the work!

 

[Silvertip]

Re: What happened to the study??

I've been looking at various tests over the years and always wished I could get data like this on an idential boat with engines of the same horsepower but with different technologies. When I saw the Alumacraft/E-tec test I knew that Yamaha had made a similar test so that prompted me tabulate the data. Since I have the same boat and have a fuel flow monitor that was the icing on the cake. I certainly don't mean to plug one technology over the other -- just to show that the differences are not as great as one might expect and except for emissions, carbed two-strokes are not as bad as they are made out to be. The results might be very different on boats of other types, sizes, and HP.