130 MPG Ninja 250
 

Ok, now that I have your attention the 130 is my best tank. I just made a couple of changes and my 4 week average is 108. Two weeks ago was extremely windy (35-40MPH winds) for several days and I dropped down to 93 MPG that week. The last change was going from a 38 tooth rear sprocket to a 33, and I was averaging 93MPG with the 38. I also changed to a non-O-ring chain. Other previous mods include a 16 tooth front sprocket (from 14), a Scottoiler chain oiler and a jell-pad seat cover. I run 44 PSI for the tires and the jell pad makes a big difference. I also added a rear view camera which is priceless when you are in a tuck. Also as seen in the top view attached I added a tail bag which is a little more aerodynamic. I believe aerodynamics is where the biggest gains can be from here as other treads also get into.
;)

Congratulations and welcome.
I'd be happy to hit 93 mpg ...
(not to mention 93 mph)

congrats,
out of curiosity, what is your typical speed? I got 130ish on a long 55mph trip last year. I'm hoping to break that this summer.

Typical trip profile
 

The driving is mixed with about 8 miles of city driving and 7 miles at 55 mph. I get up early to beat the traffic and try to time the lights ( drive as if there are no brakes), gliding with the clutch in idling at about 300 rpms. Once at speed I am in a tuck. The way home has more traffic and I take a route with the least stops, or at least I try to, and if I catch a long light I turn the engine off. I haven't been on any long highway trips yet and as long as the speeds are not too high it probably will do better than city. I am curious to see what the top speed will be in 6th gear, it pulls strong at 65.

:thumbup:

What did you do to make idle that low?

Simple idle adjustment
 

The bike is carbureted and the idle setting is a simple adjustment below the seat. I am estimating the 300 RPM's from the tachometer. Also I live in Arizona where it is relatively warm. I make a slight adjustment between winter and summer and the warm weather with thinner oil allows a low idle.

My Ninja250 would never idle below 1,300 rpm let alone 300.

300 rpm is a starter motor cranking speed, it is very low ...
Maybe the bike engine wich are oversquare can handle that low a RPM BUT your idle speed setting is there for a reason : below a certain RPM the oil pump can not provide enough oil pressure !

Re: Low idle
 

renault_megane_dci I appreciate the heads up on potentially too low oil pressure. I would like to find a way to measure the oil pressure, because I have done this on several older carburated cars which had oil pressure sensors and would find a medium setting with a lower idle with just a slight drop in oil pressure and had no problems for 150,000 miles on American cars. According to some there is a bit of a wifes tale about oversquare rules of thumb but that is a grey area and I am not trying to start an argument on the topic (see Why "Over Square" Is Good ). Also do you know a ball park figure for the design margin on the oil pressure?

I am curious about the mods you have done and appreciate any constructive criticism. You mentioned low bars on your GN 250, exactly what are those and does that just lower the suspension ?

Thanks

Oil pressure :
car iddle setting is usually a tad under 900 rpm
bikes iddle setting is usually around 1500 rpm

Bike engines usually revs up to 10.000 rpm and up.
Their oil pump has to cope with these high rpm meaning they are either small or under geared or a combination of both, requiring for a higher iddle setting.

Low bars :
It is just a lower handlebars compared to the factory high-ish bars.
Planning to fit clip-ons at some point.

Over-square engine :
just my opinion but the shorter the stroke, the least destabilized it gets at lower rpm.
More cylinders helps too.

I have two interesting vehicles, then :cool:

• The YARDIS idles at 500rpm with 4 cylinder when warmed up. Can be a bit shaky down there :D
• Teresa idles at ~1500rpm, even though the engine is a short stroke one with a redline of 7k. But she's kind of lacking at the cylinder count department (being a single) :D

What use of the term "over square" are you talking about?
.
Why "Over Square" Is Good
.
To me, over square means that the bore is bigger than the stroke. Which makes it a higher revving engine with more peak power output. Under square engines such as the new Honda NC700X have a stroke which is longer than the bore. Which moves the power band and redline lower for better fuel economy at the expense of peak power.

By oversquare I meant the usual engine layout we use down here on the ground ;-)

Did you follow his link? What is that about with the airplanes.

Apples and oranges on the airplane engine reference. The point refers to propeller pitch and rpm. Not bore/stroke.

On an ecomodder note though they are extolling the virtures high pitch and wider throttle opening (high manifold pressure). The same thing as gearing tall to slow the engine and opening the throttle wider.

Those Lycoming engines are like super reliable air cooled VW engines. Pretty basic low speed engines built to never fail. I don't know the bore/stroke often used in the Lycoming engines though, guessing they are undersquare.

So high manifold pressure is another way of saying low manifold vacuum.

(VW flat four are oversquare engines)

Who needs idle anyway ?

Re: Low idle
 

I am not trying to debate the definition of oversquare which is cut and dry and very clear and was only pointing out the associated rules of thumb have gray areas which can be very useful for economy. I believe the link is a well written article by the editor in chief of a pilots association and I respect the guy. His statements about reduced engine speed reducing friction are spot on and germane to the topic. I possibly could have gone on the low side of a safe idle and I plan to play with it a bit and see how much it affects my city mileage, because that is the reason I want for a lower idle. I don’t mind being the guinea pig or canary so to speak if others can benefit from my data, just don’t shoot the messenger. This also could lead to other solutions to the low oil pressure such as an electric oil pump that is set to kick in at low RPMs. Obviously the best savings at a light is to turn the engine off but then you have to be concerned about starter wear and tear. It seems that there are many examples on this site of thinking outside the box to gain efficiency.
Cheers,:thumbup:

Alan Smith posted 144 mpg in the latest Vetter Challenge event with his 2005 Ninja 250 streamliner this weekend so 130 mpg is not so outrageous anymore. See craigvetter.com for details as they become available.

Allen Smith's story should be interesting
 

Look's like they are going to post Allen's story in the near future. It should be interesting to see how he got the 144MPG and I'd like to know more about the winning diesel also.+