Improving low end torque: questions for the motor gurus

[greenaero]

In my ongoing quest for maximum fuel economy for my Ninjettes, I was wondering about some ways to improve efficiency by modifying the motor so that it is optimized for the lower rpm range ( 4K to 8K) that I operate my motos at.
The ideas I'm interested in are 1) advancing the ignition timimg, 2)advancing the cam timing,and 3)reducing the valve spring pressure.
Has anyone done any modifications in these areas? If so , please share the details and how successful you were with it. These mods have potential for improvements but also have the riskfor catastrophic engine damage. Any knowledge or exeperience you can share is greatly appreciated.

@Racer x, @rojoracing53, @csmith12, @Motofool, @alex.s

[ninjamunky85]

I know adjusting valve clearance to the high or loose end of spec will give you more mid range power. Tight valves give better top end power.

[Motofool]

Originally Posted by greenaero

In my ongoing quest for maximum fuel economy for my Ninjettes, I was wondering about some ways to improve efficiency by modifying the motor so that it is optimized for the lower rpm range ( 4K to 8K) that I operate my motos at.
The ideas I'm interested in are 1) advancing the ignition timimg, 2)advancing the cam timing,and 3)reducing the valve spring pressure.
Has anyone done any modifications in these areas? If so , please share the details and how successful you were with it. These mods have potential for improvements but also have the riskfor catastrophic engine damage. Any knowledge or exeperience you can share is greatly appreciated.

The most dramatic and effective way of increasing the amount of work from the same amount of fuel is increasing the compression ratio.

The valves and the detonation are the main things that limit that.

The point at which the engine generates the highest torque is what you want to sustain, for whatever gear combination it takes.
That means that the breathing of the engine is optimal at that point.

More power (number of strokes per time = HP) can be generated for higher rpm's, but increased parts' friction and difficulty of breathing are the limiters there.

http://en.wikipedia.org/wiki/Power_band

http://en.wikipedia.org/wiki/Engine_tuning

Our engines are made of fast and light parts that move as little as possible (short strokes).
That makes them peak performance, reason for which they have transmission boxes of six steps, so we can always be close to the peak of torque or to the peak of HP as convenient.

http://en.wikipedia.org/wiki/Engine_efficiency

Our engines are pretty efficient as they are.
In my opinion, timing modifications may do more harm than good to the whole orchestra of factors.

Again, higher compression ratio and injected fuel are always a direct improvement in the road of efficiency.

[Racer x]

I really have never done anything like that. I would say advanced can timing would help. Smaller ports or smaller and better exhaust resonance.

[Racer x]

Will the higher compression burn more fuel if all else is the same?

[quarterliter]

Originally Posted by Racer x

Will the higher compression burn more fuel if all else is the same?

It shouldn't

[greenaero]

Wow! quick responses, thanks guys!
@ninjamunky85 , correct, I already run my valve clearance at max loose end.
@Motofool, I hadn't thought much about increasing the CR as it is pretty high already but maybe I could it increase it slightly for some gains. I wonder what the max would be and still be able to use pumped gasoline.
Eric, thanks for the other suggestions , I would think raising the CR wouldn't raise the fuel consumption but would present more potential for detonation.

[Motofool]

Originally Posted by Racer x

Will the higher compression burn more fuel if all else is the same?

The amount of fuel is the same (whatever can flow into the 125 cc of displacement of each cylinder), but the temperature of the combustion is higher, what increases the pressure of the gases of combustion over the piston.

Higher pressure along the work stroke means higher force over the same area of the head of the piston.

Engine's mechanical work is force times distance.
Distance is fix per the stroke's length.
Force comes from the pressure after the explosion.

Power (HP) is engine mechanical work in any unit of time (more rpms' = more HP)

By restricting the aspiration duct, partial throttle allows less fuel-air mix into the combustion chamber; hence, less pressure at the end of the compression stroke and lower temperature of combustion.

[quarterliter]

Are you looking for higher mpg or lower cost per mile?

[quarterliter]

Are you running maximum tire pressure and ceramic wheel bearings? Non-O ring chain?

[dcj13]

Consider getting a KLX250 or KLR250 (or one of the other 'big 4' dualsport equivalents). The thumpers are much torquier down low (the KLR250 redlines at 9500 rpm). They get pretty good fuel economy, too: on par with the Ninjette.

And I'd like to see what kind of bodywork/fairings you'd put on it!

[ninjamunky85]

@greenaero What about swapping the head for one from a new gen 250? I don't even know if they are compatible but if they are the new gen was designed to be torquier than the pre gen.

[Ninjinsky]

Worth looking at the kawasaki el250 engine
It was a custom that used a detuned gpx250 engine, less bhp but I believe a better torque spread more appropriate to a custom.
Possibly an ecu, carbs and camshafts swap with one of those would get you on the right road. Whatever the factory changed.

[greenaero]

let's see:
@quarterliter: The Vetter Challenge winner is lowest cents/mile for fuel used which is my ultimate goal but to be achieved within a reasonable cost for the vehicle. If total cost ( vehicle,+ modifications, + fuel) were the deciding factor, I'd easily be the champ. So as long as I'm running on gasoline I need to improve on my mpg ( 146 mpg best, 131 mpg best in competition).
I'm running pretty high tire pressures ( 40/40psi minimum for regular running, 46/50 psi for competition ) and a non o-ring chain.. I'm still using conventional wheel bearings ; I've heard that the ceramics are a bit fragile for regular street use. Definitely something to think about.
@dcj13, I agree a torquey single would be the ideal choice for a max fuel economy vehicle but the use of fully enclosed streamlining presents cooling challenges for air-cooled motors. If I stay with gasoline power, I'd probably look for a Honda CBR250R ( single, water-cooled, EFI) for my next platform. If I could pick up a good water-cooled single on the cheap, I'd definitely consider switching over.
@ninjamunky85, interesting idea about the new-gen head. I wonder about CR, valve timing and profile difference too, though the new-gens never seem to produce the FE that the pre-gens do.
@Ninjinsky, agree that the EL250 would be a good platform. I've looked for them but they are pretty rare to find one at a good price. Also if I change platforms I'd probably go with a water-cooled 250cc single.

I'm hoping to close the gap with my primary competitiors( Fred Hayes and Alan Smith). Fred was about 30 mpg better in our last competition together and with his resources( 162 mpg best, diesel powered) I'm unlikely to catch him. I've stayed close to Alan but this year he is working on a radically lowered Ninja 250 with some engine tweaks. Standing still in competition is falling behind.

[ninjamunky85]

Originally Posted by greenaero

@ninjamunky85, interesting idea about the new-gen head. I wonder about CR, valve timing and profile difference too, though the new-gens never seem to produce the FE that the pre-gens do.

Don't forget that the new gens were a good 30 lbs heavier though. Also I think it was already mentioned that EFI should help to improve economy. In some of the initial tests of the 300 people were getting over 100 MPG.

[ninja250r81]

what do the rules say about turbo or supercharging, even fit an electric motor with an aircon gas clutch so it releases at a certain rpm. eg old toyota mr2 superchearger.

And tune the bike not for power but very lean

[csmith12]

Let's think outside the box for a minute.

Is there a rule that says the engine has to be running the entire time? lol

[quarterliter]

I think you have optimized everything that is relatively inexpensive. Anything more will be very expensive and for minimal gains.

A new platform would be the easiest way to Improve fuel economy. As previously noted, a CBR250 Would be a great place to start.

[jkv45]

Originally Posted by csmith12

Let's think outside the box for a minute.

Is there a rule that says the engine has to be running the entire time? lol

Vetter does not want competitors to use the typical mileage technique of Pulse and Glide in his competitions. Early Vetter Fuel Economy competitons were won with tiny full-fairing cycles using 125cc singles. The highest numbers achieved were 470 mpg with a modified Honda that had a neutral added in the transmission available directly from top gear - so you get into top gear then can directly drop back in to neutral to coast.

The new Vetter Challenges require a competitor to stay between a leading and tailing vehicle at highway speeds. If the tailing vehicle passes you - your out.

For other types of competitions it is common to accelerate to a maximum set speed and completely shut off the engine while coasting to your minimum set speed - back and forth the entire time - only running the engine when acceleration is required.

[jkv45]

Vic - as far as mods for mileage go, I don't recall exactly what you have done.

Are you running 87 octane no ethanol? Have you gone to a hotter plug? I may also go to a thinner oil like a synthetic 5W-30 oil like Motul or Redline.

Changing cam profiles and timing could help. Increasing compression would be a good idea also.

As far as bigger gains, reducing the size of the carbs, or possibly going to a single carb would be helpful, as would reducing the diameter of the exhaust to increase velocity. F.I. could be an advantage. Directing heated air into the intake might be a benefit, but you would need to rejet based on the higher temps and less air density - and that could be difficult.

[kxpower?]

Maybe take a look at the Ignition Advance Kit about 2/3 of the way down this page: http://www.factorypro.com/prod_pages/prodk04.html

Looks like an offset flywheel key to advance ignition timing. The dyno chart there does show a bump at around 6000 rpm, which is right where you're looking for help. Might be worth $70 to try?

Does seem like a lot of $$ for an offset key though.

[DaBlue1]

Ever considered better spark efficiency as part of the hypermiler solution?

Takai Hi-Output Super Coils





http://www.takai-racing.com/takai/ta...-99-p-451.html

[alex.s]

if you leave the engine off and instead push the bike, you get much higher gas milage i've found.