Low & Slow's Ninja 250 project

[renault_megane_dci]

I have been reading somewhere that you get good improvements in mid range on a DOHC bike when altering the timing 4° on both inlet (later opening) and exhaust (earlier closing).
The idea is to have (8°) less overlap which cause erratic running at low rpm but is a consequence of the longer duration cams that are found in high power / liter engines.

4° on each cam being still safe with valve to piston clearance.

There was something to do on the ignition timing too but I can't remember it.

Also, if uing the engines only at lower rpm, we could increase the compression ratio wich is a big MPG booster.

On my 250 GN, I plan to boost the CR and polish the chamber and maybe piston crown but unfortunately, being SOHC, I can't play with timing ...

[low&slow]

Renault Megane, Thanks for the suggestion. I'm interested in modifying the valve timing and the ignition timing and will have to try this out when I get a chance.

I've been working a lot at my new part time job and now have almost 2 weeks off so I can resume working on my Ninja. I need to replace the rear brake pads and I'm thinking about making a dustbin style front fairing. I need to be sure of finishing it before I leave for the 7/20 Ohio Vetter Challenge. I'm very impressed with Alan Smith's performance at the recent Carmel Vetter Challenge and I need to close the gap to be more competitive.

[renault_megane_dci]

Originally Posted by low&slow

Renault Megane, Thanks for the suggestion. I'm interested in modifying the valve timing and the ignition timing and will have to try this out when I get a chance.

Check around if there are some high compression pistons available.
The stated CR improvement together with your valve timing can give you a safe dynamic CR target.
The dynamic CR is basically a CR with stroke corrected to account for late closing of inlet => artificially lower capacity.
Also, I am sur of what I red but please check your valve to piston clearance before putting engine back together, I wouldn't want to be responsible for an engine failure ...

Ignition timing : the better the combustion, the less advance you need.
Trouble is you need to have a shop doing power runs for you and usually they are not asked to work on the lower RPM.

Are you aware of Megajolt and / or Microsquirt ?
One is a fully programmable ignition quite cheap but effective, the other, I can't remember if it has the ignition module inside (bigger version Megasquirt has) but it is a mappable injection.
Mappable ignition and injection are the way forward when it comes to economy since you don't use the bike as it was meant to and carburettors are a source of pumping loss by design, at least CV ones ...

Originally Posted by low&slow

I've been working a lot at my new part time job and now have almost 2 weeks off so I can resume working on my Ninja. I need to replace the rear brake pads and I'm thinking about making a dustbin style front fairing. I need to be sure of finishing it before I leave for the 7/20 Ohio Vetter Challenge. I'm very impressed with Alan Smith's performance at the recent Carmel Vetter Challenge and I need to close the gap to be more competitive.

If I were to spend 2 weeks on the bike, I wouldn't bother with engine jobs, even more with Vetter challenge being biased towards streamlining promotion hence higher speed were aero improvement are predominant.

[jkv357]

Another suggestion, because it sounds like you are diving into the thick of it -

Any chance you can find some smaller carbs (or even F.I)? Because you are trying to shift the power downward you may benefit from the increased velocity of smaller venturies. The stock carbs/cams/etc are all balanced to provide maximum power around 10,000 RPMs.

What did your plugs look like? Can you step-up one heat range?

You could also try dropping to a 30-weight oil. A top-quality (Repsol, Motul, etc) 30-weight synthetic motorcycle oil (5W-30 would be best for mileage) may show some mileage improvements also and should provide plenty of protection. You could try Rotella T5 10W-30 synthetic blend (no modifiers, good levels of ZDDP) if you didn't want to go up to a high-end oil. Because of the light loads and low RPMs I don't think you will run any risk of engine damage by using a 30-weight oil instead of a 40-weight.

Are you using a non O-ring chain?

I'm thinking different cams, tuned for midrange, would give the biggest gains.


Jay

[Grant-53]

Has anyone checked into ceramic wheel bearings lately and moly disulfide grease?

[low&slow]

I worked on my bike the past couple of days fixing the rear brakes and installing a new front end. It is now " dustbin" styled. I made a frame out of sheet metal bands and Pvc slats that I bolted and riveted together. I covered the frame with coroplast, installed the turnsignals and reused my old coroplast windscreen. I took it for its first ride this morning. It seemed to pass through the air plenty well but was too flexible in strong winds in the area near the front wheel. I need to make it more rigid. I also need to test the effectiveness of a front cooling vent to ensure adequate coooling. Hopefully this will allow me to close the performance gap between me and some of the other Vetter Challengers.
Thanks to Grant53, Jay and Renault Megane for all the great suggestions.

[BHarvey]

You can effectively NET a smaller carb by converting it from dual carb to single carb.
The carb will also get a better 'signal' and meter more efficiently.

As per oil if you live in a climate that does not change much, a straight 30 weight, like Delo 400 SAE30 will give top performance per dollar/miles used.

[low&slow]

I added some steel tubing over the front wheel and the front end is stiffer with much less wind deflection. I rode the bike about 30 miles today at speeds up to 75 mph and it seemed to work well with a noticeable decrease in aero drag; I'm able to hold top gear longer and able get to top gear with less acceleration. The only negative so far is that the temperature gauge is reading higher than before but still out of the red zone. More testing to follow.

[Grant-53]

What rpm range are you running with the change in gearing?
Check websites for templates of NACA intake ducts. Alan is using a single intake over the wheel. Twin intakes on either side of the fairing could work well. I'd consider wheel covers inside the dustbin to smooth flow to the radiator.

[renault_megane_dci]

Any pics in the near future ?