NSR150SP - Performance and Gearing

I will try to increase the power of the NSR150SP's Engine a little more.
 

Nothing too major.
Just tuning and bolt-ons should do.

I was not going to re-port the piston or case.

I was not going install a new head, or change compression.
And I was not going to increase the capacity higher than 150cc.
 

All I will aim to do as a first stage improvement is plug, filter, exhaust, and jetting.
This should make it a bit more tractable in the mid-range.
And may give a bit more top-end.
I will pop it on the dyno when I have done my first stage - mainly to see if I get it right.
 

The dyno can show emissions and fuel ratio through the rev range, so I should probably put it on before I rejet to have a reasonable idea of jet size and needle position.
The dyno result tells you if you are running rich or lean, and at what rpm.
Very handy.
You can adjust your Carb to get the mixture balance better through the rev range.
 

The NSR150SP already has plenty of grunt above 8000 rpm.
It has a redline starting at 11000 rpm.
It has a rev limiter cutout at 13000 rpm.
 

I have been reading a few blogs and websites about improving the Engine.
http://www.nsr150.com  seems to have some good information about  de-restricting the NSR Engine.
The NSR in their Opening picture looks really tight.
Click on the NSR Mods tab to see what they have done.

It says that they have NSR150's doing 240 kph.
Not that I really want to be on one of these at that speed !
I assume they have highly modified their bike to achieve this, and I have not seen all the modifications they have made. And they have not revealed the power output of their bike.
I reckon a few serious improvements will be needed for mine to reach that speed.

So, thanks to Korn and Zim for the above website.

Also see the legacy website called http://www.nsr125.com .

There are a few similarities in the de-restricting process for the NSR125 and NSR150.

http://nsr125.com/derestrict.htm

http://www.nsr150.com/1/nsr_mods_3876019_0.html

I did note that the NSR125 suggests a top speed of 110 mph ( 176 kph) could be achievable.
This would assume de-restricted form and correct gearing.

However the NSR150 suggests 150 mph ( 240 kph) which is a hell of a lot more for only 25cc.

From what I read, Valentino Rossi holds the Top-speed record on the Aprilia RS125  2-stroke, in 1996, at an amazing 249.76 mph ( 155.19 mph).


My gearing is a 14/40 (front/rear) sprocket combination.

They suggest going to a 15/40 (front/rear) to help achieve this 240 kph.

My gearing has 16 km per 1000 rpm, or :-

- 160 kph at 10000 rpm.
- 192 kph at 12000 rpm.
- 224 kph at 14000 rpm.

A 15/40 gearing is 0.9333 increase in road-speed.

Giving 17.143 km per 1000 rpm, or :-
- 171.4 kph at 10000 rpm.
- 205.7 kph at 12000 rpm.
- 240.0 kph at 14000 rpm.
 

This would assume that you remove the 13000 rpm  rev-limiter.
And you have modified the Engine to be able to produce more power, and at higher rpm.
I assume the modified NSR Engine would make power well beyond 14000 rpm, because it would have to get to 14000 rpm in 6th gear to achieve the 240 kph target, with this gearing.

Note: a 16/40 (0.875 gearing increase) gives 18.286 km/1000rpm or 238 kph at 13000 rpm.
 

I checked, and Honda don't make a 16 front sprocket.
And they only have one 40T rear (steel) left in the country.
They dont make any other size rear, from what Honda told me.

I ordered a Honda OEM  15T front from Tyga website today.

So for normal riding... in 6th gear.

-   68.6 kph at   4000 rpm.
-   85.7 kph at   5000 rpm.
- 102.9 kph at   6000 rpm.

- 120.0 kph at   7000 rpm.
- 137.1 kph at   8000 rpm.
- 154.3 kph at   9000 rpm.
- 171.4 kph at 10000 rpm.
- 188.6 kph at 11000 rpm.
- 205.7 kph at 12000 rpm.

And just for reference 5th gear becomes 15.0 km/1000 rpm.
-   60.0 kph at   4000 rpm.

-   75.0 kph at   5000 rpm.

-   90.0 kph at   6000 rpm.

- 105.0 kph at   7000 rpm.
- 120.0 kph at   8000 rpm.

- 135.0 kph at   9000 rpm.

- 150.0 kph at 10000 rpm.
- 165.0 kph at 11000 rpm.

- 180.0 kph at 12000 rpm.

And just for reference 4th gear becomes 12.86 km/1000 rpm.
-   51.4 kph at   4000 rpm.

-   64.3 kph at   5000 rpm.

-   77.1 kph at   6000 rpm.

-   90.0 kph at   7000 rpm.
- 102.9 kph at   8000 rpm.

- 115.7 kph at   9000 rpm.

- 128.6 kph at 10000 rpm.
- 141.4 kph at 11000 rpm.

- 154.3 kph at 12000 rpm.

They also have Aluminium T6 rears, in sizes 36 to 42.
Steel is better for the street use, lasts much longer, but T6 is lighter and used for racing.
Apparently it does wear quite a bit quicker.

Mine is already de-restricted as far as Intake and Exhaust go.

After the Dyno run, I will see what power I am producing at the wheel.
When this is fine tuned (jetted) - with existing 30mm Carb, we will re-Dyno.

Then the plan is to Open up the intake further.

- I wish to put on the 38mm Keihin PWM Carb.
- Or maybe back to the PWK 33mm - if I find that one suits better.
- I wish to modify the Intake throat into the Reed Box.
- If I use the PWM38, I will remove the Standard Airbox and fabricate a New Cold intake Tube with Pod filter.

Then back to the Dyno to fine tune the new intake setup...

After that we will have some good figures, and that is where I intend to leave the bike.

I will probably be happy with getting to 208 kph (130 mph), with 'bolt-on' performance setup.

That is my current goal.
And it is about how the bike gets there that counts.
However, if I am to achieve the 240 kph target, I may need to look into the porting a new piston, port case timing, and a performance head.

Maybe that increase in capacity to 170cc, and the Royal Rods (conrod) I see made in Taiwan.
(see KiWAV Motors)

Stay tuned...

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