Hi guys/girls,

I run my bike at two different circuts; one fast with a lot of acceleration, and one tight with a long straight.

Advice from Matt from Tyga is to run low comp, retarded timing and a loose piston for long, fast tracks.

My question is: What are the different sizes for each barrel? I.e. is an A barrel the biggest, followed by B, then C?

If that is the case, then it would follow that I could run a B sized piston in an A barrel, to satisfy the 'loose piston' requirement. Similarly, I have a spare C cylinder piston, can I safely run this in a B barrel?

Or are they not in order? Can someone in the know clarify this for me (beyond the basics of what piston matches what barrel etc)?

Cheers!

Given that the "newest" NSR250 is now 17 years old, and consequently you cannot often be sure if some barrels have already been replated or not, I would advise you concentrate more on piston-to-bore clearance than actual sizes.

OEM clearance is 0.035~0.044mm, with a service limit of 0.08mm. In my opinion, 0.08mm is VERY slack!

Those numbers should give you an idea of what's sensible to run, however I would say that Matt does go to extremes with race motors, that aren't necessarily convenient or appropriate for the majority of owners, even those who trackday a lot. As an example, Stephen RC45's MC21F3, making in excess of 75hp, always ran the same clearances, regardless of track. Not saying he's wrong, far from it, but he was racing against a Honda/HRC backed team when he was building those motors.
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Andy.
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Andy wrote:Given that the "newest" NSR250 is now 17 years old, and consequently you cannot often be sure if some barrels have already been replated or not, I would advise you concentrate more on piston-to-bore clearance than actual sizes.

OEM clearance is 0.035~0.044mm, with a service limit of 0.08mm. In my opinion, 0.08mm is VERY slack!

Those numbers should give you an idea of what's sensible to run, however I would say that Matt does go to extremes with race motors, that aren't necessarily convenient or appropriate for the majority of owners, even those who trackday a lot. As an example, Stephen RC45's MC21F3, making in excess of 75hp, always ran the same clearances, regardless of track. Not saying he's wrong, far from it, but he was racing against a Honda/HRC backed team when he was building those motors.

Fair call Andy. I see the most value for me in finding a nice compromise that doesn't need to be fiddled with all the time.

I guess the issue is determining which piston to order. It sounds like your advice would be to order the correct piston for the barrel? Followed by a careful tune obviously.

That being said, can you clarify if the C barrel is smaller or larger than the A and B barrels? It would be a shame if my spare piston was of no use (I will obviously measure it and check the clearance anyway, if I have the tool for it).

A barrel = Biggest hole!
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Andy.
NSR-WORLD.COM

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Might be worth you investing in a detonation counter if you're running at such varied tracks. Especially if you're jetting skills are as good as mine...

One step ahead of you Dave! There seems to be varied information about how to use these though. Are you able to explain how you use it, without going into the specifics of jet sizes? In particular, how many detonations per km is a standard accepted number? I've heard HRC figures of 10 per km...

Anyway, if A is the largest I take it that C is the smallest? It seems logical, but with NSR pistons and barrels it's not always so...