KR-1S.co.uk Forum

Is this KR-1S cylinder or KR-1?


















Dirk

from what I can see, it only has one transfer port opposite the exhaust port, in which case its a KR1S as a KR1 has two

opposite the main ex port there is a boost port, on the kr1 there are 2. the kr1s has one but still the 1s is about 5hp up on power against the kr1. the second boost port does nothing for power.from what i can see i think its a kr1s cylinder as i could only spot the 1 boost port.

hi folks

thanks for your information.
The kr is for me virgin soil and i very pry what the difference between both models is and how this engine work.
What does the second boost port do in the KR1?
better cylinder fill?

Dirk

nothing, well very little. have in fact read somewere that a single boost port on the kr1s is actually too big or certainly big enough. not known any tuners to do much to the boost port other than tidy up/make sure its even for the benefit of blueprinting. i think the reasoning behing getting rid of the extra port on the 1s is nothing glamorous such as ''finding more power'' but more likely that its cheaper to produce as theres less machining. another theory is that they wanted people to buy brand new kr1s barrels when they seized/wore out rather than putting the kr1 barrels on, even though they fit straight on. having two type barrels 1/2 the chances of finding a given barrel you want (kr1s) at a breakers therefore you would buy new from kawasaki! doubt it worked but i bet kawasaki had a good go at trying it on! kawasaki then rewarded us with the +5hp kr1s!

Isn't the 5hp power increase between the KR1 and KR1S mainly due to the better expansion chambers on the S? Apart from the slighty bigger carbs and altered boost port what other major improvements were added to the KR1S's engine?

Tofty wrote:Isn't the 5hp power increase between the KR1 and KR1S mainly due to the better expansion chambers on the S? Apart from the slighty bigger carbs and altered boost port what other major improvements were added to the KR1S's engine?

THe barrels fitted to the 1s were the KR1 Race kit barrels. Its also got bigger power valves.

The power valves have a bigger port but are the same external dimensions right?

Tofty wrote:The power valves have a bigger port but are the same external dimensions right?

yep

Tofty wrote:Isn't the 5hp power increase between the KR1 and KR1S mainly due to the better expansion chambers on the S? Apart from the slighty bigger carbs and altered boost port what other major improvements were added to the KR1S's engine?

yes, the the kr1-s pipes also give a gain in poke over the kr1's early tzr(1kt) lookin pipes aswell as looking 10x better but dubious as to wether the 1s pipes are worth 5hp on there own, although i could be wrong? i believe the extra zap is a combo of improvements but tbh theres little in it in the barrels alone for road use. for racing though its obvious that 1s barrels are a good start. iirc the kr1 gives a bit more midrange according to earl pb tests but cant be sure. the carbs are the same bore size from the kr1 to the 1s save for internal changes to the jetting/needle. imo the kr1s came with the best pipes on a std 250 and to this day there hard to beat considering there almost 2 decades old tech! the nikons give a similar curve but are a fraction of the weight. the only let down with std pipes is the sheer weight! i never realised that the 1s barrels were the older kr1 race barrels! effectively for kr1 owners with 1s barrels you have a kitted bike, well sort of! guess what, ive got a kr1-kr1s hybrid with tuned to buggery 1s barrels!

cheers for that guys,
I also noticed from the photos above that the cylinder to powervalve feed is also larger on the S

The larger power valves on the S gave about 2 BHP at the top end and the exhausts gave a mid range boost and added another 3 BHP at the top IIRC. Never seen any info on the various kit exhausts.

Pity that no one has any KR1S kit barrels . The only info I have gained about the kit barrels was that the base gasket was thicker so I expect that the cylinders were shorter, and the power valves had one side machined flat. There is also a bit of port opening info on MJ's site on the KR1R page as the new Zealand SP used one of the three different Race Kits, barrels as standard.