ktm/husky 300. whos spent time making more power?

portgrinder

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k so we raised the cylinder up around 2mm and machined a head to get .055 squish and around 13.5/1

total disaster. Lost everywhere. lost 10+ torque at 7000rpm. I think it was even out at around 8200.

back to the drawing board
 

HalfBrit

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I think? I'm starting to get this 2 stroke stuff???
Could it be the incoming mixture is exiting the exhaust port because the vacuum wave of of the pipe is pulling for that extra 2mm of rise before the piston closes the port?
 

HalfBrit

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Just thought I'd throw out there I put the slavens snowbike needle ($30) in my Lectron 38hv that I run on the trails the rest of the year. I love the lugablity in the dirt but I get a decent amount of spooge out the tail pipe. In the snow with the new needle It's crisp and luggy and no spooge at all. FYI no affiliation with slavens here.
 

wwillf01

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Just thought I'd throw out there I put the slavens snowbike needle ($30) in my Lectron 38hv that I run on the trails the rest of the year. I love the lugablity in the dirt but I get a decent amount of spooge out the tail pipe. In the snow with the new needle It's crisp and luggy and no spooge at all. FYI no affiliation with slavens here.
For sure I run the snowbike specific needle in my yz250 but it runs clean... my only complaint is it ices up easier than stock or the smartcarb I have on the other bikes. I have worn through 2 slides...plus on the yz you have tps which seems to give you more of a top end zing....

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Dec 20, 2007
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k so we raised the cylinder up around 2mm and machined a head to get .055 squish and around 13.5/1

total disaster. Lost everywhere. lost 10+ torque at 7000rpm. I think it was even out at around 8200.

back to the drawing board
13.5 cr is lower than you were running with stock port timing. Usually you can go higher cr when raising ex port. Did you try +1 mm before you went to +2?
 

portgrinder

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Ya the head just ended up at 13.5. Didn’t do my math right... 15/1 would have added another few lbs everywhere but it still wouldn’t have been close. I went right for 2mm as I liked those durations.

You can see some carbon in the roof of the transfers. Needs more blowdown. Raising the cyl decreased that slightly.
 
Dec 20, 2007
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Well you could still make one more try with the head. Cut out the squish pad 025 and don't cut the dome. Then go to +1 with a tight 040 squish still might work and cr will go up.

Or in the the big scheme of making power 300 cylinders are fairly cheap and even if you hog the ex higher it will still have a decent value on the used market as a "race ported” cylinder.

I just pulled off 7 days in a row riding my vintage 2 strokes and my 450 just sits in the garage. I'm so into my 2 strokes right now I have to suggest the do whatever it takes approach it will always be worth it in the end even if you back slide a bit. My 360 mod motor has the most insane throttle response, mid torque and still overrevs like a 250. The width of the power band almost makes me feel guilty of cheating. when I ride with the 4 strokes I just keep thinking what a factory built mid bore 2 stroke could totally dominate the snowbike market and just like current sleds no one will want to ride a 4 stroke anymore without a turbo.
 

portgrinder

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so on teardown, noticed one of the aux powervalve barrels was installed wrong on the bike we did the last run with. it had a left hand barrel in both L and R side. it was open at idle and closed at high rpm. so we'll fix that and test again. might be more out there that came wrong from factory. might want to check yours if you have one.
 
Dec 20, 2007
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that's gotta make a big dent on the dyno. Hope the next run shows more promise. Are you going for +2 again? Was there any place in the over rev range that had improvement? Have you run any of these builds yet on the snow?
 

chumbilly1

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Portgrinder, Please keep us updated! Is that the NPP snow specific pipe that you have mounted? I was taught to raise the cylinder till the transfers open completely at BDC, at 2mm you must be higher than this hey? Also are you doing any case porting on this 300? Also what CDI are you using?
 

portgrinder

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ya, trying +2 again. i'm lazy and didn't want to measure again. last time It was no gain anywhere. it got to as good as even steven after 8k. same exact rate of tq falloff after 8

there is some room under the transfers for sure. stock case and jug. stock cdi. the sx cdi didn't do much. tried it. I think I wrote down somewhere on here what it did.

running the pipe + carb + compression @ stock jug height on snow. really like it.
 

chumbilly1

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So I presume that the PV has been corrected. Am I correct that you never tried the dyno run again after the PV was corrected? Im excited for our winter to get right so I can play with mine.
 

portgrinder

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so after the correct valves were installed that helped a lot. raising the cylinder 2mm basically just shifted the torque curve over 1000rpm vs a stock cylinder. so yes it made significantly more power. 7 more maybe. i'm looking for wider though, so the search continues.

couldnt be happier with the snowbike pipe. tucked in way nicer than stock, big gains through the whole curve. lots of snap on the bottom and nice over rev. its been a work in progress.. 5 seasons and 5 barrels of fuel getting it right.
 

tribalbc

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so after the correct valves were installed that helped a lot. raising the cylinder 2mm basically just shifted the torque curve over 1000rpm vs a stock cylinder. so yes it made significantly more power. 7 more maybe. i'm looking for wider though, so the search continues.

couldnt be happier with the snowbike pipe. tucked in way nicer than stock, big gains through the whole curve. lots of snap on the bottom and nice over rev. its been a work in progress.. 5 seasons and 5 barrels of fuel getting it right.
Do you have a pic of the pipe?
 

chumbilly1

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so after the correct valves were installed that helped a lot. raising the cylinder 2mm basically just shifted the torque curve over 1000rpm vs a stock cylinder. so yes it made significantly more power. 7 more maybe. i'm looking for wider though, so the search continues.

couldnt be happier with the snowbike pipe. tucked in way nicer than stock, big gains through the whole curve. lots of snap on the bottom and nice over rev. its been a work in progress.. 5 seasons and 5 barrels of fuel getting it right.
So I presume that the peak HP is 1000 RPM higher with the +2mm? Do you think that the ignition is mapped sufficiently for the increased rpm?
 
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