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

i'm old school. would rather ice cold fuel cooling my crankcase and piston vs a computer program telling me how much fuel I need.

so the stock squish is .088 and about 150psi. take a straight .04 slice off that for less than $75 at your local machine shop and you end up at .049, 180 psi and just over 13/1 compression. some guys would say that's safe for premium. would be close. nyhow that's the first head mod i'll try. going to do another at 15/1 as well. have the pc pipe, 44 lectron and a few other custom pipes to try. hopefully soon
 
Just spent some time tuning a 250tpi with a jd tuner. It was so lean stock that it didn't make any power at wot. After sx head it was even worse. All indications that factory tunes it as an epa trail bike not motocross. If I had one on the snow I would make sure it has a warranty and consider adding more fuel mandatory.
 
I've been reading some porting theory by Graham Bell. He classified bikes into 2 categories motocross and road race and I notice big difference in port timing trends between the two. Road race outputs are higher and not as broad. I've been trying to guess what the newer 300s would be classified as....
 
this is great discussion! A lot of this is way over my head. Do you guys have any resources that detail the concepts like port timing, crossovers, pipe tuning etc? I’ve always been interested but much of it seems like a black art. A 4 stroke is easier to comprehend in my pea brain.

Why do the smokers run out of rev before the thumpers? It’s curious to me and I had an epiphany that sure, a smoker bangs twice as hard as a thumper, but if the thumper revs 2x higher, then the reality is they bang just as often, but the thumper just spins harder. Now, that makes rotating mass, but as bob pointed out, rotating mass isnt as important for us (I feel that having no wheels spinning also reduces this effect greatly as well)

My bike (450) has a piggy back fuel controller that allows fueling and timing changes, and it sniffs the exhaust with a wideband sensor, these sensors don’t really like 2 stroke oil, but they do work for short time periods, enough for tuning, is this correct? If so, it’s an invaluable tool for that top end stuff at altitude.

My other epiphany is that we are really in need of a whole new engine platform. Yes, a 600 v twin is what we need. But nobody will give us that because we are too small a market to develop one in ernest. So, what we need to do is find other sports that need this engine as well and somehow convince them to bolster the need lol. I dunno, go karts? Jet skis? There must be SOMEONE who could use one!

Also, is there a reason why 2 strokes must use oil in fuel? I understand that it lubes the bearings, but those could be wet lubed like a thumper. I’m thinking about epa resistance to these engines moving forward. Seems that a two stroke that uses plain fuel, computer injected, would be much cleaner than the way they do it now. I understand it would take a different approach to the process, but since they can do it with diesel then I don’t see why they couldn’t with gas.
 
sad to say

a lot of new more hp found in the 2 strokes is the result of better transfer port shape, longer transfers and the way they angle into the combustion chamber.

the reason that the serious search for hp in 2 strokes usually means recasting cylinders with more better transfer tubes. you gnaw around the edges of your ports like we all have for the last 60 years and on some motors find a little here a little there, but seldom a big jump in seat of the pants WOW!

the KTM 300 engineers were given a design mission of fair torque, easy building non abrupt power, gas mileage, quiet power.

To go 90 degrees with their cylinder ..............not so good. You can find a little hp here and there. Its hard to change the whole complexion of their designed model.
 
Good discussion for sure. What I have found is there is typically some give and take. For instance, too much compression they don't want to rev, too drastic of port changes you lose a lot of low end. Anyone ever think of methanol? Big power/ $hitty milage. IDK. I havnt played with new gen of motor, but on the 07-16 300s I found add base gasket till the transfers open all the way and then build the head to get suitable compression. Usually 190#+ on a guage, and yeah I know thats not a real cranking compression #, but much above that and mine wont rev out at 3500-6500 feet.
 
So how would you guys define "acceptable low end power" for a two stroke?

Without a dyno or even a bar mounted tachometer is going to be a seat of the pants discussion. Obviously the peak is going to be way more narrow than a 4 stoke. So we can't ever use them for comparison.

The new gen 300's I've built with raised cylinders might have lost a bit of low end at idle. The 380s/360s never seemed to loose any low end anywhere that I can tell.

Everyone will tell you a bone stock 250sx has less low end than a 300 for dirt but on the snow I have never seen a bone stock 300 work better than a bone stock 250sx.

I might be too much of a 150 rider to notice any positive benefits of low end torque but here goes my take on it:

I feel the power really only matters on a 2t after the power valve opens. Below that it really just need to start, idle somewhat and not have to smoke the clutch to get going. To me if the pv isn't open on a 2t you'd better be heading down hill on hard snow with a tail wind... That being said my current 360 build does have the ability to pull it self onto the pipe much better than a small bore but I don't think there is any way to get that same feeling on a 300 without sacrificing too much peak.

If I had a dyno I would shoot for making the bubble above the 50hp mark as wide as possible and ignore everything below it. A 2t is lucky to have 25-30 hp at 6000rpm. Tune it for low end and you might get 35 but never break 50 on top. But what are you going to do with 35hp on a snowbike? You might as well convert a 250f.
 
That would be a real sweetheart. Doing some testing this weekend hopefully. Baseline, cut head, big carb and a few pipes
 
K so did some testing. Open air box, measured off front sprocket

Stock with red spring 1 turn in is 48ish and the torque is flat at 31 from about 5000-8500

Take a flat 50 thousandths cut off the head and it ends up at 60 thou squish, 180psi and 13.3/1 compression. This makes + 2-3hp and tq thru the whole rpm range. (Pic #2 shows gains)

PC pipe doesn’t do much. A bit more over rev but that’s about it.

First try in NPP pipe got us to 56hp with a bunch more meat in the midrange. (Pic 1 shows NPP first try vs PC)

This was with a 440 main jet. It was a little rich. Could drop to a 430 or 420 and pick up a little more

Vid https://youtu.be/jVvUlOzQRko

9BA965CE-508A-452F-898A-1CB2F74BCBF6.jpeg 88691469-5474-4EF2-8CC6-29333971F96C.jpeg
 
As a comparison I was watching a YouTube vid of a 300 FI XCW on the dyno and they got 57hp. Dynos are never apples to apples as we all know, different elevations, yada yada but interesting none the less. I think it also had some head work done if I remember right. Being a 300 you would have to think there is a reliability vs power plateau and it has to be near 60ish which is plenty for a snow bike. I'm thinking a 2020 300 XC with a 2020 129 Freeride might be the bomb. Might need a second mortgage.

M5
 
Ya that would be a nice setup.

I think it needs more timing. Anyone played around with boxes (are their any?) or an old school offset key?
 
portgrinder said:
K so did some testing. Open air box, measured off front sprocket

Stock with red spring 1 turn in is 48ish and the torque is flat at 31 from about 5000-8500

Take a flat 50 thousandths cut off the head and it ends up at 49 thou squish, 180psi and 13.3/1 compression. This makes + 2-3hp and tq thru the whole rpm range. (Pic #2 shows gains)

PC pipe doesn’t do much. A bit more over rev but that’s about it.

First try in NPP pipe got us to 56hp with a bunch more meat in the midrange. (Pic 1 shows NPP first try vs PC)

This was with a 440 main jet. It was a little rich. Could drop to a 430 or 420 and pick up a little more

Vid https://youtu.be/jVvUlOzQRko
Click to expand...

I talked to Neil years ago about a twinwall snow spec pipe for 300. Never materialized. I know he can make some power. Now my overbuilt 300 sx motor will be in the milkcrate in the trailer incase .5l goes down. I will be watching this thread and if he builds a twinwall pipe i might be down.
 
https://www.ebay.com/itm/PROGCDI-R3...051311?hash=item1eae76f86f:g:AM8AAOSwZwxa1g8w

ive been using one of these on my 4stroke, and was going to try it on my 360 this week. it is easy to prog any point on the curve with the buttons. its so hard to improve timing without a dyno and my dyno is melting fast. the progcdi comes blank so i have to start from scratch. i found a cr250 curve i was going to start with as a base map.

where in the curve did they add 9deg? where is the brc owners?
 
Last edited:
that little guy would be perfect. I imagine there is a little wiring involved and you scrap the whole stock ign system, or is it a piggyback type deal?
 
Its not a piggyback, you remove the stock box and connect the tunable one must be spliced unless you have the bullet connectors to go to stock harness. Its nice because the readout is really bright and it is also a tach. Makes tuning easy without dragin around a pc. High low switch makes it real obvious what works better on the hill but still not as good as a dyno.

Any way someone can map the stock curve on a 300 with a timing light and degree wheel? My testing of the pre 2004 boxes shows the 300/360/380 the same curve. But testing a 250sx cdi on the big bores doesn't work as well. The 250sx box on the new 300's always did well. Not sure what the 300sx box is like.
 
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