Might want to know the specifics of the test bike with the porting, like what pipe/carb/reeds/compression it had.
Seems like an abnormally smooth powerband if you ask me.
One problem with porting your own cylinder with a port map, you might ruin that cylinder's viability for a top notch port job from a reputable builder.
You're probably going to spend quite a bit of money buying the tools/equipment to port the cylinder, unless you feel like spending an eternity with a dremel and hoping you don't grind too much away.
I dunno, nobody had anything good to say about it on QRHQ or SQHQ but nobody actually TRIED it either.

good answer westtex!   Anyone else

It comes with the map.  I don't think it is any kind of bull. It is a guide to do it at home. If the lt's did not have the power valves everybody would just be going with gokart/rcplane/nominal porting maps anyway. Wether we know it or not the gokarts and RC engines have been there aswell and the porting numbers do not change because the math is the same. Except there engines come apart easier and the parts are cheaper......
Im not into gokarts or rc engines im just saying.....What im saying is, we are all confused about LT porting except for a few people, and we have no dyno's of the lt250 to back it up.

Hard to say,as members more knowledgable than I said you could simply raise the exhaust port giving more HP and shifting the power peak up.usually raising the exhaust port up loses some bottom end which looks similar to what the graph shows?

i have buy the race porting  template on ebay from this guy year ago, it is not easy to do, you will need to bore after the job done... i used with 38mm mikuni TMX carburetor, fmf pipe and , boyesen rad valve system. The power output is amazing compare to stock bike. i loosed a little bit of low end but it fly like a jet lol  there the dyno result, the result was better than expected.

Is the seller of the DIY kit on ebay called mark S 5000 or something like that?

i think those are good # for mild build 250 on pump gas im assuming.

Is the seller of the DIY kit on ebay called mark S 5000 or something like that?

yes, the guy is mark and i buy it on eBay . it is a very good guy and ask me every answer during my porting process.  it is not a easy job , it tame time and you will need many replacement bit for your dremel, i suggest to buy  a air tool that is far better than electric dremel. that take  me about 6 hour to complete the porting.

I'd save the money and have a shop port your cylinder for your specific needs.
It is not simple to do. Plan on 4+ hours hunched over your cylinder, then you have to bore it anyways.
Chances are a shop would give you a break on the port, bore, and hone job. After you get your cylinder back from who ever ported it make sure you map their port job before you put it on the quad. That way if you like the porting they did you can always copy it and do your own custom port job. Having the right port, carb, pipe combo (For the terrain and how you ride) is way more important than some radical port job. I do have to say, my dad bought one of theese kits and it is well put together; but more useful for beginners who wouldn't/shouldn't attempt a DIY port job.