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      JUST IN!   04/24/2018

      HOW TO: 4-STROKE PISTON REPLACEMENT DONE RIGHT!

slicknick

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About slicknick

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  1. Its called. Its running to hot. Get a fan or better fuel. Has nothing to do with the inner oring. Usually guys that mod head drill the pins deeper in the head. And trust me. It would loose all the water if it was hanging up on the pins
  2. Your lucky that's all that broke with detonation that bad.
  3. 52hp. Very close to original design with a few tweaks. Should go 54/55hp at 9000. But out if ign . 250cc.
  4. Don't be afraid of head mods. You have some broken parts. But the tune was off not the head exaclty., numbers could have been more exact with a sq test and better yet, head filled with a burrette on engine. But there will always be something off when the engine is not present. You can't port and not do something to the head. It doesnt work that way. Can't go mx racing on pump fuel imho. Detno is the burning fuel, heating up the unbunt fuel at the edge. Burn it to fast, its over. Heats up/detnos at outside edge. Most guys squish isnt tight enough . If fuel is not there. It can not detno.
  5. Its not the porting. Your tune was off. Jbfl is right. Detno to death. The other that lasted longer probably had diff squish which =diff comp, or was ridden in different conditions, like diff weather or track conditions. Can't recut heads without knowing squish. Impossible to do correctly without you doing a squish test 1st. So either up your octane or add some jet. Octane is the more reliable answer most likely.
  6. That was a one off, lets see jbfl results, I am not even sure if I want to do it again. Most would not reliaze the time it takes to change it
  7. Give me call, but it would be a while, I have a lot of minis to do right now.
  8. Tomuch. I saw your post and I agree with you. I mentioned the same thing in your post. Yes, you did a little testing. But I have a lot of time testing/ changing the trapping efficiently. How many guys are going to change a transfer port angle by a lot and run it on the dyno? and how are going to change the angle without changing the port velocity in a bad way? There are ways to pump of the curve. It really is half porting and the other half is a lot of epoxy/transfer changes. I have many sims which are crank hp, exactly 10% less on the dyno every where in the curve. and I spend ages in the transfers to make it happen on some builds. So I will respectfully disagree the sim is inacurate. The build is inaccurate. JBFL is going to run it on a dyno down there and post the results here. We already know the torque is there, the gearing shows that, 14/48, may need a 47. he had a 14/50 on it. I want to put at least a 40mm on it, but will test with the 39 1st. You really need to get it on the dyno JBFL.
  9. To give you a idea on what is changed. Water is a good way to show you . . 1st pic is stock. Front mains took forever to get a good direction. 2nd pic is some what close to the where there at now, with wider taller transfers. I changed the rear transfers a lot as well. But not posting pics of that. Like i said. You can play on the dyno with this for years till you get a idea on how it works and its pumps up the power curve everywhere. Now think what happens when its bored out. I am sure it really throws it off.
  10. I was going to start a topic on this, but looks like JBFL beat me to it, There are very few topics or none, on changing the charging/scavenging and how this can be used to increase performance. But there sure is a lot of BB talk. About 3 months ago. JBFL called me for some porting/head work on his 06 YZ250. Me and him, have had a long relationship, ( I built him superminis to 125s then 150strokers) So I wanted to give him something no one has on a YZ250. I have done many charging/scavenging test/ changes,on 2 strokes. Most of them simmed in software and all of them dyno tested on my engine dyno. My approach is different! This is not close to a typical port job, or adding some epoxy, this is completely changing the scavenging/trapping efficiently A 250 can make 53/55hp at the tire. with a much improved power curve than stock. 180/185bmep at 8300/8500rpm is well with in what is possible and with a well thought plan, it will have a very good power curve, but the charging/scavenging must be changed. what I am trying to say is, you can port all you want, do any mods you want, but the trapping and scavenging determines the curve. So I simed it all out for 62hp at the crankshaft, took everything into account, intake area,length/reeds,carb,porting,case compression,FMF fatty pipe and the most important,good trapping/scavenging. This required higher and wider ports, which requires transfer port direction, port shape,velocity changes I recut the head to the usual I always use on these Yz 250s for AV gas. Then I sent it all down to FL, to JBFL on here. All I had was the cylinder and head with a squish test from him,no engine, even tho I should have dynoed it, it wasn't in the cards this time around. Not like me, and I hate not knowing. The whole idea on this project was to create a good YZ250 package, that will spank a KTM 250SX everywhere in the curve, should have a better curve than a KTM, that was the plan!! and even do I dare to say a 450, like I said, 53/55 wheel hp or 62 at the crank is completely possible with 250cc and a great curve as well. JBFL on here will keep this thread updated and when he gets it all dialed in, ( looks like its dialed, hole shotted a fleet of 450s) plus its pulling a 48 easy, may need a 47. I want him to take it to the dyno and post his results here. So JB, time to find a dyno in your area. I am sure FL is full of them. He also has a Pc pipe and I am trying to get him to send me a carb to mod. . Porting/Squish/comp/pv/ign only does so much, there is no replacement for air in the right place and more of it! and the YZ's trapping can be improved upon by a large margin. It took a great deal of time and I hope it works out on the dyno. We already know the bottom/mid was beyond a massive gain, now we just need to see that pk hp number on the graph. I will post some cylinder pics up.
  11. So a 125 has more low end than a 250? cause you think so? If you did some testing, you would soon realise the dyno doesnt lie. You are comparing bikes that probably where not in a good state of tune to begin with when they had there stock bores. Plus the fact that a 72mm slug has more case comp could help in the throtttle response department as well. But make less bmep everywhere as the stock engine and make you think it has more power from less reversion/ better throttle response, , when going from off to on throttle.
  12. The squish being off is huge, which should = around to adding 1 to 1.25 full point on compression ratio. This is a educated guess from cutting a lot heads, plus it has no squish effect with the loose squish. You will gain some msv also, which will help. Kit cylinders and hitting the squish is very hard as the case height.rod, vary. You can not expect perfect squish without the engine present. Some will be on the money, others will not. Not hp's fault imho. Remember the factory cant get the squish the same. You really need to test it again with the heads right. Could make all the difference. I think Derek went out of his way here and did a good job and showed everyone "what does what" with the above graphs, He used science, which never lies and is 100% more accurate than a bench build that "you think rips" guys just measuring the cylinder, or reading this thread and says it needs this done etc, "never works" its a 2 stroke, you may think you understand port timing, compression,ign timing,pipes etc etc, but it not does work like you think. Unless you tested it to death ON THE DYNO on that particular model machine,with the same bore and stroke, and changed one thing at a time,you really can not comment on what you think it needs. You may not agree or understand his findings, but again that's how the average guy and a lot of shops with no facts " think". and comments like "not interested" show how much of a clue you do not have. Most of the bigbore's out there have not even been spun up to see where the short comings are and they for sure have short comings. Other kits all have major short comings. 145 bmep G-YZ300 kit is 15% less efficient than a stock YZ250. But some guys think there great, add 50cc for 15% loss in bmep, ( brakes means effective power) This is not what I would call a good increase as its not even as efficient as a stock 250. But there cheap bench builds and the average guy doesn't know this. The is a lot of bs in this industry, but the explanations and graphs from hp are not.
  13. Polar bear, I said head and not piston, sorry. At least you chucked up a new piston, a lot of guys wont. There should be a comparison thread, there are differences.
  14. The only head I am comparing is the one you cut. I understand what you did 100%. Not all heads are created the same. Just cause thats the way it was, doesnt mean it has to stay the same. Athena kits can be improved upon greatly. My point? This is one area that can make a engine run good or like a pig.