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Matt Denecke

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About Matt Denecke

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    TT Newbie

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    Virginia

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  1. I do agree with jaguar about the utility of a good squish velocity calculator. Blindly tightening the squish and setting a compression ratio to a trail and error approximation leaves a lot of room for optimization. There are a lot of parameters of combustion chamber design that have various effects, but being able to have a target squish velocity and target corrected compression ratio for a particular application are always the second step for me when working on a head design after choosing what I want the squish clearance to be for that particular engine. That said I believe the 20m/s figure quoted from blair is outdated as a hard upper limit to where detonation becomes inevitable. I've pushed yz250 motors to the ragged edge and have found that for a modern engine 30m/s has been the limit that I design to for pump fuel. I programmed my own calculator several years ago and actually bought jaguars at one point to see how they compared. they ended up yielding very similar results and his is pretty straight forward to use. To those that will dismiss me as just a kid with a calculator, I've put hundreds of real world hours on motors running happily at just under 30m/s at both higher and lower compression than stock (depending on the desired power), and done countless head modifications for different altitudes, riding styles, fuel types, and models of bike.
  2. would love to see a comparison between rk tek's yz250 head, one of Apex technical innovations yz250 heads, and the stocker if anyone would want to do it
  3. The Apex Technical Innovations heads are polished for whats its worth. Having a polished head definitely makes a difference in terms of carbon deposits and hot spots, and hot spots can lead to detonation. Really any finish is better than the stock cast finish for reducing the amount of carbon that will adhere, also the stock casting is porous and can pit easily from detonation damage. The rk tek ones are still machined so I'm sure that they wont collect too much carbon, although having thin ridges of metal in a combustion chamber would concern me personally as an engineer. I'm sure they did plenty of reliability testing though. If you're really looking into getting into head design, the important things to consider is the corrected compression ratio, maximum squish velocity, the actual squish clearance, exhaust port timing, and the shape of the squish velocity vs crank angle curve. There's several books out there that get into the details but Gordon Jennings book is a good place to start. in terms of port texture @LuxonMX is exactly right, pretty much all flow through the ports is going to be turbulent. By having a relatively uniform roughness it helps the boundary layer stay adhered to the port walls. Otherwise, where the boundary layer separates, there can be stagnation which gives you the puddling of fuel everyone talks about. the boundary layer can also separate more easily if there are a lot of casting flaws as well, so having excessive random roughness is not ideal either.
  4. apex has a website now that you can contact them at apex-technical-innovations.com
  5. their website is up now apex-technical-innovations.com
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