pistons 14.1 or 13.5 yz450f

6 replies to this topic
  • Blackyz450

Posted June 23, 2014 - 07:39 AM


Do they make a 14.1 piston for 2006 yz450f and will a 13.5 make much more power then what I have now which is a je 12.8.. Will I see power on top end to? I drag this bike and run 110 octane

  • L. Euler

Posted June 23, 2014 - 08:02 AM


If you are going to drag this thing then you need to run the lowest octane you can get away with.  Generally, higher octane fuels have lower energy densities.  Can't comment much on the pistons, except for this: you may need longer duration cams to take advantage of higher compression.  Above about 11:1 simply raising compression has diminishing returns unless other factors are accounted for.

  • grayracer513

Posted June 23, 2014 - 11:25 AM


Higher compression usually benefits low RPM power more than top end, and can sometimes actually slow an engine down in the upper rev range.  Depends how your engine is currently set up, but 13.5:1 should be OK.  High compression also has the effect of "civilizing" intake behavior caused by very aggressive valve timing.


Octane number simply does not reveal any information whatsoever about the energy density of fuel, particularly racing gasolines.  The only thing octane number tells you is how much resistance the fuel has to being ignited by sources other than flame or spark.  Nothing else.  While it's a waste of time, and sometimes money, to pursue any higher octane than is required to prevent detonation, there is very rarely any correlation to power output one way or other that can be considered generally true of all gasolines.  You aren't gaining anything by using 110 octane, even though the basic gasoline blend probably has significantly more energy than pump gas. 


Any fuel with a Motor Octane rating of 92 or higher is plenty for a YZ450 in most any state of tune.

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  • L. Euler

Posted June 24, 2014 - 04:47 AM


I understand what octane is and realize that octane rating does not reveal anything about energy density. However, in general higher octane gasolines have lower energy density. This is probably different for exotic fuels.

Edited by GammaFunction, June 24, 2014 - 04:51 AM.

  • grayracer513

Posted June 24, 2014 - 06:45 AM


I understand what octane is and realize that octane rating does not reveal anything about energy density. However, in general higher octane gasolines have lower energy density. This is probably different for exotic fuels.


Even with pump gas, it's an unreliable generalization that simply doesn't hold up.  It was somewhat true of leaded fuels simply because tetraethyl  lead is basically inert as to the combustion process, so the greater volume of it there was in the gasoline, as there would be with leaded premium vs. leaded regular, it would naturally reduce the energy density by 1 or 2%.  There are also summer and winter blend fuels sold in many parts of the country (whether or not they actually have "winter"), and occasionally we used to see cars with cold start issues that related to using summer blend premium in a car designed for regular, and the combustibility issues were wrongly attributed to the high octane of the fuel. 


But none of that automatically follows anymore now that lead isn't used.  Gasoline at any level is not a single chemical compound, but a blend of anywhere from 6-15 ingredients.  Several of the ingredients in contemporary pump gas blends that are there for the purpose of detonation suppression are energy bearing, combustible components of the overall mix now.  With race gas, you just can't make that statement at all, especially with the unleaded blends.

  • Blackyz450

Posted June 24, 2014 - 07:27 AM


This is all good info.. But my question was what would be the better mod

  • grayracer513

Posted June 24, 2014 - 08:12 AM


See post 3, paragraph 1. 

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