Sea Level?

[midlifecrisis]

OK, so Ive had Firebanshee, SD1026, and some of the other members answering some questions for me and they seem to always come back to sea level. Im wondering why this has such as huge impact on the machine when most of us seem to live within 300' of sea level (Im at +/- 250). I guess I can see that if you lived in the rockies or somewhere higher up, that their is going to be that much less oxygen, but why is it that it seems to affect us who dont live higher up?

 

Also on a side note, I have gathered that if I wanted to run a cool head, that I should be between 21 and 24 cc domes. Does the dome size make a huge difference if there is that much variation between the sizes that have been suggested to me? How did Yamaha decide on making 24cc stock? Why does the smaller size require a higher octane? Why couldnt you run a 18cc dome with pump gas?

[bansheesandrider]

OK, so Ive had Firebanshee, SD1026, and some of the other members answering some questions for me and they seem to always come back to sea level. Im wondering why this has such as huge impact on the machine when most of us seem to live within 300' of sea level (Im at +/- 250). I guess I can see that if you lived in the rockies or somewhere higher up, that their is going to be that much less oxygen, but why is it that it seems to affect us who dont live higher up?

 

Also on a side note, I have gathered that if I wanted to run a cool head, that I should be between 21 and 24 cc domes. Does the dome size make a huge difference if there is that much variation between the sizes that have been suggested to me? How did Yamaha decide on making 24cc stock? Why does the smaller size require a higher octane? Why couldnt you run a 18cc dome with pump gas?

Sea level is the reference point and there is more oxygen in the air there. As you go up in elevation, no matter how little the oxygen starts thinning out, so jetting adjustments need to be made. As far as dome size, the size of the combustion chamber, or dome, affects the compression RATIO, which determines how hard the air/fuel mixture is squeezed. The harder it is squeezed the more volatile it is, within the limits of the fuel. The more volatile the mixture is, the more power you get AND the more likely it is to ignite from preignition. To resist preignition, you need higher octane fuel. That, in basic terms is the reason you can not run pump gas with 18cc domes. The higher your compression is, you make more power at low RPMs, but it is harder for the bike to turn high RPM. The lower the compression, the less power it will have down low, but it will rev easier and higher. That is why an engine that needs a top end will run like a raped ape once it is on the pipe. Yamaha decided on 24cc because that is what they felt was the right size for a stco bike to run on 93 octane and give them the power characteristics they wanted with their pipes, carbs, and porting. We started changing dome size becuase we changed all the other stuff and/or are willing to run race fuel.

[TwistedSheeRida]

what ^ he said. Not only is there more oxygen in the air the oxygen in the gas varies on different elevations. So say you bought gas at 3000ft and brought the gas down to 100ft, the bike will have to be rejetted due to the difference in oxygentated fuel.

[SD1026]

Sea level is the reference point and there is more oxygen in the air there. As you go up in elevation, no matter how little the oxygen starts thinning out, so jetting adjustments need to be made. As far as dome size, the size of the combustion chamber, or dome, affects the compression RATIO, which determines how hard the air/fuel mixture is squeezed. The harder it is squeezed the more volatile it is, within the limits of the fuel. The more volatile the mixture is, the more power you get AND the more likely it is to ignite from preignition. To resist preignition, you need higher octane fuel. That, in basic terms is the reason you can not run pump gas with 18cc domes. The higher your compression is, you make more power at low RPMs, but it is harder for the bike to turn high RPM. The lower the compression, the less power it will have down low, but it will rev easier and higher. That is why an engine that needs a top end will run like a raped ape once it is on the pipe. Yamaha decided on 24cc because that is what they felt was the right size for a stco bike to run on 93 octane and give them the power characteristics they wanted with their pipes, carbs, and porting. We started changing dome size becuase we changed all the other stuff and/or are willing to run race fuel.

perfect info!!!! there is also a chart that will help u figure out ur dome size to acheive ur desired compression

[rb0804]

OK, so Ive had Firebanshee, SD1026, and some of the other members answering some questions for me and they seem to always come back to sea level. Im wondering why this has such as huge impact on the machine when most of us seem to live within 300' of sea level (Im at +/- 250). I guess I can see that if you lived in the rockies or somewhere higher up, that their is going to be that much less oxygen, but why is it that it seems to affect us who dont live higher up?

 

Also on a side note, I have gathered that if I wanted to run a cool head, that I should be between 21 and 24 cc domes. Does the dome size make a huge difference if there is that much variation between the sizes that have been suggested to me? How did Yamaha decide on making 24cc stock? Why does the smaller size require a higher octane? Why couldnt you run a 18cc dome with pump gas?

 

Everyone pretty well answered most of your questions. As for the 24cc chamber being stock, Yamaha determined that it would be good for the 92/93/94 octane that is available and the various uses/riding conditions present, knowing that somewhere along the line someone was going to put in 87. Could they have designed the chamber better with a higher compression ratio? Sure they could but you have to remember that this is a bike sold to the general public with a factory warranty.