hi guys

i want to know about duration

is it true ?

low duration means needs more octane

high duration means needs low octane

 

Duration of what?

 

for camshaft

 

Not with the cams that we run for our cars

 

like this simple

is it that cam shaft

225/236 .629"/.615"

need more octane than

235/248 .649"/.615"

 

Nope it's not going to make hardly any difference all on its own

 

Sort of. More duration means the intake valve is open longer, and usually means it closes later in the cycle. That means it will increase dynamic compression and cylinder pressure. That's kinda the point, because that's how you make power. To prevent detonation, you would want to use a higher octane fuel.

But as said above, the example you've given in an otherwise stock engine probably won't be a big enough change to matter all by itself.

 

Hi Trex, I agree with your observation due to changes in cylinder pressure as stated above.

The engine will compress the Air/Fuel AND HEAT this mixture from compression energy input.
The hotter the mixture, the more octane is required to prevent Pre-Ignition.

UNDERSTAND this effect is RPM related.

Lance

 

Look up dynamic compression and that will help show you see how that is correct. The closer the intake closes to BDC the move volume that is compressed in the cylinder and the more that will heat up when compressed.

 

thanks guys ,,

 

any updates on this one? I just paid about $12.xx a gallon for sunoco 260 plus... Wondering if this is really pricey or basically the norm these days.