What do the Initial and final boiling point of a race fuel determine in reality. I'm having some knock issues. The car was tuned on C16

Specification Sheet: VP C-16

Specific Gravity: .735 @ 60°F

Lead: Leaded

Color: Blue

Motor Octane: 117

RVP: 1.85

Oxidation Stability (min.) 1440+

Distillation:
10% evap @ 211.5°F
50% evap @ 213.1°F
90% evap @ 215.8°F
E.P. @ 233.3°F


but I'm running This:

Specific Gravity 0.715
Antiknock Index (R+M)/2 112
RON, Research Octane 114
MON, Motor Octane 110
Reid Vapor Pressure 8
Distillation, ºF
Initial Boiling Point 90
10% Evaporation 155
50% Evaporation 215
90% Evaporation 235
Final Boiling Point 260
Oxidation Stability, Min 1440+
Copper Strip Corrosion No. 1
Existent Gum, mg/100ml 1


Whats the difference?

Also what would this fuel below do differently?


Specification Sheet: VP Blue

Specific Gravity: .717 @ 60°F

Lead: Leaded

Color: Blue

Oxidation Stability (min.) 1440+

Motor Octane: 108

R+M/2: 109

Research Octane: 111

RVP: 7.20

Distillation:
10% evap @ 140.1°F
50% evap @ 214.0°F
90% evap @ 248.4°F
E.P. @ 389.3°F


I'm NOT leaning out.


Maybe factory ignition is not doing well enough. 16psi using NGK 105 race plugs

 

Dunno about the boiling points but the obvious thing is that the fuel spec that you're running is 7 points lower in MON than the C-16 it was tuned on. And you're having knock issues? The Blue in the last line is even lower. Where is your question here?

 

What do the Initial and final boiling point of a race fuel determine in reality.

I don't see where 117 vs 110 octane would make a difference at 16psi but I guess if it was tuned on C16 it really would make a difference?

 

If your timing was advanced to be ok with higher octane, then you will knock with lower octane. Sounds like you were tuned without much safety factor...

 

Would water/alchohol injection help?

 

More octane would help.

 

http://www.faqs.org/faqs/autos/gasol.../preamble.html


The abridged version is that a lower boiling point relates to higher octane. The rub is that fuels that boil at a very low point may vapor lock more easily.

 

Here is something else to think about: In addition to the big octane difference between your fuels, there is a huge difference in vapor pressure between the first fuel and the other two fuels.
We have been doing some testing with alternative fuels at work, and there seems to be a correlation between high vapor pressure and ignition delay; a high vapor pressure fuel takes longer to start burning. Once it does start burning, then it can burn rougher than a low vapor pressure fuel. I don't know why this happens; it is just something that I have observed. Can anyone explain?