Technical Discussion: Octane Boosters

miloman · Feb 20, 2007

i found a good post by hotrod on NASIOC about octane boosters... since it has been pulled from the middle of a thread, i have edited it slightly to put things in context

hotrod said: ↑

MMT is not a power adder -- it is an octane booster, it only enables power potential that is already there, but unusable due to knock limited performace. Its volatility is irrelevent, as it is mixed in very small amounts. It modifies the chemical pathways and reactions as the fuel air mix is heated and burns (the opposite of a catalyist it inhibits certain reactions).

Defining it as "crap" without any qualification is pretty useless, since there is no way to discuss that sort of characterization.

The chemical octane boosters, are properly considered anti-knock agents, chemicals like MMT (CH3C5H4)Mn(CO)3, Ferrocene (Fe(C5H5)2) and TEL (CH3CH2)4Pb are compounds containing a metallic atom bound to organic molecules (organometallic ). They act by scavanging radicals during combustion and interfere with the production of products of combustion that are prone to detonate under high temperature/pressure conditions in an internal combustion engine. Of course the leaded fuels have the down side that they are hard on plugs, and emissions equipment and will if used in any quantity, kill your O2 sensor and cats if you have them. They can also increase combustion chamber deposits which can lead to detonation itself. The Ferrocene and MMT additives do form a thin layer of deposits on the piston crown and valves but in my experience they do not cause any problems, (at least when used in every tank full at near recommended dilutions for time periods of over a year). There is some research that MMT actually helps preserve cat function as it inhibits poisoning of the catalyst coating by other chemicals.

And yes the over the counter octane boosters can provide "just enough" increased octane to make a difference!

For many folks they have their place and are suitable to their needs. If all you need is a very small increase in octane to prevent detonation, they are entirely appropriate. They are handy safety tools to have available for situations where operating conditions are a bit harder than usual (very hot weather, a track day, a safety valve for a bad tank of fuel etc.)

Nitromethane was not part of this discussion -- A. Because no one mentioned it as a fuel ( the mention was of a brand name), and B. it does not have high fuel octane and does not mix with gasoline without some sort of carrier like Methanol. The last time I saw pricing for it, it was going for $40 a gallon.

Interestingly enough the NOS brand octane booster that toutes "contains Nitro Methane" does not show nitromethane as an ingredient in its MSDS sheet. Active ingredients appear to be MMT and xylene and some mysterious "propriatary polymer" all at less than <5% concentration (of a 12 oz bottle) in a base stock of kerosene, naptha and hydotreated petroleum.

Now if your talking about Methanol (methyhydrate as you refer to it), yes it is a good oxygenate, and an effective way to raise fuel octane, but buying it at the hardware store by the gallon will cost you about $10 a gallon. If you buy it at a racing fuel outlet it will go for a bit over $2 a gallon last time I bought some. Since E85 sells for less in most places and is available in pump quantities, it would obviously be a better choice cost wise. More importantly ethanol is not a skin absorbed poison like methanol is , nor is it as corrosive to the fuel system components. Methanol has been used in small dilutions in Subaru's by some, but unlike ethanol which is authorized in moderate dilutions (up to 10%) Methanol is specifically mentioned to be avoided by the factory, so use at your own risk!

Fuel volititlity (final boiling points) is not relevent to Octane, but it does enter into the discussion with some home brew octane boosters.

Toluene and xylene both have relatively low evaporation rates and high boiling points, and can in high concentrations (45%+) cause problems due to their inability to vaporize and burn in the time available in the cylinder. That can lead to them being blown out the exhaust valve while still burning which pushes EGT's through the roof.

The evaporation range of race fuels does effect throttle response and drivability but has no significant relationship with fuel octane other than some high octane fuels (like Toluene) don't do well in that regard.

The question of suitability of a give octane booster depends entirely on how much octane increase the user needs, availability in his area, how much hassle he is willing to put up with ( dumping a 12oz can in the tank is a lot easier that hauling around a 5 gallon can of a high octane blending agent).

If the user only needs .5 -2 octane numbers to reach his target boost or prevent the ECU from pulling timing, or he only needs it infrequently, then an over the counter octane booster is a good solution. If you need 3-6 octane numbers, obviously your going to have to go to more trouble and start blending some high octane fuel of your own.

The Octane boosters that contain organo-metallic compounds all leave some residue deposits in the cylinder. If used in recommended amounts they are not harmeful but if over used they can lead to sparkplug fouling. TEL Ferocene, and MMT deposit a thin layer of their oxides on the surface of the piston crown and cylinder head. In small amounts it probably improves the engines thermal performance (sort of a low tech thermal coating) as their thermal conductivity cannot be as high as bare aluminum.

If the deposits build up to excessive levels from over use, then you get into other problems like pre-ignition and detonation due to the deposits themselves.

Larry
Click to expand...

kingwrex · Feb 20, 2007

good information

Brian · Feb 21, 2007

On a related note for more boost...

I recently read a great article ( in SCC or PAS, can't remember, but I'll try to find it) where the car had 2 tanks, 2 pumps, 8 injectors. The aftermarket ECU was able to use normal gas until a certain boost level, then transition to full race gas injection at some higher boost level. Seems like a better solution than an ECU independant methanol injection system. Especially if the fuel transition happened above the wastegate's min psi.

I put this in here because it's the best solution I've found to on-demand extra boost (safely). Running race gas all the time isn't an option. And sometimes during my normally dull commute, I'll need to lay down the smack down.

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Technical Discussion: Octane Boosters

miloman Retired Admin

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Technical Discussion: Octane Boosters

miloman Retired Admin

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