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#1971410 - 07/31/10 05:34 PM MMO increases or decreases octane rating
jsap Offline


Registered: 07/22/10
Posts: 60
Loc: NorCal
Does MMO increase or decrease octane rating of gasoline?
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#1971414 - 07/31/10 05:38 PM Re: MMO increases or decreases octane rating [Re: jsap]
Boomer Offline


Registered: 09/19/08
Posts: 1747
Loc: Pennsylvania
Most oily substances are linear hydrocarbons, statiscally speaking, and would therefore be of low octane rating. So I would put MMO in that category. However, if you follow the manfacturer's recs, it should not have a large affect.
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#1971417 - 07/31/10 05:42 PM Re: MMO increases or decreases octane rating [Re: Boomer]
Lethal1ty17 Offline


Registered: 07/01/10
Posts: 684
Loc: Georgia
technically yes they would, but to such a small degree that it is negligable. like the age old question of "does peeing in the ocean raise the sea level" yes, but to such a small degree that it doesnt matter.

i put an ounce or two of MMO in each tank of gas i get now.

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#1972128 - 08/01/10 02:40 PM Re: MMO increases or decreases octane rating [Re: Lethal1ty17]
jsap Offline


Registered: 07/22/10
Posts: 60
Loc: NorCal
I see, so it would lower octane, but only to the degree of [censored] in the ocean. :)

Well, I'm trying to add up the various factors on possible contributors to pre-ignition. So far, I have these two factors:

1. MMO, by decreasing octane rating
2. carbon buildup, by increasing compression

On an old engine like mine (Mercedes M119.982) that was designed with 10:1 compression ratio and has 170K miles on it, I would think then to use a step colder heat range on the spark plugs?

(Reading the plugs would be nice, but I've been top engine cleaning, so the plugs are not readable right now.)
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#1972192 - 08/01/10 04:00 PM Re: MMO increases or decreases octane rating [Re: jsap]
demarpaint Offline


Registered: 07/03/05
Posts: 23106
Loc: NY
Incorrect timing can cause pre-ignition, so can carbon deposits on the valves, along with the wrong octane gas. Using MMO at the recommended dose isn't going to lower the octane. [censored] in the ocean pretty much sums up the effect on octane.

Have you tired very hot water via a vacuum line? That will get the carbon deposits out. Read up on it, it has been discussed several times on the site.
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#1972226 - 08/01/10 04:51 PM Re: MMO increases or decreases octane rating [Re: demarpaint]
jsap Offline


Registered: 07/22/10
Posts: 60
Loc: NorCal
I've done water through pcv and brake booster, but the appearance of the piston is still the same. (Btw, I don't have any pre-ignition problems. I'm just looking for info for future reference.)

Regarding MMO, do you know the actual octane rating undiluted? Any quantitative info?


Edited by jsap (08/01/10 04:51 PM)
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#1972848 - 08/02/10 09:25 AM Re: MMO increases or decreases octane rating [Re: jsap]
Jax_RX8 Offline


Registered: 12/13/06
Posts: 345
Loc: Northern VA, USA
This has been ask of Rich Kelly, Marvel Technical Director, and he has stated MMO is "Octane Neutral" in that it neither increases or decreases octane.

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#1973720 - 08/02/10 11:00 PM Re: MMO increases or decreases octane rating [Re: Jax_RX8]
SAATR Offline


Registered: 04/15/08
Posts: 109
Loc: Here
In the proper concentrations, it would have no measurable effect much like most (if not all) octane boosters.
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#1974328 - 08/03/10 01:14 PM Re: MMO increases or decreases octane rating [Re: SAATR]
Lethal1ty17 Offline


Registered: 07/01/10
Posts: 684
Loc: Georgia
run some seafoam to clean off those exhaust valves, or try some more water, ignition is caused by hot spots in the cylinder and carbon buildup is very good at this.

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