Detonation

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shiftless

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Can someone give a detailed description of what I should be looking for on a spark plug to determine if detonation has occurred? I have heard something about black specks on the insulator. Are these visible to the naked eye? What do they look like under magnification? I have also heard that the edges of the electrodes will be rounded off instead of sharp if detonation reaches a certain level.
 
They can be seen with the naked eye. Looks like small specks of pepper on the insulator. I don't know about the look with magnification.
 
Best description I've ever heard is "fly-shit" - depending on how good your eyes are, you may be able to see it with the naked eye, but a jewelers loupe will help immensely either way.

What you will see is actually little droplets of melted aluminum that stuck to the insulator.  Scarey stuff, but an indicator that you've been too close to the bleeding edge.....
 
Yeah, I saw a few of those specs on the porcelain the other day when I looked at the plugs. The fuel tank was not completely fresh 93 octane premium; there was some older 89 octane mixed in there. I'll have to avoid getting on it until I get that stuff flushed out and make 100% sure the timing is where it should be.
 
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94 octane only if you can get it. You can also add say a gallon of Xylene (117 octane paint thinner) to a tank.  No more fly shit.  To be safe you can add an ounce or two of Marvels Mystry oil to your Xylene for lubricant.  The Xylene also might only be something you use on really hot salty days or when you plan to race.  The Xylene should give you both some detonation resistance and power if you are on the edge.
 
Vern,

What's your take on Toluene vs Xylene?

fwiw, [flame proof suit on], 110LL avgas is $5 per gallon here. Afaik, like most base blue "race" gasolines, it's apx 105 when rated like pump gas.

Dave
p.s. - shiftless, how much total you running? The KBs may make the engine want 2 or so less than normal. Got a wide band?
 
Quote from Wiki for Toulene:

It undergoes nitration to give ortho and para nitrotoluene isomers, but if heated it can give dinitrotoluene and ultimately the explosive trinitrotoluene (TNT).
Click to expand...

So a mini quasi-derivative of tnt in your engine? Nice. :)
 
Something else you could look for which i'm sure would be difficult considering the application is if you could look down a spark plug hole you will notice almost like a pitting on the piston and a sandy color.  Which is a sign of detonation.  This only works if you can see down the spark plug hole though. Hope it helps.
 
mt83 said:
Something else you could look for which i'm sure would be difficult considering the application is if you could look down a spark plug hole you will notice almost like a pitting on the piston and a sandy color.  Which is a sign of detonation.  This only works if you can see down the spark plug hole though. Hope it helps.
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Ohh..  kind of like this?
http://www.thor-racing.co.uk/images/pis ... nation.jpg

Saw that and wasnt sure if that was a result of the detonation
 
Dave,  Either will work well.  I have used Xylene a fair amount over the years with my GN.  (Prior to adding a methanol/water injection kit.)  Xylene was more readily available for me as I just went to the local paint store and bought it wholesale in a 5 gallon can.  Also you only use either one as a mix and with a little lubricant and since Tolene is I believe only 114 octane the Xylene gives a little better mix number.  In my case I used to use a 5 gallon can and then immediately top the tank with 94 octane for a 100 octane mix.  Going to a 100 octane from 94 would allow me to run 22 pounds of boost with my stock turbo/intercooler (which was about the efficiency limit) instead of 17 pounds.  About 50 HP on that setup.  Its still not race fuel but it was a little cheaper and met my needs.  fwiw It also will not kill your cataletic (sic) convertor or O2sensor.  A 30% mix is suppossed to be about the practical max.  For Shifty ie natural aspirated you just need enough to get you over the hump which I'll bet a gallon or maybe less per tank would suffice.  Hopefully he will only need or want it on hot muggy race days for detonation protection as much as for power.
 
Guys, I haven't done ANY tuning to the timing or carburetor. I do not have my wideband hooked up (carb is a stock 800 edel with only change being lighter power piston springs), nor have I checked total timing (it's somewhere in the neighborhood of 32-36, but who knows exactly where), nor have I ran all of the old gas out of the tank yet. So it's entirely possible that once I have all this stuff sorted out, there won't be any problems with detonation. There were only just a very few specs on the plugs anyway so it would seem that it has only experienced very light detonation. This was after probably 3-4 WOT runs before I looked at the plugs. I am also not hearing any pinging, now that I have installed an exhaust and can actually hear. I will get all this stuff sorted out when I get a chance, then swap in a fresh set of plugs and see how it does.
 
Vern said:
Dave,  Either will work well.  I have used Xylene a fair amount over the years with my GN.  (Prior to adding a methanol/water injection kit.)  Xylene was more readily available for me as I just went to the local paint store and bought it wholesale in a 5 gallon can.  Also you only use either one as a mix and with a little lubricant and since Tolene is I believe only 114 octane the Xylene gives a little better mix number.  In my case I used to use a 5 gallon can and then immediately top the tank with 94 octane for a 100 octane mix.  Going to a 100 octane from 94 would allow me to run 22 pounds of boost with my stock turbo/intercooler (which was about the efficiency limit) instead of 17 pounds.  About 50 HP on that setup.  Its still not race fuel but it was a little cheaper and met my needs.  fwiw It also will not kill your cataletic (sic) convertor or O2sensor.  A 30% mix is suppossed to be about the practical max.  For Shifty ie natural aspirated you just need enough to get you over the hump which I'll bet a gallon or maybe less per tank would suffice.  Hopefully he will only need or want it on hot muggy race days for detonation protection as much as for power.
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Sorry about the hijack, but I wonder Vern if I could use some xylene safely mixed with 110 leaded Sunoco. I am way past the limit of the MON rating of the gas for my compression. I don't seem to be getting the horspower out of my engine and believe I could with more octane :scratchchin:

                  Ron
 
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