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Old 06-18-2002, 09:35 AM   #1
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Default Help with switching to 30%.

I need some advice on switching to 30% nitro content. What do I have to do to my engines so they run on 30% fuel? Do I have to put any shims? All I know is that I should be running a hotter plug and richening the engine out a little after the switch.

BTW, the engines are mt12's both turbo and non turbo if it helps.

Thanks.
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Old 06-18-2002, 02:00 PM   #2
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You are almost right. You want to run a Colder plug with higher nitro and a hotter plug for lower nitro. As far as shimming, i have been running 20-30% nitro for a few years and the only thing you will have to do is adjust the mixture.
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Old 06-18-2002, 02:27 PM   #3
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Are you sure I should be running a colder plug? I noticed a lot of good racers both local and factory sponsered running really hot plugs with 30%. This is what I was told by some really good racers. Since the engine has to run a little richer with the 30%, you need a hotter plug to burn the extra fuel. This makes sense to me anyway.
Any help would be apprecaited.
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Old 06-18-2002, 02:31 PM   #4
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I personally have never heard that. The problem with running a really hot plug with high nitro is premature detonation. Now if it is cold out yes you may want a hotter plug than usual. Are the guys that are telling you this winning races?? I run an OS # 8 which is a cold plug. Sorry I cant be more help, I will try to find something that explains it alittle better.
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Old 06-18-2002, 02:35 PM   #5
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#8 is not a cold plug. The heat rating go like this


R5 is cold
A5 is medium
#8 is medium hot
A3 is hot
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Old 06-18-2002, 02:39 PM   #6
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Yes, these guys that are telling me this win races. Even Robbie Collins use mc-59 plugs when its really hot out with both 30% and 40% fuel in mt-12s.

mc-59 plugs have a hot base and hot filament and I think they are the hottest plugs around.

I would think premaute detonation would occur if your running really lean with a really hot plug.
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Old 06-18-2002, 02:39 PM   #7
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My bad , I can tell you this much, the A5 is crap. Well at least to me.
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Old 06-18-2002, 02:40 PM   #8
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I am just going to shut my mouth and leave
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Old 06-19-2002, 06:30 PM   #9
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I'm not going to get into the plug issue, run what ever the engine runs the best on , but when you switch the 30 percent you must add a .02mm head shim to cut the compression alittle or predetonation will occur in most cases.
Ballpy: you say you never change the shim from 20 to 30 percent fuel? Ever removed the head on your engine and see the small dimbles or craters on top of your pison and wonder what caused that? It also causes premature rod and crankshaft wear.
Most factory drivers and good drivers that spend the bucks to win races really don't care about the plugs that much, if it melts down they just replace the engine!!!!!
I will say that the mc59 is the best all round plug you can use in non turbo applications for me.

Last edited by bbntc3; 06-19-2002 at 06:38 PM.
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Old 06-19-2002, 09:11 PM   #10
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I only use MC9s with 30% BK fuel and Redline fuel.......no problem.
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Old 06-20-2002, 02:00 PM   #11
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Hey Tambok, what is BK fuel? I see a lot people metioning this fuel but I never seen it before.
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Old 06-20-2002, 03:26 PM   #12
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bbntc3: I have the little dimples on all of my mt-12 motors. They were all run on 20% fuel and never ran too lean.
The fuel mileage on these motors ranges from1 quart to 5 gallons.
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Old 06-20-2002, 03:50 PM   #13
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It's just one of those brand name fuel.....Ralph Burch, sponsored Serpent driver extraordinaire - uses it.......see r/c mags ads. I like the Redline better coz it has more lubricant than any other fuel out there.
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Old 06-20-2002, 05:28 PM   #14
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bk is hand mixed and delivered......

higher number colder plug..... mcoy 9 is colder then 8

nova 9 is colder than 8 etc

os is on ther own sheet of music.....

run a colder plug if you have a track that const†utes the reving of the motor, a hotter plug on smaller tracks to avouid flame out.....

a hot plug on a large track will detonate, and will be slower... there is no ggrey area you do not make power when detonating... weather you are a team driver or not......... just ask dennis if you do not bielieve me....
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Old 06-20-2002, 09:39 PM   #15
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My 2 cents and ammdrew is correct.


stock head shimming provides .018 head clearance

Stock motor 20%
MC 59 on tracks with 160 to 180 ft straight
above 95 degrees go to an MC8

Stock and Mod motor 30%
MC8 or 9 On tracks with 180 to 250 ft or where sustained high revs are achieved at the end of the straightaway

above 85 to 90 degrees ambient temp add .003 additional head shim(thousanths not MM, the MM equivilent is .001) when using 30% gives .021 head clearance

Causes of detonation: to high of compression for ambient temp or fuel percentage
Tuned pipe is to short
plug is to hot causing preignition for given condition.
lean condition
bad engine bearings(not common but it does occur usually causes the crank to drag on the case overheating it causing the engine to go lean because of vapor flashover of the fuel as it travels through the crank)
Low oil content in the fuel

If its detonating the piston and head will look like you sand blasted it and all the carbon buildup will be gone

Ammdrew as much as I like BK fuel (kick butt power)in my 15's and 21's(its the jazz in the big block motors) I have stopped using it in my 12's. My opinion is that the oil content is just a squeek low at the temps the 12 engines run. I have gone back to mugen or byron 30% race blend fuel (11 percent oil) in the 12 engines and I won't run anything else period. I need to call Terry and discuss this with him to see if he will make a specific 12 blend fuel with 11% oil. He said he may be at the nats for the mains to spectate.
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