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Navin Johnson
 
TimT's Avatar
 
Join Date: Mar 2002
Location: Wantagh, NY
Posts: 8,810
plugs for twin plug conversion

I just got my heads back from being machined for twin plugs, Im wondering if I should just get 6 more of the plugs I already use? or do I need to go to another heat range?

I know I have to use less ignition advance with the twin plug set up.

Also im thinking of having the a thermal barrier applied to the combustion chambers and piston domes, would this affect the heat range of the plugs I need and willl it affect the ignition advance that I have to use.

thanks fo any help.

BTW the engine is a 2.2 with all the racy mods you would expect 10.5:1 cr rad cams, etc


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Old 05-12-2002, 11:53 AM
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Author of "101 Projects"
 
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The plugs on top and bottom should be exactly the same, as they are basically symetrical in the combustion chamber.

Not too sure about the coating question, but I don't think it would affect combustion chamber temps - just piston dome temps.

It's not really that you "have" to use less ignition advance when you twin-plug, it's that you *can* use less ignition advance. The further you can reduce the timing, the closer the combustion will be to TDC, which will reduce lag time in the chamber, increase power, and also decrease detonation. You can save about 10 degrees on the max advance...

Come to think of it, I haven't heard too much about coating the inside of the cylinders. That wouldn't seem to make too much sense to me, as you *want* heat to dissipate through the cylinder walls and out to the fins where they are cooled. You want to keep heat off of the pistons and the valves...

Anyone else have more info on this?

-Wayne
Old 05-12-2002, 02:09 PM
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didn't that SC in the Porsche World SC911 rebuild article have some coating? Weren't you are part of that article Wayne???

I thought it wasn't something I was going to do for my rebuild...
Old 05-12-2002, 02:48 PM
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Umm, yes, Phil used my photos because of a 'problem' with his camera. But I didn't write the article. You're right though, he did have some type of coating on the inside. Final dyno numbers gave no increases in power though, if I remember correctly...

-Wayne
Old 05-12-2002, 03:07 PM
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Navin Johnson
 
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Join Date: Mar 2002
Location: Wantagh, NY
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Bump, anyone?

coatings are used to keep the heat in the combustion chamber, and the extra heat causes higher gas velocities, and greater scavenging of the cylinder. In a perfect world where the thermal barriers worked 100% no heat would go into the heads,valves or cylinder walls, and then the operating temp of the engine would be lower, which is a good thing

F1, nascar, and many big buck race teams use these coatings. Porsche thermal coats the exhaust ports on the 3.6

Im guessing I would have to go with a colder plug and less ignition advance if I do decide to have the coatings applied.

but I really want to know if I should use a colder (or hotter) range plug than what was required when the engine only had 1 plug per cylinder



thanks for the help

Tim

__________________
Don't feed the trolls. Don't quote the trolls
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'69 911 GT-5
'75 914 GT-3
and others
Old 05-13-2002, 12:20 PM
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