Ken's corner #1: spark plugs

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Ken's corner #1: spark plugs

Postby ken.lagarec on Mon Sep 16, 2002 2:33 pm

Well, according to the vote, you guys wouldn't mind having a thing Isa calls Ken's corner. You ask and I try to answer. Obviously, I need a disclaimer here. I am not an expert and I don't know everything. However, I have read alot and worked on a few cars so I have a basic idea of what I'm talking about. I also studied physics all my life so I could usually read up on anything related to thermodynamics, engine mechanics etc. and understand it, then relay the information in layman terms. These posts are open for discussion, so if you disagree or think you can explain something differently/better, go ahead. We might not be able to anwser everything here or have all of us understand all the intricacies of cars but I'm pretty sure this is a good way for a lot of you (and me) to learn things you've always wanted to know.

Our first topic comes from a man found clueless in the spark plug aisle at Canadian Tire. He was found, after many sleepless nights, scaring customers away by frantically engaging them. "What kind of plugs do you use?". When the store closed, he was found weeping in the corner screaming out the to 15 year old aisle manager. "Why do you torture me like this?". Here's to you Alex (who has officially been banned from CT stores and is being sued by the boy's parents for causing a traumatic experience).

The question was: what's the difference between platinum and iridium spark plugs and are they worth the extra cash?

The answer, you will find here: http://www.automotivearticles.com/get.php?action=getarticle&articleid=18. But I'll condense it for you anyway. A spark is caused by ionizing the air/fuel mixture in the cylinder by applying a large voltage (more than 10000 V) between the electrodes. The best way of generating a spark is by having very thin tips as opposed to flat surfaces. So the best design for a spark plug would be to have needle-like electrodes. Unfortunately, the spark creates a lot of heat that can actually melt the metal of the tip, thereby changing it so that it won't work the same over time. You'd have to change it very often. So the first thing is to find a material that has a very high melting temperature. Copper melts at 1083 °C, platinum at 1772 °C and iridium at 2410 °C. This means that an iridium tip can be made much sharper without it degrading much over time compared to a copper or platinum tip. So theoretically, you can make a plug that will create a spark with less voltage or that will work with a denser air/fuel mixture (high pressure turbo). The next problem though is heat dissipation. If the tip stays very hot, it might auto-ignite some new air/fuel from the next cycle or just keep getting hotter and eventually melt. Copper dissipates heat much better (4.01 W/cm.K) than iridium (1.47 W/cm.K) and platinum (0.72 W/cm.K) so a copper plug would be best to avoid runnaway melt-down or auto-ignition. A platinum plug would not dissipate heat quickly enough and would probably auto-destruct. So a good spark plug is made of a copper core for heat dissipation, with a tip coated with platinum or iridium. The plug is also cooled by the jacket around it and it's possible to have the same plug tip with different heat ratings (i.e 5 or 6) but I'm talking only about the tip heat conduction here.

So is it worth it to pay more for an iridium plug vs. platinum? Theoretically, an iridium plug can be made to have a better geometry (thinner tip), leading to a more consistent spark and burn, even under adverse conditions. It should also last very long (comparable to platinum). Will you gain any hp or mpg by using iridium vs platinum? I really doubt it in an NA engine because the conditions aren't so extreme that a platinum plug won't do an excellent job. On a high pressure turbo, with tuning, you could probably get better combustion from an iridium plug and it might be worth it. But don't expect noticeable gains by just dropping them in a driving away.

Of course, the only real way to know is by experimentation and tuning, but who of us as dyno time to waste to tune for spark plug changes. You won't be able to see 3 hp gains on a dyno anyway.

My .02$. Take it for what it's worth. Post your questions for next episode of Ken's corner.

Tell me what you think. Too long, too technical not long enough?

Ken
Ken
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Postby Nismo on Mon Sep 16, 2002 2:48 pm

My doctor says I might be able to go back to the spark plug isle a year from now. It's gonna take alot of work to get back to my normal self again. On the plus side the anti-depressants they gave me make me feel like a purple chipmunk (le swisssssss)! So it's not all bad.

Seriously, thank you Ken.
The feedback was perfect and it helped me better understand.
Keep up the good work in 'the corner'

Nismo (aka Alex)
"Don't put the power on, till you know you never have to take it off" -- Sir Jackie Stewart
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Postby Nismo on Wed Sep 18, 2002 11:05 pm

johnnyz wrote:Pushin' a rod and gettin' nowhere in Nepean


LOL!!!! :lol:

[70's time warp]
This has nothing to do with your answer... but it relates in a weird way. The other night I got to drive a prestine 1979 Camaro Z28 all original except for the 350 small block punched out to a 396. Wow what a brute! The power was so much fun but it made me appreciate the ability to turn! If every road was straight this car would be so much fun, but it makes me appreciate my 240's ability to corner like you would not believe. That is all. :)
[/70's time warp]
"Don't put the power on, till you know you never have to take it off" -- Sir Jackie Stewart
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Postby Black Madgic on Wed Sep 18, 2002 11:49 pm

Ohhh Pushrods...What an easy easy design and still being used by the General in the Corvette. So simple and yet works so well.

I spent about 20 months working in the plant where the Corvette, 5.3, 4.8 and 6.0 truck engines were made as well as the 5.7's for the Camaro/Firebird and Holden Monaro. So I know those engines very well.

Note to Ken:> I've got a great book here that you may want to see. Introduction to Internal Combustipon Engines. Actually I don't recommend anyone who does not study or has not studied engineering look at it. It is quite complex in areas and if you understand thermodynamics and fluid dynamics well you can understand the book. I've also got a wide range of information on engines and designs so if you need help or are looking for a conversation about engines in depth I can help. I am always looking for people who know and understand these great IC engines as well as I do.
'Happiness is the corner, not around the corner.'
Speed kills but so does driving a Honduh.
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Postby ken.lagarec on Thu Sep 19, 2002 4:17 am

OK pushrod vs OHC (overhead cam) will be the next topic. Interesting 'cause there are advantages/disadvantages to both.

Black Madgic: I can't say I've looked much at the specifics of combustion engines as opposed to tuning them: ever since I found a really good book by A. Graham Bell - not the telephone guy - I've wanted to quit my job, buy a garage and spend all my money working on cars. But that would last 1 week 'cause I can't really afford to quit my job. Anyway, it's good to see there's people on the board who have hands on experience with these things (mine is small but growing). Finally, yes it would be an interesting read!
Ken
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