Iridium sparkplugs?

[Owl]

I paid $90(4) for my FZR at part sponcership almost cost price so are we talking the same plugs or did someone put the wrong price against yours.

Who's cost? These plugs (CR9EIX) retail in the US for about $11 and can be purchased as low as $7.40 ($10.70NZ)

Perhaps the price was wrong or maybe someone here is making a killing!

[Bonez]

Who's cost? These plugs (CR9EIX) retail in the US for about $11 and can be purchased as low as $7.40 ($10.70NZ)

Perhaps the price was wrong or maybe someone here is making a killing!

Typical NZ 300% markup I would imagine. Anyway I normally get over 30,000kms out of a "standard" set of plugs, is that good? Or am I doing something wrong......

[Henk]

Depends why you are considering them.
If it's for performance a better option might be to go with (from memory) NGK CR9EK's. They are "ordinary" plugs but extend slightly further into the combustion chanber, thereby slighty increasing the compression ratio which equals cheap power. It's not much but it's cost ya absolutely nothing if you were going to change the plugs anyway.

Unless they extend a little too far and end up smacking into the piston.

[Owl]

Depends why you are considering them.
If it's for performance a better option might be to go with (from memory) NGK CR9EK's. They are "ordinary" plugs but extend slightly further into the combustion chanber, thereby slighty increasing the compression ratio which equals cheap power. It's not much but it's cost ya absolutely nothing if you were going to change the plugs anyway.

The CR9EK's are not ordinary plugs as they have dual electrodes.

[slowpoke]

Unless they extend a little too far and end up smacking into the piston.

Like no-one would have thought of that.....they aren't 50mm long for fucks sake. Open valves protrude faaaaar further into the chamber than any spark plug.

The CR9EK's are not ordinary plugs as they have dual electrodes.

What is this, a meeting of the Anal appreciation society? It's a conventional plug, with conventional electrodes (albeit 2 of them) rather than iridium or surface dischage etc bloody etc.

[SS90]

Like no-one would have thought of that.....they aren't 50mm long for fucks sake. Open valves protrude faaaaar further into the chamber than any spark plug.

Not quite!

As the piston comes to TDC (let's chose the compression stroke here), the inlet valve closes JUST before the piston gets to the top.

On a "tuned" 4 stroke engine, you would expect 30 thou "piston to valve clearance", that is, there is 30 thousands of an inch CLEARANCE between the inlet valve as it closes (or the exhaust valve) as the piston comes up to TDC.

On such an engine, at TDC there is often only 2mm between the crown of the piston and the spark plug electrode.

Particularly when you have "high compression" pistons (raised dome)

That isn't much at all. (less that 1mm)

More expensive stuff has even tighter clearances.

With that in mind, on a performance engine, it is quite possible to chose a plug that is too long, and have it touch the piston (particularly at high RPM)

Quite often if you modify an engine (i.e remove material from the head to increase compression) you have to find shorter plugs that have enough clearance.

The majority of "day to day" stuff has big safety margins, but as the consumer demands more and more power, things like this become part of the equation when servicing your bike.

30 years ago, this was not a problem, because the engines where so often "low spec" that the valves could be completely open, and still not touch the piston.

Of course, these days are long gone!
Simply put, cam lift and duration go longer, RPM got higher, and engines became more fragile.

[vifferman]

With that in mind, on a performance engine, it is quite possible to chose a plug that is too long, and have it touch the piston (particularly at high RPM)

Isn't that because the conrod can actually stretch a minute amount?

[Owl]

What is this, a meeting of the Anal appreciation society? It's a conventional plug, with conventional electrodes (albeit 2 of them) rather than iridium or surface dischage etc bloody etc.

Apologies slowpoke! I see now what you were getting at.

[dipshit]

just go with the factory ome ones, they cant be that bad if they put them in from the factory. unless ya wana rossi or biggles that is lol

Iridium plugs are factory OME in K8 600/750 GSXR's

[firefighter]

I can't believe the prices quoted, or maybe I just got a really good deal at $11.50+gst

They didn't fare too well in the triple though and I've since gone back to the stock CR9EK.

Where did you find these? Ebay U.S did'nt show these same prices.....(either that or the shipping was what fucked it)

I paid $90(4) for my FZR at part sponcership almost cost price so are we talking the same plugs or did someone put the wrong price against yours.

Geez dude. I just bought some (4) today from Ebay U.K for $82 including shipping......evidently $2 more than the cheap ones were going to cost.
I have to put the service back a couple of weeks while I wait but it's worth it for the sake of $2 and getting the best.......

Now I can use the spare $40 I have to go towards the front brake pads I need to replace and get EBC sintered HH pads instead of the cheaper ones! (unfortunately I could'nt find a reasonable discount online to make it worth importing them so full shop price)

[Owl]

Where did you find these? Ebay U.S did'nt show these same prices.....(either that or the shipping was what fucked it)

Local and at mates rates.

I have to put the service back a couple of weeks while I wait but it's worth it for the sake of $2 and getting the best.......

Apparently Denso Iridiums are the best, but substantially dearer.

[quickbuck]

However (but!) I've laso read (but can't validate this) that they are also prone to becoming unserviceable if they get fouled.

Interesting....
That piece of literature is worthless.

Aircraft run Iridium Plugs (they are able to run non-iridium too)... and we service the plugs all the time... Fouled ones clean up easily.
Slight difference in construction though, but shouldn't make a difference.

[mossy1200]

Where did you find these? Ebay U.S did'nt show these same prices.....(either that or the shipping was what fucked it)



Geez dude. I just bought some (4) today from Ebay U.K for $82 including shipping......evidently $2 more than the cheap ones were going to cost.
I have to put the service back a couple of weeks while I wait but it's worth it for the sake of $2 and getting the best.......

Now I can use the spare $40 I have to go towards the front brake pads I need to replace and get EBC sintered HH pads instead of the cheaper ones! (unfortunately I could'nt find a reasonable discount online to make it worth importing them so full shop price)

I got mine when the exchange was around 55cents to dollar so that would have made some difference.DPR8EIX-9 was $13usd each at the time retail plus freight so I thought $90 was fairly good.

[slowpoke]

"Many a truth is said in jest" but who would have thought the truth could be so scary........

[jono035]

Isn't that because the conrod can actually stretch a minute amount?

I remember working out how much a conrod changed in length in high school with the help of my physics teacher.

Steel elongates (strains) when exposed to stress according to its modulus of elasticity...
Found some conrod data (AISI 4340) that says it has a modulus of elasticity of 205GPa.

Modulus of Elasticity = stress divided by strain.
Strain is change in length over original length.
Stress is the pressure the material is subjected to (force divided by area)

Yield strength is 786MPa which corresponds to a 0.3% change in length just before the material deforms permanently.

On a 100mm long conrod that is a 0.3mm change in length...

That is a lot less than I would have thought, but then again that is a performance conrod, a factory one would probably be a lot worse.