Forum » General Tuning Discussion » Iridium vs copper on E85 and other plug stuff

Iridium vs copper on E85 and other plug stuff

General Tuning Discussion

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So about spark plugs, conventional oem recommendations usually say no platinum or iridium for Re85, do you know whats behind this? In a recent 1k+hp 2jz dyno the copper plugs just did not ignite with re85 and high boost levels, but denso iridiums did the trick.

Same thing with another 1kkw motor on an engine dyno (2jz and 7M motors here) altought they ignited fine, the coppers were running just too hot, with 9,5-10 iridiums the plug kept fine after a hard pull.

Also, have you seen any difference in the required heat range of the plugs when switching from gasoline to re85 ? In theory re85 should burn cooler but due to the ability to resist knock, higher cylinder pressures can be obtained which might just turn this into a gain in torque while keeping the cylinder temps at the same level.

Is there any convenient way to measure, check or estimate this save for reading the plugs on a dyno. On road its not really the option since you would need to do it directly after a hard pull and with these power levels, getting a clean pull is too scary since the speeds required for traction are nuts.

the engines are built for standing mile which is quite a stress for the engine, you essentially go through all of the gears at WOT which essentially results in the engine running at the top end of the power curve for more than 25 seconds straight.



no pointers here ? no personal experience ?

With the majority of the high powered engines I've been involved with running on E85 I've used a plug like the NGK BR10EG which uses a nickel electrode. I can't think of applications where I've chose a platinum or iridium plug. Most often these platinum and iridium plugs tend to be specified by manufacturers as they offer a longer service life than a conventional plug. I'm not sure I've seen a performance advantage from them.

The heat range of the spark plug needs to be based off many factors, not just the fuel you're running. You can read the plug and look at the discolouration on the earth strap to confirm if your heat range is suited to the application. You're looking for the the ground strap to discolour approximately halfway along its length which usually coincides with where it bends through 90 degrees. I normally run similar heat ranges between gasoline based fuels and E85 in high power applications.

Hi Andre, and thank you very much for the answer.

So to recap: from your experience, similar heat rangers regardless of the fuel is your experience and you have not seen any ignition gains when switching from copper to iridium.

Thank you, this is valuable input for me since reading the plugs is not really feasible for me on most occasions.

You're always safer to be a little on the cold side for the plug heat range in my opinion for a race application. The biggest downside with cold plugs is that they tend to foul up at idle or cruise but that's not a huge concern for you. I'd still examine the plugs though after a run to see where the discolouration is on the ground strap to fine tune your choice.