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burton9010

lower heat range spark plug for E85

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I have seen a few threads on here about how you want to lower the heat range of the spark plug you are using when you switch over to just burning E85. I am tuning in a 2 stroke jet ski and was just wondering if someone could explain the theory behind this?

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Not sure thats what I am trying to figure out. I figured that e85 being 105 octane and being a fuel that burns cooler I would be able to step up to the next heat range but I guess that theory was wrong. I am trying to figure out what is wrong with my way of thinking.

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I have seen a few threads on here about how you want to lower the heat range of the spark plug you are using when you switch over to just burning E85. I am tuning in a 2 stroke jet ski and was just wondering if someone could explain the theory behind this?

 

It's a theory that they would prevent preignition of the ethanol.

Hotter plugs could stay hot enough to ignite the fuel before the spark does.

 

Heard iridiums with small electrodes (Like denso .4mm center electrodes) could also

preignite the fuel.

Heard about the densos after I switched to E85 and had run 20000 miles on it. :o

No issues so far. 

Knock on wood!!!!!!

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There may be a couple of issues at work here:

 

1)  When some people switch to E85, they also turn up turbo boost, compression or other performance factors.  With higher performance usually comes a recommendation to reduce the plug heat range.

 

2) E85 burns cleaner than gas, so there isn't as much need to keep the plug hot. And/or a switch to E85 can sometimes mean running a bit leaner/hotter, so a cooler plug can be tolerated.

 

3) Some have claimed a change in plug heat range helps certain characteristics...idle, cold starting, etc.

 

I can't vouch for the starting as I haven't had reason to change the plug heat range...beyond running a cooler plug for the turbo.  My general thought:

 

For a stock engine, the stock plug should be good on E85 or gas.  I don't think the OEM's have any different plug for flex fuel vs gasoline - and they sure don't require a plug change when you fill up with a different fuel.  So overall, as long as you aren't detonating on the hot end or carbon fouling on the cold end, the plug heat range should be OK.

 

For a modified engine, I would adjust the plug heat range the same as indicated for gas...ie "one heat range colder per 100hp added power" or what ever rule is prevalent in your community.

 

As far as starting, idling, etc - IMHO, all the plug heat range dictates is the length of the insulator in contact with the body of the spark plug.  More contact means an easier path to the relatively cool cylinder head and a cooler plug.  Less contact means a hotter plug.  It has nothing to do with the voltage, firing characteristics, etc.  So there should be minimal, if any, changes in actual start/idle characteristics.  All plugs start out 'cold' in a cold engine. 

 

There 'may' be some slight benefit due to the small electrode diameter of the platinum / iridium plugs (regardless of heat range).  This requires less voltage to fire and should fire just a bit sooner which would be equivalent to a slight advance in timing over a stock plug.  At the same time, there is no performance benefit in running hotter/colder plugs...you're really just trying to balance detonation and carbon fouling.

 

Overall, this may be somewhat of an experimental application.  Don't know as I've heard of an E85 jet ski before.  I've considered converting, but haven't seen any 2-stroke oil I would trust into the high HP range yet.  Overall, I would say run what ever plug you would run on gas.  E85 has less tendency to detonate and less tendency to carbon foul.  So if you are not detonating or carbon fouling, the heat range would be pretty good.

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Ok that makes sense to me. Thanks for the write up. I thought people were saying you have to go down in heat range on a plug because of E85 but its really just the fact your running your motor harder if you set it up for higher performance.

The oil I use is klotz benol. It mixes great and is very high quality http://www.klotzlube.com/proddetail.asp?prod=BC%2D175%5FPint&cat=6

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