I'm tuning a turbo RX-8 for the first time and noticed he had very old stock plugs which need to be replaced. I was wondering what the stock heat ranges for the RX-8 are? I'm assuming its the same as the FD RX-7's with 7 leading and 9 trailing.

I've been trying to figure out what would be considered as an upgrade to stock plugs. I use the Greddy Racing Plug Pro (NGK Iridium R7420's) with 9 leading and 10 trailing in my RX-7. I was considering get these same plugs for for the leading only in 9's and leave the stock trailing there as I heard its a different length and the trailing doesn't do much of the work anyway.

Any ideas/suggestions?

thewird

I have run the rx7 9's in mine for some time now (all 4 plugs) with a 2mm spacer on the trailing .
Seems to work well

Is there any reason not to use the RX-8 plug on the trailing? An iridium plug generally has a stronger spark then a platinum one. I don't really like the whole spacer idea either in case the owner goes to another mechanic who has no idea.

thewird

im running 7 plugs on my car too...no problems and im NA

I'm pretty sure a lot of turbo owners use the stock plug in the trailing posn. so that does work as well .

I'm just wondering from a performance perspective if there is an advantage of going with anything else.

thewird

I use stock trailing, NGK BUR9EQP in leading, no spacers

Why do you guys change to rx7 plugs? Any advantage other than being MUCH cheaper?

Why do you guys change to rx7 plugs? Any advantage other than being MUCH cheaper?

They are actually a stage colder than the stock leading plugs.

They are actually a stage colder than the stock leading plugs.
So the stock rx8 leading plugs are 6's?

thewird

They are running "9" RX-7 plugs in the leading.
As am I with "9" OE RX-8 plugs in the trailing.

So the stock rx8 leading plugs are 6's?

thewird


Stock Leading are 7's....

Oh, just making sure. So its the same as the RX-7 and the only reason people use the rx-7 plug is to get it colder with the trailing since its the same size.

thewird

Basically the BUR9's are inexpensive non-beam type plugs that fit.......

There are other much more expensive options...but so far they don't seem to be needed

forgive me for my lack of knowledge on Spark plugs... but since it's a stage colder, does it make it better? In what way?

forgive me for my lack of knowledge on Spark plugs... but since it's a stage colder, does it make it better? In what way?
Means your plugs are less hot as they dissipate heat quicker. This makes running higher boost safer and makes more power. However, if you run too cold of a plug, it won't ignite the fuel as well. Especially with normal street driving, running a hotter plug is preferred as it increases gas mileage and won't foul as easily.

That's how I've always pictured it but NGK seems to explain it better...

Let's make this really simple: when you need your engine to run a little cooler, run a colder plug. When you need your engine to run a little hotter, run a hotter spark plug. However, NGK strongly cautions people that going
to a hotter spark plug can sometimes mask a serious symptom of another problem that can lead to engine damage. Be very careful with heat ranges. Seek professional guidance if you are unsure.

With modified engines (those engines that have increased their compression) more heat is a by-product of the added power that normally comes with increased compression. In short, select one heat range colder for every 75-100 hp you add, or when you significantly raise compression. Also remember to retard the timing a little and to increase fuel enrichment and octane. These tips are critical when adding forced induction (turbos, superchargers or nitrous kits), and failure to address ALL of these areas
will virtually guarantee engine damage.

An engine that has poor oil control can sometimes mask the symptom temporarily by running a slightly hotter spark plug. While this is a "Band-Aid" approach, it is one of the only examples of when and why one would select
a hotter spark plug.

I've also noticed that when running stock 7-9 plugs on an RX-7, that the rotor housings internally get heat scored when running more then stock boost/power and it gets more noticeable as you increase the boost and power.

In my opinion I think the stock RX-8 plugs (7-9 heat range) are not suitable for turbo application as the renesis is a high compression motor (10:1) compared to the FD motor (9:1). Mostly I think the issues is with the leading as it needs to be colder. That is why people use the stock FD trailing plug in the leading since its a 9 heat range spark plug and is relatively inexpensive.

thewird