Boost and spark plug question
 

I been running all 9s spark plugs and 18 psi for about seven years with no issues. I don’t beat on the car but I’ll make an occasionally wot run through second and third gear.

I am just now hearing that 9s with this much boost is a disaster waiting to happen. And that I should be running 10s. What is the consensus view on this? If I should run 10s does anyone know the exact plug I should get? And should I gap it differently?

the car has a large street port, full exhaust (no cats), 2200cc injectors, smic, intake, hks twin power, meth injection, bnr stage three turbos setup to run parallel. It’s tuned with the fc tweak. And for those that don’t have the fc tweak. Make it priority number one in your life to get it. It’s awesome. I’d go as far as to say it’s far superior than any human tuner could get.

If I do switch to all 10s do I need to add anything to the ignition or elsewhere to support them ?

thanks for insight.

First, I'd say that the notion of plug heat range being more critical is a fairly new notion, so I wouldn't fee too out of the loop if I were you.

I don't think there is a strict rules for plug temperature, ie. at X boost, use YY heat range. We are seeing evidence that would support the idea of a more generalized guideline for doing some individualized testing to confirm the correct heat range for your applicaton.

I'm sure you are going to get a bunch of people tell you "I've run 9s forever with no issues" or, from the other side, "I ran 9s and ruined my engine." So, for me, the most logical thing to do is get a set of 10 heat range plugs with a ground strap (so you can accurately do a plug read), and confirm EXACTLY what YOUR engine and YOUR setup wants. Then, get a set of surface gap plugs in that heat range for regular duty.

And no, you wouldn't need to do any type of adjustments to your current setup to switch plugs.

I'd also add that another big factor in plug selection that lots of folks neglect is how the car is normally used/driven....

For example, let's say you built up a 500HP 13B-REW beast, but in reality you just street drive it to your favorite cars & coffee and you never push it hard enough on the street to see the kinds of combustion pressures & temps it experienced when racking up that 500HP number on the dyno - in that case, running a 10 heat range or colder plug will likely lead to shorter plug life & quick fouling, while a set of 9's would be perfectly happy & last a decent amount of time. OTOH, if you drive it like you stole it every day, do frequent track time, and ANY time on a dyno, then that same engine should be running the colder 10 and/or 11 plugs.

great points by both of you thanks. I am actually pretty mellow on the car exact for right now since i am tuning my FC Tweak.

@REnaissance_Sle7in can you elaborate about he grounding strap? Cant i just measure EGT with the differing plugs?

Not really. You can have 'good' egts while still utilizing the 'wrong' plug.

To avoid the risk of steering you wrong, I would recommend doing a deep dive into Howard's thread:
https://www.rx7club.com/3rd-generati...plugs-1161011/

You can find out more about the difference between surface gap plugs and more traditional style plugs (with a ground strap). There is also discussion on how to read the ground strap to decide on which plug your engine is really wanting.

What’s the risk of running plugs that aren’t cold enough. knock? If that’s the case, you could log with FC Tweak, do a few pulls, then swap the plugs for 10s and compare the knock events side by side. I just logged my first knock on Master FC Tweak, but it was in the decel range or fuel cut, (full vacuum, closed throttle). From what I’ve read, that could just be noise from the exhaust or heat shields expanding, or it could mean I need a colder plug, 7 to a 9. I already talked to Xavier about it, so I’m going to switch to colder plugs anyway since my new setup should be pushing me past 300hp.

9s are the go to for mildly modded. Since I am very modded I am hearing I need tens. But I’ve run 9s with 18psi for ten years with no issues. I also read that that tens foul if you drive passively. I don’t beat on the car. I may wind out second and third occasionally. But I am not doing it constantly. So I don’t know what to do

on decel it can be stuff in the drivetrain as well. the knock sensor is sort of a microphone, so any noise, particularly in the 3500hz range will show up.
i wouldn't worry about knock on decel too much, although if you went and made sure stuff was tight under the car that would always be a good idea.

Yes, run 10's.

Denso IRE01-31

I run these and they are a billion times better than stock 9's. They idle better too and last way way longer.

You're welcome.

I thought some knock is very common. Getting 1/2/3/4 knock is meaningless no. Especially in decel.

@lOOkatme ty. I’ll check them out. They appear to be flat on bottom so no need to gap them differently right ?

curious what power and boost you are making?

The long-term risk would be heat transfer from the plug to the housing. Causing the spark plug holes (particularly the trailing) to deform, which causes the chrome to bulge from underneath. Howard outlines the situation in the thread I posted earlier.

I'm no engine builder, nor am I a tuner, but I've dove into all of the spark plug conversations over the past 5-6 years (hell, I can think back to the autolight plug discussion of probably 15 years ago), and watched people smarter than me bicker back and forth on this subject on here and facebook.....and I've come to a very simple conclusion: Trust but verify.

To me, the downside of doing a plug read is: I'm out a few extra bucks and some time
The upside is: I catch something that allows my engine to stay more reliable, for much longer.