Colder plug, BCR8ES
 

I took a chance on these since they are a step colder than the common BKR7 that everyone runs. I have been fighting knock forever if I run leaner than high 11s or more than 15* timing up top. And this on e85. Have retuned a zillion times trying to work around it with no success. Gave up until I recently looked for a colder plug and found this one. $25 shipped for a set of four from eBay UK.

In the last few weeks since installing them I've leaned out to mid 13s and have added 3-5* timing everywhere with no effect on knock. Nothing else with the car or fuel has changed, so I can only credit it to the plugs. These things are magic.

In a turbocharged e85 application most people do not run leaner than 12.2-12.4

Dann

in before carnage

Send your injectors out for cleaning. You are likely only running lean on one of the cylinders.

I didn't leave it in the 13s, it's down in the mid 12s. Merely noted as the point where I pushed it.

I left all of the timing in it, though, so maybe you'll get your window with a view after all, Vlad 😀

I still credit the plugs with the extra headroom on knock, whether I pop the engine or not.

Sixshooter, thanks for the suggestion on cleaning/flowing the injectors. I've had some weird IDC stuff going on that leaning out the mix helped resolve; the injectors are the one thing I have not pulled to inspect/address.

that's interesting. what are you monitoring/recording knock with? sensor? det cans?

I'm the nut running his car with a DSM ecu. Native knock sensor integration with active timing retard.

Yes but is it calibrated to actually work precisely on a BP? While similar, it's nowhere near like the 4g63 it was designed to work on.

It would likely end up being effectively more sensitive on a BP than a 4g63 because paintshaker POS motor.

As far as I know there is no way to address the response/calibrate the knock circuit in this ECU as it was likely never intended to be used with anything other than a 4g63 or related engine. The sensor itself is identical best I can tell to what is used in a 323GTX/GTR (dug around quite a bit when putting this all together), but that's not necessarily related to how the signal is processed on the back end.

I do feel like it is overly sensitive as speculated. Seems as though everyone here can run far more timing than I've been able to (until recently), and I have not been willing to ignore the sensor input on the off chance that it is accurate.

I also have never had anyone listen with a set of det cans to verify that what registers from the sensor as knock is audible, so that's an unknown.

it's about the frequency response.

the 46g3 knock sensor is 11.8kHz (this comes from people who have read the ROM from mitsu ECUs). We are using a value of 6.94kHz in the 1.8L miatas... that's a big difference in the resonance it's trying to look for -- it's possible that the knock sound waves in a miata cylinder are too short to accurately tickle the 4g63 ecu

I have done pulls in Acamas at ~27psi, 12.6:1 AFRs, and ~18deg of absolute timing. The knock sensor says no knock (raw per-cylinder data interpreted by hand). I don't actually know what the knock threshold is on my setup because I am scared to find out.

I am highly, highly incredulous of your claims of knock at 15psi on E85. The GT2560R is simply not capable of making enough airflow to generate the cylinder pressure required to induce detonation on E85 unless you run it leaner than stoich or something.

As am I, but I decided to play it safe over the years and run with a tune that showed essentially no knock in the logs.

If the info Brain offered up is accurate (no reason to doubt that it is), then perhaps the calibration is off towards the overly sensitive side of things, which is fine with me if it keeps the motor safe. Seven years under pressure and no engine damage, so whatever is going on is working. If I was struggling to make power I'd have been looking harder at this, but I made over 300wtq SAE on the 15* tune so I don't necessarily feel like I'm getting robbed.

On cold nights Acamas is probably chucking out ~440wtq at 295kpa. I think your knock sensor is way, way sensitive :)

sounds perfectly reasonable. but that brings us back to your original discussion: if what you're seeing is noise and not knock, then how does a set of plugs reduce/lower noise in an engine?

Sav, at 6k feet above sea level this turbo runs out of steam around 18-19psi. Maybe it is hurt otherwise, but it is definitely making more torque under the curve now. When the 6spd goes back in I'll turn it up again and see where it ends up.

Vlad, I still think it's the plugs. I literally have tried all of the same tweaks and alterations in the tune multiple times over the last 6 years that got me where I am now, and the only thing that changed was the plugs. I even tune on the same 2mi stretch of road every time I work on it. I don't have any other explanation.

Interesting, colder plugs are hard to find. I was considering trying a denso plug, but it was special order so I passed.

I am currently running around 15° in the 300kpa range on e85 without knock, but targeting 11.9:1 AFR.

I run NGK BKR8E-IX on everything I tune, no exceptions. There are literally no downsides to using them.