Detonation: Do I have it or not?
 

Hey guys, let me start off by saying merry christmas! Now to my question: Today I took the car out for a nice drive it was very cool outside and my intercooler pipes were not even hot, infact they were extremely cool. I did a bunch of runs and when I was goin flat out in 4th gear I would get some sort of noise between 5,000- to redline. It only happens in fourth gear fifth gear no noise nothing. Now my down pipe does rattle sometimes so I think that is what is making the noise, but I feel that the noise could be detonation what do you guys think? Owe this might help: 8psi, frontmount, stock ecu, 330cc inj., td04-15gHL

Check your plug color. Detonation happens, or can happen, in any gear. What are you using for ignition management?

90-94? watch the oil gauge next time.

and by that he means if it gets jumpy/shaky when you are hearing that noise its detonation

I wanna chime in here. Question - even with the oil pressure gauge, is there any way you can have detionation without it affecting the gauge? And how dramitacally goes the gauge shake?

The gauge wiggles back and forth about the width of the needle. It's noticeable. You can have detonation that doesn't affect the gauge, too, though.

I have a 99 so unfortunately I can not tell by the gauge as for ignition management I have none because I never noticed any detonation and wanted to keep stock timing. Also, what should I look for on the plug that would indicate detonation?

I believe you can also see detonation in the boost gauge (if under boost obviously).

The easyest way to tell by the plug is if the electrode is all chewed up/the plug is damaged. Detionation is very hard on everything within the combustion chamber

why not fix the downpipe rattle than asses if it still happens? that will rule out the downpipe

+1 on that. Process of elimination.

http://www.verrill.com/moto/sellingg...colorchart.htm or
http://www.centuryperformance.com/spark2.asp

Look at the overheated, preignition, and the detonation plugs.

Do you have any form of air/fuel or wideband gauge on the car? Maybe your running lean as well. I have a '94 with the 'real' oil gauge and I've had detonation and never noticed the gauge moving. You can try retarding your timing a few more degrees and see if that helps eliminate the noise your hearing. If it's detonation it should get quieter or stop. What are you using for ignition management?

99 has knock sensor for the ecu, which pulls ign if detected- and it's fairly sensitve

If knock is detected what can the stock ecu pull? 2-4deg? Infinite? I've never actually heard what the Miata's knock system is capable of pulling or if it has a limit. It might be interesting to find out. I still need to program mine.

I don't know for sure. I ran the mazdacomp production shim-under-bucket valve train and custom cams in my 99 with stock ecu. The knock sensor picked up the new valve train noise as knock and killed all our new power. I never measured it as an ecu went in after that race.