Knock tuning, the Predator and You - Dodge SRT Forum
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post #1 of 164 (permalink) Old 09-16-2009, 08:35 AM Thread Starter
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Knock tuning, the Predator and You

I've see threads week end and week out asking about knock and what to do about it and I usually post the same thing over and over again so I've collected a few posts into one concise set of guide lines.

NOTE: A new 93 tune[9r18 and newer] with revised Knock tables should be coming out soon(thanks to your's truly) and will help reduce ST KR for most if not all 93tune users. Look for it in 9r18. more details here and on DS forum here

UPDATE
NEW CROM IS OUT THAT INCLUDES THE NEW IMPROVED 93TUNEDiabloSport PREDATOR UPDATES


I: WHAT IS ST and LT Knock???
Both KNK LT RETARD(aka Long term Knock retard) and KNK ST RETARD(aka Short Term Knock retard) show the amount of timing pulled because of Knock in degrees(you can see the units are "deg"=degrees. )

ST Knock is the real time instantaneous knock. If your timing was supposed to be 25 but you have 4 ST knock, your timing will display as 21.

If you're are getting ST knock constantly and a particular RPM/MAP the PCM will start to pull LT knock to try to keep ST at 0.

So using the same example: if your timing was supposed to be 25 but you have 4 ST knock AND 4 LT knock your final timing will only be 17(25-4-4=17)

__________________________________


II: How can I see how much Knock Retard I have?
How??Datalog, Datalog, Datalog and Review it on your PC-------use these PIDS

The Trinity, Predator or pos scanguage will display KR as you drive But that's really not any better than an idiot light and its not a very accurate way to tune. You will get a MUCH better view of the Knock profile from looking at the log file by exporting it and viewing it in the DS Dataviewer. Here's what I mean:

I was viewing Knock on my Trinity and it looked like it extended from 3k-5k. But after I looked at it in the Dataviewer I could see that I had ONE initial spike at 4300 and the PCM was just slowly tapering it off to 0.

I would have pulled too much timing(i added 2 degrees from 4k-5k) if I had just looked at the display

see what I mean:



__________________________________



III:Ok wise guy, I have Knock what do I do about it?

First off, for the Diablo tunes: <1.5 degrees of KR, every once in a while is perfectly acceptable. NOTE: For a 100% STOCK tune 2-3 degrees is ok. The difference is that Diablo tunes use less sensitive knock settings.

If for the majority of the time Kr is less than that, I would not remove any timing. So if you're not getting ANY LT knock and ST knock is less than 2.0 you should NOT remove any timing.

If the A/F is ABOVE 12.0[stock turbo] in the same RPM range that is experiencing knock, Lower the A/F BELOW 12.0 and retest.

If you still choose to remove timing use these guidelines:
Example:
A) If you're getting 4 KR but Only from 4k-5k don't go overboard and remove timing from 1k-6k.
You should remove 1 degree from 3k-4K and 1 degree from 4K-5K. 90% of the time that will reduce KR to under 2.0 for the majority of pulls. If ST KR is still above 2.0 pull 1 more degree from 4k-5k; do not pull any from 3k-4k and retest.

B) Rule of thumb is to keep the amount of timing you pull to 1/2 the amount of KR.
Rarely should you ever have to pull timing 1:1 with KR. If your getting 6degrees of ST KR, the 3 degrees of timing is the most you should need to pull. BUT always start with 1 degree first and work up to it the max.

__________________________________


IV:LOOK OUT for the 5000-5400RPM KNOCK TIGER TRAP

If you're only getting a bit of knock around this RPM range, you can usually ignore it. I had always noticed it at around 5200-5300rpm but Mindmelt101 aka Brian (Diablo SRT 93tune calibration developer) had seen it on other Chrysler's too. Here's his post and my response to it:
Quote:
Originally Posted by Mindmelt101
You'll find that 5K-5400rpm dodges have a tendency to knock I'm really at the belief that it's harmonics of the engines bbecause I've done back to back to back testing on numerous engines and it always seems to occur at the same place. Then check the plugs with a scope and nothing.... So I'm at the belief it's harmonics... Any input Duster?
Keep in mind I see it on anything from SRT4s to 440ci hemis of all various types and setups.
Quote:
Originally Posted by duster360
I agree 100%. Knock in that RPM range is too predictable and repeatable to be actual detonation.,,,,, Usually 5200-5300rpm is where I noticed that the 2.4l SRT-4 will most often "show" Knock.

I just assumed it was inherent to the 2.4l, but if Hemi's show this too, it might be tied to hysterious of the Bosch Knock sensor (they are "tuned" to Chrysler's spec), the Algorithm use by the PCM, which is probably common to most PCMs, or the balancing spec used during assembly(much less likely because a 440 hemi is custom balanced).

Last edited by duster360; 03-17-2014 at 01:29 PM.
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post #2 of 164 (permalink) Old 09-16-2009, 09:48 AM
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Why is it that you can throw some race gas and have that kr go away? (In 5k RPM) How is that not a clear sign of detonation over improper sensor readings?
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post #3 of 164 (permalink) Old 09-16-2009, 09:57 AM Thread Starter
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Quote:
Originally Posted by Adionik View Post
Why is it that you can throw some race gas and have that kr go away? (In 5k RPM) How is that not a clear sign of detonation over improper sensor readings?

Its very possible that real Knock can exist between 5K-5400K. Not every single knock count on every engine, in every car, at that RPM range is suspect. like I said "Knock in that RPM range is too predictable and repeatable to be actual detonation" since Brian substanciated this same anomally even on other Chrysler engines, you should be suspicious especially if you ONLY get knock within this small RPM range.
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post #4 of 164 (permalink) Old 09-16-2009, 11:36 AM
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thank you. Great write-up!!!!!

05 Red Srt 432whp/425wtq SOLD
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post #5 of 164 (permalink) Old 09-16-2009, 02:55 PM
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Originally Posted by Kason23 View Post
thank you. Great write-up!!!!!
x2. I've never been that lucky with my knock though. Never had it peak like on that graph and just fall back off like that, basically causing false knock - always been consistent straight across.
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post #6 of 164 (permalink) Old 09-16-2009, 04:04 PM
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Great write up.

I have Stage 3 w/toys and no DSP yet. (well, long story. Used to have one and as soon as I flashed the 93 oct tune, I was in the 13's A/F ratio so I sold it, as I was always running high 11's on my car before the DSP flash)

I have since installed a high flow cat to my 3" TBE and back to the stock airbox with drop in filter and my A/F ratio is now in the 10s, BUT I can only get 91 octane here in Las Vegas and I do see knock around 3 - 4 KR during WOT at times. (Seems to change with the brand gas I use)

The DSP leaned me out bigtime last time and I could not add fuel at all. (Not sure if it was a DSP fault or if my car was plain out of fuel, but I could not also get the fans to come on early either after inputting them into the DSP)

If I install the 93 tune now, will my knock get worse? I believe the last revision I used was 11.
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post #7 of 164 (permalink) Old 09-16-2009, 04:26 PM
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great write up
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post #8 of 164 (permalink) Old 09-16-2009, 07:03 PM
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Very good write up, thanks duster.
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post #9 of 164 (permalink) Old 09-16-2009, 07:55 PM
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sticky this for the numb nuts out there that are going to post a new thread about timing and knock tonight.
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post #10 of 164 (permalink) Old 09-16-2009, 08:28 PM
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bump...and sticky

Juan

04 Neon SRT-4 - on to a new owner
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post #11 of 164 (permalink) Old 09-16-2009, 09:07 PM
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great work!!!
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post #12 of 164 (permalink) Old 10-18-2009, 10:08 PM
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precious info i may add...thanks for taking the time


2005/stock turbo/3 inch down pipe/Charge pipe/HKS bov/Catch can/FM wastegate/Transmission Mount Inserts/ Diablo tune /Stage 3 South Bend Clutch
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post #13 of 164 (permalink) Old 10-18-2009, 10:24 PM
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Thanks

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post #14 of 164 (permalink) Old 10-19-2009, 01:09 PM
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Love it, but how about AFRs and knock? Any correlation between the two? Whats the best AFR to tune for? Should you tune AFR or knock first?
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post #15 of 164 (permalink) Old 10-19-2009, 01:31 PM
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Great information Duster!
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