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Thread: Corvette LS2 MY05 opinions on KR

  1. #1
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    Corvette LS2 MY05 opinions on KR

    Hi sirs,
    it is more or less one year that i'm following all the discussions in this website forum, tuning instructions on other website and last but not least i purchased and read carefully Advanced Engine Management Tuning of Mr. Greg that i noted he is also a member of this forum. Then i decided to purchase hptuners pro and MTX-L wideband and started working on my car for fun and the more i use it the more i love it.

    What it is not so clear to me is the KR issues. I have seen a lot of posts talking about the oversensibility of KR sensors on ls2 so i understood from respectable tuners posts that once they tune for spark advance (after fueling tune) they multiply by 2 the decay rate and divide by 2 the base retard in order to decrease the risk of false knock once tuning.

    I've tuned my car with a single wideband inserted in the cross of the x-pipe (to average both banks)to make a PE flat of 12.5 on all RPMs with the MAF at WOT. (The MAF and VE table were prior tuned by myself using LTFT and STFT method on non-WOT areas in either MAF only or Speed Density MAF disable). I've decreased PE enrichment RPM a little not sure if it is good or wrong but decrease to 0 seems more for FI or H/C package, for a bolt-ons it can be enough as i think (but maybe i'm wrong i'm not experiencing burst knock).

    Now that i have tuned the MAF at WOT and the fueling is correct (as per my wideband numbers) i have a question. If i change the decay rate and base retard for KR sensor as per above i do not have any KR (so far) during my logs session either at cruise/non wot or at wot so i can also try to increase further the spark advance but if a move back to stock settings for KR i log some cells with 3-4° of KR.

    What do you suggest me?May i rely and run the car with modified KR settings (decay and base) or after the tune it is better to put it with stock KR settings and have the low octane table with 3-4 degrees less for safety?
    With the First option obviously the car will not pull timing during driving because of no KR but if true KR is oscured it can be bad. Second option will pull timing even for false KR....

    At now my car setup is :

    LS2, K&N CAI, 160°F Therm, Fast 102 LSXR, 1-3/4" custom made in Italy LT headers no cat, Borla xpipe, Borla touring exhaust.

    The previous setup i had (without Fast102,with HF cats and custom tune) the car ran 391 SAE rwhp on a Dyno.

    Now i'm tuning on the street (not able to go on a dyno) but i can feel the car run really much faster than before!!
    I checked also the previous tune in my car and i really really said to myself i did well to go for hptuners and tune by myself as the shop simple did an increase of 3 degrees on High Octane table and 2 degrees on Low Octane table over 3000rpm without changing any other tables!!

    I noted also another strange matter, the narrowbands have been placed on a single cylinder on my LT headers on both banks, cylinder 1 and cylinder 4. Don't know why the shop didn't design and place the narrowbands on the bottom to get the average of each bank but it seems the NBs are working the same, maybe not an optimal case for fine corrections on fueling and 100% trust on STFT...

    I don't want to put too many things on the table now as i'm also experiencing some small random numbers of misfire events (i just ordered a complete new set of 8 stock spark plug wires as most probably they are the cause and i will change them soon)...i attach my current tune and the last short log for your opinion.

    The car is tuned to run with your 90-91 AKI octane fuel that it is equivalent here in Italy to our 95 octane RON.

    98-100 octane RON (93 AKI octane) is not so easy to find but in any case it costs like Champagne (more than 2euro/litre , yes there is no typing mistake...) so i will not go for it unless for some litres to be mixed with in case of a track day for safety.

    Thanks to all in advance for your comments.
    Last edited by ingsteve; 10-03-2012 at 10:18 AM.

  2. #2
    Tuner Mez's Avatar
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    Timing seems very low in the higher RPM at WOT. Why?
    2014 Corvette, Z51, 3LT, 7-Speed, NPP, 2 tops, Exposed Carbon Fiber roof, FAY, Laguna Blue, Kalahari, Museum Delivery.

  3. #3
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    hi Mez,
    as i'm not tuning with 93octane i started working with stock low octane table. Also from stock LS2 HO and LO table at WOT there are cells with 10degrees less. Now i have also the fast102 and you know normally you have to reduce timing with this modification but i didn't (only a few in some cells). Even to me it seems i can add some degrees at wot considering the value itself (around 13°) but as per the post, with stock KR setting i'm already getting some degrees of KR so to add timing i have to rely on desensitizing the KR setting and running all the time with double decay rate and half base retard.
    What are your settings?Are you running all the time with these fields modified?
    That is the question

  4. #4
    I'm not an expert on this, but I don't think there is anything wrong with changing the KR decay and base retard settings in the manner you did. You aren't desensatizing the sensors themselves -- just making them less intrusive when some KR is detected and quicker to recover when no KR is present.

  5. #5
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    Quote Originally Posted by BMWMD82 View Post
    I'm not an expert on this, but I don't think there is anything wrong with changing the KR decay and base retard settings in the manner you did. You aren't desensatizing the sensors themselves -- just making them less intrusive when some KR is detected and quicker to recover when no KR is present.
    You are right this is not a desensitive matter but in any case the risk to onscure true knocks situation increase. To me it seems strange to go frim 0degrees to 5degrees of retard by changing only tese two settings...the point is which settings i have to trust and keep for every days driving?

  6. #6
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    ok i tried a lot of logs today using double decay rate, half base retard and around half max KR vs RPM vs MAF tables.
    I increased very much the spark advance (see comparison table from the start in the picture), whenever i got a KR a subtract half of it and stop adding advance, for cells with no KR i added +1 on each logs...i noted an increase of power on4th and 5th gears...

    Now the spark table is the one below, there are some spikes where i stopped adding timing...what do you suggest me to do? Do you think i still have enough room to add timing even if i experienced some KR on the cells with spikes or it is time to end and smooth something?

    Thank you all in advance for your suggestions

    Attached log and tune i used, i think i should add also 1% of fueling on next tune from 9600-10400MAF hz to keep the fueling in line with the wideband.