vertC6

I just recently completed my build of a 2013 427 (LS7) convertible, here is the link of the work that I did.

https://www.corvetteforum.com/forums...e-details.html

I installed Pfadt 1 3/4 headers, FAST intake (ported), Halltech CF112, Yella Terra RR, and heads done by AHP with .030 milled to put my CR at 11.6:1.

Once I got everything back together I took it to Alex Pietz who is a professional tuner from the tuning school. Upon tuning he immediately notice KR retard upwards of 7 degrees at 20 degrees of timing. We brought it back down to 18 degrees with at 12.4 AFR. Still I was getting KR which at that point he believed was false, so he turned the sensitivity of the knock sensors down 20% and still we say 2 to 3 degrees of retard at 5000 rpm.

I drove the car for 3 more weeks and only saw KR on my HUD a few times mostly under load at low rpm (normal). I decided to buy some torco and bump my octane up to 102 to confirm once and for all if the KR was real. Once we put it back on the dyno sure enough at 5k it retarded 2 degree and 3 degrees at 6200 rpm.

Now that I know if is a false knock how do I find it! I rechecked the header clearance and nothing is touching. I re-torqued all the header bolts, I checked the belt tensioner and anything I could think of to cause a false knock and I found nothing! Any ideas on what to do next? The tune is plenty safe but I would like to figure this out if I can.

Unfortunately, this is not my first experience with this, I had a 97 eclipse GST turbo that would nearly stall because the computer was picking up a knock that wasn't there. After replacing the ECU, knock sensor and a few other parts I finally moved the sensor from the block to the base of the intake manifold and it was gone! Drove it for 5 more years like that.

User Omega

How many years has your tuner been professionally tuning cars?

rio95

06-07 alternators can cause this but you should have an updated clutch style one. Could be bad still though. Might be worth checking.

vertC6

I checked it and everything was ok, I have a 2013

vertC6

Quite a while, he was a teacher at the tuning school in Florida, roughly 15 years

Celero

1 3/4 primaries seem small for a built 427. Isn't 1 7/8 recommended?

regorih

There's a bunch of parameters that deal with knock retard besides desensitizing the knock sensors and taking timing out . If it is indeed false knock I would adjust the other tables related to knock.

Tech

I chased this for months on an LT1 car I tuned many years ago. I finally gave up after being unsuccessful trying to find the source. If you have a better outcome, please share it.

I saw some people jumping all over your tuner saying he shouldn't desensitize a knock sensor. Ideologically, I agree with them. But there are situations where I think it's the best solution and yours could be one of them. Do what you can to try to find it, but if you can't, don't lose sleep. You could dump hundreds of dollars into finding this issue and end up with nothing more than an empty wallet and frustration.

vertC6

I agree, at this point there's no telling for sure what is causing it, but I know it's a false knock. Alex is a professional and I know he knows what he is doing. We tuned the car very safe and he only turned the sensitivity down by 20%.

I am definitely not going to lose sleep over it, but if I can figure out what is causing it I would like to find it and fix it. At this point I am just talking with other guys who have had the same issue and see if I can pin point what causes it.

schpenxel

If you can figure out what's causing false KR on my truck while you're at it that would be great. I swear that thing looks like it's about to explode on every log I take, but it's been that way for 200K miles and no issues.

emoFTW

How can you tell if its false KR or not? and how can you tell how much timing its pulling? I have HPTuners and when I did get knock it read, 1 or .5

schpenxel

If it's only reading 1* or 0.5* then it's not worth worrying about, assuming someone hasn't jacked the knock settings up. That might as well be nothing.

emoFTW

Well then, at what point should I start worrying? 3*-4*? Just trying to learn!

schpenxel

Something like that, for me it's more that if when KR starts to drop off then it comes right back, i.e. looks like a saw blade if you graph it out, then to me that's likely real

vertC6

We reduced timing all the way down to 16* at WOT with 12.1 AFR and 102 octane and we still saw 2* at 5000 rpm and 3* at 6200.

tblu92

The only true way to determine if your KR is in fact real of false is to have your engine data logged---This also must be done when the engine is under MAX load like an auto trans at WOT in 3rd gear-or on a manual trans or a 5 speed auto where the trans is a ratio closets to 1:1-----
You will NOT get accurate KR in any trans ratio where it is undedriven as the load value is not at the max
You need to data log your 'actual final timing" and compare it to your " commanded timing----If they do not match then you need to see how much timing is being removed from high IAT temps and high coolant temps--- As an example if you are asking for 28* of timing at WOT and you only see 20* actual final timing then you know 8* is being removed---Check your IAT temps and see what is being removed as well as your Coolant temps to see how much timing is being removed there---If you determine that like 4* is removed from IAT temps and that 1* is removed from ECT temps and you only have an actual final timimg of 20* then yout commanded timing of 28 minus the 5* from IAT and ECT temps you should have a final timing of 28- 4 which would equal 24* If you have LESS than that then the timing is being removed from from KR------IF you hear NO pinging then the KR is FALSE--Meaning you need to " desenitize your knock tables to eliminate this false knock---False knock is very common with certain mods--The greatest culprit is LT headers-----Aftermarket valve train----LT or shorty headrs and finally ona manual trans car an aftermarket light clutch or flywheel

schpenxel

If it's showing under just plain "KNOCK RETARD" then it isn't all the other IAT/ECT spark adders or anything else you're mumbling on about, so no need to go through your usual schpeal

tblu92

What ? I am just trying to help you determine where your timing deducts are coming from-- It is over most people's head as it is rather complex---But there is no need to criticize as everything I tried to explain to you is what all tuners do to find out where in fact the timing reductions come from----If you on your own deem there is no timing loss from IAT or ECT temps then it is most likely coming from KR---If you hear NO detonation then the KR is false---

vertC6

Well after months of speaking with you guys and some local tuners I decided to take my car to Michael at Serious HP in Houston. I cannot stress enough how impressed I am with him and his customer service. He spent over 5 hours tuning my car on the dyno and on the street. He explained everything that he did and most importantly he got rid of the false knock!!!

You guys were right, if the tuner spends the time and goes through the knock tables of each cylinder the "false knock" can be removed. I could not be happier and he was able to pick up 7 hp and 19lbs of torque! We did the runs in 95 degree weather, so I am sure it would pick up another 10 or so at 70 degrees.

The squiggly lines on the dyno are related to there drums not my car, they had some flooding in the shop last year that did something to the dyno to make the smoothing look rough. I encourage anyone in Houston looking for a great tuner go see Michael.