Phanton Knock

[dubbsix]

Seeing some small spark retard in my tune but having a hard time detecting whether it is timing that is being pulled because of knock or whether its because of TQ management or BKR. In the graphic I see no indicator of knock, but the channels shows the occasional -2* of knock at idle / tip in but never at WOT.

I am running stock ignition timing, my fueling looks good with fuel errors (less than +- 5%)

The only change are the VVT cam angles to keep the cam retarded below 4K and then transitions to more advance up to redline.

[dubbsix]

Anyone??

[tbrtuning]

Possible it's false but kind of hard to tell. Looks to me like cruising around cam is full advanced. Aftermarket cam? It might not like stock spark advance running cam that advanced. Log knock sensor voltages to see just how loud it's getting too. Might be just over theshold but might be really loud.

[dubbsix]

Possible it's false but kind of hard to tell. Looks to me like cruising around cam is full advanced. Aftermarket cam? It might not like stock spark advance running cam that advanced. Log knock sensor voltages to see just how loud it's getting too. Might be just over theshold but might be really loud.

No stock cam with updated VVT tables. Good idea on the knock voltages I will log those and capture new logs.

[Hemituna]

Try put cam angles back to stock first....I think you are going the wrong way with the numbers based on what you stated about retarding low down...it looks like more advance to me.

[dubbsix]

Try put cam angles back to stock first....I think you are going the wrong way with the numbers based on what you stated about retarding low down...it looks like more advance to me.

Hemituna -- its an honor What I meant was retarding on the exhaust side. I think what I see in spark retard may not be in relation to actual knock. I did another log session and in some cases there was -2.5* being pulled while knock voltage was 0.50 and in other times voltage was 1.0v and 0* retard.


knock2.PNGknock voltages.PNGknock3.PNG

[tbrtuning]

I think you are going too far with cam timing with a stock cam down low but you definitely have the right idea not having cam retarded and moving all over the place like factory has it. Try something like 125 max for cam and see if that stops it from picking up knock.

The voltages are a little hard to compare because some cylinders are closer to knock sensors so you will always see more voltage from them. The factory calibration takes this into consideration with their thresholds for what is considered knock.

[dubbsix]

I think you are going too far with cam timing with a stock cam down low but you definitely have the right idea not having cam retarded and moving all over the place like factory has it. Try something like 125 max for cam and see if that stops it from picking up knock.

The voltages are a little hard to compare because some cylinders are closer to knock sensors so you will always see more voltage from them. The factory calibration takes this into consideration with their thresholds for what is considered knock.

Yea I readied a new tune but haven't loaded it yet because I really like how the car responds down low. When I see other examples of knock it looks like a staircase while a lot of videos say false knock looks like the little blips I have. I guess this is just about more testing which I love about tuning.

Are you saying 125* Max on the exhaust or intake side?

[tbrtuning]

Exhaust cam is the only adjustment that matters on the Hemis. It moves the entire cam and uses exhaust side as a reference for cam position. The staircase thing I see people talk about too but it's misleading when tuning a PCM that pulls more timing depending on knock severity (most seem to). You could have one really bad knock event be completely real and pull 5* of timing and not see more timing pulled after and it still be a completely legit knock event. Peak timing torque being a bit too high is a common cause of a knock event that can be pretty severe and cause timing to be pulled for a bit before the knock retard decays away.

[dubbsix]

Exhaust cam is the only adjustment that matters on the Hemis. It moves the entire cam and uses exhaust side as a reference for cam position. The staircase thing I see people talk about too but it's misleading when tuning a PCM that pulls more timing depending on knock severity (most seem to). You could have one really bad knock event be completely real and pull 5* of timing and not see more timing pulled after and it still be a completely legit knock event. Peak timing torque being a bit too high is a common cause of a knock event that can be pretty severe and cause timing to be pulled for a bit before the knock retard decays away.

For sure, just making sure I was thinking correctly. So i retarded the cam a bit to 126* (exh) and while the car drove just as well I also observed the same 1-2* of spark retard with the more aggressive advance where most of the knock happened at roughly 1500rpm right before a big throttle rate change. I think I named this one appropriately lol "Phantom".

[dubbsix]

Why do you think the cam is too far advanced?

[tbrtuning]

Mostly just from experience on the 392 stock cam. Aftermarket cams you have to consider what LSA compared to the OEM LSA stock tune is setup around and how much advance they have ground in also.

It helps to use a visual can calculator and put in the cam specs and then add advance to see what the valve events look like.

It may be fine like you have it but when you advance past the point where you have gains you're probably just eating fuel. Good experiment you can do is move the cam around and watch how fuel trims change as you start filling the intake better and needing more fuel

[dubbsix]

Mostly just from experience on the 392 stock cam. Aftermarket cams you have to consider what LSA compared to the OEM LSA stock tune is setup around and how much advance they have ground in also.

It helps to use a visual can calculator and put in the cam specs and then add advance to see what the valve events look like.

It may be fine like you have it but when you advance past the point where you have gains you're probably just eating fuel. Good experiment you can do is move the cam around and watch how fuel trims change as you start filling the intake better and needing more fuel

Ok that is good info, just trying to get an idea if there was a general rule of thumb for the 392. I think alot of it may come down to tuner preference right? I do plan to schedule some time on the dyno and run through my tunes and see in real time the impact of tuning the VVT system. I dont think there are huge gains to be had as Dodge did a pretty good job on the base tune, but I think by tuning the VVT you can tailor the car to the owners preference and make a more engaging driving experience.

I've kept an eye on the STFT and LTFT and they seem to be all within average corrections which made me feel like the cam was OK at 109. Actually in some spots in the stock tables, it advances to 109.6 (intake side) between 1500-1800. All in all thanks for the feedback.

[tbrtuning]

It is somewhat preference and there is a bit of room to go either way with something like AFR, cam timing, and spark and have one cancel each other out and end up at similar power levels. More cam retard up top with more spark maybe abs also his rich someone tunes impacts what it is going to like