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I gotta say my 5.7 Challenger is the most temperamental car I've ever owned in the performance catagory. One day it starts up and runs like it's 1,000 pounds lighter and I'd swear it's twice as fast then what the factory rates it. The next day it starts and the way it runs I feel as though my 1985 motorhome could beat it in a drag race. Maybe cause I have a few small bolt ons with stock tune? Who knows but I'm curious if anyone else has experienced this with the 5.7 or any other car for that matter, my Jeep and 300 don't act like this and neither does my Camaro ? but maybe it's just me
 

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intake air temp & engine heat soak really can hinder the hemis. I think its more noticable in the 5.7 cars.
I also noted improvement with the right fuel. I now run nothing but shell nitro.
all of those, plus added weight in thr car (full fuel tank, passengers, etc) can certainly play a factor in how sporty they feel from 1 day to the next, if you are really tuned in to the car and its subtile changes in behavior.
 
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Discussion Starter #3
intake air temp & engine heat soak really can hinder the hemis. I think its more noticable in the 5.7 cars.
I also noted improvement with the right fuel. I now run nothing but shell nitro.
all of those, plus added weight in thr car (full fuel tank, passengers, etc) can certainly play a factor in how sporty they feel from 1 day to the next, if you are really tuned in to the car and its subtile changes in behavior.
I know all those factors can affect it, and when they do it makes sense, but what dosent make sense is all those factors the same, it still reacts differently. Maybe it's just me ??‍♂
 

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I know all those factors can affect it, and when they do it makes sense, but what dosent make sense is all those factors the same, it still reacts differently. Maybe it's just me ??‍♂
Is your car new, or is the engine broken in? In other words, does it have a few thousand miles on it?
 

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Is your car new, or is the engine broken in? In other words, does it have a few thousand miles on it?
'15 with 33K and I'm the original owner, like I said it's just weird I've noticed it ever since I've owned the car. It just has lazy days, my guy doing my Dyno tune said it should help it be much more consistent
 

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heat soak and fuel octane have an effect on 5.7s

for the A8 & 5.7 - run 89 at minimum or 91 for warmer climates

for the M6 & 5.7 run 91 minimum and if you can get 93, better yet

when you're in slow traffic or sitting; IAT will climb very quickly - like 20 - 30* above ambient as the hot air wash from the radiator / engine bay gets drawn in
 

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Discussion Starter #7
heat soak and fuel octane have an effect on 5.7s

for the A8 & 5.7 - run 89 at minimum or 91 for warmer climates

for the M6 & 5.7 run 91 minimum and if you can get 93, better yet
Yeah I've run 91 octane only the last 20K miles or so and better quality gas ( no 7-11 gas or equivalent)
And heat soak definitely effects it but I notice it being sloppy right at start up sometimes, and sometimes not. Just a weird thing
 

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Might I suggest:
run only 1 brand of fuel.
Like I said, my R/T when I had it, ran the best on Shell Nitro. Everything else, even in the same oct rating, was not nearly as smooth & soem down right sucked. Mixing gas from brands and octane levels in the tank can factor in.
Also, do a batt disconnect (both cables, 5 mins) this will reset all of your adaptives. Put the car in 1 setting (sport) and drive with all this for a while, same setting, same gas, etc and see if it levels out.
Check tire psi and keep an eye out on engine temp & IAT (if so equipped with the gauge) when it acts up, see if its related..
 

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Might I suggest:
run only 1 brand of fuel.
Like I said, my R/T when I had it, ran the best on Shell Nitro. Everything else, even in the same oct rating, was not nearly as smooth & soem down right sucked. Mixing gas from brands and octane levels in the tank can factor in.
Also, do a batt disconnect (both cables, 5 mins) this will reset all of your adaptives. Put the car in 1 setting (sport) and drive with all this for a while, same setting, same gas, etc and see if it levels out.
Check tire psi and keep an eye out on engine temp & IAT (if so equipped with the gauge) when it acts up, see if its related..
I might try Shell gas, I've been pretty consistent with Chevron gas unless I'm traveling and it's not available. And if not il try the battery trick, I've done the fuze pull but never notice a difference. I've probably been pulling the wrong one ??‍♂ thanks for the ideas
 

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In 10 years and 160k I can tell you HEAT is the number one reason. On 50 degrees and colder she runs so good you'd swear she added 50 ponies but at 80 plus degrees it feels like a Prius would walk it. As was said gas brand makes a big difference. Stick with at least 89 in an AT and whatever brand your car seems to prefer. Mine Likes BP.
 
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I might try Shell gas, I've been pretty consistent with Chevron gas unless I'm traveling and it's not available. And if not il try the battery trick, I've done the fuze pull but never notice a difference. I've probably been pulling the wrong one ??‍♂ thanks for the ideas
no prob, hope Ive maybe been some help.
what year is your R/T?
if its 2015 & newer, pop open both inner healight ports, thats good for some 10-12 degree drop in under hood temps once the car gets going and much faster heat soak recovery times.
 

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no prob, hope Ive maybe been some help.
what year is your R/T?
if its 2015 & newer, pop open both inner healight ports, thats good for some 10-12 degree drop in under hood temps once the car gets going and much faster heat soak recovery times.
Yes you have! And it's a 2015,
984118
way ahead of you on the headlight cap though ? it really does help especially on the highway plus the light tubes are always a kick at car shows
 

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Yes you have! And it's a 2015, View attachment 984118 way ahead of you on the headlight cap though ? it really does help especially on the highway plus the light tubes are always a kick at car shows
Are the light tubes an add-on? I don't remember my 2015 having the R/T on the inside like that.
 

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Discussion Starter #18
Maybe that’s the problem. The new throttle body and the computer not working correctly
Pherhaps, il be getting a Dyno tune in March so if that is the case hopefully it cleans up then. I can live with it for now cause 75% of the time it reacts just as good if not better then before
 

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It’s a good news/ bad news situation I’m afraid. The good news is you are not imagining things; I know exactly what you are talking about. The bad news is there is no easy fix for the problem, mostly because the car is operating as it was designed to operate - be overly cautious about possibly harmful behavior and don’t allow the engine to continue to do anything that would result in permanent damage.

What you’re feeling when the car runs great is the car running as it should be, near maximum potential HP/TQ output.

What you’re feeling when it doesn’t run as great is the effects of the PCM‘s reduction in spark timing to combat knock it thinks is occurring. Whether that knock is real or not is a whole different thread, but as long as the PCM believes it’s present, it will pull timing until it no longer ‘hears’ it.

The automatic timing reduction I’m talking about is called KR (Knock Retard), and if you have a tuner, you can observe it in real-time when it occurs. Logging the LTKR and STKR PIDs from a tuner’s datalogging screen will show you when the PCM is puking timing one response to knock, and it will show you how much timing is being pulled.

Each degree of KR is lost HP/TQ. I’ve heard different numbers, everywhere from 2 to 10 HP/TQ per degree, but whatever it is, it is enough to be felt when you know your car well enough to know it’s running differently.

So the next logical question is how to reduce or eliminate the KR so the car runs great all the time. Well, if you figure that out, write a book about it and you’ll be rich beyond your wildest dreams, because that’s what everyone wants but no one has figured out completely.

All the advice given so far is good, it will help reduce KR, but even doing all these things and anything else you can find on the internet to try, you may still get unexplainable KR that has no reason to be there. This is probably in response to false knock - the sounds the knock sensors picked up did not originate from an actual knock event in the combustion chambers - and there little we can do to address it short of identifying the source of the errant noise and stopping that.

That could be the transmission shifting more harshly, a worn out sway bar end-link, or any number of other things. Or it could be actual knock too, which is why adjusting the sensitivity of the knock sensors is a terrible idea. You’ll see that mentioned from time to time as a defense against false knock, but I would advise staying away from that unless you are drag racing and have the money to replace engine parts when you inevitably push it too far in search of a few more tenths of a second.

I’ll end this reply-turned-diatribe now with the hope that it was of some use to you, though I would not blame you if you already stopped reading by now. This is a subject I have been thoroughly looking into myself, so much so that I have taken to driving around with my laptop in the passenger side floorboard, turned on and actively outputting data from my Trinity for the PIDs I can watch to see when KR is present and what could be causing it.

Here’s a couple 10 second clips I recorded recently to help in answering a different thread, but they show what I’ve got setup in my car everywhere I go:



Why yes, I do have a sad life, however did you know ?? ?
 

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It’s a good news/ bad news situation I’m afraid. The good news is you are not imagining things; I know exactly what you are talking about. The bad news is there is no easy fix for the problem, mostly because the car is operating as it was designed to operate - be overly cautious about possibly harmful behavior and don’t allow the engine to continue to do anything that would result in permanent damage.

What you’re feeling when the car runs great is the car running as it should be, near maximum potential HP/TQ output.

What you’re feeling when it doesn’t run as great is the effects of the PCM‘s reduction in spark timing to combat knock it thinks is occurring. Whether that knock is real or not is a whole different thread, but as long as the PCM believes it’s present, it will pull timing until it no longer ‘hears’ it.

The automatic timing reduction I’m talking about is called KR (Knock Retard), and if you have a tuner, you can observe it in real-time when it occurs. Logging the LTKR and STKR PIDs from a tuner’s datalogging screen will show you when the PCM is puking timing one response to knock, and it will show you how much timing is being pulled.

Each degree of KR is lost HP/TQ. I’ve heard different numbers, everywhere from 2 to 10 HP/TQ per degree, but whatever it is, it is enough to be felt when you know your car well enough to know it’s running differently.

So the next logical question is how to reduce or eliminate the KR so the car runs great all the time. Well, if you figure that out, write a book about it and you’ll be rich beyond your wildest dreams, because that’s what everyone wants but no one has figured out completely.

All the advice given so far is good, it will help reduce KR, but even doing all these things and anything else you can find on the internet to try, you may still get unexplainable KR that has no reason to be there. This is probably in response to false knock - the sounds the knock sensors picked up did not originate from an actual knock event in the combustion chambers - and there little we can do to address it short of identifying the source of the errant noise and stopping that.

That could be the transmission shifting more harshly, a worn out sway bar end-link, or any number of other things. Or it could be actual knock too, which is why adjusting the sensitivity of the knock sensors is a terrible idea. You’ll see that mentioned from time to time as a defense against false knock, but I would advise staying away from that unless you are drag racing and have the money to replace engine parts when you inevitably push it too far in search of a few more tenths of a second.

I’ll end this reply-turned-diatribe now with the hope that it was of some use to you, though I would not blame you if you already stopped reading by now. This is a subject I have been thoroughly looking into myself, so much so that I have taken to driving around with my laptop in the passenger side floorboard, turned on and actively outputting data from my Trinity for the PIDs I can watch to see when KR is present and what could be causing it.

Here’s a couple 10 second clips I recorded recently to help in answering a different thread, but they show what I’ve got setup in my car everywhere I go:



Why yes, I do have a sad life, however did you know ?? ?
Thank you I've heard of the knock issues before but never thought about that, makes perfect sense. This weekend I guess il go through and make sure things are all tight and secure so it's not giving false knock, but definitely not adjusting the sensors il give up some HP/TQ to save the engine
 
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