Dodge Challenger Forum banner

1 - 20 of 25 Posts

·
Premium Member
2012 Charger Pursuit
Joined
·
5,570 Posts
Discussion Starter #1
I've always heard the 5.7L stops making power in the upper RPM range (can't remember if the old adage specifies an RPM after which the power starts dropping), but it was never something I could detect with my butt dyno, so I wasn't sure how much stock to place in it...until now, that is. Now, I can see it, although I still do not detect it with my butt dyno, but nevertheless it's there in my datalogs, clear as day (never thought to watch the Air Charge, VE, and RPMs all at once to look for it).

What I have circled in orange in the datalog snapshot below, and what I see play out in every data log I generate now, is the datalog information from my Trinity for my car while going WOT through 2nd gear. The PIDs' colors are as follows:
  • throttle is in white (and pegged the whole time),
  • RPMs are in yellow,
  • VEs are in light purple and light blue,
  • AFR is in green, and
  • Air Charge is in orange.
987697


If you watch the Air Charge and VE lines, you can see them parallel the RPMs - all rising steadily toward the shift point @5500. However, at about 4900 RPM, you will notice the Air Charge and VE lines start to go downward and keep going downward until the shift point, at which point they start over in rising steadily upward again. It is that point in each gear, at about 4.8 to 4.9K RPMs, at which the 5.7L stops making power and starts losing it even though the RPMs are still building. I suppose this is what that old adage I referenced at the beginning of this post is talking about.

I will venture a guess that it is no coincidence that the 6.4L intake manifolds with their dual runner design choose the 4K RPM point to switch the runner lengths from long to short. This likely counters the effects I see in my datalogs and allows the 6.4L engine to continue to build power in that range where my 5.7L is dropping it. Sneaky bass-turds!!

That's about it, nothing else to this post. I just wanted to illustrate what can be discovered by utilizing your tuner for something besides loading a canned tune and then throwing it in the glovebox, Pull that puppy out and start recording some datalogs! You just might learn something about how your engine runs (NOTE: you will have to peruse those datalogs of course; it's not good enough just to record them!).

Nuke, OUT!
 

·
Premium Member
2014 Challenger SRT 8
Joined
·
620 Posts
A lot to be learned from this post !!! Good work !
 

·
Registered
2016 Jazz Blue A8 Scat
Joined
·
677 Posts
That's just how VE works. VE will peak at peak torque and start falling from there.

Now, while the cylinders may not be filling as efficiently, they are pumping more frequently so the actual horse power should still be increasing with RPM until cylinder filling can't keep up.
 

·
Super Moderator
Joined
·
15,092 Posts
/the peak power rating of the 5.7 is 5,150 rpm - the cam is the major limiting factor. Spinning the engine to higher rpm beyond that with a stock 5.7 cam gains nothing.

the Eagle 5.7 ('09+) has pretty good flow in the heads, but it runs out of breath. Put a higher lift / longer duration cam and good tune and it wakes up
 

·
Premium Member
2012 Charger Pursuit
Joined
·
5,570 Posts
Discussion Starter #6
like to see a data log of a 6.4l and see exactly what it shows when the intake switches from long to short runner. Just curious, I bet it has a drop and then build back up.
Me too! Now if someone who owns a 6.4L will loan me their car, I can make this happen....?
 

·
Registered
2015 RT 5.7 M6
Joined
·
6,798 Posts
Not sure if you can make that conclusion. Airflow is based off MAP which essentially indicates engine load.
 

·
Registered
2016 Jazz Blue A8 Scat
Joined
·
677 Posts
Here is a log from a pass I made back in April of last year. Not exactly the same pids displayed, but you should get the idea.

The yellow reference line going across is 4700rpm, which is where the runners switch. Trans was shifting at about 6150, 6200 give or take.

392.jpg
 

·
Registered
2016 Jazz Blue A8 Scat
Joined
·
677 Posts
And here is the same data, but zoomed in on 1st gear, the only gear where the engine spends time below 4700rpm.

392_2.jpg
 

·
Premium Member
2012 Charger Pursuit
Joined
·
5,570 Posts
Discussion Starter #11
Not sure if you can make that conclusion. Airflow is based off MAP which essentially indicates engine load.
I can, I will, and I have!!

Wait, which conclusion?
 

·
Premium Member
2012 Charger Pursuit
Joined
·
5,570 Posts
Discussion Starter #12

·
Premium Member
2012 Charger Pursuit
Joined
·
5,570 Posts
Discussion Starter #13
And here is the same data, but zoomed in on 1st gear, the only gear where the engine spends time below 4700rpm.
It appears as though your 6.4L does not suffer from the precipitous drop off in making power in the upper RPMs like my 5.7L, but just to be sure, I should probably do a run myself in the 6.4L, you know, for science ?

Also, what’s the throttle blip in that graph just after the onset of WOT, is that the BAS/ESP system automatically backing off the throttle due to detected wheel spin?

987861
 

·
Registered
2016 Jazz Blue A8 Scat
Joined
·
677 Posts
Yes, that is torque management stepping in for some reason. It could have been wheel slip or torque could have exceeded the torque limit. To be honest, I don't remember exactly.

Take a look at the vertical line on that graph at 18.02.39.9. That markes 4700rpm and from that point on airmass and fuel mass (afr stays relatively constant) both drop from there on up as a result of reduced pumping efficiency. That is the intake changeover point. You can see that it has already begun dropping even earlier than 4700rpm. The airmass peak is at peak torque.
 

·
Registered
2015 RT 5.7 M6
Joined
·
6,798 Posts
There are several things preventing the throttle/engine from hittping WOT immediately like:
  • throttle voltage vs rpm table (there are a few tables that limit throttle)
  • torque vs rpm
  • tip in spark retard
  • WOT delay (not so much on the Hemis but it's there for the V6)
The autos have more torque management than the manuals which is why I like tuning the manuals. :)
 

·
Registered
Joined
·
5,497 Posts
There are several things preventing the throttle/engine from hittping WOT immediately like:
  • throttle voltage vs rpm table (there are a few tables that limit throttle)
  • torque vs rpm
  • tip in spark retard
  • WOT delay (not so much on the Hemis but it's there for the V6)
The autos have more torque management than the manuals which is why I like tuning the manuals. :)
So what would happen if you tuned off Torque Management on an Automatic?
 

·
Registered
2015 RT 5.7 M6
Joined
·
6,798 Posts
So what would happen if you tuned off Torque Management on an Automatic?
Turning torque management completely off on automatics can lead to driveability issues. Most tuners on HP tuners forum and The Tuning School recommend reducing torque management but not getting rid of it completely...at least for a DD.
 

·
Premium Member
2012 Charger Pursuit
Joined
·
5,570 Posts
Discussion Starter #18
So what would happen if you tuned off Torque Management on an Automatic?
The 93 octane canned tune on DiabloSport tuners supposedly reduces TQ mgmt to near zero.

I cannot say how close to zero it makes it, but I can say it reduces it too much for my liking. So much so that I prefer to start out with their 91 octane canned tune and modify its spark parameters toward the 93 tune’s settings.

That way I still get the spark advance at WOT I’m looking for with some TW Mgmt left in the tune to watch over me and tuck me in at night and sing me night-night songs...well, maybe not the tucking in thing, but definitely the other two!
 

·
Registered
2015 RT 5.7 M6
Joined
·
6,798 Posts
I know the 93 tune halves the throttle tip in retard, reduces knock sensor sensitivity but I don't think it completely disables torque management. At least on my JGC it did not.
 
1 - 20 of 25 Posts
Top