Dodge Challenger Forum banner

For R/T owners curious about the 392 intake with short tubes

6K views 40 replies 5 participants last post by  PrestonRT 
#1 · (Edited)
EDIT: Leaving the original text below, but just wanted to write up front that I recently found that my active runners aren't actuating. Will update once I correct the issue.

Hi all. I've recently installed short tube headers and the 392 active runner intake manifold on my 2016 R/T, and the great news for everyone here is that I've got before/after dyno results to share! Please check out the attached photograph which I painstakingly angled to capture a reflection of the car in the glass.

The upper plot shows horsepower while the lower plot shows torque as a function of engine speed. The red curves are the car's baseline performance before the intake and exhaust mods were installed, and the blue curves are after install and tuning on the same dyno. While I only got a few horsepower increase at the peak, the horsepower stays higher beyond the peak and I picked up a ton of power across the low- to mid-RPM range. I spend most of my time in the 2-4K RPM range, so I'm pretty happy with the extra 25-30 horsepower in that range.

For reference, my headers are JBA 1964S-1JS ceramic-coated short tubes and my intake manifold is programmed to actuate the runners at 4600 RPM. I'm also running a Corsa 14985BLK Xtreme catback, but the catback is present in both the before and after runs. Hope this is helpful to anyone considering this modification combo.

Text Font Parallel Subcompact car Diagram
 
See less See more
1
#2 ·
Very useful before/after comparison, thanks!

If I am reading the data right, it looks like the exhaust upgrade was the most beneficial by far of the 2 mods. As you pointed out, it added performance across the torque band down low, right where the engine spends the majority of its time operating.

The intake’s contribution does appear to be minimal, but I think this is to be expected in this particular application. Its true value as a performance mod would be realized with an upgraded camshaft that helps the engine breath in the 4500+ RPM range.

An upgraded camshaft without the intake upgrade would still run short on breath up top I believe, but that intake’s switch to the short runner design in high RPM operation allows for more breath when it’s needed most by the upgraded cam.

That my understanding of how it all works anyway.

These two upgrades are if particular interest to me BTW, as I am planning on installing a 392 cam in my 5.7L soon. The intake isn’t an upgrade I’ll be doing at the same time, although I know I should. The exhaust was further down the list on future upgrades, but after seeing your Dyno results, I may have to move it up the list a few slots.
 
  • Like
Reactions: PrestonRT
#3 ·
The last thread I saw you in, I was worried you were trying to talk yourself out of the cam upgrade, glad to see it hasn't worked!

I agree with your assessment, I think the headers gave me most of the low-mid power, but the intake will be a good complement to a cam upgrade that opens up more on the top end. I'd also like to do the camshaft, but I've done a lot in a short period of time and I'm going to need a financial recovery period before I start trying to convince my wife that I need a cam.

Talk to you later!
 
#5 ·
Seemed like I had read somewhere on here that another member had better results at 4600, but really I don't have a good reason for picking it. At the end of the day the curve is pretty smooth, so we didn't bother trying to adjust the switching RPM.

I have always wondered though, how would I even know if they're actually switching? Suppose your actuator failed one day. Its not like you can see inside the manifold, how would you know when something failed?
 
#11 ·
The RPM at which the short runners become more efficient is dependent upon the actual length of both the long and short runners. For these intakes, the lengths put that switch-over RPM somewhere between 4500 and 4800. We could do the math to figure out exactly where it becomes more efficient, but there’s little value in knowing it actually.

The switch-over RPM won’t be as significant in overall power-making (assuming it’s relatively close to the right RPM) since the engine will likely spend such a small amount of time operating in that range at WOT.

If we say the exact RPM is 4789, and you have it set to switch at 4600, that means the engine spins through 189 RPM operating less than most efficiently. But how long, and how much power is made (and therefore lost) in those 189 RPM? Not very much.

So getting it close is good enough...for WOT operating that is. If the car were being raced in a Grand Prix type race or something, that exact RPM might be much more significant to dial in just right.
 
  • Like
Reactions: PrestonRT
#13 ·
Quick question regarding your intake upgrade: are you running a catch can with it?
 
  • Like
Reactions: PrestonRT
#17 ·
In regards to the switchover point, if you're running the 8spd it's even less critical due to the minimal rpm drop between gears. Depending on the shift rpm, at WOT you may never fall below the switchover point once you're out of first gear.
 
#18 ·
OK, so bad news for me, good news for all of you. I have confirmed that my active runners are not actuating. As a result, the dyno result I posted is significantly more straightforward showing only the benefit of adding the short tube headers.

I know I've seen other R/T dyno's with the 392 intake which showed a big dip in power when they haven't been tuned to account for the extra airflow after they go short mode. I found it odd that I saw no power dip in the baseline run, so I had to investigate. I double checked the wiring and confirmed that I have 12 V, ground, and the actuator wire throwing ground when engine speed surpasses the ON-RPM, so I am confident that the wiring is OK. I ended up sticking a borescope into my intake manifold and just watched the flaps as I changed the ON-RPM setting over and under my idle RPM to test functionality; they're not moving.

I've removed the actuator and I can move the flaps by twisting the knob that the actuator couples to by hand. The flaps move freely, so they're not stuck or anything.

I then plugged the wiring back into the actuator and left it out to watch its behavior. I had to tape the hole on the backside of the intake manifold to turn the engine on, and upon doing so I note that the actuator performs a single actuation cycle when the car turns on, then nothing. The fact that it can always cycle once on startup tells me that my circuit delivers the required current to make it operate, but for whatever reason it is blind to the "actuate now" signal.

I feel reasonably confident that the problem is the actuator, so I'm going to replace it and see if it behaves. It should be ready for pickup on Monday. In the mean time, I'm gonna sit around being pissed at myself for not figuring this out before I paid for the tuning session.
 
#20 ·
OK, so bad news for me, good news for all of you. I have confirmed that my active runners are not actuating. As a result, the dyno result I posted is significantly more straightforward showing only the benefit of adding the short tube headers.

I know I've seen other R/T dyno's with the 392 intake which showed a big dip in power when they haven't been tuned to account for the extra airflow after they go short mode. I found it odd that I saw no power dip in the baseline run, so I had to investigate. I double checked the wiring and confirmed that I have 12 V, ground, and the actuator wire throwing ground when engine speed surpasses the ON-RPM, so I am confident that the wiring is OK. I ended up sticking a borescope into my intake manifold and just watched the flaps as I changed the ON-RPM setting over and under my idle RPM to test functionality; they're not moving.

I've removed the actuator and I can move the flaps by twisting the knob that the actuator couples to by hand. The flaps move freely, so they're not stuck or anything.

I then plugged the wiring back into the actuator and left it out to watch its behavior. I had to tape the hole on the backside of the intake manifold to turn the engine on, and upon doing so I note that the actuator performs a single actuation cycle when the car turns on, then nothing. The fact that it can always cycle once on startup tells me that my circuit delivers the required current to make it operate, but for whatever reason it is blind to the "actuate now" signal.

I feel reasonably confident that the problem is the actuator, so I'm going to replace it and see if it behaves. It should be ready for pickup on Monday. In the mean time, I'm gonna sit around being pissed at myself for not figuring this out before I paid for the tuning session.
Just read this last post........it will be real interesting to see if you get them working if it makes a big difference. I can not see any on my car
 
#19 ·
I think what you are seeing is mostly the effects of the intake. If you look the air flow at 4800 for the additional displacement of the 6.4 and the more aggressive cam vs air flow potential of potential of the 5.7 with the milder cam my guess is the air flow of the 5.7 at 5400 to 5600 is about the same as the 6.4 at 4800. Every test I have seen . That is why most are not seeing any major lift on the top end of the 5.7 with the intake. The 5.7 is camshaft limited on air flow! All the benefits everyone is seeing are the longer runner length creating more velocity to fill the combustion chamber down low. My belief is Dodge used the longer runners to clean up the bottom end of 6.4 and the runner switch over and cam to make more power up top. No other reason i can see for the added expense and engineering.

The real test will be when someone runs a 5.7 with a healthy cam and compares the intakes! That is where I believe we will see the big difference! I also have the 6.4 on a 5.7. I drop .3 sec 0-60 with no other changes. The bottom end pick up with the 6.4 intake is probably the best buck. I have run it with and without the runner switch and the 0-60 does not change.

Just my thoughts
 
#22 ·
I think what you are seeing is mostly the effects of the intake. If you look the air flow at 4800 for the additional displacement of the 6.4 and the more aggressive cam vs air flow potential of potential of the 5.7 with the milder cam my guess is the air flow of the 5.7 at 5400 to 5600 is about the same as the 6.4 at 4800. Every test I have seen . That is why most are not seeing any major lift on the top end of the 5.7 with the intake. The 5.7 is camshaft limited on air flow! All the benefits everyone is seeing are the longer runner length creating more velocity to fill the combustion chamber down low. My belief is Dodge used the longer runners to clean up the bottom end of 6.4 and the runner switch over and cam to make more power up top. No other reason i can see for the added expense and engineering.

The real test will be when someone runs a 5.7 with a healthy cam and compares the intakes! That is where I believe we will see the big difference! I also have the 6.4 on a 5.7. I drop .3 sec 0-60 with no other changes. The bottom end pick up with the 6.4 intake is probably the best buck. I have run it with and without the runner switch and the 0-60 does not change.

Just my thoughts
If the SRV were bad, it would fail that initial actuation at startup, wouldn’t it?

As I understand it, there is some sort of black box (figuratively speaking) installed as part of this mod whose job it is to send the signal to the SRV to actuate once the specified RPM is seen. Can you hook up something to that wire to test for power once the engine RPM exceeds the predefined RPM?

I have a Fluke DMM that has a detachable screen for viewing it output remotely. I would use something like that if I were trying to confirm the voltage on the wire at 4x00 RPM. Do you have anything similar?
 
#25 ·
All right, here's the latest. I'm very happy with the look of my newly implemented LED. I mounted it up and to the left of the MSD box, both of which are embedded into an ABS cover. They can be seen in Attachment 1.

As for functionality, I am seriously perplexed. I replaced the actuator, and I have the exact same results. I've conducted several experiments, so I'll start here with the simplest test configuration and expand from there.

To eliminate any external variables (my wiring harness, the MSD box, etc.), I've tested the actuator simply sitting on my workbench (not attached to the manifold). Here I can apply 12 V to pin 1 and ground to pin 2 to power the unit. I am certain that I have the pin order correct, as they correspond to the pin designations inscribed on the MOPAR 4-pin connector. Upon powering it up, it quickly cycles the actuator roughly 20 degrees back and forth one time. Pin 3 is open at startup, representing the conditions of the default long runner mode. In this scenario I should see voltage on pin 4 which would drive my LED, but pin 4 only gives a small negative voltage (-0.08 V). Next I can ground out pin 3 by connecting it to pin 2. This should direct the actuator to actuate, but it does nothing.

So in this simplest implementation; 12 V on pin 1, ground on pin 2, and signal by grounding out pin 3, I get a single actuation upon powering the unit and no response to the signal on pin 3. I've replaced the actuator once and got the same result, so I can't really blame the actuator but the electrical inputs seem consistent with every build guide I've seen. Can anyone identify what I might be missing?

Any advice would be much appreciated.

Thanks!
Preston

Electronics Technology Electronic device Auto part Bumper
 
#26 ·
All right, here's the latest. I'm very happy with the look of my newly implemented LED. I mounted it up and to the left of the MSD box, both of which are embedded into an ABS cover. They can be seen in Attachment 1.

As for functionality, I am seriously perplexed. I replaced the actuator, and I have the exact same results. I've conducted several experiments, so I'll start here with the simplest test configuration and expand from there.

To eliminate any external variables (my wiring harness, the MSD box, etc.), I've tested the actuator simply sitting on my workbench (not attached to the manifold). Here I can apply 12 V to pin 1 and ground to pin 2 to power the unit. I am certain that I have the pin order correct, as they correspond to the pin designations inscribed on the MOPAR 4-pin connector. Upon powering it up, it quickly cycles the actuator roughly 20 degrees back and forth one time. Pin 3 is open at startup, representing the conditions of the default long runner mode. In this scenario I should see voltage on pin 4 which would drive my LED, but pin 4 only gives a small negative voltage (-0.08 V). Next I can ground out pin 3 by connecting it to pin 2. This should direct the actuator to actuate, but it does nothing.

So in this simplest implementation; 12 V on pin 1, ground on pin 2, and signal by grounding out pin 3, I get a single actuation upon powering the unit and no response to the signal on pin 3. I've replaced the actuator once and got the same result, so I can't really blame the actuator but the electrical inputs seem consistent with every build guide I've seen. Can anyone identify what I might be missing?

Any advice would be much appreciated.

Thanks!
Preston
Didn’t want to give you crickets, P, so I’m responding, but I don’t have any thoughts yet... still digging...
 
#27 ·
Ok, I’ve got something for you;
digging deep I went back to the writeup from the guy who started it all (I think) and he claims there won’t be any movement (or erratic) if there isn’t a load on the butterfly (meaning pressure within the manifold). I take this to mean that bench testing may not give the simple test you are looking for. Here’s his thread, I’m still rereading:

 
#28 ·
If you read through at least the initial writeup from the gracious Hemissary, he explains pins 3 and 4 are logic level at 5v. Now I confess this most simple concept goes beyond my understanding (even if this is the most basic stuff to someone like Hemissary) but perhaps it alludes to not being able to simply jam your pin 3 to ground, OR expect pin 4 to function without the correct level within the correct circuit. I’ll keep trying...
 
#29 ·
I have an idea of what’s up, but I don’t have the facts to back up my claim yet. I’m currently combing thru the 2000 page service manual PDF I have to find the data I need, so I should have a reply ready by, oh, Thursday probably...oh yeah, and I am limited to viewing that PDF on my phone, so it might actually be Friday before I can find what I’m looking for 😔
 
  • Like
Reactions: PrestonRT
#32 ·
N


N/m, I found what I was looking for and it proves me wrong
 
#30 ·
I actually read this whole thread long ago, and I’m re-reading for you now... here’s a little excerpt from page 4:


rgot to mention; some folks have tried testing the actuator on the bench with no load on the output shaft. In most cases grounding pin 3 results in no response (a no-load condition can result in zero commanded movement). What you will observe during PWR-up though is the actuator cycle through it's range of motion once and stop. If you want to test it, install it on the SRV manifold.

A simple actuating test is to use a 12V source (lead acid is fine - need adequate peak current flow). Connect pins 1 (B+) and 2 (B-) to power up the unit. Then simply ground pin 3 to B-. Some folks have found the actuator's output shaft and the SRV manifold input shaft do not initially line up. During the actuator install, rotate the actuator until it keys to the input shaft, then gently turn the actuator so the bolt holes line up. In some cases you might need to apply PWR to the actuator so it cycles through it's range of motion while simultaneously lining up the two shafts. Harder to write / explain this than it is to perform...
 
#31 ·
I’m sorry to be inundating you all, but this is important, too;


Some folks have run into a glitch that I did not point out regarding the rpm switches I tested on the bench. I forgot that in order for a (any) rpm switch to function properly on our rides, it must have a one cylinder mode. The ones I tested using a signal generator and an oscilloscope on the bench all have 4/6/8/10 cylinder options, but not one cylinder.

Because we have coil-on-plug, each injector pulse is a single event just prior to the combustion stroke. I lost sight of this! The negative lead to the injectors that I normally tap into as an rpm signal works just fine for, say the Predator which has an option for single-cylinder mode during data logging. I forgot about it!
 
#33 ·
Ok, here’s my last one for the night, reiterating that you MUST test it installed in the manifold:
A few folks have, or are trying to test actuators on the bench; they here clicking after power-up, but observe no movement of the actuator's driveshaft when pin3 is shorted to ground.

The clicking upon initial power-up is similar to our throttle bodies, the actuator performs one cycle (open / close) then enters standby-mode.

There must be a load on the actuator's driveshaft itself in order for the device to operate properly. This means you must install it on the manifold, then test by observing cylinder #2's SRV valve through the intake plenum with a flashlight (if off the engine) or a boroscope.
 
#34 ·
Yeah, at this point I think you work as if the SRV is functional and concentrate further diagnosis efforts on the signaling of that module. Is it being commanded properly, etc.

I think that’s a much more likely failure point versus hardware malfunction
 
  • Like
Reactions: PrestonRT
#35 ·
Wow, thanks guys! I actually came across this thread too, probably about the same time you did. As soon as I read,

"NOTE: trying to make the actuator operate without a load (the manifold's actuator rods / valves) will result in erratic operation, or no movement at all. "

I realized my folly and ran back to the garage to plug the actuator back into the manifold to resume troubleshooting. Great news, its working! To thank you for your help, I'll share my final findings with you guys.

Upon plugging the actuator back into the manifold, I was able to watch the runner valves move with my borescope which I piped through the PCV return port into the manifold. I wrapped duct tape around the port so the manifold would remain air-tight with the borescope in place, and made the valves move by changing the ON-RPM below and above my engine idle. On startup, the valves do not cycle open/closed like the actuator did when it was on the workbench. In retrospect, I've realized that the actuator is not cycling open/closed, but is actually cycling closed-open! What is happening is that on startup the actuator rotates in the closed direction until it meets resistance, and it identifies that point as full-closed and stays there until commanded to open. When functioning normally, the valves are already closed so they don't move and the unit declares that the fully closed position. However when the unit is on the workbench, it rotates about 15-20 degrees towards closed, does not find a closed position, and subsequently rotates back close to its original position and sits idle. It does not function thereafter (until cycled off/on again) because it did not identify its closed position.

Prior to all of this, I had observed that my original setup was not working while installed on the manifold via the same borescope method. This seems to confirm that the original actuator was in fact bad. If I had just installed my replacement without trying to bench test it then I wouldn't have gone through all of this headache, but in the end we learned a lot more about how the system works, so that's worth a lot.

Afterwards I took the car out and hammered the gas a few times. I do not feel any power drop when the runners switch to short mode, but perhaps I'm just not very attuned to the feeling.

And the last bit I wanted to share is related to the LED. Unfortunately the LED set up to be powered by actuator pin 4 still does not work. I haven't been able to put a voltmeter to it yet as its a bit harder to access its wiring now that everything's put back together, but I'll try to probe it tomorrow and report back on whether I can get it to indicate the runner status.

Thanks again, talk to you all later!
Preston
 
#36 ·
On startup, the valves do not cycle open/closed like the actuator did when it was on the workbench. In retrospect, I've realized that the actuator is not cycling open/closed, but is actually cycling closed-open! What is happening is that on startup the actuator rotates in the closed direction until it meets resistance, and it identifies that point as full-closed and stays there until commanded to open. When functioning normally, the valves are already closed so they don't move and the unit declares that the fully closed position. However when the unit is on the workbench, it rotates about 15-20 degrees towards closed, does not find a closed position, and subsequently rotates back close to its original position and sits idle. It does not function thereafter (until cycled off/on again) because it did not identify its closed position.
Brilliant! Now that’s some great new insight I’ve yet to see ANYWHERE! So glad also it’s working! Major props to you and one more shoutout to Hemissary for laying the groundwork!
As far as “the feeling” that it’s working, my wife used to own a Honda with a “VTEC” and I’d describe the sensation pretty similar to that, in that, as you’re climbing into the upper register of rpms, you can feel the engine running out of air (due to the cam on my car at least), so when the short runners do finally open, it feels a little like a clogged drain “whooshes” free. I can’t wait to upgrade my cam to really take advantage.
As far as the LED, you used a 5v, right? I’ll be curious what you discover on this ‘coz it’s something I was hoping to implement as well.
Well done, sir!
Jason
 
#38 ·
The engine tune should be modified to account for the extra air coming in at WOT above the set RPM
 
  • Like
Reactions: PrestonRT
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Top