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DODGE CHALLENGER SRT392
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Discussion Starter #1
Hello Team,

I have a challenger, pretty much stock making 455 hp 470 lb ft torque on dynojet. Add ons are Unlocked PCM, Tune, exhaust, CAI, Straight pipes exhaust, 90 mm throttle body, 275 front and 305 rear tires.

What can I do to make it 485 hp and any quick mods? I was thinking of throwing in some fuel injectors as I have a 90 mm after market BBK throttle body. Any suggestions? Do I have to do any other mods if I consider fuel injectors as my next mod? What are my other options to get more hp out of stock SRT392.

My ultimate goal is 600 horsepower naturally aspirated. But right now I am only looking to reach 485 - 500 rwhp .

Thanking in advance,
Alien Cop
 

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I don’t think there is much left to add performance without going forced induction.

A bigger cam and ported heads might return close to 30HP, but you would need to have the tune redone to accommodate the new parts.

What transmission do you have, the A8 or the M6?

If you have the A8 and anything less than the 3.9x rear-end that the M6 cars have, you could swap out whatever you have for the lower geared one from an M6 car.

That won’t add any HP, but it will make it accelerate quicker, and I’m guessing that’s the ultimate goal for your upgrades.
 

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DODGE CHALLENGER SRT392
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Discussion Starter #3
I don’t think there is much left to add performance without going forced induction.

A bigger cam and ported heads might return close to 30HP, but you would need to have the tune redone to accommodate the new parts.

What transmission do you have, the A8 or the M6?

If you have the A8 and anything less than the 3.9x rear-end that the M6 cars have, you could swap out whatever you have for the lower geared one from an M6 car.

That won’t add any HP, but it will make it accelerate quicker, and I’m guessing that’s the ultimate goal for your upgrades.

Thank you for your valuable inputs. I do have A8. So to accelerate faster what would we do? As I have a throttle body, I was thinking of adding injectors, so that we could get a few more horses out of the 6.4 L engine. What do you think?
 

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Thank you for your valuable inputs. I do have A8. So to accelerate faster what would we do? As I have a throttle body, I was thinking of adding injectors, so that we could get a few more horses out of the 6.4 L engine. What do you think?
Unless the current injectors are unable to provide the necessary amount of fuel for the amount of air being ingested, I don’t know that newer, bigger injectors would yield any extra performance. They would just provide the commanded amount of fuel like the current ones, and thus no difference in performance would be had I think.

And there is no guarantee the bigger TB is allowing the engine to ingest more air than the stock one. If the stock one were restrictive in some way, maybe. But I haven’t heard of lack of air coming in being a bottleneck on the 6.4L’s power.

The best way to know for sure would be to catalog some WOT runs, and if you see something in the logs that would indicate more fuel is required (like KR from lean knock condition maybe), then the newer injectors might be a mod to try.

Absent any data pointing to a problem or deficiency in the engine’s power output now, it would be a gamble to further add mods to the car in the hopes more power is returned. Those engines are already tuned very well, and with your custom tune, there is likely little left to gain thru mods except in small increments (5-10 HP)...or through forced induction obviously.
 

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DODGE CHALLENGER SRT392
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Discussion Starter #5
Unless the current injectors are unable to provide the necessary amount of fuel for the amount of air being ingested, I don’t know that newer, bigger injectors would yield any extra performance. They would just provide the commanded amount of fuel like the current ones, and thus no difference in performance would be had I think.

And there is no guarantee the bigger TB is allowing the engine to ingest more air than the stock one. If the stock one were restrictive in some way, maybe. But I haven’t heard of lack of air coming in being a bottleneck on the 6.4L’s power.

The best way to know for sure would be to catalog some WOT runs, and if you see something in the logs that would indicate more fuel is required (like KR from lean knock condition maybe), then the newer injectors might be a mod to try.

Absent any data pointing to a problem or deficiency in the engine’s power output now, it would be a gamble to further add mods to the car in the hopes more power is returned. Those engines are already tuned very well, and with your custom tune, there is likely little left to gain thru mods except in small increments (5-10 HP)...or through forced induction obviously.
Thank you again. No I do not think I wopuld do anything to add 5-10-15 hp gain. It would simply make things complicated. I would run and check the log and find out. The reason the thought came to my mind was for lean A/F mixture. 15.5. If I could get 12.9-13.5 for naturally aspirated, I thought it might help to add low end power. So the idea of injectors was running through my mind.
 

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Thank you again. No I do not think I wopuld do anything to add 5-10-15 hp gain. It would simply make things complicated. I would run and check the log and find out. The reason the thought came to my mind was for lean A/F mixture. 15.5. If I could get 12.9-13.5 for naturally aspirated, I thought it might help to add low end power. So the idea of injectors was running through my mind.
Well this is just a guess based on what I’ve encountered missing my Challengers and this Charger, but that leaned out A/F mixture could be due to the bigger throttle body.

The way I understand it, because the naturally aspirated Hemi doesn’t have a MAF sensor and has to calculate the air charge coming in based upon preset VE values at WOT, any change to the engine that alters VE, like a bigger TB, could result in an A/F mixture that’s not ideal since you’re altering one side of the equation (the air on this case) without making a correlating adjustment on the other side (the WOT VE tables in this case).

In other words, it’s possible your throttle body is bringing in a more air at WOT, but the PCM isn’t adding the extra fuel necessary to account for that extra air because it doesnt know the extra air is there without the updated VE tables it uses to calculate injector pulse width at WOT.

If that’s the case, the newer injectors would not help, as the problem is not insufficient pulse width capability, it’s incorrect (insufficient) pulse width commanded by the PCM. To correct that, the PCM needs the updated VE tables that tell it about the extra air charge coming at WOT from the bigger TB.

If you are comfortable making the changes, you could use a handheld tuner to adjust the WOT fuel parameters in the tune, adding 0.5% or 1.0% (richer) in the RPM ranges you see the leaned out A/F in the data logs. Then make some WOT runs and data log them to check how the A/F mixture responded to your changes. If it responded favorably, continue to adjust the WOT Fuel Parma’s until A/F is in the acceptable range.

Also, all this hinges upon you having a wideband to report the A/F. If you’re depending upon the narrowband PID from the car’s PCM, you’re not getting accurate information due to the aforementioned VE tables being inaccurate for the mods on the engine.

Clear as mud?
:geek:
 

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Are you running long tube headers or just cat back? Long tubes might squeeze out some more ponies but a lot of work and fair chunk of change to simply swap out the stock shorties. Bigger cam would help but considerable amount of work. Could do a supercharger like procharger (quickest, easiest and possibly safer than a PD SC to get +100HP) but that is +$6K.
 

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Discussion Starter #8
Well this is just a guess based on what I’ve encountered missing my Challengers and this Charger, but that leaned out A/F mixture could be due to the bigger throttle body.

The way I understand it, because the naturally aspirated Hemi doesn’t have a MAF sensor and has to calculate the air charge coming in based upon preset VE values at WOT, any change to the engine that alters VE, like a bigger TB, could result in an A/F mixture that’s not ideal since you’re altering one side of the equation (the air on this case) without making a correlating adjustment on the other side (the WOT VE tables in this case).

In other words, it’s possible your throttle body is bringing in a more air at WOT, but the PCM isn’t adding the extra fuel necessary to account for that extra air because it doesnt know the extra air is there without the updated VE tables it uses to calculate injector pulse width at WOT.

If that’s the case, the newer injectors would not help, as the problem is not insufficient pulse width capability, it’s incorrect (insufficient) pulse width commanded by the PCM. To correct that, the PCM needs the updated VE tables that tell it about the extra air charge coming at WOT from the bigger TB.

If you are comfortable making the changes, you could use a handheld tuner to adjust the WOT fuel parameters in the tune, adding 0.5% or 1.0% (richer) in the RPM ranges you see the leaned out A/F in the data logs. Then make some WOT runs and data log them to check how the A/F mixture responded to your changes. If it responded favorably, continue to adjust the WOT Fuel Parma’s until A/F is in the acceptable range.

Also, all this hinges upon you having a wideband to report the A/F. If you’re depending upon the narrowband PID from the car’s PCM, you’re not getting accurate information due to the aforementioned VE tables being inaccurate for the mods on the engine.

Clear as mud?
:geek:
I roger. So I would try to throw in some injectors and then alter the WOT VE table to see how it goes. So all I gotta buy are the fuel injectors . Do you recommend any? I am using HP Tiners for making the changes. Lets see if I could get to 485 rwhp :p Thank you for all your support though. I will keep you posted.
 

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Discussion Starter #9
Are you running long tube headers or just cat back? Long tubes might squeeze out some more ponies but a lot of work and fair chunk of change to simply swap out the stock shorties. Bigger cam would help but considerable amount of work. Could do a supercharger like procharger (quickest, easiest and possibly safer than a PD SC to get +100HP) but that is +$6K.
Is it okay to just throw just some headers and see the difference. I currently have catback from solo performance exhaust. Also I am assuming fuel injectors as I have a after market throttle body. Using HPTuners as programming device. Any other suggestions you have for me? Thank you for your suggestions though.
I do not want to add supercharger as I want to keep it naturally aspirated and see how far can i go. :(
 

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You seem to be hung up on replacing your injectors for some reason. Injectors alone do not add horsepower and I'm sure your stock ones aren't even close to being maxed out.

I also doubt that throttle body added anything as the stock one was up to the task based on your few mods.
 

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Injectors only need replacing if you plan on going E85 or are producing so much power that your injector duty cycles are consistently pegged past +80%. Lean AFR at WOT is also a sign but only if commanding more fuel does not fix it. Also bumping up the injector size would also call for an upgraded fuel delivery pump/system. As for the exhaust, you would see a little more gain with long tubes as they improve scavenging. IMO cat back systems do little to improve performance on these cars as the stock system flows well with the 2.75" pipe. Not sure how your tune was done, but according to the Tuning School they were able to eek out some more ponies at the top end by tweaking VVT (they blogged about it). If you plan on staying NA then making more power requires more drastic mods like high flow heads, big cam, more displacement (stroker) and nitrous.
 

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Discussion Starter #12
You seem to be hung up on replacing your injectors for some reason. Injectors alone do not add horsepower and I'm sure your stock ones aren't even close to being maxed out.

I also doubt that throttle body added anything as the stock one was up to the task based on your few mods.
I guess I would have to re-think all over again. You are right. I am also not sure why I added wider throttle body, doesnt seem any sense now to me. I was looking to do some mods that wopuld make use of wider throttle body. So what would be those?
 

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Discussion Starter #13
Injectors only need replacing if you plan on going E85 or are producing so much power that your injector duty cycles are consistently pegged past +80%. Lean AFR at WOT is also a sign but only if commanding more fuel does not fix it. Also bumping up the injector size would also call for an upgraded fuel delivery pump/system. As for the exhaust, you would see a little more gain with long tubes as they improve scavenging. IMO cat back systems do little to improve performance on these cars as the stock system flows well with the 2.75" pipe. Not sure how your tune was done, but according to the Tuning School they were able to eek out some more ponies at the top end by tweaking VVT (they blogged about it). If you plan on staying NA then making more power requires more drastic mods like high flow heads, big cam, more displacement (stroker) and nitrous.
I am not sure how it was done, but this is just the PCM tune, I guess I would go back for TCM tune, noit sure if the tcm tune would be of any help getting some more ponies.
 

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2018 Scat Pack Charger 11.995 first time out stock tune
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On a charger here now. But the Scat needs the long tubes and... Think about this. An underdrive crank pulley. 25% UD that will get you a 10/10 plus to the rear. Not many talk about this and don't know why Not. Did years ago on Daytona... Worth every penny. Mine is NIB right now with belt for the Scat.
 

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On a charger here now. But the Scat needs the long tubes and... Think about this. An underdrive crank pulley. 25% UD that will get you a 10/10 plus to the rear. Not many talk about this and don't know why Not. Did years ago on Daytona... Worth every penny. Mine is NIB right now with belt for the Scat.
No issues with charging system going under driven like that?
 

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unless you can move more air through the engine, larger injectors won't gain any power unless as stated in previous posts unless you have lean A/F ratios.

its either more cam or forced induction and those are "cheap" items. Long tubes might add 15 to top end, but the costs of parts, installation and tune will still be in the $2k range or better just for that.
 

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2018 Scat Pack Charger 11.995 first time out stock tune
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No issues with charging system going under driven like that?
No issues then or now. Buddy has it on New 19 Scat Challenger he just can't seem to hook up right now. Still figuring it out. Got part numbers right here. I know 2 places that stock the unit. His volts on dash are still in the normal area within a tenth or 2. We both ran 11.995 at the track. My only time out. Stock tune stock weight low gas 6$ 91 closest gas station. I got plenty of room to grow. Give me time.
Diablo on sale 1 more day.
 
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