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Discussion Starter #1
I just got my SRT 392 and I'm already thinking about making it go faster, once I have some 305's or 315's on the rear. The car already has a catch can, a K&N cold air intake (which I might replace), and what sounds like aftermarket exhaust of some kind (haven't lifted the car to confirm).

Here's what I'm considering in addition:
  • Diablo Sport Trinity 2 Hemi Tuner
  • MMX 87mm Ported Throttle Body
  • MMX Ported Intake Manifold
  • New tune for 93 octane (these cars are factory tuned for 91)
  • Hellcat Airbox
  • Hellcat hood (for better cooling)
I don't want to do long tubes because to make my car 50-state legal (which it needs to be, I'm in the military), I'd need new catted mid-pipes which are half the cost of the headers. What kind of power output could I reasonably expect from these basic bolt-ons and tune, either to the crank or the wheels?
 

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Congrats on the new addition!

Your list of mods should give you about/approx a 30 - 35hp bump up, with the tune doing most of the heavy lifting to maximize the combined output. Premium fuel is a must.
Hellcat airbox, hellcat headlight tube and Non-oil type HP filter is good to go, as is the Diablo PCM & tune. Ditch the K&N, they can lead to sensor problems from "mysting". Hellcat stuff is all OEM and thus no need to worry about emissions legality down the road.
Similar to exhaust, larger throttle bodies add almost nothing in regards to HP and are low on the best bang per $$. Not to say they dont help add power, just that you'll need to dig much deeper into mods and be chasing every last hp, for them to really pay off.

Better underhood cooling can be gained by removing Both left & right side inner headlights plugs. Add some genpartsco D.I.P.S. screens to keep the junk out. Removal of the underhood blanket/mat & any engine covers in combo with the above, also helps move air underhood, the side effect being a bit more engine noise.
Wider summer tires make a huge difference in getting the power down, otherwise any added HP is useless if the car wont hook.
The other thing which you can do is look to lighten the car up some, this is like free HP.
Good luck!
 

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Discussion Starter #3
Congrats on the new addition!

Your list of mods should give you about/approx a 30 - 35hp bump up, with the tune doing most of the heavy lifting to maximize the combined output. Premium fuel is a must.
Hellcat airbox, hellcat headlight tube and Non-oil type HP filter is good to go, as is the Diablo PCM & tune. Ditch the K&N, they can lead to sensor problems from "mysting". Hellcat stuff is all OEM and thus no need to worry about emissions legality down the road.
Similar to exhaust, larger throttle bodies add almost nothing in regards to HP and are low on the best bang per $$. Not to say they dont help add power, just that you'll need to dig much deeper into mods and be chasing every last hp, for them to really pay off.

Better underhood cooling can be gained by removing Both left & right side inner headlights plugs. Add some genpartsco D.I.P.S. screens to keep the junk out. Removal of the underhood blanket/mat & any engine covers in combo with the above, also helps move air underhood, the side effect being a bit more engine noise.
Wider summer tires make a huge difference in getting the power down, otherwise any added HP is useless if the car wont hook.
The other thing which you can do is look to lighten the car up some, this is like free HP.
Good luck!
Thanks, it's my first Challenger!

Gotcha, maybe I just won't worry about the throttle body unless I eventually decide to do a cam and/or stroker kit. Part of me wants to build this thing into a nasty NA 426 stroker.

I'm pretty set on the Hellcat hood, I think it just looks way better than the standard SRT hood.

I see I can get a Hellcat airbox kit from Speedlogix and they offer a drop-in K&N filter for it. Is that a good choice or is there a better one?

I would like summer tires, but I live in a part of Florida where it gets fairly chilly in the winter and it rains fairly often. Summer tires probably aren't my friend for a lot of the year since this is my daily.
 

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Those “ported” throttle bodies do nothing because of their cross section style porting.
I have never seen any real data on the ported plastic manifolds but it definitely wouldn’t hurt, just don’t know if the cost would be worth the gain.
If you plan any other serious mods later, the diablo will most likely get ditched for HPTuners as most are starting to swap over to that platform. So that is up to you whether you want to invest in that or not.
The hellcat airbox is the best stock (and possibly aftermarket) cold air setup you can get. My only other go to would be Legmaker.
Everything else is just personal preference or track oriented (reducing under hood temps will only last so long when daily driving).

My 2 cents: tires then dyno tune then save for longtubes/cam/heads/stroker/nitrous/supercharger or a mix of those.

If you do the mods you are listing, most of the power will be from the tune, maybe 25hp to the tire.

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Discussion Starter #5
Those “ported” throttle bodies do nothing because of their cross section style porting.
I have never seen any real data on the ported plastic manifolds but it definitely wouldn’t hurt, just don’t know if the cost would be worth the gain.
If you plan any other serious mods later, the diablo will most likely get ditched for HPTuners as most are starting to swap over to that platform. So that is up to you whether you want to invest in that or not.
The hellcat airbox is the best stock (and possibly aftermarket) cold air setup you can get. My only other go to would be Legmaker.
Everything else is just personal preference or track oriented (reducing under hood temps will only last so long when daily driving).

My 2 cents: tires then dyno tune then save for longtubes/cam/heads/stroker/nitrous/supercharger or a mix of those.

If you do the mods you are listing, most of the power will be from the tune, maybe 25hp to the tire.

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I believe MMX claims their throttle bodies are the only "true" 87mm ported TB's, so I'm assuming they don't use cross sectional porting?

I'd heard some negative things about HPTuners recently, I'm assuming you've had good experience with them?

Not sure what else I want to do yet. Good drivability and reliability/longevity are important to me as long as this is my only car, and I do plan on eventually upgrading to the next generation Challenger when it comes out in 3-4 years so I dont want to dump too much money into this thing.
 

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there is no real data on the ported tbi's, however porting the front and rear section without increasing the blade side to match is detrimental, true billet tbi's, ones that are new true 85 or 90 or 105 have proven to be very effective

the other issue with ported style tbi's, is the narrowing at its center which may actually cause air flow disturbance which can be detrimental and reduce performance instead of increasing it

we have not spent anytime researching it them simply because we have use new billet true tbi's since the beginning
 

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I believe MMX claims their throttle bodies are the only "true" 87mm ported TB's, so I'm assuming they don't use cross sectional porting?

I'd heard some negative things about HPTuners recently, I'm assuming you've had good experience with them?

Not sure what else I want to do yet. Good drivability and reliability/longevity are important to me as long as this is my only car, and I do plan on eventually upgrading to the next generation Challenger when it comes out in 3-4 years so I dont want to dump too much money into this thing.
MMX uses cross section porting for their 87mm throttle bodies. Try fastman’s 84mm true bore or buy a new 85 true bore from someone like bbk. Picture for reference:



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Here is evidence that the RIGHT throttle body does have the potential to net some significant gains, considering $/HP ($100 per horsepower is usually what I use as a conservative reference). Keep in mind, TB's are more of a piggyback mod specifically for N/A motors, in that they produce better results when combined with other mods like intake/manifold/opened motor. The car in the video is a 6.1L with heads and cam. Like hemi4us said, the majority of your power gains will come from just the tune, but you could expect 35-40 HP and 40-45 TQ if you went with a Hellcat TB, also from MMX.
 

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You can learn a lot about throttle bodies here: The Fastman Throttle Bodies

As for getting an HP tune, they are very new to the Mopar world, and the main reason some switch, is to able to do their own tunes. For those who do not know how to tune, it is a very quick route to blowing an engine. The proper fuel/air ratio is extremely critical to achieve, and cannot be done without a wideband installed in the car.
 

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Here's what I'm considering in addition:
  • Diablo Sport Trinity 2 Hemi Tuner
  • MMX 87mm Ported Throttle Body
  • MMX Ported Intake Manifold
  • New tune for 93 octane (these cars are factory tuned for 91)
  • Hellcat Airbox
  • Hellcat hood (for better cooling)
That list is a good starting point for the basics...move more air. Hellcat airbox, tb and ported manifold with an appropriate custom tune will yield enough power to feel for sure, likely around the 30-35 whp peak gain BUT the mid range torque gain will be what you REALLY love from even just the above! Get it done!
 

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Discussion Starter #13
That list is a good starting point for the basics...move more air. Hellcat airbox, tb and ported manifold with an appropriate custom tune will yield enough power to feel for sure, likely around the 30-35 whp peak gain BUT the mid range torque gain will be what you REALLY love from even just the above! Get it done!
Yeah, mid-range torque is something I was definitely hoping to pick up, seems these 392's have tons of low-end grunt but are just a tad lacking in mid to high-range RPM's. I'll get these done as soon as I have the cash :p

Also, just curious, saw you previously had an M6 Hellcat and now have an A8 Scat Pack. What made you go back to the 392?
 

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Also, just curious, saw you previously had an M6 Hellcat and now have an A8 Scat Pack. What made you go back to the 392?
Lower cost... I really wanted something to daily and the A8 392 is more ideal. If I had gotten another HC not only would it have cost $20k more or so...BUT I'd have wanted to mod and race it a bunch and my cash and time is tied up in my own business and pursuit of another...

If I could go back several months I'd have gotten a slightly used HC to be honest. I just dislike buying used performance stuff...no telling how abused it was or how poorly maintained. Was it modified and returned to stock? Etc. But if I was patient for ONCE and just did my homework on the car and bought smart I'm sure I could have gotten a nice gently used HC for $10k more than I spent...maybe next year I will trade up once I get on top of this loan a bit.
 

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Lower cost... I really wanted something to daily and the A8 392 is more ideal. If I had gotten another HC not only would it have cost $20k more or so...BUT I'd have wanted to mod and race it a bunch and my cash and time is tied up in my own business and pursuit of another...

If I could go back several months I'd have gotten a slightly used HC to be honest. I just dislike buying used performance stuff...no telling how abused it was or how poorly maintained. Was it modified and returned to stock? Etc. But if I was patient for ONCE and just did my homework on the car and bought smart I'm sure I could have gotten a nice gently used HC for $10k more than I spent...maybe next year I will trade up once I get on top of this loan a bit.
Makes sense.

I bought the 392 because it's what I could afford on a 2nd lieutenant's salary with a girlfriend :p but like you said it's more daily driver friendly and the insurance costs are much lower for me, being only 22. And it's a good 1st performance car, the Hellcat would be way too much car for me right now.

It also sips on gas (relatively speaking) on long highway trips, which is nice. Makes my weekly or bi-weekly trips back home to see family and girlfriend easier to afford. I'm actually spending a tad less on fill-ups with an increased highway driving radius compared to my old 2001 Durango.
 

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Makes sense.

I bought the 392 because it's what I could afford on a 2nd lieutenant's salary with a girlfriend :p but like you said it's more daily driver friendly and the insurance costs are much lower for me, being only 22. And it's a good 1st performance car, the Hellcat would be way too much car for me right now.

It also sips on gas (relatively speaking) on long highway trips, which is nice. Makes my weekly or bi-weekly trips back home to see family and girlfriend easier to afford. I'm actually spending a tad less on fill-ups with an increased highway driving radius compared to my old 2001 Durango.
Yeah I'd not want anyone to start with a Hellcat...not ideal. And yeah insurance savings is nice also...it's about 30% less than what it would be with the HC but I also have a Ram 2500 cummins so that brings it down some as I drive that about 1/3 of the time.

Honestly I bet the HC gets the same if not better fuel miles on the highway than the 392:
The rear end gear is a 2.62 instead of 3.09 (comparing auto to auto for ease).
And the displacement is slightly smaller.

It wouldn't be much different as with a supercharger it's always having to be spun which takes some power as well...but I'd bet the HC gets possibly 1-2 mpg better under identical highway conditions (IF and that's a very capital IF lol, you can keep your foot out of it which I for one could NOT which is another reason I went 392 this round).
 

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Yeah I'd not want anyone to start with a Hellcat...not ideal. And yeah insurance savings is nice also...it's about 30% less than what it would be with the HC but I also have a Ram 2500 cummins so that brings it down some as I drive that about 1/3 of the time.

Honestly I bet the HC gets the same if not better fuel miles on the highway than the 392:
The rear end gear is a 2.62 instead of 3.09 (comparing auto to auto for ease).
And the displacement is slightly smaller.

It wouldn't be much different as with a supercharger it's always having to be spun which takes some power as well...but I'd bet the HC gets possibly 1-2 mpg better under identical highway conditions (IF and that's a very capital IF lol, you can keep your foot out of it which I for one could NOT which is another reason I went 392 this round).
Hmm, good points...

So what you're saying is, if I want to get better or equal fuel mileage as well as add power, I should slap a supercharger on my car? :p
 

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Hmm, good points...

So what you're saying is, if I want to get better or equal fuel mileage as well as add power, I should slap a supercharger on my car? :p
lol
Wouldn't have much impact as an add on...but it wouldn't be a positive one MPG wise...
Unless you swap to a hellcat rear diff for the higher (numerically lower) gearing...then sure maybe 1 mpg better. Supercharger and diff would pay for themselves in just 60-70 years of daily driving 😂
 
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