If its true, FCA either doesn't know it, our doesn't want to advertise it. Without objective evidence its just rumor.

 

Very truuee

 

I've thought about that before, I think they just don't go thru the bother of recertifying the engine for 5-8 hp but I have to think putting the active exhaust on all the 5.7 cars in 2017 had some effect. From 2009 to 2021 the 5.7 has been rated at 370 hp. You aren't going to notice a 1-2% power increase either way. Have you ever read that article from Car and Driver on premium gas? Here it is Car and Driver Premium Gas they got way better dyno figures on 93 than on 87 but the track was almost the same!

We know it certainly sounds much nicer but maybe with the stock manifolds there is only so much air you can flow?

 

With the small gains, they are still gains nonetheless. As a Racer , everything that makes a difference at the end of the 1/4 is worth it.
For around town the R/T would be great with just 89 octane. Then when you want to go to the track, run the 89 down and refuel with 93. I would not run 93 in a R/T daily , to me that's a waste of money.
I had a 2017 Durango R/T that I did just that. 89 around town and 93 at the track. Worked out well for all reasons.

 

The only suspicion I have with the thought FCA did not want to recertify the 5.7 with active exhaust , is the fact they went to that trouble to recertify the 3.6 in the GT to say it has 8 more hp.

 

In 2017 the Daytona got the CAI system and the Active Exhaust but the numbers where the same. Doesn't inspire someone to go run out and buy a Daytona over a non Daytona model like a R/T or Scat Pack.

 

I thought the active exhaust was the exact opposite. When it's open you get the full power rating. When its closed you get a lower figure. I always assumed the active exhaust was to quite the car down for pulling into neighborhoods at night etc. I really wish that you could configure the valves as you want like other cars have the option to do. The Mustang has a Good Neighbor mode that keeps the baffles closed when you start the car.

I live in a cul-de-sac and my house is higher than the rest of the properties. A cold start in my car sounds like a gun going off from the first crack of the motor. It would be nice to able to keep the baffles closed to not wake the block up at 5 AM.

 

Kas....If your house is higher than the neighbors....Why not just release the brake, roll away , far away...then start it...! Ha! Here's my take on the active exhaust...it's real purpose is to allow 4 cyl mode to run smooth...whereupon back pressure is needed for clean combustion chamber [EPA happy }. just something I recall reading many years ago, that engineers were struggling with [needing backpressure], may have been tied to EGR circulation....or maybe I missed the whole point on those older articles...Either way...ya got a 8 cyl and a 4 cyl trying to find a compromise...best to allow each it's own path to Emissions and economy standards...Hence, two exhaust backpressure systems in one...

 

When Corvette came out with their LS3 engine, there were two versions. The standard engine was a 430 HP LS3, the performance version had 436 HP. The only difference between the two engines was an active exhaust, which Corvette named the NPP option. There was a 6 horsepower difference at 5900 rpm because of better exhaust flow. I assume the difference in Dodge's 5.7 liter engine with active exhaust would be about the same. My 392 has an active exhaust that I believe makes somewhere between 6 and 7 extra horsepower. I raised the added horsepower for 392 because this engine makes a small fraction more power per-cubic-inch than an LS3 Corvette. The power ratings for both the Dodge Charger and Chevrolet Corvette are SAE Certified, meaning they both meet the same rating standard, which is checked by a third party to see that SAE J1349 rating protocol was properly followed. That way you know your car's engine rating is correct with little variation in power.

Concerning which octane gas to use: If your engine requires 93 or 91 octane, use it. You can get away with 89 octane for awhile if you don't put much stress on your engine, but you're taking a chance of ruining the engine. You should realize the only thing that's saving your engine from being damaged by engine knock from using too low of an octane gas are sensors and what we call spark retard engine management, which is also referred to as knock retard engine management. When those sensors detect preignition (engine knock), they send a signal to the ECM which than retards timing. Hopefully the engine is not experiencing a heavier load than spark retard can handle. You should also realize when the engine is in spark retard, the engine's power and efficiency is diminished. Our 392 Hemis have a 10.9:1 compression ratio and the 5.7 Hemi has a 10.5:1 compression ratio. Both of them are considered to be high-compression engines which are designed to run on gas with the recommended octane rating. By running 89-octane in either of these engines, you're not getting the best mileage and performance possible, not to mention the engine damage you're risking.

Besides my 392 Scat Pack, I still have the LS2 Corvette that I bought new in 2006. Even though 93 octane is the best pump gas available in my area, when running hard, it works best and with the most power on 95 octane, especially in hotter temperatures. If you're running a high performance engine like the 5.7 Hemi or the 392 Hemi, use the highest octane fuel that's available. Anything less is a disservice to your engine.

 

The 5.7 comes with a recommendation of 89 ocatane.