392 Challenger Scat Pack - what’s holding it back?

I’m working in Mexico now on a short assignment.  When I got to the airport in Mexico City and went to pick up my VW Golf from the Hertz desk, I pointed to a picture of a V6 Charger and asked how much to upgrade to that one.  He told me $25 a day and that sounded good to me so I went for it.  After about an hour of paperwork later, the conclusion was drawn that they had no more of those so long story short I ended up with said 392 Challenger Scat Pack.  Shaker hood.  

Now this is completely the wrong car for Mexico City.  First off you can’t see out of the Berking thing.  Secondly the roads are beating it into the ground.  24000 kilometers on the clock and it squeaks and rattles like an old city bus.  But what I can’t figure out is why 485 hp feels like 260 hp.  

Checked the obvious.  Air filter.  Looked fine.  I was surprised though that the filter isn’t contained in the shaker.  This shaker is a faker.  There is a warning on the dash saying oil change required.  Could the computer be holding it back for that reason?  When I romped on it this morning even my non car person colleague said it was more about noise than speed.  She’s Mexican so I doubt she’s ever sampled too many fast cars.  It’s seems to be legit as there is a real orange V8 under the hood.

it’s quite the opposite experience of the 300 I had in California.  The one where I easily ran over 100 mph up the grapevine, stopped at the bottom and popped the hood to admire the Hemi only to find a V6 Pentastar!

I have driven a scat pack challenger with the 6.4l many times.  Yours is broken.   

I'm sure you knew that, but just to reassure you you're not crazy :).

Who knows how it was abused, what may have been swapped in after a engine failure, or if the rental company has it electronically neutered.  

I'm just surprised Hertz would have one of them available for rent.

I don’t have it in ‘Sport Mode’.  I didn’t know how until I just watched a YouTube.  I’m wondering too if it could be crappy Pemex gas.

it seems to run and drive just fine.  I just felt like it should go like stink and it isn’t living up to that expectation.  Probably a good thing really since the roads here aren’t really that great nor are the drivers.

stuart in mn said:

I'm just surprised Hertz would have one of them available for rent.

it depends on the airport.  You can get an Aventador in Phoenix or Vegas.  Probably others too.

Nothing is wrong, you have a normally aspirated engine at 7300' elevation.

^ winner winner chicken dinner

I NEVER EVEN THOUGHT OF THAT.  And where I am (Pachuca) is 7800.

4300lbs

Mopar 

The Scat Pack I drove last year was awesome. In fact, it's probably my favorite car that I've driven. It was not slow in any way. I think yours has something wrong with it. Or like others said, the elevation is messing with it. 

Keep in mind, it's 99% guaranteed that it's running on mexican regular gas. Running regular gas in a car that calls for premium is usually "safe", but it will retard timing. This is lead to an obvious decrease in HP/TQ. 

Also it's funny because I've done nearly the exact same trip. Contracted to solve an issue at a plant. Flew into Mexico city, and I had a great time. 

Must be a thing I also have worked in Mexico City, making spring machines run properly.  I remember the giant Corona factory, caravans of black cars that no one messed with, and finding clothes that fit me.

My first few workouts were tough, biking at that elevation was also a struggle.

I had a hemi charger in Denver recently for the same 25 / day upcharge.  It was fun but not fast.  I would have expected the scat pack to move despite being engineered from lead.

Wow. Looks like you’re down over 100 hp due to altitude!

This was mine for a week in March, also out of Denver.

The funny thing is it was how I ended up with it. I booked a convertible simply because it was the cheapest booking class available - I guess nobody wants a convertible in Denver in March, but we were driving to New Mexico. When we got there they didn't have any convertibles, so we got this. It was more than quick enough, and made nice noises, but my GF's description of it as "a lumbering oaf of a car" summed it up pretty accurately.

goingnowherefast said:

Keep in mind, it's 99% guaranteed that it's running on mexican regular gas. Running regular gas in a car that calls for premium is usually "safe", but it will retard timing. This is lead to an obvious decrease in HP/TQ. 

 

Also it's funny because I've done nearly the exact same trip. Contracted to solve an issue at a plant. Flew into Mexico city, and I had a great time. 

But how big of a difference does it really make? 

I know when I bought my '13 Mustang GT it was advertised at 420 hp...on premium. If you looked through the docs, it was only downrated to 412 hp on regular. With that much HP and weight, I'm not sure 8 hp is even noticeable. 

And when I had my BRZ, the difference between the tunes for 91 and 93 was 2° more timing after 5k rpms on the 93 tune. 

A 401 CJ said:

 

stuart in mn said:

I'm just surprised Hertz would have one of them available for rent.

 

it depends on the airport.  You can get an Aventador in Phoenix or Vegas.  Probably others too.

 

I'd bet I could get one in Miami or Orlando as well. 

Besides the altitude and gas quality, I would also wonder if the rental company has it de-tuned? 

It is possible to put the SRTs in Valet Mode and require you to input a pin to switch back to normal but that doesn't sound like what's going on here. It's mostly altitude. That's why when you look at drag racing videos from Mexico (am i the only one that does that? Mexico is closer to me than any other US state) usually the only fast cars are turbo and everything NA runs E36 M3ty times. 

As far as HP difference between octane levels, the published HP figures are peak figures. But, the engine is most likely to suffer detonation at peak torque. So, the difference between a lower octane and higher octane tune would generally be more pronounced at the torque peak than the hp peak. 

Maybe they put a block under the gas pedal to curtain shenanigans? 

z31maniac said:

goingnowherefast said:

Keep in mind, it's 99% guaranteed that it's running on mexican regular gas. Running regular gas in a car that calls for premium is usually "safe", but it will retard timing. This is lead to an obvious decrease in HP/TQ. 

 

Also it's funny because I've done nearly the exact same trip. Contracted to solve an issue at a plant. Flew into Mexico city, and I had a great time. 

But how big of a difference does it really make? 

I know when I bought my '13 Mustang GT it was advertised at 420 hp...on premium. If you looked through the docs, it was only downrated to 412 hp on regular. With that much HP and weight, I'm not sure 8 hp is even noticeable. 

And when I had my BRZ, the difference between the tunes for 91 and 93 was 2° more timing after 5k rpms on the 93 tune. 

Really depends on the engine. Some engines can reach MBT (Maximum brake torque i.e. the optimum spark timing above which no additional torque is produced), on 91 octane. In this example, not much extra power can be produced. 

Again, depends on the engine and the engine control strategy, but it's definitely a factor in why it probably felt slower. 

Possible it just has badges on it and is not a true 392?

Tom Suddard said:

Wow. Looks like you’re down over 100 hp due to altitude!

I reckon Tom is correct . It is probably down 15 to 20 percent depending upon barometric pressure and temperature. Full throttle in a naturally aspirated airplane at sea level gives about 30 inches of mercury manifold pressure. At 9,000 ft above sea level full throttle gives about 23 inches of mercury.

You can run crappier gas at altitude (lower compression) without knocking, so if its knock based its likely not the gas. Power might be down as much as 20% from sealevel. 

Anyone know of any good non-forced induction ways of making more power at alt? I live at 8500, and its brutal to power. Bigger intake? Bigger exhaust?