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post #12 of Old 08-09-2019, 08:50 PM
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Join Date: Jul 2018
Posts: 398
Originally Posted by arudlang View Post
Sure and you mention that a lot but like, I think we have to take into account that we are often discussing the absolute maximum PEAK advertised horsepower it can make on its BEST day at sea level, and the fact that it has to wind up to ~6400 RPM to reach that peak, and although I can't find a dynograph for this particular engine anywhere I'd wager its a sharp climb the last 2000 RPMs to that peak as thats about the point at which the ECU suddenly realizes you really want "every drop" of power and makes the most of its ability to tweak the lift, duration, and timing to do it.

Engineers and marketing teams know people get easily hung up on peak advertised numbers so they say "Well fine, we can string this poor thing out to make a big number near the redline. Nobody is hardly ever going to use it, and it won't make anywhere close to that power in the normal operating range, but with the fancy tricks of the multiair system we can squeeze out a big number at an ungodly RPM that nobody hardly touches three times in the entire life of owning the car, sure, for the marketing ads."

Just about none of us are going to rev past 4500 in our day-to-day driving, so the real "max" horsepower we are typically ever using for regular driving is nowhere near 180 HP, probably roughly 140 or 145 for normal driving around acceleration (if we're lucky).

This effect is consistent with pretty much all N/A gas engines so a dude driving a 300 HP car also isn't using a full 300 HP every day to go to work and back, but his power at 4500 is probably still 100 HP more than ours at the same RPM so still feels noticeably faster than something like our car.

Not to mention the losses at high altitude, which we certainly noticed on our recent road trip through the rockies and the cascades, we were climbing hills at 3400 probably making a whopping 85 HP ... but thats the deal. You can't use 6000+ RPMs every day on every hill, the little thing will blow up. That's actually what happened to my aunt's 2.4 Cherokee last year, they live in the mountains in Virginia and after not quite two years of mountain torture treatment it gave up the ghost. She was quite merciless with that motor on the switchbacks and hill climbs.
I attached a HP dyno-curve for the 2.4 engine on a dart, blue one is the 2.4 and I think red is 1.4turbo.

As curve show, for HP it is actually a pretty stable raise without any sharp climbs in high RPMs. It hits close to ~95% of the max HP around 4.5k RPM. It is definitely high and not something you would hit everyday (maybe in highway passing etc you can hit it), but not as bad as needing to hit 6k. This multi-air technology FCA uses is something they initially developed for Ferrari engines. Having a stable HP curve is important for sports cars since it prevent uneven acceleration patterns that both kills the driving experience and track times (probably the two most important think for sport cars). Ofcourse engines they developed for those are much larger and rev to much higher RPMS like 8-10k. Ferrari doesn't prefer making turbo engines, so their natural aspirated engine tech is top notch. I am pretty sure if you could modify the 2.4 to rev to 10k RMP, it could also hit ~250 HP. Although it would require a significant engine modification to do it.

For altitude, there is a 3% decrease in engine power for every 1000 feet above see level. So at 3400k feet, it probably makes about 10% less.

Last edited by Tripod; 08-09-2019 at 08:55 PM.
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