…and, more importantly, what useful information can I, a pretty average driver, glean from them?
While poking around Volvo’s web site, I discovered that they offer a performance upgrade for my car through Polestar. On the information page for the car, they have torque and horsepower curves for pre-and post-upgrade. So, I can tell from the chart that the upgrade gets me more horsepower and more torque, but I could read that same information in the other numbers they present. As a driver, what information do the graphs give me, and how can or should I use that information when driving the car?
Also, and this is probably more of an IMHO, but Polestar is claiming these performance improvements come with no adverse effect to gas mileage. That sounds really, really suspect to me - is it realistically possible for the higher performance to come with the same fuel efficiency?
Generally, you want torque sooner in the RPM band.
Often, but not always, jacking up power pushes the torque curver higher up in the RPM band. Sure, you might save 1/10th of a second in wide open acceleration, but daily driving might cause you to rev the engine more to get sufficient response/power.
You can make engines more powerful and more fuel efficient in any number of ways. One way is through the use of better electronics that manage everything. This is already done, of course, but there is always room for improvement. Engines can be tuned to exact specs based on individual needs, use, geography, elevation, etc.
Letting an engine breath air better and flow better through the exhaust returns better power and economy.
These are just examples. The last one – exhaust – is a classic example where you might push the torque curve farther up the RPM band. This can make daily driving less pleasant (think of all those little hot rod with loud pipes that have to rev like mad in regular driving), hurt towing, etc.
There are many variables. Merely getting more HP and torque = insufficient info in an ad. The real trick is getting me some extra HP and torque, but preserving or improving the curves (you want that torque to stay early in the RPM band. A hop up that flattens the early torque curve = worse drive-ability).
From the shape of the pre and post upgrade torque curves I would say that you as a driver would need to put zero thought into what you do differently.
Both Torque and HP curves are higher across all RPM bands all the way down to idle in the post upgrade curve vs the pre-upgrade curve. You’d just have more power all the time. Normally, I would call bullshit on a curve that looks like this, but I see that this is a purely electronic upgrade, and that your car is turbo.
I suspect what is occurring here is that the electronic tuning doesn’t do anything until the turbo kicks in, and then the electronic tuning comes in. While I don’t know this for certain, I suspect there are lots of reasons why the car isn’t tuned to the max straight from the factory. Reasons like noise levels, reliability, emissions, and other regulations. Therefore this would leave room for improvement over stock factory settings. So basically, I believe the performance upgrade can be had from this pure electronic tuning.
What I don’t believe is no change in fuel economy. Although, since i’m pretty sure the fuel economy is rounded they could theoretically get away with going from 25.49999 ->> 24.50 and still call it no “change” in fuel economy.
I am not a car expert. This is just a hypothesis.
I think RICK (or garyT?) is a factory trained volvo mechanic and would probably know wayyyy more thne I do.
Thanks, both of you. I think I’m also looking for more general info regarding reading graphs like this. For example, if I had a manual transmission in the car (I don’t, but work with me here) is there anything on these graphs that would inform my shifting patterns? Like, some ideal RPMs at which to shift if I want maximum acceleration, or fuel efficiency?
A simple overview - first, the torque curve gives you no additional information beyond what you can tell from the power curve. The torque curve is simply equal to the horsepower curve, multiplied by 5252, divided by the RPM. The reason it’s displayed at all is because most dynamometers measure torque directly and then calculate the horsepower from that.
Torque = Horsepower * 5252 / RPM (assumes units of horsepower and foot-pounds)
The reason people like to talk about torque, when discussing engine specifications, is that engines that produce a lot of horsepower at low RPM have higher torque values than those that produce the same horsepower at high RPM (as you can tell from the equation). In many applications, the ability to produce a lot of power at low RPM is beneficial - you don’t want your pickup truck screaming at 6000 RPM when you’re trying to tow a load up a hill, and similarly, you don’t want your luxury sedan to have to rev like crazy to pull away smartly from a light. On the other hand, in a sports car or motorcycle, revving the engine is part of the fun, and you probably don’t care if it has relatively low torque figures, as long as the peak power is high enough somewhere in the RPM band.
In any case - if you care about maximum acceleration, all you need to do is look at the peak of the power curve. This represents the RPM at which your engine is producing the greatest amount of energy, and thus the greatest amount of acceleration. When shifting for maximum acceleration, you want to keep your engine as close to the peak of the power curve as possible, which for your car is apparently 5000 RPM (without this Polestar chip, anyway).
I don’t think you can really tell much about fuel efficiency from these graphs. They are generally performed with the engine at full throttle, which is not going to deliver maximum fuel economy at any RPM. Fuel efficiency is pretty easy - just accelerate as little as possible, at as low an RPM as possible.
Regarding what that performance upgrade does - it most likely just increases the maximum boost pressure of the turbo. You could probably get 800 hp out of that engine if you wanted to with similar software upgrades - of course, it would blow up after about a minute.
Regarding fuel efficiency - it is quite likely that, if you continue to drive as you currently do, your fuel efficiency will not change. However, the whole point of the performance upgrade is to upgrade your performance - and if you actually take advantage of the increased performance, your fuel efficiency will suffer.
As for other tradeoffs - the increased boost pressure and increased power production will inarguably lead to higher stresses and greater wear on every component of your engine, transmission, suspension, etc. Note that the chip apparently increases the redline from around 5900 RPM to 6500 RPM.
As far as aftermarket upgrades go, this is relatively mild - something like a 10% horsepower increase - but if it were a car I planned to keep a long time, I would think carefully about it.
The graphs indicate the chance to shift ever so slightly sooner without lugging the engine, which can generally improve fuel economy slightly.
Emphasis is on ‘slightly’.
I didn’t see the graphs earlier, but they are generally unbelievable when offered by a performance shop not partnered with the manufacturer. Why? Because it is incredibly difficult to not hurt the power curves when adding power; i.e., the HP and torque tend to come on later, so the power curves are less steep. Generally, drivers don’t like this. The car performs better at higher throttle settings and worse at lower throttle settings, but the overall return is more power. Feeling the torque missing relays the sensation of an engine struggling slightly more to the driver.
Given that Volvo seems partnered with this company, I will give credence to the performance enhancements. Working with the builder, it is possible to add HP and torque and slightly improve the power curve. In this case, it is helped ever so slightly, but the big win is having more power while not flattening the curve.
This is the kind of win that is attainable when the builder is involved. It’s much less likely when some aftermarket company sells aftermarket parts alone. In those cases, they merely claim some HP or (less likely) torque gains, but their power curves are likely to be flatter.
I believe you could theoretically calculate optimal shift points for maximal acceleration from this chart if you knew your transmissions gear ratios and final drive. In manual transmissions you can calculate how many RPMS you drop between shifts if you knew the gear ratios. You could then see which of these shifts gives you a pattern that gives you maximum area under the curve between shifts.
I’ve never owned a turbo car, but I imagine you want to go fast you would probably want to shift in such a way that the turbo is at an RPM that is high enough to always be engaged. It looks like you want to stay above 17-1800 in your car as that’s when the turbo kicks in.
Philster - as Harmonix pointed out, this is a turbo car. Therefore it’s perfectly possible to get more performance across the entire RPM range at the expensive of reliability, by just turning up the turbo boost. More air -> more fuel -> more power.
Yes, in theory. Just to expand on the good information others have given, the important thing to look at on a graph like this is the area under the horsepower curve, specifically in the RPM range that you’re likely to be running. Peak numbers don’t tell you the whole story.
For a more extreme example, here’s a dyno of one of my old motors. The motor made 174hp at the wheels, which seems pretty good, but that peak number hides the fact that at 3500 rpm, I was making about 70hp. A GM 3800 Series 2 will also make about 175 hp at the wheels, but it will do so at a much lower RPM, and if you compare the total area under the horsepower curve for both cars, the big V6 is likely to win. That’s why it’s useful to see the graph versus just getting a peak number.
The other useful thing you can learn from my graph is where to shift, or more accurately, how high I needed to rev the darn thing. The original rev limiter was set at 8200 rpms. I lost about 2500 rpms between shifts, so if I shifted at 8200, I’d drop down to 5700. I’d be shifting right at my peak horsepower (174) and dropping down to a paltry 125hp. It’d take a bit of time to get the engine back up to steam. The first graph showed that power was still building right up to the redline, so I removed the rev limiter and went back, and this graph is the result. The car felt wheezy at 9500 rpms, but that was all in my head (a function of a ridiculous amount of noise and a decreasing horsepower curve). In reality, I was still making good, usable horsepower at 9500 (north of 150hp), and when I shifted, I’d only drop down to 7000 rpms, where I was still making 150hp. In other words, if you drew two vertical lines between 7000 and 9500, that’s where I wanted to spend most of my time, because that’s where the area under the horsepower curve was the greatest.
People tuning automatic transmissions will use this same principle to define shift points. For a lot of big V8s, revving high is bad, because the heads can’t breathe enough to support any kind of power up there. Turbos, on the other hand, produce very peaky horsepower curves, and tuners will generally try to keep the revs as high as they can. Conversely, if you’re trying to get good fuel economy, you want to shift before the horsepower spikes.
