Superchargers vs. Turbos, again, part 2

It has been a couple days and we welcome a response from @Bill from Hahn RaceCraft on this discussion also.

Before talking about the dyno graph posted earlier, I wanted to explain some details about dynos and how they work for those that may not be familiar.

Dyno graphs are posted all over the internet and fortunately/unfortunately have been used for comparisons of who makes the most power. Since horsepower is what sells a lot of people on kits, these numbers are important. To use these dyno graphs though, there needs to be an understanding of what type of dyno is being used and how it is being used. Without this basic knowledge, there will not be a remote chance of comparing different dyno numbers against each other fairly. The main thing to remember here is that dyno's are strictly a measuring tool and like all tools, they can be used correctly or incorrectly along with the information that they give. If used correctly, they will give reliable and repeatable results, but they can also be used incorrectly to give results and comparisons that sometimes people want to see.

A dyno is just a machine that is used to measure force being applied to it by the wheel(s) of a vehicle in the case of chassis dynos. Most chassis dyno's use a large roller or rollers of a given mass, that are accelerated and allow the dyno to calculate the force being applied. That force, measured in torque along with the engine RPM, then is used to calculate the horsepower of the engine and generate the graph. The equation the dyno uses for horsepower is pretty simple - horsepower = (Engine RPM x Torque)/5252. Looking at that formula for Horsepower, note that torque and horsepower should always be equal at 5252 RPM.

All modern dyno's that I know of also have settings in their software that allow a correction factor to be applied. Since ideally you want to be able to make changes to a vehicle and come back later to test it, there needs to be a correction that can be applied that takes into account things like a change in temperature, ambient pressure and humidity between runs. There are several different correction factors out there that take changing conditions into account and apply a correction to the actual readings to standardize them. These correction factors include - SAE, STD, DIN, JIS and ISO to name a few. The standard that we have used and have seen used by most other dyno's is SAE which corrects the dyno runs as if they were ran at 77 degrees F, 29.23in/hg and 0 percent humidity. There is pretty good, short article that talks a little more about correction factors here - Dyno Correction Factors - Real Wheel Horsepower - GM High-Tech Performance Magazine

Looking at the dyno posted earlier, a couple issues become noticeable with it, here is the graph again -

- Since we know that horsepower is calculated and that torque and horsepower should always equal at 5252RPM, we can look at the graph and see that the supercharger horsepower and torque does match at that RPM. Looking at the turbo graph though, we see that the graph has been shifted to the right and the horsepower and torque do not cross at the correct RPM. This is something that can not happen based on the calculation

- Also, since horsepower and torque are directly related by the equation listed above, there is no way that one engine can be making less torque and make more horsepower. Looking at the dyno graph above once again at 2500RPM, the supercharger is showing more torque, but less horsepower than the turbo, which is not possible. This incorrect trend continues up the graph, at 2750 this is even more obvious, as both engines are making the same torque on the dyno, but the supercharger is being shown to make less horsepower.

- Different correction factors are being used also. The correction factor on the dyno by Hahn is using an STD correction factor based on the dyno published on his website -

The correction factor that we use on our dyno is SAE, so different correction factors are being used in this comparison, which gives different readings. Here is the dyno that Hahn used for the comparison dyno posted with SAE correction -

Now, the exact same dyno graph using STD correction, which increases the power of our kit by 11Hp and 9ft/lbs of torque.

We completely welcome all turbo vs. supercharger debates and we understand there will never be a clear winner for everyone. We understand that both forms of forced induction have pro's and con's that means some people will like turbos, some will like superchargers. The differences between the forms of forced induction are going to be what make some people pick one over the other. The imperfections of each form of forced induction are what also gives them character and is part of the experience for either form. That being said, it is really hard to have a debate if incorrect comparisons are being published, all other things being equal, people might make decisions based on that incorrect information, which I don't think anyone wants happening.

Honestly, the dyno on our site is a little outdated also, here is another recent install that we did with a base Rotrex supercharger kit on our dyno showing the before and after runs that is more representative of what we see with our kits now -

Hope that helps,
Dave

Something that did come up while testing our new turbo kit this past weekend was the response of our new turbo system compared to other systems we have ran on our dyno. We did some work on a Hahn turbo last year to fix a couple things and optimize the system and ended up making right around 300HP and 350 ft/lbs of torque with that setup. The graph below shows that testing with the Hahn turbo being the green line and the blue line is our DDMWorks turbo kit. Looking at just that dyno graph, both systems look very comparable at this power level as you can see the peak numbers and curves are very similar -

Where it becomes really interesting though is when the X-axis on the dyno is changed to time instead of engine RPM, then it shows a completely different picture -

That chart above is the exact same run as the first chart, just with the X-axis changed to show time instead of engine RPM. With this chart, even though the peak numbers are the same, the much faster response of our turbo is very apparent and what we have really been focusing on with our turbo kit. Since doing the supercharger kit, we wanted to make sure our turbo kit would be the fastest responding system available, we are confident it is.