Dyno FAQ
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This is a discussion on Dyno FAQ within the Tuning: Electronic Engine Management forums, part of the Tech & Modifying & General Repairs category; "What mods do I need to get XXXwhp?" "I have WW, XX, YY, and ZZ. How much whp do I ...

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    Master Baiter EJ257's Avatar
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    Dyno FAQ

    "What mods do I need to get XXXwhp?"
    "I have WW, XX, YY, and ZZ. How much whp do I have?"
    "I'm getting a custom tune done at XX tomorrow, what will I put down?"

    All are common questions you will see if you spend time on an enthusiast car forum. Honestly, none of the questions can really be accurately answered. Why? Because dynos and cars vary...

    What is a dynamometer?

    From Wikipedia:
    A dynamometer or "dyno" for short, is a device for measuring force, moment of force (torque), or power. For example, the power produced by an engine, motor or other rotating prime mover can be calculated by simultaneously measuring torque and rotational speed (RPM).
    Dynos measure torque and engine speed because that's how horsepower is calculated. Horsepower = (Torque * RPM) / 5252. Ever notice how the lines always cross between 5K and 5.5K RPMs (for dyno readouts in Horsepower and foot-pounds)? That's why.

    Why would you want a dyno tune?

    There are three main reasons people like having a dyno tune:
    1) Printout. This one is obvious. It's always fun to show off your numbers to your friends and oogle over the curves. Kinda like when you land a significant other who is outside your league.
    2) Controlled environment. Proper tuning will require the vehicle to get to speeds well above a legal limit anywhere in the country. Being able to do so in a controlled environment makes things more legal, and safer.
    3) Easier to hit most variables. When road tuning a vehicle, you're limited to the environment you're tuning in. On a dyno, it's easier to simulate the conditions you'd see in the real world.

    I hear all this talk about different kinds of dynos. What gives?

    There are different types of dynos. The two most common are roller dynos and hub dynos. A roller dyno has rollers that go under the wheel, and it spins to make its calculations. A hub dyno requires the wheels to be removed, and it connects to each of the four corners at the hubs.

    Within the different categories, there are multiple brands of dynos, but the most common are:
    • Dynapack
    • DYNO-mite
    • Dyno Dynamics
    • Dynocom
    • Dynojet
    • Mustang
    • Road dynos (these aren't real dynos, they use calculations to plot HP/TQ)

    We know the different types and brands of dynos, what's the best one?

    There is no answer to that. Honestly, the dyno you want to be on is the one that has the most experienced/competent tuner operating it.

    I was tuned on a "heartbreaker" dyno...

    Let's face it, the days of "heartbreaker dynos" are, for the most part, behind us. Customers are uninformed about dynos in general, and want to brag to their friends what numbers they put down. Unfortunately, this has lead to a war of correction factors (CF).

    Almost every dyno is able to be manipulated by giving things a CF. There are very limited shops still running "heartbreaker" dynos unmolested. Somewhat recently, two of the last remaining shops have given in and gone with a CF that puts their output equivalent to everyone else.

    To put things into perspective, you can drive one mile down the street to two different dynos. Nothing in the tune is altered, and there's an hour time lapse between runs (unloading the car, driving, loading the car), and have a 50whp difference between printouts, all due to the way the dyno is calibrated. Obviously, this is an extreme example, and not likely in the real world, but it's to emphasize the point.

    This person and I have the same mods, why do they make more power than me?

    There is no easy answer to this. There are many factors:
    • Different dyno. Different dynos will read differently, as I pointed out above. If you're not using the same dyno/tuner, you shouldn't be comparing plots.
    • Different conditions. While there are corrections for things like altitude/weather, unless you're tuned in the same conditions, these can be off. If you want to compare, look for similar environmental conditions.
    • Factory "freak". Some cars just are; they put down more/less than what they should.

    Based on the two statements above, that means my dyno sheet is pointless?

    Absolutely not! When looking at a dyno sheet, the peak values aren't the big picture...you should be concerned with the delta and area under the curve.

    Before/after results come from the delta from when you gave your car over to the tuner, to when they hand it back to you. Alongside the delta, you're concerned with the curves themselves. There are many ways to tune a car; flattest torque curve, highest peak values, most area under the curve, etc. Personally, I like the car to have the most area under the curve as possible. How you get your car mapped should be discussed beforehand with the tuner. In general, most people will tune for area under the curve, if not given instruction to tune it differently.

    We'll use one of Cobbs images (2012-2013 WRX) to discuss both...

    See how Cobb listed both the peak and the maximum gains? The peak is typical for a dyno graph, but the maximum refers to the increased area under the curve. Looking solely at peak values, some may say that the Cobb map is pretty lame (NOTE: I am not); when you take a look at the two plots compared with each other, you realize it's going to be a lot more fun to drive. Notice how they provided their data in delta (%) rather than actual values? That's because they understand that delta is more important than the actual numbers, and numbers vary.

    In that example (we'll compare Stock vs S2), peak torque hits ~3000-3100 RPMs (S2) / ~4000 RPMs (Stock), but the greatest delta happens ~3300-3400RPMs. For horsepower, however, peak values don't come into play until ~6000 RPMs (S2) / 6300 RPMs (Stock), while the greatest delta happens ~3500 RPMs.

    Now that I understand that, what do I need to do to get dyno tuned?

    Determine the tuner you want to map the car. This is pretty straight-forward. Advice on forums is great, but often is typically "I got tuned at XX, they're the best, etc". Honestly, that's not the best advice; quite often, that's the only person to have ever mapped the car, and no offense to the individual, they don't know any better. Tuners will build up a reputation as they put out cars. There are always a few that get high praises from a lot of places. The ones you want to really take note of are the ones that other tuners will give props to. There isn't a big tuner base here, but there is on Nasioc (blasphemy, I know).

    Once you've got a shop in mind, you need to reach out to them. Request to speak with the tuner. Typically, some kind of text-based communication (e.g., PM, email, etc.) will be best, as they're busy, and they can get back to you at a good time for them. Discuss what you're looking to get mapped, what you're looking for in the car, etc. Get a feel for their customer service, and see how you "mesh". Find out if there's anything they like to see on a car, if there's a part they feel better about (vs one you're considering buying), etc. As a tuner, you can only do make due with what you're given; there may be certain parts they're more comfortable using. During this conversation, it's imperative to talk to them about the tuning process. A key part of dyno tuning a vehicle is going out afterwards for a check/cleanup of the tune on public roadways. While dynos can do a decent job at simulating real-world conditions, they aren't magical.

    Make sure you discuss any pre-tune things that you should go over. Cobb offers a pre-tune checklist (other shops may want additional/different things done):

    If you have a shop in mind, it's important to do a baseline. They can tell you what cars typically baseline, but this is where the factory freaks I alluded to earlier comes into play. Typically, baseline pulls are under $100; if you have a tuning appointment scheduled with a deposit down, some shops will give you a discount (even if you have to pay full rip, I'd urge you to do a baseline, if you can). If you have a certain goal of power you want to make, the best person you can ask is the tuner (since you have a shop in mind); they will know their equipment and results from previous setups better than anyone; obviously, there are "freak" cars, but they should be able to give you a pretty good indication of what your results will be.

    What was the point of all of this?

    A quick overview of how dynos work, how to ask questions properly, and what to expect when you sign up for a dyno tune.

    As a quick recap, things to know:
    1. Peak values. Are only a small part of the story; before/after (delta) and area under the curve is what you should be most focused on.
    2. Road check / cleanup. Dynos can simulate real-world conditions, but you need to go out on the street and verify everything is in line. You can get things dialed in most of the way on the dyno, just make sure to do finishing touches on the road.
    3. Comparing. It is pointless to compare dyno graphs, if you weren't on the same dyno, same tuner, same conditions. At least if it's the same dyno and tuner, it's close, but it's not a proper comparison.

    One more example, as your final exam...

    One car. Two shops, two tuners. Both tuners get the car in the same condition, and both put a safe tune on, in their own style. Results are 280whp and 300whp. Which one would you rather drive?

    Trick question! Only peak values were discussed. Both cars have similar shaped curves. On the 280whp tune, the car baselined at 210whp, while the 300whp dyno baselined the car at 240whp. Knowing that additional information, which car would you rather drive?
    Last edited by EJ257; 03-27-2013 at 05:15 PM.
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  3. #2
    zax is offline
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    Excellent Matty.

    I'd also like to add a quick explanation of a "Virtual Dyno."

    As Matty has mentioned, the Dynamometer is merely a tool used to measure the effective torque applied on the rollers (or hubs in the case of a Dynapack). From the torque and rotational velocity, the Dyno can mathematically derive the effective power output, since power is merely the calculated derivative of Work (force). We, as low-budget tuners, can ascertain the same information without having to spend $15k on a dynamometer.

    So how does this translate to a "Virtual Dyno" or "Road dyno?" Well, we can measure the effective torque output to the wheels using a few initial parameters. Torque calculation is T = r x F where F = ma (mass * acceleration) and r represents the radius of the leverage force. Immediately, we know the variable 'r' as the radius of the wheel + the tire. Now, we merely require the mass of the vehicle and the acceleration. The mass we enter using common sense (your bugeye does not weigh 2500 lbs, trust me!). Our torque calculation is now T = r x (m*a). Since the vector between the applied force and the rotational center (hub of the wheel) is always 90 degrees, this equation is further simplified to T = r*m*a. The acceleration at any given time is the change in velocity over the sample period (dv/dt), so the equation is finalized at T = r * m * dv/dt. The final addition to the equation is that of aerodynamics. As the speed increases, the aerodynamic drag loading the car increases as the square of the velocity. The aerodynamic loading becomes F = 1/2 * rho * v^2 * Cd *A where F is the force, rho is the density of the fluid, v is the velocity of the car, Cd is the coefficient of drag (0.31 for bugeyes), and A is the cross-sectional area of the front of the car.

    Now you can see that a Virtual dyno is, in many ways, governed by the same forces at work as a Dynamometer: the peak numbers can be manipulated by adjusting the sample period for the acceleration calculation (smoothing) as well as the mass of the vehicle. In a load-based dyno, aerodynamic drag can be simulated by manipulating the load as the effective dyno speed increases. However, like a Dynamometer, since the mass is proportional to the measured torque, the % change will be the same regardless of entered vehicle weight. It is always best to enter the approximate weight of the vehicle, but as a tuning tool it is not necessary for the number to be precise. Remember that the input vehicle weight includes the vehicle, driver, and cargo.

    A few rules of the road here. As Matty mentioned, "Virtual Dynos" should be done using 3rd gear for the WRX and 4th gear for the STi. In every state this will result in illegal speeds on Public roads. It is imperative that Virtual Dyno pulls be performed on private property. Furthermore, since much of the dyno's calculation is based on acceleration, it is very important that you choose a flat road/course on which to perform the pull. Furthermore, since this is a tuning tool, you should repeat runs on the same stretch of road in precisely the same start location. More recent road dynos (such as Virtual Dyno or Airboy) use secondary calculations using vehicle load to gain a better picture on acceleration and resulting in more precise torque calculation.
    Last edited by zax; 04-19-2013 at 06:58 AM.
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  4. #3
    Master Baiter EJ257's Avatar
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    Quote Originally Posted by zax
    A few rules of the road here. As Matty mentioned, "Virtual Dynos" should be done using 3rd gear for the WRX and 4th gear for the STi.
    The comment about STIs depends on the gearing...
    04-06 STIs = 4th
    07+ STIs = 3rd
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