Power Explained: Horsepower, and why your car does not make what you think it makes.

Welcome back to Power Explained; a multi-part series where I explain the tuning process and mechanics involved and how they affect your horsepower numbers. One of the most common questions I get asked in the aftermarket performance world is "I went to XYZ Shop and they said my car made 140hp, but I think it should have made 200hp. What is wrong with their dyno?"

Generally, my response to this is nothing. No I don't mean that I do not respond, but rather, nothing is wrong with the dyno. Now there are sometimes legitimate cases where something is off on the dyno, usually atmospheric readings, but we will get into how various readings can effect your output in a later article.

Usually around this point I ask what modifications your stock EK civic has, to which the response is cold air intake, weld on fart can, and pep boys spark plug wires, or in other words, nothing that actually gives you power.

Power Explained: Horsepower, and why your car does not make what you think it makes.

Now as you recall from last week, a dyno is nothing more than a tool, just like a hammer, so when you hit your thumb with a hammer, do you blame the hammer or the user? Exactly, the hammer, then you immediately banish it to the outskirts of the garage for it perilous ways. Unlike the hammer however, when the dyno does not give you the horsepower number you want to see, it is usually because of the car.

The key to understanding why your car is nowhere near what you think it should be is understanding how OEM horsepower ratings are calculated. Many time I hear people say things like "My car makes 300 hp from the factory. My intake is good for 10hp, my exhaust for 25 hp, and my tune for 50hp." They then pull out their fingers and toes and 20 minutes later arrive at the conclusion that they should be making 7 million horsepower. I then correct their math, where the sum of those numbers does equal 385.

So my car should be making 385hp then, right?

No. Your factory rating is in Brake Horsepower (BHP). BHP refers to your engines output at the crankshaft, before losses in drivetrain, exhaust, and drive accessories (alternator, power steering pump, etc.). As of 1972 automakers define power output in SAE net output. This indicates the power of your engine at the crankshaft, including losses from exhaust, emissions systems, and drive line accessories. Essentially, your 300 hp engine is 300 hp before any power is lost in the transmission, differential(s), and wheels. Chances are, your 100% stock, 300 hp car is putting anywhere from 240 hp to 260 hp to the wheels.

Great, okay, but my aftermarket parts said they would give me 85 more hp. 260 + 85 = 345 hp right?

Wrong. Most aftermarket manufacturers like to beat around the bush with their advertised numbers. They aren't exactly lying to you, but they aren't always telling you the whole truth either. They did get an extra 10 hp from the same engine as yours, except that engine also already had a full, high flow exhaust, high flow intake manifold, larger throttle body, ported heads, and larger valves. Adding that same intake to your all stock motor might net you 2hp. The same goes for the exhaust and the email tune you got. Your combined intake and exhaust might net you 10 – 15 hp, and if the tune is any good, you might an additional 20 hp from that.

Power Explained: Horsepower, and why your car does not make what you think it makes.

So the 295 hp I put down is actually accurate?

Yes. And to gain more power from your mods, you need to understand how they all work together.

Tune in next week for: Understanding Atmospheric Conditions.