When we talk to our buddies or to that new lady we have met, most of us tend to embellish things. I recall my days in the Marines when my sergeant would walk in the squad bay and yell, "Quit the chatter, you're all just lying to each other!"
When it comes to telling our car buddies how many horses we have under the hood, the figure tends be a bit higher than the powerplant really puts out. KIT CAR Editor Mike Blake often tells those car owners he interviews: "I will believe whatever you tell me concerning your horsepower, UNTIL you get it dyno'd. Before a dyno run, it is an estimate; afterward, anything that isn't accurate is a fisherman's lie."
Since horsepower is what most of us are after when we tinker under the hood, the fine art of fine-tuning and pony-building is a series of lessons learned and applied. When we build (or buy) our engines, most of us sit down with that paper and pencil and estimate our horsepower based on claims by the companies that made the components we chose to use.
Using that logic on one of my builds, I found the following: Hmmm, now let's see...351W block bored 40 over; 350 hp to start with and I gained a few ponies with the extra engine work; those AFR aluminum heads with polished ports and big Chevy intakes can add a few more horses; and that should also reduce the weight of my engine...so the horsepower-to-weight ratio calculation is now .135 instead of the .1335 with the iron heads I used to have. My Harland Sharpe roller rockers should add a few horses. The March pulley setup provides another 5. That Edelbrock aluminum intake gives me more weight loss, so the hp/weight is now at .1357. The Edelbrock cam and the Barry Grant 650-cfm Speed Demon Carb gains me more power. Now, let's add in that "T" road race pan that keeps the oil off the crank for another 3 hp. Hey, we're getting close to a stampede here! Now, with the indexed spark plugs and synthetic oil in the engine, trans, and rear, my calculations come out to...hmmm. HOLY SPARK PLUGS, Car Man...410hp! I figured that at that point, I could go out and honestly brag about my 400-plus-hp engine. Wrong, Inflated Horsepower Breath!
While estimating horsepower, even using estimating software, is only an estimate and, often, not even a close one, you will never know just how much you are ACTUALLY putting out until you dyno it. Don't forget that your calculations only reflect POTENTIAL. Even crate engines are dyno'd under ideal conditions. As the standard ad disclaimer says: "Your results may vary!"
During a recent engine buildup, I took my Antique and Collectibles Cobra replica over to Bruce's Speed Shop in Rockaway, New Jersey, and, at $80 for three runs, put it on his portable dyno. I wanted to see, on paper, all those 400-plus horses I've been bragging about. Bruce also dyno-tunes, which means that he will assist you and make adjustments to your engine between runs. This costs $125 an hour for Bruce's expertise. In addition to horsepower and torque, the results will also give me current temperature, humidity, air/fuel ratio, and barometric pressure, all factors and variables in proper tuning of an engine.
My engine was originally purchased as a short-block from The Engine Factory. They built the block and rotating assembly to my specifications. I built the rest of the engine, installed it in my Cobra, and did the initial tuning. The car ran fine, no stumble or backfiring, and seemed to perform well. Actually, the car, while accelerating, felt like a rocket.
You have no idea how disappointed I was when I saw my rear-wheel horsepower at 267 and torque at 330. Even allowing for 18 percent power loss through the drivetrain, that is still only 315 hp at the crank--still very, very disappointing. I really thought that the engine would be much more powerful than that! Hey, with a 2,400-pound car, 267 hp will still propel it down the highway at what feels like ballistic velocity, but still, I should be getting more, right? What the heck did I spend all that money on parts for anyway? I went home with my tail between my legs and wondered where the heck I went wrong.
To remedy my angst and power-loss, I spoke to the tech guys at Barry Grant, and at their suggestion, I faxed the dyno sheet down them. They were very helpful, got back to me right away, and based on the air/fuel ratios on the dyno sheet, they suggested I make the following changes:
1. Replace the progressive linkage to a one-to-one setup on the 650 Speed Demon mechanical linkage. This is a common part and can be found at any performance shop, and the part is made by Holley, Moroso, and a few others.
2. Raise the throttle cable on the carb to the big 1/2-inch hole to allow for full stroke of the linkage, letting the secondaries to fully open and get better leverage.
3. Rejet the carb down two numbers, front and back, from the stock 70/78 to 68/76. I purchased the jets at Bruce's Speed Shop.
4. Replace my 1/2-inch open spacer with a 1-inch four-hole spacer (watch your hood clearance).
Well, I did all this, at very little cost and effort, and took another run on the dyno about a week later. I made three runs and all were about the same: 291 hp at the wheels and 365 lb-ft of torque!! What an improvement!! This is almost 350 hp at the crank, and there is still room for improvement.
I faxed the results down to Demon for more suggestions. On their recommendation I am now running the jets at 66/74. I have not been back on the dyno yet, but just from feeling the difference in performance, I know I'll get better results the next time out.
Anyway, I guess the point I'm trying to make is that we all tend to talk up our cars, but you never really know what you have or where you need to tweak that engine until you get it on the dyno. I certainly had the potential, but without that fine tuning it remained just that, potential.
Why kid yourself? You can only estimate potential and that estimate is not actual performance. You could sit around all day and believe you are running 375 hp in that puppy, but reality sets in when you find you are actually running 300 hp. Then depression sets in along with the loss of power. I find it a better experience to spend a few bucks and get to a dyno. Get that engine tweaked and running at its peak potential, otherwise, you will never know just what your car is capable of.
Some people are comfortable telling everyone they've got 400 hp, but don't you want to know what you really have under that hood? Don't you want that engine running to the max? I certainly do. I spent a total of $160 for the dyno time and less than $100 in parts. What I got back was well worth the price.
I also learned a valuable lesson: Rely on the tech guys from the manufacturers of the components. These guys, for the most part, are extremely knowledgeable about their products and their only purpose in life is to help you. Use them, call often, and always get a name so you can deal with the same person every time. Keep notes and records so you can go back and review the suggestions in the future. There's nothing more fun to a car guy than a well-running, horse-pumping powerplant, and while getting there is half the fun...being there and staying there is dyno-might. KC
Dyno Definition
Dyno is short for dynamometer, a device that measures torque and can therefore calculate horsepower. The two main types of dynos are an engine dyno and a chassis dyno. An engine dyno is used when your engine is out of the car and connected to a water brake that measures torque and, therefore, horsepower.A chassis dyno is two large rollers on which your car's tires rest and are strapped to, and the car is actually driven. The rollers also measure torque and horsepower. The chassis dyno is a great way to find out how much power your car is making. At the dyno you can tune your car and stop guessing if the change you made actually did anything. Dyno time is not cheap, but it can save you a lot of time and a lot of guessing.
