To dyno or not to dyno? That may be the ultimate question. But it really shouldn't be a question at all. It should be considered a necessity when building any high-performance engine. You see, even if you've built one before, and even if someone say, for example, an engine magazine like ours, gives you the recipe to build it by and you follow it to the letter, there can still be something wrong and your engine will be down on power when you drop it between your fenders. And you may never know if you're missing that extra 15 ponies, but don't you owe it to yourself and your engine to find where they might've gone?
THE DYNO CAN TELL YOU MORE
There's more to dyno testing than just horsepower and torque. Here's a short list of just some of the things a dyno can tell you about your engine and the things you can do to your engine on a dyno before it ever hits the road, but there're a zillion more depending on how many probes you want to plug in and how much time you want to spend testing.
Horsepower and Torque
Air temp for best power
Oil and water temps Carb/engine cfm
Exhaust gas temps
Check for oil/water leaks
Air/fuel ratio Adjust valves
Break-in a cam
Obviously, some of these are no-brainers and some will take time to figure out. But all of them are important aspects to building the perfect machine.
HORSEPOWER AND TORQUE
The best thing about a dyno is it can find horsepower for you if you know where to look. And that's where our first dyno recommendation comes in. Talk to your dyno operator and ask him how much experience he's got on the dyno. It's not a bad thing if he's only got a few years, but with many years comes much experience. And since you're paying for his time, as well as his dyno, he's going to be your biggest asset during the test. There've been times where I've banged my head against the wall, only to have the pain relieved by a sharp dyno operator who's seen my problems before and helped me correct them so I could move on.
Before your test day arrives, talk to the dyno operator. Give him your full combination of engine and parts that you plan to test and see if he has any ideas/suggestions of something that might not work or might work better. Then, bring as many spare parts as you can carry in your truck to the shop the day you test so you can swap them out if, and when, needed. Don't bring them into the shop until you're ready to bolt them on however, lest they get misplaced or some unknowing guy working in the back of the shop picks them up and installs them on a motor (don't laugh, it's happened). Things like spark plugs, different headers, different carbs, different rocker arms, different intake manifolds, etc...are all things that can easily be tested in just one day, and you might be surprised what you find when you try them out. In fact, even if you make less power after bolting a new part on, at least you'll have a better understanding of what works and what doesn't on your combination.
Here's a list of some parts you should consider bringing with you on dyno day to swap and try to find more power. If you don't already own them and don't want to buy them, see if you can borrow them, either from the dyno shop, or a buddy.
Water injection kit
Different octane fuel
TOOLS FOR THE TEST
Most dyno shops do this for a living and will have every tool needed to test your engine. That is, unless you have goofy fitting or a part on there that takes a special tool. So you should consider bringing anything special you may need, but again, leave it in the truck until you need it. Also, make sure it's clearly labeled as yours before you bring it in.
When testing and swapping parts, most dyno shops will welcome your assistance in the cell, and some will require it. But remember that they do this for a living and have probably seen your combination before, so don't contradict their ideas/suggestions just because your buddy told you last night that his way was best. Also, don't go into this expecting to find some miraculous horsepower-making part that no one's tried before. They don't exist. Share your ideas with the dyno operator and listen to his suggestions. He knows what he's doing.
One of the more frustrating things about testing at as many different dyno facilities as we do is that we can't keep track of where the shop tools are. This means we typically have to waste time looking for something, but dyno operators are very helpful and they understand that we can't memorize their toolboxes. It's just the nature of the business.
When the dyno operator sets up his system for the day's runs, one of the things you'll want to go over with him is how much data you want to record and see on your print out. Things like fuel pressure may not be important if you're just testing intake manifolds. And although the dyno operator will make sure it's correct for the tests, you may not want to see its readings on your printout. Instead, you might want to see things like EGT, vacuum, and carb cfm, in addition to BSFC and air/fuel to really make a decision on which part is best.Don't worry if you take home the data sheets and later find out that you wanted to know that fuel pressure after all. The dyno shop can burn a disc for you containing all the information recorded on your pulls, and even though you may not be able to open/read it on your computer, if you bring it back to him he can alter the print outs from the disc to show you whatever you need.
Although it's very hard to ignore, try to not pay too much attention to peak numbers when you're testing different parts. Look at the averages to give you the whole story. Average power and torque is a much better indicator of a performance gain than a few extra top-end horsepower. Often you'll find little-to-no difference in peak values after a part is swapped, but there'll be a slight gain in average, indicating that there was more power across the board. This is very important, and if you don't pay attention to averages, you may miss something.
But this brings us to another important area of dyno testing. The dyno can record tons of data--much more than just power and torque. The crew at DTS tells us that even their most affordable dyno system has the capability to record 50 data input channels, plus upgrades are available. It's simply a matter of information and how much you want or need to know. The dyno can be set up to measure air/fuel in every cylinder. It can measure combustion temps and pressures in every cylinder, it can monitor air temps going and coming out of a things like intercoolers, blowers, and even just plain old carburetors, if that's what you want to see.
Temps are another area of critical importance. If you want to know how much power that new part just added, you better make sure your temps are equalized on every pull. That means air, water, and oil. And the dyno operator can keep a close eye on that for you since it's not something we're all accustomed to looking for.
Remember that all dyno shop employees have lives outside the cell and they want to go home at the end of the day, which is typically around 5:00 p.m. That means that your engine needs to be off their dyno and into your truck by 5:00 p.m. as well. You're renting him for the day, not a day and a half. If you didn't find the power you wanted by day's end, you need to decide if you want to pay for another day. It's taken us three, sometimes four days on the dyno to get where we needed to be, and that's only when the dyno shop has those days available for us.
The way data is collected and then displayed can be a little confusing. There are several correction factors involved to compare data. This is so a shop on the East Coast can compare data to a shop on the West Coast, hypothetically. But there is more than just one correction factor to choose from and not all of them tell the same tale.
Basically, the correction factors will take your engine's raw data and recompute it to optimize for the day's conditions, usually by a factor of around 1.03-1.07. The higher the correction factor, the higher your corrected data will be. But beware, things like the altitude, weather, and fuel (specific gravity) can all play a part in the way the data will read. A hot, humid day in mid-summer's New York will not produce as much power as will a cool winter day in Arizona. Typically, the correction factors will not be too high, meaning they'll add only a little power and torque to your raw data. But a little can still be a lot when comparing data from six months ago, even on the same dyno. So look at the correction factors used for the day, and also pay attention to the raw, uncorrected data to see if there's a huge discrepancy.
Raw data can be very useful when testing on the same day. Since the correction factors can change from morning to afternoon, sometimes the raw data is a good indicator of how much power is gained/lost from swapping a certain part. But remember that the correction factors are recomputing the data based mostly on atmospheric conditions and the changes in weather during the day will affect the power output of your engine.
THE EMC DYNO DATA
Back when we first held the Engine Masters Challenge preliminary qualifying rounds at several facilities around the nation it was difficult to compare data from one shop to another, even using the corrected data. When all qualified contestants shipped their engines out to California for the final runs a month later, the weather could change so drastically that their tune-ups no longer applied and the people coming from other states had to reevaluate their situations and tune on-the-run in order to make the challenge a success.The engines that came to California for the finals typically picked up power because the air they were testing in back east was not so good. This made things very confusing, and we knew we needed to move to just one facility. Luckily, World Products opened its doors and let us use its three matching DTS dynos for the challenge, making things a huge success in 2004 that will continue in 2005.
This brings us to another issue of dyno testing. When you've got an ongoing engine development program, but not your own dyno, be careful where and when you test. Although both of those factors could be out of your control, it's best to retest your engine at the same facility every time. That's because things like the dyno cell's layout, the exhaust system used in the cell, and the way clean air is introduced to the engine can all have an effect on power. If you took your engine from one cell to another and not made any changes at all, the results could still be surprisingly different. Now, we understand that scheduling conflicts may prevent you from always testing on the same dyno, but try to keep your variance to a minimum for the best results.
DYNO SHOPS ON THE RISE
Luckily for all of us, more and more dyno shops are opening up and more engine shops are buying dynos. They see the need to have their own cell, and by you giving them your business, they may also work to improve it. In the long run, dynos and dyno testing are not expensive when compared to the results of not testing at all.
Dan Roberts from Dynamic Test Systems (DTS) sits at the controls of one of its two in-hous
Everything can be checked and adjusted on the dyno much easier than it can in the car. On
Parts' swapping is one huge benefit to dyno testing. When you spend your money for the day
Before you choose a dyno facility, take a look around and inside and outside of its dyno c
And speaking of exhaust, it can get painfully loud in the cell, and mufflers are always a
Here's a look inside the dyno's absorption unit. This giant bronze impeller is connected t
Looking straight down inside DTS's "tower" you can see the twin starters built into the dy
The custom-designed servo valve is controlled by a very quick-acting electronic motor on t
The DTS dyno carts are some of the fastest to install and remove engines from on the dyno.
Oil temp is only one of the myriads of data that can be collected by the dyno. Make sure i