High Roller


Written by Carl Heideman

From the Dec. 2015 issue

Posted in Shop Work ,Features

When it comes to finding that last bit of power or putting the final tweaks on a tune, there are few substitutes for a chassis dyno session. However, successful dyno testing doesn’t just happen. Wing your session with a laid-back attitude, and you’ll typically leave the shop with frustration and unanswered questions. Follow a well-planned procedure, on the other hand, and you’re likely to reap performance rewards and solid, useful data. Guess which approach we prefer. Here are 13 lucky tips to make it happen.

1.Make Sure the Baseline Tune Is Pretty Good:

Is your car running rough? Coughing? Does something just seem “off” about it? Do you suspect it has faulty parts or fundamental tuning issues? Don’t bring it to the dyno. Only in extreme cases is it appropriate–or cost-effective–to try basic tuning and diagnostic work on the rollers. Take care of your baseline tune beforehand, then use the dyno for the final 10 to 15 percent of the job.

For us, a baseline tune includes a valve adjustment and a compression or leak-down test. Go over the basics: ignition, vacuum leaks, carb or EFI diagnostics, and so on. If you can’t get the car to run pretty well on your own, take it to an expert for repairs before heading to the dyno.

2. Have a Clear Testing Plan:

If your car is ready for the final stage of tuning, make a clear plan for your dyno session. Start by listing the tests you want to perform.

3.Test in a Logical Order:

Then, carefully determine the order of your tests. We generally start with the ignition side, then move over to induction, and finally tackle the exhaust (if applicable). To save yourself the trouble of installing and removing the same part multiple times, consider whether a test will make setting up for the next one easier.

4.Rehearse Your Session:

Especially if you’ll be swapping parts on the dyno, rehearse all the changes before you go. In doing so, you’ll know exactly which tools, fasteners and bits you should bring to make the change on the dyno. Ideally, you should also testdrive the car with the changed parts to make sure it doesn’t misbehave. No need to find that out on the dyno.

5.Get Plenty of Rest, Eat Well, and Bring Water:

Leaning over a hot engine bay, inhaling exhaust fumes, and absorbing the general stress of the day takes a toll on the body–not to mention the trapeze act required to get off and on a raised dyno setup.

Go in feeling strong and fresh, and make sure to stay hydrated as the session progresses. It’ll help keep your mind sharp and able to problem- solve.

6. Fresh Fuel?

Last year’s fuel won’t behave like fresh fuel. Enough said.

7. Warm the Driveline:

If you’re trailering the car to the shop, make sure you get the driveline up to operating temperature before your testing begins. Either drive the car around the parking lot or run it on the rollers long enough to make sure temperatures and clearances are in their operating range.

8. Get to Know the Operator:

If you’re working with a busy shop, the dyno operator has probably seen it all–good, bad and indifferent. Make this guy your friend and seek his advice. Nothing trumps experience, and if he’s got more than you, he’s adding as much value to your session as those rollers and numbers. Hand him a copy of your session plan so he knows what to expect, and see if he has any tweaks to make before you get started.

9. Take Notes:

Follow along closely to track your progress through the plan. Make sure you can correlate each dyno run to a specific step. Throughout your session, jot down notes and results in the margins or in a notebook.

10. Repeat, Repeat, Repeat:

Make at least two runs for each test, and make sure they yield nearly identical results. If they don’t, keep tracking down the issue and repeating the test until the numbers match up. And be extra cautious with outliers: If you get one run that’s really good news or really bad news, don’t trust it until it repeats–and repeats again.

11. Don’t Split Hairs:

Many very successful tunes have some issues here or there, so don’t sweat the minutiae. We’ve seen people worry about a few tenths of an air/fuel ratio at one point. We’ve seen people obsess over a tiny dip in power or torque. Honestly, those guys were chasing perfect graphs more than a good tune. That’s usually an expensive, frustrating exercise that won’t lead to any tangible improvement.

12.Know When to Quit:

This maxim is the companion to “don’t split hairs,” and it applies to a couple of situations. The first: Once your tune is “good enough,” stop. The second: If things just aren’t working, don’t try to salvage a doomed session. It’s usually better to pack it up, go home, figure out what’s wrong, and return another day.

13. Get All of the Data:

Don’t settle for just graphs and printouts. Bring a jump drive and get the entire data set electronically. It’s typically available in two different formats: a proprietary file compatible with the dyno’s software, and an open file usable in a spreadsheet. Get both.

It’s often possible to download the proprietary software on your own computer, giving you full access to the notes and smoothed graphs from your session. You can use a spreadsheet for further analysis. Much of a dyno session’s value is in the analysis after you go home, so don’t miss this opportunity by leaving the data behind.

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