To Dyno Or Not To Dyno?
Well, our first pull was 474 hp. The last, 616 hp. So…yeah. To dyno.
By Eric Jackson, Vintagemusclecarparts.com
Racers are a strange bunch. They’ll shell out cash hand-over-fist for the latest and greatest cylinder heads, or a killer roller cam and valve train without batting an eyelash. They’ll build a giant stroker engine, install the latest mega-frosty nitrous system or turbo kit, and pound on it like they hate it. Sometimes they haul ass. Other times they haul parts back home in a bucket. Yet, suggest a guy dyno his engine to find every last ounce of power – and to prevent problems down the road – and you’re generally met with blank stares and the sound of crickets.
Why is that?
We have our suspicions why racers shy away from running their engine on a dyno, but only one reason is typically offered. Some simply think it’s a waste of money that could be better spent elsewhere on the car. Maybe some aren’t sure what they’re doing and don’t have anyone to explain things to them. Maybe some don’t think an engine dyno can help them dial in their program. Or, maybe they’re afraid of what the dyno might tell them, who knows? But one thing is certain, there is much to be learned if you’re willing to do the work.
You’ve probably heard the old saying “There’s never enough money to do it right the first time, but there’s always money to fix it after it breaks.” We get it, budget is usually an issue. But an engine dyno can easily save you wasted time, money and grief. And provide the info you need to get your convertor and gearing right the first time. And also where to begin experimenting with shift points. There’s no guessing; your engines power band is right there on paper. Compare the time required to learn these things on the dyno versus how many passes it might take in the real world. You could be looking at multiple trips to the track to confirm the same info found in one dyno session. And there would be no changes in weather to skew your results. Not to mention traction variables, missing run sessions while making changes, and waiting on other racers who cause down time (think crashes and oil downs). And if you don’t live close to a dragstrip, an engine dyno is the only way to confirm this info without trial and error assembly of the entire car.
To illustrate, we’ll hit a few of the high points on a 496 Big Block Chevy project we’ve been working on. It’s a mild street mill with unported, cast iron, closed-chamber square port heads, a factory high performance dual plane intake and a fairly conservative Crane flat tappet cam. This particular engine, which powers the authors ’67 Chevelle street car, was originally built in 2006 and made almost a dozen pulls on the dyno in its first configuration.
Initial testing was done at George’s Speed Shop in Dayton, Ohio (as in the legendary “Ohio” George Montgomery of Malco Gasser fame). Some of the testing was intentionally conducted in a “worst to best” manner to avoid unnecessary time and effort swapping parts back and forth, but to get to the point, the initial figures from the very first pull were 522 lb-ft @ 3000 rpm and 474 hp @ 6000 rpm. Not exactly earth-shattering figures from a 500″ big block. However, through basic tuning, a carb swap, some minor intake work and the right headers, those figures climbed to 546 lb-ft @ 4000 rpm and 534 hp @ 6000 rpm. Between the first and last pulls the power climbed by 72 lb-ft and 67 hp at various points in the curve.
While those gains are significant, they should really be considered “low hanging fruit.” In other words, relatively easy gains. At this point many would’ve called it good and went racing, but we knew there was even more power to be had. But those gains weren’t going to come as easily.
The engine saw street duty for several years until a nagging ring seal issue became too much to bear and the engine came back out for a freshen-up. Upon tear-down the problem was revealed to be a little more severe than poor ring seal (bad machine work) and required a fresh set of slugs to go with the new rings. The compression ratio was dropped from 11.2-1 to 10.5-1 to allow a little more tuning room, and the engine was buttoned back up. Once again the engine found its way to the dyno, but due to scheduling conflicts at George’s the second round of testing was conducted at Kammer Racing in Huber Heights, Ohio. Since we needed to reestablish baseline power and torque numbers, the basic tune was put back as closely as possible to the 2007 tune. The new dyno figures essentially mirrored the previous numbers, so we called that good. That’s when the serious tuning began.
We’ll go into more intimate detail in future stories, but in a nutshell the engine was subjected to another 30 pulls on the dyno. We left no stone unturned in our quest for max power. We ran lash, timing and carb jetting loops; we tested coolant and oil temps; we tested several changes to the exhaust; we tested two more carburetors; we tested ignition systems; we even tested another intake manifold and another oil pan. (Watch for our upcoming series, A Funny Thing Happened On The Way To The Dyno, where we discuss all of this in detail – Ed.)
When the exhaust fumes had cleared (and our ears stopped ringing), the engine had clawed its way up to a max of 616 lb-ft @ 4300 rpm and 616 hp @ 5800 rpm. Not bad after starting out with a measly 474 hp and 522 lb-ft. At the peaks, that’s a gain of 94 lb-ft and 142 horsepower. However some of the spreads were even more pronounced at various points in the curve.
Any lingering doubts as to whether or not dyno time is worth the investment should be put to rest by this point. But there’s one point we want to stress. While the initial gains came somewhat easily, most of the improvement during the second round of testing came as single digit figures. Some as low as 2-3 hp.
If you’re thinking such minuscule gains are inconsequential, consider that we inched our way from the plus-67 hp mark to plus-142 hp. Yes, there were a few big jumps along the way, but ultimately we got there thanks to curiosity, analysis, experimentation and ignoring conventional wisdom. So, when at the dyno, remember our motto: Find 10 places to find 2 hp rather than swing for 20hp with every change. It’s less often you’ll find single 20hp gains, but you will find small gains that quickly add up.
So before you shoehorn your next engine project between the fenders, consider going to a dyno with it first. After reading our complete series, you’ll not only know where to hunt for hidden power, but you’ll know how to ensure the engine is happy and the tune is sorted out. If you’re still not confident about where to start, ask some local racers who they use, or spend a little time on the internet researching speed shops close by. You might be surprised just how many dyno facilities exist.
Once you’ve chosen a dyno facility, be sure to ask if they will be making the tuning calls and changes or if they’ll be leaving that up to you. It is worth mentioning that some dyno shops aren’t too hip on the idea of pounding the daylights out of an engine hunting for power. Time is money to them and some charge by the job, so they will want an engine on and back off their dyno as quickly as possible to make room for the next customer. If this is what you encounter, move on to another shop. You’re there to sort out your stuff, not line their pockets.
Costs will vary between shops, generally $500 to $750 for a full day (where you’ll have control over the schedule, unlike at your local test ‘n tune). You’ll be required to provide your own parts, fluids (fuel & oil), and gaskets. Many shops will have race fuel available if you can’t source it yourself. Pump gas is obviously not an issue if that’s what you’ll be running, but you will be expected to provide that yourself. Don’t forget things like spare spark plugs & wires, silicone sealer, paper towels or shop rags, and even some hand cleaner. The better prepared you are the more efficiently you’ll use your time, and again—time is money. Make a check list of the things you’ll need to bring with you, and do it well ahead of time. You should also make a list of the tuning steps you want to run, such as ignition timing (base, total and curves), carburetor tuning, any carb spacers you might want to try, different ignition components, air cleaners, headers/exhaust. And if you’re running a mechanical cam (flat tappet or roller) you can experiment with valve lash as well.
Don’t get discouraged if your engine doesn’t perform up to your expectations at first. Some builds are pretty well sorted right out of the box (literally speaking), while others take some time to dial in, such as our 496. Be realistic with your expectations as well. There is more BS about dyno figures being thrown around than there is during election years (well, maybe not that much). Don’t expect 500 horsepower from a 9-1 compression small block with a mild cam and stock heads, unless you’re a seasoned Stock Eliminator racer.
In basic terms, you should be able to expect roughly .8 to 1.2 hp per cubic inch for a mild to moderate street build (like ours). More aggressive combinations can produce somewhere around 1.2-1.4 hp per cubic inch (add compression and/or porting), and 1.5 hp per cubic inch requires a pretty serious effort (all that plus higher rpm, maybe a more aggressive cam). Balls to the wall killer efforts can easily make 2 hp per cubic inch, and Pro Stock and Comp eliminator engines have crested the 3 hp per cubic inch mark.
Throwing money at a project hand-over-fist isn’t a good way to make it fast. Our 496 picked up over 140 horsepower, and roughly 50% of that came from precision refinements, not major component changes. How many racers would go after those same sort of gains by swapping heads, intakes, cams, etc. instead? To be blunt, once you’re leaning on stuff this hard, it’s foolish not to sort it out on the dyno first.
Spending money wisely and refining what you already have is the difference between winning and losing. If it’s worth doing, it’s worth doing right. The first time.
Besides…losing sucks. – CI
Watch for our multi-part series, A Funny Thing Happened On The Way To The Dyno, where we delve into the details of how testing carburetion, exhaust, oil pans, and hunting for hidden horsepower helped us find over 140 additional horsepower. Only right here at carsillustrated.com
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