After reading the latest Car & Driver I won't be spening any money on a dyno. They did a chasis dynamometer test. I would post a link, but C&D won't let you link to current issue stuff. Pick up the latest issue.

 

They are not outwardly false, they are simply relative to themselves

 

Exactly.

To compare one dyno to another... waste of time.

 

Thats right................

 

Or one car to another car. More importantly if the dyno operator is not very good the results are dubious.

 

very true. I have run dynojet dynos for about 8 years and there sooo many things that can easily alter readings. If you are not careful tire pressure, strap tightness wrong gear etc. can skew readings. I have seen Intake temps, coolant temps fan placement all change readings. On a recent car dumping the'good' fuel the car had in it and refilling it with fresh 91 added 5 hp. Once a car is tuned right a good operator should be able to get very repeatable graphs.... and tell the difference if it the car or the operator. I love it when people show me graphs of stuff done at a different shop done 1 year ago in freezing weather... 'why arent my results the same now?'
j-bone

 

its a rough estimate. which is why Id place very little faith in bolt on dyno numbers.

but you can get a general idea about larger hp stuff like FI.

 

The tests were done at Dinan BMW with Steve Dinan. They did various runs with the same car and got HP readings ranging from 330-420HP. The Home Depot fan gave them 37 HP. They brough in a industrial fan capable of 38,000 cFM at 75 mph and blow it into a duct into the radiator, result 411 HP vs 371 w/o. Dinan claims he would get another 4-5 hp if he ran in the morning with an ambient temp 10 degrees cooler.

Bottom line that I gathered is that unless you can maintain ambient temp & humidity as well as air flow and engine temp through all the runs you make then the dyno runs people make after adding a mod are probably useless. Especially if you run on a different day.

All in all an interesting article.

 

Thats why ya gotta go back to the same dyno, unless they are upgrading there fan on a daily basis you will get a basic idea if your mods are helping or not.

A stock mustang gt was on the dyno before me, did three pulls, his best was 234hp at the wheels, I got on and ran 251 to the wheels.. Maybe the dyno #'s aren't exact, but they sure give you an idea of how your car would stack up to someone elses on the same day/same dyno or after you put some mods in, I still think its better than not knowing at all.

 

Getting consistent and accurate results from a dyno isn't that hard. You have to monitor a few things:

1. Knocking. If the car is knocking, especially a 350Z which is very sensitive to knock, your results will not be consistent. Make sure you have good fuel, or at least the same fuel in your car if it's sensitive to knock. Older cars like a 240SX with older knock controlling systems and aren't tuned to run on Premium to begin with won't be as sensitive.

2. Heat soak, or air intake temperature. If you do 12 runs back to back, chances are the 12th will be worse than the 2nd* or 3rd due to heat soak.

3. Coolant temp. Some cars retard massive amounts of ignition timing when the car is cold, to aid in warming up catalysts. If your car sits for 4 hours (like during a dyno day) and you throw it on, chances are your first run won't be as good. You also run the risk of running lean and blowing stuff up. *That's why I usually go off the 2nd or 3rd run.

4. And if you're really not paying attention, gear position. Run it in the same gear everytime.

The Dinan test was pretty much specific to BMW. They talked about the M5 having windspeed sensors to determine if the car was moving fast enough in accordance to the gear position and RPMS. If all three sensors match up, the full engine potential becomes available. To my knowledge this doesn't apply to anything other than a new M3 or M5.

DynoJets for example are all exactly the same provided it's the same model. DynoJet 248C #1 should give the same reading as DynoJet 248C #2 unless there is seriously something wrong. If you've ever taken one apart there are hardly any parts: A barbell looking thing which is the roller, brake pads to slow the dyno down, some non-serviceable bearings, a speed sensor and some stands to hold the rollers up. You can't calibrate it and there really isn't anything to go wrong.

Given that and the correction factor given by the DynoJet, there's no reason they numbers should be different. In addition I've done several tests on several cars ranging from the summer in AZ, which is typically 110 degrees, to the winter which is closer to 50 and they are extremely consistent. If someone claims they made more power in the morning than in the hot afternoon it's because either A. their correction factor wasn't turn on so it's basically like going to the 1/4 mile strip, or B. the car was knocking. Dynos as well as magazine tests are not responsible and can't control it.. you just have to be careful.

I'm not the world's biggest expert on Dyno testing, but I've done hundreds if not thousands of tests with every car you can think of. Keep your intake temperatures reasonable and watch knocking on modern cars (350Z!!) and you should get consistent runs. If not, come to Phoenix and I'll show you how to do it.

 

Well, instead of dynoing, why not just take the car to the Track? You can get a very good idea of the bolt-ons that you did by comparing your MPH at the end of the 1/4 mile.

IMO, this is probably more realistic than DYNOS. Then again, you don't have HP numbers to talk about

 

1/4 Mile times are almost just as bad as a dyno. Different days, different temps, different track conditions, good or bad run, etc. etc. Too many variables. IMO you have to take dyno readings for what it's worth and not believe it is the true answer. Use it to assist in knowing what the car is putting down and if the mods are gaining any power.

 

Except:

-1/4 mile tracks don't have correction factors to adjust times for weather conditions (unless you're a magazine tester). Dyno's do. DynoJets at least.

-Traction is an issue at the 1/4 mile, it's not on the dyno until you reach the 400-500+ mark

-Driver skill is an issue at the 1/4 mile strip

-You can't monitor and control conditions nearly as well at the 1/4 as you can on the dyno. You are told when to run, you sometimes have to wait with the car running which can heat soak it etc.

Important dyno variables that can affect readings: Engine heat soak, knocking, gear position. Control those and you'll be fine

1/4 mile test variables: Driver skill, driver consistency, traction, weather conditions since the times are not corrected, and figuring out how to control water, air and oil temps.


Chassis dynos aren't the most precise instruments in the world, but 99% of the aftermarket world is getting by just fine it seems. Like I said, they can be very accurate if you know how to test properly. If you're not getting accurate results, you have a car problem or you're not doing it right. Like I said, come here and I'll show you.

 

Hmm, it's called forced induction.

If you go out of your way to screw up results you can basically render any type of measurment device ineffective.

The whole point of dyno's is that they provide a relatively controlled environment for testing. Even though the runs won't be exactly the same every time, you will get a decent idea of where you are performing, but more importantly, you can see the torque curve which is very useful (well, interesting at least).

The article sounds interesting, so I may have to check it out. However, based on your one example above, I wouldn't treat it as gospel. It does sound like it provides good insight towards the effects of changes in environment, but it certainly doesn't give you any idea how useful or not useful a dyno can be (maybe they covered that more in the article, though).

Sport Compact Car did a test where they took the same car to multiple dyno's and tried to determine how repeatable the tests were. They wanted to get results from each dyno and then see how much of a difference the operators, equipment, and set-ups made. To me, that test is a better indication of the usefulness of the dyno because they tried to control as many factors as they could.

-D'oh!