Just read the thread....quite interesting,
Why does the rpm on the dynojet graph stop before 7000?
I know for a fact my car is still making good power past that, and the red line is set at 7800!....I would wonder if this dyno has been set up correctly, to make that much torque at the wheels with your mods seems a bit high...
I have always heard that it is always best to dyno a car on a Dynojet in 4th gear as most of the time the gearing on a car in 4th is close to a 1:1 ratio...because an inertia dyno like a Dynojet calculates it's data by measuring acceleration of a know mass (the roller) and because acceleration is effected by gearing I am sure the power would read even more on a dynojet if the pull was attempted in 3rd....Just a thought

 

Maybe the tac pickup wasnt set right?

 

Exactly what Al said. Dont pay att to numbers as long as you are happy. Anyways, STD factor on dynojet reads higher than SAE (about 15~20WHP)...

I dynoed @ 297WHP at Shiv dyno with 91 gas it was = to 350WHP on 91 at Harmanmotive in LA. (SAE factor)


Were you on SAE or STD ?

 

well actually they asked me what I usally run the car to and I told them redline, so the first 2 runs I noticed they ran it to 7k, Me not knowing what my rev was moved up to from the XEDEflash, I then told them on the 3rd run to take it to 7.5k, which is the run I made the most power. It is all soo confusing.

 

you are correct. fourth gear on a dynojet will read lower. the reason most shops dyno in third is because fourth gear is so long it can lead to more knock. try dynoing an srt4 in fourth and you can physically watch the motor knock. the difference in numbers among dyno's isn't siginicant. what's important is that it is a measure of increase from mods. if you use a dd and you got 5 horsepower from a mod and you used a dynojet and you got 10 you might be upset. but if you look at the increase in percentage gains i think the difference may not be so disturbing. long story short dyno's are tools and tools are only as good as the people that use them. at the end of the day the only numbers that really count are on the track.

 

The difference between a 4th gear pull and 3rd on the dynojet is that it usually makes around 10 more ft/lbs of tq from spolling the turbo up sooner whille droping around 5hp on the topend. We usually use third unless the car is over 400hp or we are logging the run as to gain more resolution from it taking longer to make the pull.

 

STD can sometimes be lower than the SAE number depending on weather conditions.

 

that if it was 0 D outside. I am talking about normal weather 60~80

 

For starters, if one compares the two sets of data from page 1, he wouldn't believe it's the same car. The HP and TQ trends from one dyno strongly disagree with the other. This being the case, the data from one of these dynos should be thrown out the window, as the two sets are absolutely incomparable.

Forget about niggling over the accuracy of these dynos, the name of the game here is precision, which essentially means repeatability. Ideally, one wants to tune his car with the same dyno, same settings, possibly same operator. The more variables one has at his disposal with a given dyno, the more room for error. Where repeatability is concerned, I've seen much better repeatability between two different DD dynos than amongst the various DJs and Mustangs that I've witnessed over the years. In other words, I'd have no problem taking data from one DD dyno and carrying it over to another DD, but I can't say the same for the other two brands, sorry.

Traditionally, the gear ratio that is closest to 1:1 is used for dyno pulls. In an EVO, this is 4th gear (1.031). Third can be used (1.407), but it will give a higher power reading on the same dyno. One can use either gear, so long as he uses the same gear for tuning on the same dyno and refrains from comparing his numbers with others who did things differently. Just remember that given the same load, using a lower ratio should be expected to kick out higher power numbers, which may be deceiving.

Finally, the more load applied, the longer the dyno run,and I would dare say the more accurate the numbers. Less load = shorter dyno run. Higher load = longer run. If the run is too short, it may not give as accurate a reading. If the run is too long or repeated runs are conducted, heat soak could become a problem. In any case, when I see jagged lines in a graph, I have a difficult time taking the numbers seriously. If the power was really generated that way, we'd probably have rattled our teeth out by now.

 

excellent points.

 

so if you run your car on the dyno in 4th and you have 200hp. What would you get in 1st gear? 400hp?

 

On a Dyno Dynamics it would not make the slightest difference

 

SO cliffs notes...

A Dyno Dynamics Dyno Generally reads lower then A Dynojet

A Dyno Jet Dyno Generally Reads Higher Then a Dyno Dynamics

The reason why the WHP was so close was because the Dyno Runs were performed with different gears.


Ok, this just defeated the defeated the Purpose?

 

Yep, a DD will *always* read lower than a DJ. As for the graphs illustrated in the initial post, they look like they came from different cars. Nevermind the power numbers, the power peaks aren't even the same rpm!

If we think about it, so long as the load applied by the dyno is constant, the hp needed to accelerate the wheels is the same between different gears. What happens however is the change in speed of the rollers in a run taken in a lower gear is less. This could possibly translate to less resolution of the power curves, but the overall result is dependent upon the dyno software. So long as the dyno computer can monitor rpm, I think the results between gears will be similar. This was not true for the old dynos, which were largely mechanical.

 

Ted,
Isn't there more whp loss due to the drivetrain and wheels when dynoing in a higher gear? It just seems that a car would lose whp due to having to spin four tires at 110mph vs. 80mph.