$75.00, three runs, and Jim the tuner at southwest tuning was behind the wheel. I was taking pics and video, that I can't seem to download onto the thread. www.swtuning.com

 

Changing the rear end ratio has no effect on the transmission. The 1:1 ratio refers to the speed of the transmission input shaft in relation to the output shaft. Changing the rear end ratio only affects the relationship between the driveshaft and the drive axles. Get it?

 

TMS can't take vids as attachments.

Can you upload them on YouTube or Streetfire? Must register for both, but it's free.

 

Rob, with the C&L and a custom tune shouldn't your number be closer to 280+rwhp?

 

I found this article that talked about chasis dyno's.

... Aside from the usual testing variances, results obtained on different dyno’s of the same manufacturer are generally very close. A comparison of results between different manufacturer’s dyno’s e.g., Dynojet and Mustang will show some variation possibly up to 5% of the whp reading.

Reference article

Up to 5% difference in RWHP readings between dyno's? And some experience higher differences than that? It's no wonder why these numbers frustrate people.

 

And the drive axles spin the tires which are what spins the dyno........ Changing gear ratios will affect your dyno readings, but not in a huge way. This has been covered here and also in other forums, you can find more info if you want to search.

I would guess that OKLACOP's numbers would probably be around 280 on a standard dynojet, with standard (stock) gears.

Tom

 

I was hoping so. My tune isn't exactly custom tho, it's Lidio's 93 octane tune. I didn't have it done at his shop, I ordered it.
I am disappointed in the numbers, but I was told they were gonna be low before hand since it was a Mustang Dyno.

 

I would send a printout of your dyno run to Lidio and see what he thinks about it. Where was your air fuel ratio at?

 

I am also curious as to what the A/F mixture was?

 

Rear-end gears has no effect on peak horsepower and torque. In other words you can not lose or gain horsepower and torque due to rear-end gears other then any weight difference they may be from one gear set to another and then the horsepower and torque difference would be so minute you would never know.

Now, rear-end gears could change your horsepower and torque curve, thats to say it could change were you see your peak horsepower and torque...

 

Those seem pretty low for your mods, I too think you would be closer to to 280rwhp. Did you ask them how long it had been since they had lubricated their rollers. I know when I had my Corvette dynoed, the numbers at one time went down, after we dynoed it a couple of months later after we had added some more mods, and it had even cooled down. They said that the amount of lube on the rollers can make a difference. Mustang dynos do tend to give lown numbers than dyno jets do.

 

Like i said, the Mustang dyno will show about 30hp lower than the Dynojet. I think his numbers look about right.

 

Not to change topic or start a war of words, but changing your rear-end gears WILL effect the dyno reading. This is valid info to this thread, because he has changed gears. Here's a previous thread on the topic: http://forums.bradbarnett.net/showth...ight=dyno+loss

 

So how do you get a true dyno of the rear wheel on a gear swap? is there a scale to convert or a formula?

 

The difference between the mustang and dynojets, if both are calibrated correctly, the weather is input correct (or station calibrated correctly), the numbers will actually be 8-12% different on these and sn95 cars. The auto does eat some more power(3-5%) usually. Many mustang dyno owners will also tweak their dynos to purposely read high, because many folks like to *****, with their "bad dyno defense".

Since a dynojet only loads about 2500-2700# of load on your car, you can see that the dirtier the vehicle aerodynamically is, and the more it weighs, the more erroneously high the numbers will be, and the AFR(often sampled incorrectly, as well), and the tune, if done on one, will be inaccurate for these discrepancies in accurate testing. This where we come up with the term "dyno queen". Big numbers at the dyno, but no driveability or faster times at the track.

As far as any questionability of SWTUNING's dyno accuracy, it is less than 6 months old (they only need to be lubed once every year, even when they get used alot), and it is checked for calibration, parasitic losses (also done with some vehicles in each test session-drag radials, when gummy, eat lots of power) every week, and the weather is updated every 15-30 minutes, with a laboratory grade weather station, IN THE DYNO BAY.

Lower gears do lower the power numbers, but very little, like 1-3%. The power is read by stretching the load cell against the force of the rotating mass, made accurate with the load absorber, and not loading the car enough, or lowering the gears make it work less, stretch less. If a vehicle is struggling in 4th (or 1:1) gear, then the testing (and tuning) is done in the next lower gear. Bottom line, the vehicle needs to be worked hard, but not to the point of struggling to have an effective and accurate test run. The automatic is simply run in drive, and the highest power numbers, regardless of gear they are sampled in, and it cannot get any simpler than that.

When I tune, I will lock a vehicle in gear(when necessary), but not on a test without a tune.

As far as the tune accuracy, unless a FULL and complete datalog is performed with the test, it's just an AFR and power pull. Yes, if you hear detonation, you know it's not safe, but you can be in knock retard, and never know it, just by running a simple WOT test, and even then, you are not sampling any PT, steady state, transition test data. This even a worse problem with GEN3/4 GM's, whereas, they will learn knock, and bias to a lower timing number, further fooling a laymen or a nooby tuner. To accurately test another tune there, you really need to reset knock learn.

As far who's tune is better, whatnot, it's pretty much like 2 different beers. They both tell you they are great, but an accurate comparision can be made when both are drank. That make sense?

EACH VEHICLE IS UNIQUE, AND EACH TUNE, TO BE 100% EFFECTIVE, NEEDS TO BE PERFORMED BY AN EXPERIENCED, PROFESSIONAL TUNER, IN A REAL-WORLD ENVIRONMENT. In 16 years, I have NEVER, ever, written the same tune twice, for this reason.

In summary, the numbers mean nothing, from the standpoint that the dyno is a tool, it's job is to provide a real world testbed, for a competent tuner to do his job. The results when it LEAVES the dyno is the only thing that matters.

HTH unfuzzy some things for you guys.

Jim

 

Jim,

I'm glad you posted that. I hope I didn't give the impression that I was unhappy with the dyno at swtuning, I'm just unhappy with my particular tune, which is why you have all of my future business and I can't wait for you to custom tune my car.

 

No, that was for clarity and hopefully, the elimination or minimization of speculation on the concept of operation and dyno design and EXACTLY why output dyno numbers vary. Speculation without knowledge is not an effective use of time.

jim

 

well said!