Ketchmi

All of our testing was done on a DynoJet and the charts I published were same day, same car, same dyno without even unstrapping it from the dyno. I didn't want any variables.

We have just bought our own Dynojet w/load control...got tired of scheduling by other peoples whims.

I did tune an 86.5' on a dynapak and it was extremely low power wise, around 200rwhp. I know for a fact that this car is in the 280rwhp range on a DynoJet.

928ntslow

I got to thinking...and this is no disrespect to anyone out there as I know not of what folks do or don't do to their cars...there can be any one small factor in a chain of components, hoses or wiring that can tax the performance of any vehicle. We have all seen the conditions of these cars when we buy them from others. Most of the time, the maintenance has not been performed on a regular basis. If you think about it and add up all the little "someday I'll replace those hoses or wires..." they add up to a lack of performance.

I say this because I have been down this road with every 928 I have owned...even the GTS. When I first got the car, I stuck it on jack stands for a month and did a complete service on the car. That meant ALL fluids (except for the PSD as it wasn't necessary) questionable hoses, gaskets, wires and so on....even electrical plugs.

An old saying, but a chain is only as strong as it's weakest link. Everything has to be as close to perfect as possible. Questionable plug wires will make the difference for example. I think my car made those numbers because it IS near perfect.

Tom. M

yes..exactly Keith...Your car is as Porsche intended...right off the factory floor. You've basically brought the car back to optimum condition.... It would be nice to see if Cobalt's tune up will bring his numbers up. Again..one can use dyno numbers as an indication as to issues with a particular motor...if comparable cars don't make good numbers...start digging in to see what is off..perhaps a sensor, poorly timed cams etc...

RKD in OKC

Naw Keith, your car is just making more power because it is about to break. Race cars always run strongest just before they fall apart.

hacker-pschorr

What correction factors (if any) were available on the Dynpak?

The number one problem with this entire discussion is the software itself. Any and all dyno software (including Dynojet) can be manipulated on the dynos controlling software.
This is why your best use of a dyno is to use the same dyno for all of your runs and modifications.

I know Dynojet and other dyno manufacturers like to claim their systems are setup a certain way, they are all the same etc.... Sorry, that is like saying every drag strip around the world will produce the same results. You wouldn't believe that for a second, so why does everyone blindly believe that every dyno (including those from the same manufacturer) will produce the same results?

Not only are there different versions of their software (all brands) but their mechanics change over the years as well. I would not expect the Dynojet that was installed 10 years ago to produce the same results as a brand new one.

drnick

hacker, i think this is right - dynos are a usefull comparative tool but not definitive! my car on a dyno with ott x and dual 2.5" pipe didnt produce the same rwhp as the dyno on louis page for a GTS with these mods - but it went down the road very promptly. the dyno ive been using is a dyno dynamics, all the runs are in 3rd as well - maybe this machine reads low?? i will stand by the corrected numbers from that machine as they seem about right when compared to how the car runs. most usefull though is seeing the comparitive gains from modifications.

heinrich

You guys are saying that dynamometers are as much as 28% variant between each other .. . and I do not buy it. It would be like Porsche's claims of horsepower at 320 for an S4, being totally valueless because Chevy's claims of a car doing better, were produced on a totally different dyno. Or at a different time. Pish-posh.

What IS different, is the set of variables OUTSIDE the dyno ... like ambient temperature, ALTITUDE, etc.

cobalt

I don't think my initial comments were much different than what everyone is saying. I take peak Hp numbers with a grain of salt there will always be variables. I have also seen cars with crazy numbers but absolutely useless power curve.

I had my C2 dynoed first and the smoothing was set at 0. When I went home to pick up the GTS they ran a number of other cars and somewhere they had made adjustments to bring the smoothing to 5 without me knowing, so that in itself may be chopping off peak HP. I will be having the car tunned in September and I will see if I can get the same place to do a dyno run to see if it makes a difference. I will also have them run it with smoothing at 5 and smoothing at 0 and see what differences that makes.

I do know that their is no set loss that can be considered accurate but we do need to have a standard figure we can all assume is close to accurate. So as I was told 15% for a 928 in 4th gear is as close as one can use without pulling the engine and running it on an engine dyno. Of course there is always a margin of error. Does anyone have a number they feel is more accurate? (13%-16%) I know a lot of you have put a lot of effort into this but I feel comfortable with the info I was given from a mechanic I trust and was basically the 928 guy that most of the dealership sent their cars to work on back in the late 80's and 90's before he went independent.

I think we all agree the X pipe has it's merits. I would think of installing one but I am trying to keep my car as close to stock as possible. I already have a car that is too fast for the street this one is there for those nice long rides and serves its purpose with flying colors with more than enough power. 295 or 313 to the wheels is not going to be that noticeable to me. Still a strong running car and at whatever the drivetrain loss is it is within a % of the factory #'s which works for me.

BTW here is the best I have of my chart as you can see it is so smooth due to the smoothing who is to say what peak numbers were chopped.

heinrich

As I recall, the numbers are the numbers and you the reader set smoothing etc in your client software.

cobalt

I was told smoothing will clip the high and low peaks and valleys on the chart. So it would take the average of the 2 and plot the line based on that. If that is incorrect I am curious to how it would work.

hacker-pschorr

As mentioned before, apples to motor oil. When an engine is certified with an SAE hp figure it’s a very precise test will all variables controlled. An SAE representative is also on site for the certification test. It’s not a quick pull either, it’s an extensive test the motor is put through before it’s certified.

Your example did happen a few years ago to Ford and Mazda. The published numbers were way off form the actual power measurements.

Yes. Bottom line is results are going to vary. How you want to explain the reason is up to you, doesn’t change the bottom line. The SAE / STP / STD numbers are supposed to level things out.

You also need to factor in age of the dyno, how often if ever it was serviced. How up to date is their software, are they using the current SAE standard etc….

Another variable you have to consider. Does the software you have at home match the software at the dyno shop? This was an issue about five years ago with Dynojet. They had a different version of the software on their website then the shops had. Z posted some comparison charts a while ago showing the difference.

Friend of mine who owns a SuperFlow dyno has his dyno serviced and calibrated a couple times a year.
I was at a dyno (no 928 content at this shop) a while ago and I asked the owner / operator the last time it was serviced / calibrated. He said never, it’s not necessary.

Assuming you take the file home and calculate it yourself. From the last Jersey dyno day, most just went home with a piece of paper.

So, to say this again. The best way to use a dyno is to stick with the same one before / during / after your modifications.

heinrich

I disagree that dynos out there will vary by as much as 28%. If they do, we may as well stop dyno-ing our cars. A point or maybe 5, I could believe. .... if you're right, then again ... why bother.

It is commonly-accepted practice to bear in mind humidity; temperature, and especially altitude...

cobalt

I know that whenever a car I know of has been tested on a Mustang Dyno the numbers vary significantly vs the same car being tested on a dynojet or dynapac.

I also feel that the dyno we used in NJ was not well setup. The room was cramped and circulation was poor with limited fans for cooling. You can see a drop in power in my 2 runs because the car was running hotter than normal.

hacker-pschorr

Why bother? Becasue it's the single best and safest way to tune a car.

As for the percentage difference, I have documented up to 20% difference just between the five different correction factors on the same dyno. Then you also need to factor in variables that are user changeable in the dyno software (at the shop) and all of the other factors I've listed more than once.

Nothing with dyno's is commonly accepted, that is why this thread is going on for so long.

heinrich

Correction factors are software. The dyno runs as a piece of hardware and it outputs an SAE or other standard output. If you choose to alter its results in different ways with correction factors that is all software.