atb

YOWZA. Killer numbers.

Flappy-less on the N/A run? (not that it matters now)

DoubleNutz

Yes, I have seen MUF DVR in Hawaii on a red 911 some years ago, but the State of Oregon rejects applications for obscene or offensive plates. Getting this one through was a bit of a hope that they would not read it too closely.

Shane

Bigs has nothing to due with the S/C, it is just a matter of when the dyno operator hits the data record button.

all4woody

Let me see if I can answer a few questions.
The HP and TRQ lines don't intercept because the before and after HP are in the top frame and the before and after TRQ are in the bottom frame. We were starting the runs at 2500 RPM but with the SC we started at 3500 RPM. This was the first day I have driven the car since the install, so I guess we didn't miss any bolts.
Car setup. Stock engine with 151K, never rebuilt. Otte X Pipe(made by Tom Cloutier), in place of cats. RMBP. Kenne Bell Twin Screw with Intercooler. 66mm pulley making about 7lbs boost. Lots of race upgrades, but you don't care about that. Always been a strong car.

all4woody

Sorry, I was actually making around 7.5 lbs boost.

Lagavulin

Those are very nice numbers, but something is not right.

The first thought which must cross anyone who's 'in the know' must be, why are these numbers so much higher than the other twin-screw dyno sheets? For those who study various dyno sheets of similar hardware configuration, one learns what the trends look like; likewise, since one learns the trends, it becomes rather easy to spot the outliers, and this dyno is one of those cases.

So why did the dyno report such an outrageously high number with respect to the other 928 twin-screws?

Take one look at the 'Red' SAE correction factor: 1.16
..whereas the 'Blue' SAE correction factor is 1.01, a much more reasonable number.

Just for kicks, let's 'un-correct' the 'Red' peak horsepower number, and then use the 'Blue' SAE correction of 1.01 to see what the rwhp would hypothetically be.

First we'll find the 'non-corrected' rwhp number:

Non-Corrected rwhp = rwhp / (SAE correction factor)
Non-Corrected rwhp = (471.74 rwhp) / (1.16) = 406.67 rwhp

Now let's find the 'corrected' rwhp using the 'Blue' correction of 1.01:

Corrected rwhp = (Non-Corrected rwhp) x (SAE correction factor)
Corrected rwhp = (406.67 rwhp) x (1.01) = 410.74 rwhp

The 'hypothetical' 411 rwhp is a much more reasonable number given the trend set by previous 928 twin-screw dyno runs.

So what happened? Why did the 'Red' dyno get a *HUGE* 1.16 SAE correction factor?

Look at Red's barometric pressure: 26.10 in-Hg. You may say, 'What's the big deal?' The 'big deal' is, the lowest barometric pressure EVER RECORDED in the Western Hemisphere was 26.84, and that was during Hurrican Camille in 1969! Go here and see for yourself:

http://www.geocities.com/hurricanene/gulfcoast.htm

So unless the car was dyno'd during a hurricane more powerful than the most powerful hurricane all-time, Hurrican Camille in 1969, it is IMPOSSIBLE for the car to be dyno'd with a barometric pressure of 26.10, and that barometric pressure was used to come up with the correction factor of 1.16.

The punch-line is, that dyno run for whatever reason has an invalid SAE 'Correction Factor'. The good news is, the dyno sheet itself provided us with enough clues to solve the 'mystery'. If it were me, I would go talk to the dyno operator/owner and see what's up with their equipment.

Interestingly enough, here's a recent post discussing whether dynos provide reliable results:

https://rennlist.com/forums/928-forum/214013-aftermarket-cam-grinds-for-4-valve-motors.html

all4woody

Can't answer why the settings are different. I will stop by the dyno next week and ask. Andy Keel was working with me at the dyno (more like I was looking over his shoulder), and I am going to his local dyno next week. We will see if the number jive.

Shane

Just so happens that there is a Hurricane in the works and He does live in Alabama. Could still be off some but maybe not.

Lagavulin

No, I don't think so: current barometric pressure is 30.02 in.

http://www.weather.com/weather/local...om=search_city

m21sniper

Derek 86.5: "Arent the torque and HP curves supposed to intersect at 5250 rpm?"

They do.

Top chart is HP, bottom chart is torque.

If you look at each chart they're in the same spot at 5250rpm, about 410 hp/lb-ft.

m21sniper

Lagavulin: Good eye for detail bro.

Corrected for atmo pressure at SL the correct baro reading is 32.16, so it's safe to say the above dyno runs are wildly optomistic.

Hence my problem with dynos.

It's obvious that using the same multiplier for both runs he still made gobs more power than stock though.

Take it to the dragstrip and then use the ET/Trap formulas of your best runs and average the two. You'll know within about +/- 5hp how much you're actually effectively using.

Shane

Ok give it another 12-14 hours then maybe it will be right?

all4woody

It was also 105 degrees in the shop. I think it was discussed and decided not to correct for biometrics, but I will have to check. I plan on going to Atlanta next weekend to finish tuning, so I will have another shops dyno results. I am curious to see the difference myself.

Lagavulin

Thanks. 'Z' is the one who came up with the hurricane stuff.

One could look at it that way, but not me. Those results clearly showed something was not right, and the dyno-sheet 'ratted' on itself by reporting the bogus barometric pressure. The real question is, where did that barometric number come from?? That number stands out like a sore thumb, and makes one wonder...

Using your reasoning, the next time you get a flat tire, are you going to forgo using rubber-based tires, and install wooden-spoked-wagon-wheels instead because they'll never lose any air? I don't think so since you'll examine why you got the flat, and subsequently avoid construction sites and their nails lying all over the place. It's the same thing with this dyno: all the clues were right there.

No doubt!

As I stated before, drag times are an excellent performance metric. However, for meaningful comparisons from around the world, there are so many variables from track to track such as types of surfaces, whether those surfaces are clean, resulting traction, driver skill, fresh/old tires, clutch condition, etc, etc, etc, whereas SAE dyno run is just that, an SAE dyno run, with none of the problems encountered at a track, making comparisons meaningful from location to location. The run made in this thread is NOT as SAE dyno run, and is obviously so.

bcdavis

I totally agree....

Dynos have much less variables, and they can be corrected.

There are far too many factors in a drag race. Vehicle weight, driver weight, driver skill, tire type, tire diameter, track conditions, etc... It's impossible to correct 1/4 mile times to accomodate those factors. But a dyno chart is pretty easy to compare... It will show what power you have, then it's just up to you if you can use it properly, and actually get good times...