Stummel

Hi AZ,

Not bad at all.

If you read the posts of Bill and TB you will see that speedo video times and "real" times measured with an AX22 are a good second too optimistic.
I think your 930 could do a 9 sec 100-200kph run.

The stock 930 did 100-200kph between 13 and 15 seconds.
What is your (real) hp and torque?

AZ930

My car has pretty basic mods but is lightened up a lot. Here is the info and video http://web.mac.com/zpruett/iWeb/Site/930.html
I would like to do it again without my girlfriend filming and our luggage in the boot. She is not the best camera person LOL . I think there is room for improvement on my time but we had the camera handy so what the hell.

TB993tt

Nice little web site:
http://web.mac.com/zpruett/iWeb/Site/930.html

I need some of these magic cams
Frank threw in some billet 964 cams which increases low end and also top end power

Red rooster

Bill,
Reason I asked the rpm question was that at one time I used to calculate optimum shift speeds for race cars.
To do that you multiply the torque curve by the gear ratio and then overlay .
The answer in 1st, 2nd was always the rev limit . Further up the box the answer was not the same ! All to maximise the area under the curve.
Maybe a few 1/10ths are available by slightly short shifting in the higher gears?
The sums will show if this is true .
If you put a straight edge on your graph results for each gear you can see the torque curve , much bigger variation than the Ferrari , which is what you would expect.

TB993,
To get to DIN corrected bhp you also need the barometric pressure . 1013mbar is the standard figure.

This is getting really serious !!!

All the best

Geoff

TB993tt

Geoff
Am I right in my assumption that the pressure variation has a much smaller effect on the size of the DIN correction factor (compared to temperature) ?

Edit
Just checked the dyno data, at 30DegC and 959mbar the CF is 1.074, a drop of 1 mbar (at 30DegC) to 958 changes the CF to 1.075.
With temperature, at a constant 959mbar rise in temp from 30 to 31DegC increases the CF from 1.074 to 1.076
I am guessing the relationship between the CF and the temp or pressure is not linear ?

Bill S.

Geoff, I'm not sure. Some people think so. Ruf says the fastest times can be had by shifting at 7200. He says that's the way the engine is designed with the cams and turbos.

LAT

Red,
I am not clear on the methodology of calculating shift points, could you give an example.
Thanks
LAT

AZ930

Thanks. The 964 cams gave me a very small bump in power in the low end and a lot more on the top end.

Red rooster

The motive power to drive the car is the torque times the gear ratio .So if gear 1 has a ratio of 1.1:1 and gear 2 has a 1:1 ratio ,the gear 1 delivers 10% more torque to the wheels.
Say the motor torque @ 6364 is 100nm and at 7000 is 90nm .

At a road speed where the motor is doing 7000 rpm in gear 1 , torque to the wheels is 1.1 X 90 = 99 nm

If you change to gear 2 the motor revs become 7000/1.1 = 6364 and torque to the wheels becomes = 100nm = faster!!

With high rev N/A motors the torque can fall off pretty quick near the rev limit so, depending on gear ratios , the red line is not always the best shift point for maximum performance .

I have never done the sums for a 993tt motor and maybe it doesnt matter but when you are looking for 1/10ths every possibility should be checked ?


The temperature correction is

Pcorrected = Pmeasured x { temp ( C ) + 273 } / 293

So for 30 deg C 30 + 273/293 = 1.034

Relying on memory , always dangerous ! , I believe that the pressure correction is just 1013/ ambient pressure.

So 1013/959 = 1.056


Something to think about ?

The Canadian Grand prix is calling !!!!!!!!!!!!!!!!!!

Geoff

Red rooster

TB993tt,
Whoops . I said I was relying on memory . Must not do that !

The pressure compensation is 1013/ ambient mBar.

Temperature is [ {ambient ( deg C ) + 273 }/293 ] 0.5 .

In other words ambient + 273 , divided by 293 , then square root the result.

Forgot the square root , as you do.

That is DIN70020.

So 30 deg C Square root 303/293 = 1.017

959 mB 1013/959 = 1.056

Correction Factor = 1.017 X 1.056 =1.074

That low pressure has more effect than temperature on power.By the way, 959 mB is a very,very low reading . That was a bad day for power measurement .

All the best

Geoff

TB993tt

Geoff
Thanks for the clarification, I was going to question it, but a hangover and England match took my eye off the ball
Very interesting, and thanks again for the explanation.

Jean

Interesting topic Red Rooster and thanks for sharing the formulas!

There is a lot of reading that can be done on the net about this subject of performance vs temps vs. pressure...

If I may look at this from a bit more practical POV, HP is proportionally impacted by air density and air density is a function of pressure(altitude), temperature and humidity. Humidity has a much more limited impact on performance and can be somewhat disregarded, DIN 70020 standards use dry air for the conversions.

Here is a calculator by Longacre that will let you have some fun with the calculation of air density if used creatively, I use it quite a bit and find it very simple while maybe not the most accurate out there.

Air Density Calculator

Here are some examples:



Once you have the density calculation sorted you simply apply the following:

New HP= Old HP x (New density/Old density) or for practical purposes here: New HP= Old HP x (New correction/Old correction)

Assuming the stock 993TT HP was measured at sea level (29.92in.Hg) and 59F at the factory, then the following measurements will be noted with temp or pressure changes:

1) 86F temps and sea level, your new HP will be:
New HP= 408 x (95.0496/100)= 388HP
2) 86F and 28.3in.Hg. pressure (approx. equivalent to 1500ft altitude)
New HP= 408 x (0.89903)= 367HP

And so forth.

One needs to keep in mind that turbocharged engines are not very impacted by pressure changes as N/A engines, I would not know how much, but usually adjustments are disregarded below 1000ft altitude.

Red rooster

Jean,
The factory will use DIN70020, 1013mbar and 20 degrees C .

Quick temp. conversion 20 C = 64 F ( long time since I thought in degrees F ! )

I have no idea what the conversion from inches Hg to mbar is ?? Do you ??

Interesting that the 959mb pressure would mean a 6% drop in power as that is 30bhp for the 500 bhp motor. Or does the system + turbo reclaim most of that ?
With the performance tests being done it looks like the ambient conditions could be playing a major role in the outcome.
Wait for a really high pressure day and do a run in the evening when the temperature has dropped ! Easy +50bhp !!

All the best

Geoff

Jean

Geoff, the above 408 BHP@29.92 and 59degrees F inches was just an example, not what the factory uses, which is indeed DIN 70020

1013Mb = 29.92 Inches of Hg. aprox.

I think that temperature affects much more than pressure these engines, I would not really worry about outside pressure as much as temperature. Also, I don't think that if you go to very low temperatures you will be getting more HP, since the AFRs will not be optimized to the parameters under which the engine was tuned if it was done at, say, 20 degrees C. AFRs will change with air density and its content in O2 of course.

Bill S.

Here's the much anticipated run for a CGT. Our fastest run only hit 128.5 MPH, so 60 to 130 is about 9 seconds.

Factor-in the two people, .4 second shifts, and a slightly bumpy road, and we could get closer to 8 seconds. I'm not sure how some US mags, like Car & Driver, got low 7s. We just don't see this on the street or track, and the AX-22 doesn't show this either.