996 Turbo / GT2Turbo discussion on previous model 2000-2004 Porsche 911 Twin Turbo and 911 GT2. Sponsored By Vivid Racing
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Yes Joe, I did brake boost, afterall, no rules in street racing My 6.2 was done an a 55deg night wth drag radials, you know almost perfect...But my car consistantly traps 129-130.
In all my years of dragracing, I have never been able to figure out why a better 60ft (or brake boosting) for that matter doesn't increase trap speed as you technically are going a faster MPH sooner and can gain more speed sooner? Mysteries of life?
The below was written by Carver a few years ago and I had it posted along with the 1/4 mile list for a couple of years (I only removed recently).
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Originally Posted by Carver
My education and background is in mechanical engineering, working in the past for Borg-Warner as an ME and currently write financial market algorithms for index mapping software on the side in addition to my day job.
Quote:
Originally Posted by Carver
Scott and I were talking about why so many of the calculators out there are wrong. After looking at the data and the formulas, I came to the conclusion that it was an issue of the formulas being written too closely to theory and without adjusting the assumptions by taking enough real world data into account. A simple way to see this is through a graphical analysis of data points. If you look at the Hale formulas along with the graphical points shown below, you can see that a) the formula is close, but needs slope and curvature adjustments to be more accurate, and b) there aren't enough points from a variety of vehicles to represent the outcome within a reasonable statistical confidence window for most cars. What I did was include many more data points from multiple vehicles and graph the results next to the Hale equation lines. I then rewrote the algorithms to more closely represent the real world graphical results. These formulas now work well for street vehicles in the 50-1000bhp range. Adjustments to the algorithms would have to be made for pro drag vehicles that can transfer launch energy at a statistically abnormal rate.
Regarding the trap speed vs. e.t. discussion, there are multiple ways to visualize what is happening to make it more clear. And to be fair, both sides are correct for their given questions. The problem is that the specific question in each case is not clearly defined. Think of the difference as transferred energy to the ground in time (e.t.) and transferred energy over distance (trap speed), which are two very different ideas, as we’ll see. If it weren’t for launch energy transfer and tire capabilities ie. all of the power/energy could be transferred on the launch immediately with consistent accuracy, we wouldn’t be having this discussion as e.t. would be as representative as trap speed. But that’s not the real world.
The force available to accelerate a vehicle from a stop to the first 30-60ft. is mostly based on traction or g-force capability. That’s why a mid-hp car can have similar 60ft. times to a very high-hp car. It’s not a good indicator of hp since the max g loading of street tires is around .5-.6g no matter what you do. In first gear along with a revved engine (significant stored flywheel/crank/piston/rod/pressure plate energy) most cars have the ability to generate .5-.6+ g or break the tires loose for some distance. That’s why as one car may hook better than another, they’re still limited to approx. .5-.6g on the launch….this enables a car that has spun its tires or bogged off the line to essentially re-match the other car’s acceleration and speed, at a given distance within the .5-.6g exceedance zone, very quickly since in the lower gears it’s a traction issue and not a power issue. Notice I said speed at a distance and not speed at a time. The time already left the station, so to speak, the distance didn’t.
And here is where people get the disagreement. The time measurement is a constantly moving reference which is unaffected by the car’s performance. But distance is not ie. as you are slower than another car, you have more relative distance left but not more time left. So if you make a mistake on the launch ie. excessive spin or bog, that time measurement will be permanently changed because time marched on unaffected by your mistake. But your rate of distance coverage was changed and reduced giving you some distance to make up the mistake. And in addition, the distance where the loss took place is approx. 3% of the distance of the race, and a distance where max power could not be transferred due to the .5-.6g tire limit….as a result, speed at a snapshot time ie. 2 sec., with time continuing at the same rate, was affected but speed at a distance past the spin/slip zone, with distance traveled reduced, along with the ability to rematch .6g quickly, had little to no change. If the tire spinning/bog continued much beyond the zone where the car could no longer exceed .5-.6g acceleration, then you would start to see the reduction in trap speed in addition to the increase in e.t. as overall avg. power over distance would start being affected. But since it takes place in this “.5-.6g max zone”, the speed at time is changed but not the speed at distance. This is why e.t. is significantly affected by launch and trap speed isn’t.
Now here is where it all comes together. Both cars weight the same. Car A runs a 1.7 60ft. and turns a 12.2 @ 120mph. Car B runs a 2.0 60ft. and 12.6 @ 120mph…..what happened? Car A got a better launch enabling a .3sec better 60ft., but car B had an extra .3sec at .6g to accelerate up to car A’s speed at the 60 ft. They were both going approx. the same speed after the 60ft., although car A reached that speed in less time, but the same distance, and have the same whp because they accelerated together after that point. Car A was able to transfer more avg. power to the ground over time ie. in 12.2 sec it had traveled farther and reached 120mph quicker but at the same distance as car B (the difference in time being in the launch energy transfer) although car B was still able to reach 120mph in the ¼ mi. distance ie. the same total power transfer with respect to distance showing whp and not transferred whp over time. So as has been stated before, if you take the .5-.6g launch window out of the equation, and compare cars from say a 3rd. gear roll, you might as well throw away the e.t. too and go by trap speed because the e.t.'s variables are no longer in play.
1-1.2g (.5-.6/tire) and in this case a total of 1.5g of thrust....and the car is still losing traction in second gear. This is what causes e.t. to be launch dependent, or responsible for a time loss, and not responsible for a trap speed loss. Consider for a second the main point that I illuded to but didn't explain well enough in my previous post. Speed curves over distance look like 1/2 parabolic curves ie. they start off steeply vertical and than begin to shallow and converge at an asymptote as distance passes, with speed on the Y axis and distance on the X axis. One more way of saying this is that the whp of a vehicle is most influential to a car's acceleration as speed increases ie. as a greater percentage of the distance of the 1/4mi. elapses, the launch becomes a smaller percentage of the performance, and drag, and as a result whp, becomes the most significant factor. This favors a confluence or matching of trap speed, or speed at a given distance, for a given wt/whp and a lessening of the effect of the launch. This effect continues to build, throughout the run, obviously, since on a percentage basis the launch distance/total distance traveled, is decreasing at an increasing rate as speed increases while time of launch/time of run is decreasing at a fixed rate as time elapse rate is constant. This causes the et differences at the launch to be maintained while the trap differences at a given point or speed at distance tend to merge. That is your key.
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Great information. I just hoped that the car with the Tial GT28 "Alpha" turbo's was a 6-speed, so we can get a better overall view. Thanks for sharing.
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2001 TT, EVO GT700 , 9ff modified Tiptronic transmission, GT-2 Intercoolers, EVO Silicone Boost Hose Conversion w/ Diverter Valve "F" Hose, Bilstein PSS9 Coilovers, H&R swaybars (front & rear), carbonfiber strut bars, MA Shaw carbonfiber front hood, 9ff carbonfiber mirrors, MA Shaw GT-2 rear wing w/carbon wing blade, TechArt side intake inserts, 18" Champion Motorsports RG5 Wheels.
I think what Scott was saying is that you can compare the two different setups, but it should be expected that a car running meth or race gas with advanced timing is going to be faster.
For this reason, the data may be accurate, but one car has a known potential advantage, so it should not be a surprise.
It can be expected that one car is faster then another for any comparison...different mods/tunes (even different cars for that matter)...but that doesn't mean one might be surprised by an outcome or disqualify results b/c of different factors.
I understand the argument of meth being similar to race gas and people not wanting to compare one car on race fuel vs. another car on pump fuel. I just don't completely agree with it (it being pump+WI vs. pump....not race vs. pump) b/c if a comparison was done with race fuel in both cars but one had meth I doubt the unfair fuel advantage arguement would be applied...
Regardless of my view, this thread has sparked some interesting points and conversation.
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It can be expected that one car is faster then another for any comparison...different mods/tunes (even different cars for that matter)...but that doesn't mean one might be surprised by an outcome or disqualify results b/c of different factors.
I understand the argument of meth being similar to race gas and people not wanting to compare one car on race fuel vs. another car on pump fuel. I just don't completely agree with it (it being pump+WI vs. pump....not race vs. pump) b/c if a comparison was done with race fuel in both cars but one had meth I doubt the unfair fuel advantage arguement would be applied...
Regardless of my view, this thread has sparked some interesting points and conversation.
of course it has and the interest was sparked well before this thread. The point is that it is harder to compare two "builds" when taking WI or race fuel into account. And then to compare them to factory supercars like the Veyron. Factory supercars aren't running race tune or WI tune. They run pump. It is easier to compare one tuners built to another on pump than on different types of race fuel. Pump gas tune is a pump gas tune, and this will tell us how everything else works together.
makes lots of sense.
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No , The 1 bar k24/18g car is mine. Yes this time we ran multiple times with the GT28 car and the results are even. The other car is Jason's K24/18g with injectors running 1.2 bar file which pulls 1 car on the Gt28 on a roll race.
We havent met up with O Ace yet.
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2003 911 Turbo,997 SSK, EPL Tuned K24/18g,71 lb injectors Milltek Sport Exhaust.
2005 BMW X5 4.4l
2002 Jeep GC
I did not brake boost in my 60-130 run...And it was with street tires...i will try it to see the differences...However i am not sure if ECU mod is needed in order the DME to allow boosting while braking...
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'04 996TT 60-130:6,32sec!!! K24/18g,upgraded WGs,RC 60lb inectors,Fabspeed headers,remus exhaust,AP blow off valves,AP hoses,AP intercoolers,964RS single mass flywheel,Sachs carbon clutch,custom PSS10,GT3 Sway bars,AP drop links,GT2 allignment,BMC filter,Greddy boost controller,Dymag CF wheels...All from Vivid Racing...fine tune by Salias...
'02 996C2C (sold)
'04 986 Boxster S (sold)
...However i am not sure if ECU mod is needed in order the DME to allow boosting while braking...
FYI, I didn't think my car allowed brake boosting because if I was on the gas and hit the brakes, it seems the throttle was being cut off.
What I found was that if I come completely off the gas (foot off completely), hit the brakes and then apply throttle, the car will allow brake boosting.
Damn that Tony character is a bad ass... Taking time in Europe to answer all of our questions If only his iPhone had tethering like mine so he could rack up a huge phonebill and not have to pay a hotel for net Wait next time I'll just use the hotels internet LOL!
Damn that Tony character is a bad ass... Taking time in Europe to answer all of our questions If only his iPhone had tethering like mine so he could rack up a huge phonebill and not have to pay a hotel for net Wait next time I'll just use the hotels internet LOL!
What are you talking about? Im on AOL dial up from my hotel room....dialed into an NYC number.
My 6.2 was done an a 55deg night wth drag radials, you know almost perfect...But my car consistantly traps 129-130. 
If only his iPhone had tethering like mine so he could rack up a huge phonebill and not have to pay a hotel for net 
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