What is the RPM at the Top Speed?

[Specracer]

At these speeds everything increases exponentially, force it takes to propel through the air, tires rotating forces, heat, etc. I had the honor to talk at great length with several of the engineers at the rally, about suspension, tires, pads etc. A few notes: the reason for the 205 limiter is because that is the highest rating ford and good year would certify. These tires were specifically designed for the car. There was extensive lab testing as well road situations to get the certification. As for lighness at speed, as mentioned the top speed was 212. The car at speed will produce a couple hundred pounds of down force, why not more? Because you would have to carry a spring rate that would not really be streetable to most drivers, or the car would bottom out.

Weight, my car was 3437 (has mac and optional wheels but otherwise stock) with, if I remember, about 1/2 tank of fuel (loosly gas is about 8 lbs per gallon). Measured with a set of longacre 4 pad scales, rear was 56.7 of the total weight.

FWIW, I am sure MANY compromises were made in the design of the F1 tire, which included, the ability to certify to 205. Tread life, imagine the threads here if you only got 1000 miles out of a set of skins, or 6 heat cylces? Remember the NSX lawsuits against Yokohamma? Cost, I read in one of the mags that a set of tires for the veyon is $15,000 (runflats with monitoring is something like $40k?) The heat at these speeds kills tires. Everything is a balance, top fuel dragsters can't turn, but F1 cars can't cover the quarter mile in 4 seconds, but both are cars. Each make compromises to be the best at what they are designed for.........

 

[Hennessey Performance]

Many talk about how they could take down the Veyron, etc. I say its far easier said than done. 4400 lb cars that run 10.3 @ 144 mph on street tires with full pressure on non-prepped non dragstrip surface running 91 octane likely have some advantages that go along with a 1.4 mil price tag. sure i think i can beat one too, but if i did beat it, it would take 3/4 of a mile or more to catch it and pass it.

 

[BlackICE]

Many talk about how they could take down the Veyron, etc. I say its far easier said than done. 4400 lb cars that run 10.3 @ 144 mph on street tires with full pressure on non-prepped non dragstrip surface running 91 octane likely have some advantages that go along with a 1.4 mil price tag. sure i think i can beat one too, but if i did beat it, it would take 3/4 of a mile or more to catch it and pass it.

John, you are being so modest. Here is what Motor Trend said about one of your Vipers:

The Hennessey Viper did a better than expected job of clawing for traction with PS2 radials as it hustled to an 11.7-second e.t. However, full throttle can't be used until mid-third gear or the PS2 rear treads turn to molten goo. (Check the graphic below right to see how hard we worked just to keep it straight.) Wearing BFG Drag Radials, things get better for the twin-turbo coupe as times improve to 10.5 seconds at 152.6 mph. About a year back, we tested a similarly prepped Hennessey Viper convertible that ran a 9.5-second e.t. on slicks.

With drag radials you are only 0.2 behind in the 1/4 but going 152.6 vs. 144 you would pass it before the 3/4 mark. With slicks you beat it in the 1/4. Of course that is not a fair comparision. Who said car racing is shoud be fair. Is it fair the other car cost more than 1 million more?


From http://www.motortrend.com/roadtests...upe_comparison/quarter_mile_test_results.html

 

[californiacuda]

The Gt 's rear bias weight has a big advange over the Viper on initial launch. With substantially less hp(650) and same tires the Gt substantially out launched the 1000+ hp TT viper in the 1/4 mile by almost a second if I remember correctly.

 

[kumar]

The Pirelli Pcorsas are very sticky, I believe the wear rating is below 100, and they also have a very high speed rating. They are an example of a tire that would be very helpful for a good launch and stability at high speed.

Now, if Joe chose not to use something like the Pirelli's, that's his prerogative. But they provide substantially better tire to road friction than the stock tires, something that is needed for a good launch with a higher hp Gt and a superior 1 mile time compared to the Veyron.

If the Pirelli came in a 40 sidewall, possibly. Ive found that a big sidewall is almost as important as tire compound and more important than the width of the tire.

Im not changing the tires on my GT unless someone else comes out with a sidewall as big. The Hoosier is not street friendly enough.

 

[RALPHIE]

Speed/Acceleration

This is and will continue to be a great discussion. Thought I would throw my 2 cents in...

FRPP is coming out later this year with a smaller supercharger pulley (higher boost) and a reprogramming of the ECM and claims that, with the rear exit headers and exhaust, will boost the vehicle to 700 bhp and 650 lb-ft of torque. I think this power level might be capable of pushing the car to near red-line in 6th gear, with the limiters removed.

Yet, I for one, do not intend to remove the speed limiters, as I'm not willing to take chances on tires and ground effects that have not been tested or proven. Just the sticker that advises tire pressures be increased to 40 psi for continued speeds over 150 mph is a warning in itself, as the tires will heat considerably higher at these pressures, notwithstanding the variations in road (or track) conditions' and compositions' effects on the frictional forces against the tires.

Suffice it to say that as I have the pulley installation and reprogramming performed (I already have the exhaust) that I will be happy to have the increased acceleration and throttle control provided by the additional power and torque which will get me to the next corner faster, rather than worry about the final top speed which would be attainable with the power. I can't think of any domestic road courses where this would be possible anyway, and to take such a chance on an open road is foolishness - all it would take would be a rabbit or squirrel to destroy a beautiful piece of machinery.

I will like the resulting quickness and will be happy to stay within the design limits of the tires and aerodynamics.

Ralphie

 

[Kirby Vieira]

Well said Ralphie. The sky ius more forgiving for test pilots than a highway.

 

[californiacuda]

Hennessey understands the significance of tire to road friction. He was specific about tire compound, road conditions and tire pressure.

When the Ultima set the record for "production" vehicles in a 0-100-0 run, it was performed on a 1/4 mile track. Who knows how sticky the track was, can make a big difference.

 

[CobraChamp]

Hennessey understands the significance of tire to road friction. He was specific about tire compound, road conditions and tire pressure.

When the Ultima set the record for "production" vehicles in a 0-100-0 run, it was performed on a 1/4 mile track. Who knows how sticky the track was, can make a big difference.

CalCuda- As an owner of a Ultima GTR, I would like to correct your point about the 0-100-0 test being conducted on a drag strip. Here is the exact email I received from Richard Marlow regarding this point:

"Hi Paul,

Our 0-60mph, 0-100mph, 100mph-0, 0-150 mph etc etc world record times were definitely not recorded at a drag strip, as otherwise they wouldn't have qualified as official verified road car world records. They were achieved at official vehicle testing stations called MIRA and Millbrook in the UK where all road cars are officially figured. (www.mira.co.uk and www.milllbrook.co.uk)

All of our world records had an official guiness book of records timekeeper present whom ensured that the test was conducted independently in a fair and proper manner.

Incidentally having had a brief look at the GTM article in Car and Driver magazine, I noticed that it stated that the GTM was fitted with what was described in the article as "grippy DOT race tyres". These would have been prohibited for any official road car world record performance and lateral g runs as they are considered unfair by the timekeepers.

Best Regards

Richard"

Thanks,
Paul

 

[californiacuda]

With modern car engines able to generate so much torque, the issue with acceleration on road surface with "street" tires is FRICTION.

The Ultima's time for Guiness has not been repeated by any other Ultimas, many with substantially more power.

For the Ultima to get the time that it did, the friction coefficient of the tires would have to approach 2. A number that is not obtainable with a street set up. I can go through the physics if you would like.

My guess, is that the tires were pre-treated with tire friction compund such as VHT to increase friction.

Just as with Cold-fusion a few years ago, for a result to be valid, it must be tested and repeatable. I would like to see other Ultimas similarly equiped match the outcome, before I believe the result to be valid.

 

[B O N Y]

thanks cuda

 

[satx]

...

FRPP is coming out later this year with a smaller supercharger pulley (higher boost) and a reprogramming of the ECM and claims that, with the rear exit headers and exhaust, will boost the vehicle to 700 bhp and 650 lb-ft of torque. I think this power level might be capable of pushing the car to near red-line in 6th gear, with the limiters removed.

sorry but ~650rwhp will not push a GT or any other car to 260MPH. With ideal gearing you would be lucky to see 230. It would take a minimum of 1000rwhp to reach 260 in a GT under ideal conditions. Notice that it takes Veyron HP to reach Veyron speeds. At 200+ it is all about aero and HP weight is irrelevent.

 

[HHGT]

sorry but ~650rwhp will not push a GT or any other car to 260MPH. With ideal gearing you would be lucky to see 230. It would take a minimum of 1000rwhp to reach 260 in a GT under ideal conditions. Notice that it takes Veyron HP to reach Veyron speeds. At 200+ it is all about aero and HP weight is irrelevent.

Don here on the forum hit 235.4 mph w/ the TT Hennessey. I do not believe he did any gearing change.

 

[BlackICE]

Here is a chart showing required horsepower vs. top speed. The assumptions made are that a stock GT makes 500 RWHP and was geared optimally when Mark McGowan made the 212 MPH Nardo run and that any changes in HP are matched with optimally gearing changes.

Here is a table showing RPM vs. speed for both the stock rear end at 3.36 and the optional Stillen's gears at 3.90

 

[CobraChamp]

With modern car engines able to generate so much torque, the issue with acceleration on road surface with "street" tires is FRICTION.

The Ultima's time for Guiness has not been repeated by any other Ultimas, many with substantially more power.

For the Ultima to get the time that it did, the friction coefficient of the tires would have to approach 2. A number that is not obtainable with a street set up. I can go through the physics if you would like.

My guess, is that the tires were pre-treated with tire friction compund such as VHT to increase friction.

Just as with Cold-fusion a few years ago, for a result to be valid, it must be tested and repeatable. I would like to see other Ultimas similarly equiped match the outcome, before I believe the result to be valid.

CC-Please show me the physics, so I can have my son (a Mechanical Engineering Major at UC-Irvine) review your logic.
Thanks,
Paul

 

[BlackICE]

v = velocity in ft/sec
a = acceleration in ft/sec**2
t = time in seconds

v = at**2 so a = v/(t**2)

100 mph = 147 ft/sec

a = 147/(t**2)

solve using t for 0-100 and t 100-0 and I think you will find a > 32 ft/sec**2 which is one G. Using street tires without down force will be hard press to get much over 1.1G

Have fun.

 

[californiacuda]

Here goes.

The Ultima GTR weighs 2200 lbs, has a 100 in wheelbase, a 40-60 weight distribution, and an estimated center of gravity of 15 in.

Standing still, 60% of 2200 lbs = 1320 lbs of weight is over the rear tires.

But, when the car accelerates, weight is transfered from the front to the rear at a rate equal to: the center of gravity (15 in) / wheel base (100 in) x the gravitational acceleration (approximately 1 G or 32 ft/sec) x the weight of the car (2200 lbs). This weight transfer is around 330 lbs.

So, there is 1320 + 330= 1650 lbs of force from the rear tires pushing on the road, and the road pushing against the tires. The tire friction coefficient determines how much maximum force or torque can be applied from the weight over the rear wheels to the road surface. If the tire friction coefficient is 1 then 1650 ft/lbs of torque can be put into tires. any more than 1650 ft/lbs and the tires ability to grip the surface will be exceeded.

I looked up numbers for street tire to road friction and found no numbers higher than 1.2.

So for the GTR, the maximum weight over the rear tires including weight transfer is 1650 lbs x (a very generous 1.2 friction coefficient) equals 1980 ft/lbs of torque that can go through the tires.

The car weighs 2200 lbs divided into 1980 = .9 g's as the maximum acceleration possible.

In GTR's publication, they state that the car went 0-60 mph in 2.8 seconds. During the run, 1 shift was required. A time of .25 seconds is a very, very fast manual transmission shift time.

For the purpose of this analysis, the .25 seconds should be subtracted from the 0-60 time because during the shift, no acceleration was possible, allowing for only 2.55 seconds for the tires to accelerate the car.

60 mph is equal to 88.2 ft/sec. the car went 88.2 ft in 2.55 seconds = at a constant acceleration rate of 34.5 ft/sec, 34.5/32(1 G)= 1.08 G.

The GTR accelerated at .18 g's faster than should have been possible.

The correct minimum time for the cars acceleration = change in velocity/ change in time, with a little manipulation gives us change in time= change in velocity/ acceleration, t=88.2 ft/(.9 g's x 32 ft/sec)= 3.06 + .25 shift time = 3.31 sec.

The only possible answer for the 2.8 0-60 time was that the tire to road friction was substantially higher than anything ever recored with street tire on a standard road surface.

They say they are using the same tires that we all might use, than how can they get more friction than anybody else??????

 

[CobraChamp]

CC-That is a great explanation! I don't know where you got a required CoF of 2 in your first post, but it really makes me wonder about their results too. I have to admit, I've never seen the type of the tire they used which makes me wonder. The fact that Guiness Book was there tells me the time was real, but since Guiness Book folks aren't "car" guys, I wonder if there was some gaming done with the tires, or something else, as you suggest. There are so many unbelievable cars around that these acceleration times that everyone hangs on are almost irrelevant. I've driven many GT's and other high performance cars at Willow Springs and a tenth here or there is ridiculous for the average guy. By the way, if and when, I sell the GTR, I will get a Ford GT.

Great explanation. Thanks!
Paul

 

[Neilda]

Here goes.

The Ultima GTR weighs 2200 lbs, has a 100 in wheelbase, a 40-60 weight distribution, and an estimated center of gravity of 15 in.

Standing still, 60% of 2200 lbs = 1320 lbs of weight is over the rear tires.

But, when the car accelerates, weight is transfered from the front to the rear at a rate equal to: the center of gravity (15 in) / wheel base (100 in) x the gravitational acceleration (approximately 1 G or 32 ft/sec) x the weight of the car (2200 lbs). This weight transfer is around 330 lbs.

So, there is 1320 + 330= 1650 lbs of force from the rear tires pushing on the road, and the road pushing against the tires. The tire friction coefficient determines how much maximum force or torque can be applied from the weight over the rear wheels to the road surface. If the tire friction coefficient is 1 then 1650 ft/lbs of torque can be put into tires. any more than 1650 ft/lbs and the tires ability to grip the surface will be exceeded.

I looked up numbers for street tire to road friction and found no numbers higher than 1.2.

So for the GTR, the maximum weight over the rear tires including weight transfer is 1650 lbs x (a very generous 1.2 friction coefficient) equals 1980 ft/lbs of torque that can go through the tires.

The car weighs 2200 lbs divided into 1980 = .9 g's as the maximum acceleration possible.

In GTR's publication, they state that the car went 0-60 mph in 2.8 seconds. During the run, 1 shift was required. A time of .25 seconds is a very, very fast manual transmission shift time.

For the purpose of this analysis, the .25 seconds should be subtracted from the 0-60 time because during the shift, no acceleration was possible, allowing for only 2.55 seconds for the tires to accelerate the car.

60 mph is equal to 88.2 ft/sec. the car went 88.2 ft in 2.55 seconds = at a constant acceleration rate of 34.5 ft/sec, 34.5/32(1 G)= 1.08 G.

The GTR accelerated at .18 g's faster than should have been possible.

The correct minimum time for the cars acceleration = change in velocity/ change in time, with a little manipulation gives us change in time= change in velocity/ acceleration, t=88.2 ft/(.9 g's x 32 ft/sec)= 3.06 + .25 shift time = 3.31 sec.

The only possible answer for the 2.8 0-60 time was that the tire to road friction was substantially higher than anything ever recored with street tire on a standard road surface.

They say they are using the same tires that we all might use, than how can they get more friction than anybody else??????

Brain full.

Am I the only one with a nose bleed here? :biggrin

 

[tpraceman]

If I read that graphh right, Torries car would dang near beat our Cessna 340 twin turbo. :willy

Time to step it up and get a Jet..........first win the lotto........for the fuel:ack