Okay. I understand that the SRT-6 tops out at 158. Now, I think, from what I've read, that the limited and base top out at 155. So, will the SRT-6 only go 3 MPH faster than the others? Please correct me if I am mistaken.

 

only because it's limited to 158. if there was no limiter i'd say it could go faster.

 

Sure doesn't seem like much of a difference. But it's how you get there that
matters. The SRT-6 will be at 158 while the Limited is still passing through
70 mph. That might be a little exaggerated, but not much.

Coyote

 

i took mine out the other night and i got my speedo up to 165 are you sure they are set at 158. and i'm 100% sure it was at 165 and not 155.

 

~ almost all speedometers read higher mph than actual... especially true at high speeds. 10 mph greater than actual mph at the speed is about right.

 

I think that's extremely exaggerated.

 

At the 6200 RPM redline the SRT6 should top out at about 188 while the non-SRT6 should top out at about 178 if there was no electronic limitation on the speed. The top speed doesn't depend on the supercharger, only on the engine RPM, transmission and differential ratios, and rear tire diameter. For any given RPM, the SRT6 should be about 6% faster (3.25/3.07) since only the differential ratios are different (I'm assuming the transmission is the same). The supercharger just helps you get there a lot quicker.

 

The supercharger helps immensely. The poor little naturally aspirated 112 motor doesn't have the wheaties to push the air out of the way at 170+ mph. Without the blower, the car won't be able to hit the number.

 

power has nothing to do with top speed, it has to do with gearing and aero dynamics.

 

Possible, but I think you go as far in one direction as I go in the other. The
truth is most likely somewhere in the middle (between little and extremely).
Of course, that was merely a side issue to the discussion. The main point is
that though top ends are fairly similar, the quickness in getting to that top
end is what sets the two cars apart.

Coyote

 

SRT6 hits 150 mph in 37.6 sec (hits 130 in 23.4), according to the article:
http://www.caranddriver.com/roadtest...ire-srt-6.html

XF hits 70 mph in 8.2 sec, (hits 130 in 32.2) according to the article:
http://www.caranddriver.com/roadtest...crossfire.html

extremely exaggerated seems about right to me...

 

What are you smoking?
Power has EVERYTHING to do with top speed.

Here's a little food for thought...
Aviation people distinguish air resistance as parasitic and induced drag, but the critical thing to understand is that drag increases as the square of speed. That is, while power increases in a linear fashion, drag increases exponentially with speed, in a parabolic function. For example (neglecting the effect of rolling resistance), if 100 horsepower would push a certain vehicle 100 miles per hour through the air, doubling the speed to 200 would require two-squared or 400 horsepower to overcome air resistance, while 300 miles per hour would require 900 horsepower.

Reducing drag will make a huge difference in the power required to hit a target speed. However, if you have a streamliner that's only cranking out 300 hp you're going to have a far lower top speed than the vehicle that makes 600 hp. Gearing and RPM capabilities must also be tailored to the target speed, but if your engine doesn't have the power to hit the required rpm, you're not going to make it.

 

I think torque must get in there somewhere. All that horsepower without alot of torque is no fun. The same goes the other way alot of torque with no horsepower is no fun either.

 

Exactly.

Thank you.

 

The base model is drag limited to 151 while the srt is governor limited at 154. If it wasn't governor limited my guess it would go close to 175. So it does seem that more power makes a car go faster. And more torque.

 

I like torque. That's why I've got a turbocharged big block and a BOMBed Cummins.
Torque can be compared to how much work you can do.
Horsepower can be compared to how fast you can do the same work.
They're essentially two different ways to measure the same thing.

(torque * rpm) / 5,252 = horsepower

In street cars, torque can be thought of as the 0-60 run. Horsepower would make the difference in the 60-90 run.

 

So if the SRT gets to 130 in 23.4 seconds and the XF gets to 130 in 32.2 seconds, then isn't the SRT 37.6% faster to 130 as a percentage of its elapsed time? Seems to me that 37.6% is not an insubstantial figure. In fact, that's the same percentage difference between a 0 to 60 of 4.8 seconds versus 6.6 seconds. And that, too, seems like a meaningful difference in quickness and speed. Having owned both models, I can verify that the SRT is noticeably faster, which is hardly surprising since it has 53.5% more HP than the standard XF.

 

in re: Speedometers. I recall that there is a law in Germany that it is verboten for speedometers to read ***under*** the actual speed. This is so you can't argue with the Poleizi that "well, my speedo only read 150, so I couldn't have been doing 160!" Still and all, the speedos in German cars typically seem more reliable than the ficcione found in Italian cars.

 

Horsepower does have a lot to do with top end speed. Gearing and aerodynamics also play into the equation.

 

That's right, there are times were horsepower doesn't mean squat when it comes to top speed.
Even if there were two of the same cars, one with 700 hp and one with 900 hp and both were able to hit redline in top gear, their both going to top out at the same speed due to the gearing/rpm limit of the engine.