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      10-25-2007, 04:36 PM   #33

Drives: IS300
Join Date: Oct 2007
Location: New York

iTrader: (0)

Here's the Dyno results from the Automobilemag:

Originally Posted by Swamp2
Looks about right and it consistent with a top speed of 172 (limited). CarTest computes 179 unlimited. I still had to make a few estimates for CarTest. I assumed a frontal area of 25.2, Cd = .29, curb weight = 1690 kg, compression 11.8, weight on front 53%. Last but not least I gave the automatic tranny a big benefit of the doubt with enagage time and shift time of exactly .1 seconds (fast). Still the numbers are nowhere close to quoted figures. I think they are significantly under rating! Either way if they do get the straight line numbers the mag. reported it will be a really fast car. I have to try a few more custom transmission parameters as it looks like the sihifts are not quite fast enough in the acceleration graphs but for now I fully call under rated.
Originally Posted by swamp2 View Post
OK did some tweaking with CarTest to get a ball park estimate of the power and torque figures required to obtain the quoted numbers could not get perfect - a few numbers ended up a bit quick and others a bit slow but it is way closer than with the as quoted figures.

hp: 470 (94 hp/l)
tq: 440 ft lb (88 ft lb/l - probably unreasonable, F430~80 ft lb/l)

0-60 mph: 4.6 s
0-100 mph: 10.1 s
0-150 mph: 23.7
1/4 mi: 12.8s @ 114 mph
Originally Posted by Swamp2
So again, to be clear, I am not saying the car is speced at 416 hp and is hiding a full 470 hp. CarTest is a simulation tool and can not predict every car right on the money. It does however do a very accurate job on many cars. My point is simply this. One or more pieces of the following puzzle are completely and largely inconsistent:

1. The reported performance figures from the car mag in my opening post.
2. The weight figure for the car.
3. The reported hp and tq figures for the car.
You've got to be kidding me!? How do you figure it's under rated? You'll see that the results is comparable to what they got for the RS-4 with 420hp. And remember that the U.S. spec RS-4 is almost 4000lbs and the performance figures are quite similar. And also, Car and Driver has always gotten the best performance figures on any car compare to any other magazines. So the 0-60 @ 4.2 secs and 12.7 1/4 mile they got for the IS-F is no surprise. In other words, i'm almost sure this car is not underrating it's hp and weight figures. Besides, it's not like they could hide that or get away with it anyway. Car and Driver already has the full test on it and all the specs as well.

Originally Posted by Automobilemag
2008 Lexus IS-F Dyno Run
By Jason Cammisa

You're in a compact sedan with a 5.0-liter, 416-hp V-8 with four-valve Yamaha heads that contain titanium intake valves. Where do you head? The dyno, of course.
And so we did. The fellas at Ralph Willis Automotive in Salinas, California cleared their schedule for us to sneak the IS-F onto their DynoJet dynamometer. The results, as you can see from the chart below, are impressive. The IS-F is rated at 416 hp and 371 lb-ft of torque at the engine - and it delivered 333 of those horses and 318 lb-ft of torque to its rear wheels.
Those are impressive numbers given that the engine's output is funneled through an eight-speed automatic transmission. And how do they compare to the competition?
An RS4 we tested (see the link below to the full story) put out a very close 331 horsepower (and 276 lb-ft of torque) to its wheels. We should mention that the RS4 was tested on a Dynapack, which may be calibrated differently than the DynoJet model used for the Lexus.
As always, it's not the peak numbers of a dyno graph that are important, it's the shape of the torque curve. The Lexus' torque builds in a linear fashion as revs rise, but then things get a little hairy. Torque dips slightly between 4500 and 5000 rpm, and then peaks at 5200.
What happens afterward is disappointing - the curve drops off steeply, confirming our seat-of-the-pants impression that the engine is running out of breath. If you compare the shape of the curve to the RS4's, you'll notice that the RS4's V-8 doesn't make as much peak torque (it is, after all, 800cc smaller) but its twist is distributed much more evenly over a long rpm range. And from 6500 rpm up, where the Lexus is simply done, it continues pulling - all the way to over 8000 rpm.
The IS-F's V-8 certainly produces a lot of power and torque. We wish, however, that it didn't have such a steep dropoff in torque at high revs - that kind of rev-happy motor would suit the IS-F's track-star personality much better.