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Automobilemag's Dyno Run On The Is-f


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0710_1_z%202008_lexus_isf%20dyno_graph.jpg

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.

0710_z1%202008_lexus_isf%20left_front_view.jpg

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Bartkat, you don't happen to know if the RS4 also had an auto transmission? Some people say you cannot get comparitive readings, or the results through the autobox are suspect.

I got that piece of the article from another forum and have been unable to find the original entire article.

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