RedRX

Excuse me if this has come up before but I believe that the S4 produces in excess of 300 crankshaft hp from the factory. In fact, crankshaft hp on these cars may be in the 315-330 hp range.

It is common knowledge that trap speed in the 1/4 mile is a good indicator of average hp produced over the course of the strip. So, given trap speed and weight of the vechicle being accelerated, one can get a fairly decent estimate of hp using a simple equation.

In any case, running the numbers on a stock S4, which I believe weighs about 3815 lbs with driver, and using 99 mph as the trap speed (I have seen this number in a few magazines, and it seems to be consistent with the traps run by the people on this forum), yields 250 - 260 WHEEL horsepower. Add 20% drivetrain loss to those numbers and the car appears to produce somewhere between 310 and 325 hp at the crank.

So this begs the question -- why would Audi underrate the S4's horsepower? The only plausible answer I can think of revolves around the marketing of some competing Audi models -- namely the A6. Now, I'm not an Audi expert by any stretch of one's imagination, but if I'm not mistaken, the 2.7t motor in the A6 is identical to the S4 2.7t, and is also manufacturer-rated at 250 hp. I also seem to recall that the A6 is available with a 4.2L V8 that is rated at about 300 hp, and costs considerably more than the 2.7t version of the A6 -- about $10K more.

So, as my reasoning goes, Audi chose to underrate the 2.7t horsepower so the folks who spend a lot more money for the V8 model of the A6 would feel like they were getting something for their money. Audi may have thought that charging a 10K premium for a car that was rated at the same (or less) hp than the 2.7t V6 would make for a tough sell. And since the 4.2L V8 really does make 300 hp, Audi had no choice but to underrate the 2.7t.

Of course, this marketing mumbo-jumbo is all speculation on my part. I just couldn't think of any other reason why Audi would underrate the hp on their incredible 2.7t motor. If any of the readers here have any other ideas, I sure would like to hear them.

One last thing. I took an interest in Audis, and their actual hp after racing my brother-in-law, who owns a beautiful yellow S4. I just couldn't believe how fast it was, given it's heft.

-Dave
Boulder, CO

NickS

It's actually more like 260hp....no way it makes more than that stock.

LCP

Anybody who is running 99mph trap speeds in a stock S4 has a real ringer that probably makes 270hp, but I don't think mine's that fast.

LCP

...the thing to remember about a stock S4 is that it does make about 260hp PEAK, but also makes 250+HP from about 5200 to 6800 rpm. That is an immensely broad horsepower plateau, that will make it seem as if it produces more HP than it really does. And BTW, lots of S4's run at the strip under 3700 lbs. With 60 lbs. of weight saving upgrades, mine was 3435 lbs. on a near empty tank with no spare. Make that 3495 without those upgrades, and put a flyweight 150-lb. driver in it, and it only weighs 3645 lbs.

katana

Just to clarify, you're saying your car weighed ~3550 pounds stock? Shouldn't it be ~3600?

EdLove

My old Probe GT 1989 was rated @ 145hp, but could get 190hp for small periods of overboost straight from the factory. Why the hell can't audi's two turbo set up do the same ?

LCP

...add 15 more gallons of gas and it's in the 3620-3630 range. That's without ESP - sunroof's the only option.

katana

I thought the published weight is without gas, and I guess it's possible all the options add up to 50 pounds (ESP, Bose, Premium, etc.). Just wondering.

mys_iii

1) What weight saving measures did you take?

2) Did you or anyone else actually weigh an actual inhabited S4 with a full tank of gas to see what it comes out to in real life? The weight figures are quoted differently all over the place.

katana

I've weighed my S4 to verify my theoretical 180 pounds of weight saved were real savings.