Ali B

I have yet to see a satisfactory explanation about the following topic. Please enlighten me.<p>Almost every review and test drive of the A4 2.8 with the 30v engine mentions that despite a significant power improvement over the old 12v engine, the low rpm response (or grunt) of the engine is still lacking, and the car nly really comes alive after 3500 rpm. Now according to Audi, the peak torque of this engine is 207 lb-ft @3200 rpm. Wouldn't you expect that with peak torque at such a low rpm, the response between 2500-3500 rpm should be better than say a BMW 328i?<p>The new Double VANOS BMW 2.8 engine has its peak torque of 206 lb-ft at 3500 rpm. The older engine in the E36 body had its peak of 206 lb-ft at 3950m rpm. Yet, you never hear about lack of low-end power about either of these BMW engines. <p>Now, with an engine like the 3.2 liter VTEC on the Acura 3.2TL which has its peak torque at 4500 rpm, I can see why the engine feels somewhat sluggish below 4000 rpm. <p>Is Audi misquoting the rpm at which the 30-valve engine reaches its peak torque, or is there some rational explanation other than the usual answer given before like gearing or final drive ratio? I don't think these should have anything to do with how alive an engine feels at a certain rpm. <p>Thanks for any educated explanations.<br>

John

The reason the BMW Double Vanos system gives their cars such low end "grunt" is not JUST that the torque peak is low, but that the torque curve extends both directions from the peak to give an incredibly flat curve.<p>The other reason probably lies in the gearing, although that's just conjecture.

Bob

For low-end acceleration, you'd have to look to the available HP at this RPM. That matters. <p>Basically, there is no direct relation of torque and time (thus acceleration). <p>(However, HP is calculated with the product of torque and RPM. I don't care what the exact formula is)<p><br>

Ali B

Therefore, I think there is a definite correlation between available torque and acceleration at any given rpm. I don't mean a simple mathematical formula, but that torque, more than hp, has a lot to do with acceleration.<br>

stevebrown

is that MOST (not all) writers in car mags believe their own BS like it's gospel. You see the same comments over & over about a particular car as if they all share notes! Go look at every article about the new Volvo S80. You cannot tell me that of the six jillion people who have driven & written about this car all came up with the EXACT SAME pros & cons. I see how people find reason to believe in conspiracies.<p>Hell, these are the same people who ran articles touting the benefits of Splitfire sparkplugs, Slick 50, and the like.<p>Here's my guess: spend more $$ advertising in the magazine & they think of creative ways to complement your car (even if it sux rox). Don't spend enough & they spear your car with a "could use a tad less body roll," or "hard to modulate clutch," or the perennial favorite, "really makes you wonder what the designers were thinking."<p>MY 30V (with tip), seems to "wake up" at 25-2700. No it's not a Camaro or Corvette. <p>When I asked my car what it thought of the 3500RPM comment, it blared its new Hella Supertones in contempt.<p>steve

Bob

-<br>

Jim Meyer

Torque is directly related to the force applied at the tire contact patch. The torque about a drive wheel's axle is the force at the contact patch multiplied by the radius of the tire. Since the major law involved here is Force = Mass x Acceleration, you can see that the torque at the wheel is directly proportional to how fast a car accelerates.<p>The thing about torque is that is gets multplied up or down by gearing, so the torque the engine is putting out gets multplied by the total gear ratio to create the torque at the drive wheels. But in any given gear, the maximum force (and hence acceleration) will happen at the engine's peak torque RPM. In the case of the 2.8 engine I think that's near about 3200RPM. So if you pick any gear and start out at maybe 1000RPM and just floor the gas pedal the car will start accelerating. As the RPM's rise above 1000 the car will accelerate faster until it reaches the torque peak at about 3200RPM. Once past that point the car will accelerate at a slower rate, although it will continue to accelerate.<p>Now the reason we don't all drive around at 3200RPM is that by downshifting you gain a more advantageous gear ratio so the torque which ends up at the drive wheels is greater. In other words:<p>Engine torque@3200RPM x Gear ratio #1 < Engine torque@5500RPM x Gear ratio #2<br>even though<br>Engine torque@3200RPM > Engine torque@5500RPM<p>An engine's peak horsepower RPM is the point at which a car can accelerate the fastest as long as the gearing can always be adjusted to keep the engine at that RPM. That's why a continuously variable transmission would be the ideal way to get the fastest acceleration. You would simply floor the gas pedal, the engine would immediately climb to its peak horsepower RPM and stay there, and the transmission would adjust the gear ratio continuously to provide for the change in vehicle speed.<p>In the current real world we use discrete gear ratio transmissions instead of variable ones, so for best acceleration the engine must have a fairly flat torque curve near its peak horsepower RPM in order to get the fastest acceleration.<p>Ali B. is correct in stating that the engine's peak horpower has more to do with a car's top speed than torque does. (As long as the gearing can be adjusted so the engine is operating at peak horsepower just as the car reaches its top speed.)<p>I hope this was useful.<p>Jim Meyer<br>'98.5 2.8QMS

KurtW

You mean that all those Motor Trend Car of Year Awards and 37 page ads for the car COMPANY in the same issue AREN'T just coincidence? The shock!!! Now, where did I put Mr. Stone's #. . . .

stevebrown

At least 2 manuf. have cont. variable trannies (prod. within 3 yrs)nt

vic

Car (the British magazine) did a comparison a while ago on A42.8Q, new 328i with the double VANOS and Alfa 156 2.5V6, and by far the A4 has a much stronger low end. I think the problem is that the BM's are seen as a sporting car and as such people expect to rev the engine. Not so with the Audi. In any case, I wouldn't be surprised to hear that from "The Land of V8"....