500E vs 500SL

[pentoman]

Hey

Reading up on the 500E, I've noticed it had modifications done to the engine which gained it 22 lbft extra over the 500SL, but no (or was it 1) extra bhp. Can that really be right?

Looking at the latest E55 AMG, it is quoted as only 470 bhp, versus the SL55 (identical engine) with 500 bhp. Supposedly due to different exhaust/intake, BUT bizarrely they still have identical torque figures.

In the press this is being recognised as the ploy that it is - MB just playing with quoted bhp numbers to maintain 'model rank' (SL55 is above E55 and much more expensive, so they quote less power for the E), whereas both are really around 500bhp.

Did this perhaps occur for the 500E? Did those engine mods REALLY gain so much torque but no hp? How did the costs of 500SL and 500E compare when new? Anyone got stock dyno figures to perhaps support this?

later

Russ

[yhliem]

i haven't had a chance to confirm this with the family mechanical engineer (dad ) so i may be somewhat mistaken or downright wrong:

hp is a function of torque and engine rpm. I don't know what the actual formula is, but i believe the relationship is a direct one. ie. x(torque) * y(rpm) = z(hp)

i don't know what the exact formula or co-efficients are, but it is entirely possible that torque could increase or decrease without affecting hp. it all depends on what the engine rpm does; in otherwords, the shape of the torque curve.

which is why torque and hp numbers are entirely useless unless associated with rpm. you could have an 800hp engine, but it's ability to do useful work depends on whether that's at 500rpm or 15,000rpm.

[Michael]

The Sls, introduced in 1990, had the KE-Jetronic (I think?) injection, whereas the 500Es and 500SELs (intro in 1992) had the new-at-the-time LH (hot wire) injection, which accounted for the differences. Later SLs (I think after '94) adopted the LH system, and gained the improved torque (which those heavier cars really needed)

[need2speed]

A quote from the E55 review in the Dec 2002 issue of Mercedes Enthusiast:

"If you pore over the specification sheets, it also becomes apparent that while the E55 and SL55 offer the same maximum torque figure, in the SL55, now uprated to 500bhp at 6,100rpm thanks to intake tract and ECU modifications, peak torque occurs between 2,750-4,000rpm. The E55 reaches that torque output at 2,650rpm and holds it to 4,500rpm."

Another interesting point from the article is the comparison of vehicle weight. The E55 is 120kg (264lb) lighter than the SL55. This weight difference is enough to give the E55 a power/weight ratio of 3.85kg/hp vs the SL55's 3.91kg/hp!

In comparison, the W124 E500 was 400lb lighter than the similarly-engined R129 SL500 and had more absolute torque.

[Benzmac]

It has been a standard for years that auto makers would let the flagship have the higher HP figures.

Take for example the '86 Buick Grand National and the Corvette. The Corvette was rated with higher HP, but the GN would walk from it.....You do the math.

Mercedes HAS to do the same thing.

[need2speed]

Originally posted by Michael
The Sls, introduced in 1990, had the KE-Jetronic (I think?) injection, whereas the 500Es and 500SELs (intro in 1992) had the new-at-the-time LH (hot wire) injection, which accounted for the differences. Later SLs (I think after '94) adopted the LH system, and gained the improved torque (which those heavier cars really needed)

Just to add to Michael's post a bit....the 500E had the LH-Jetronic injection system, which was physically smaller than the 500SL's KE-Jetronic. In addition to having better gas flow, the LH unit allowed a longer induction manifold which provided more torque and a broader torque curve.

At least, thats what the magazines said in 1991.

[David Hendy]

I think the 500E has bigger cats that the SL.

[-fad]

yhliem- -

jees..... your post/reponse appears to contain soooo much conjecture...it'd be more helpful to check w/ your resources before submitting such info (truly a friendly suggestion)

best regards
-fad

[suginami]

I don't know if his formula is correct, but his basic premise is correct:

Torque is a measure of hp available at a given rpm. High amounts of hp that are not available at low rpm's is not usable in everyday situations, unless you like flogging your engine at 8,000 rpm's to get the most of its power.

I don't think any of this applies to the 500E as it has gobs of hp down low, but I thought I'd just give this post as a freebie. No charge to the reader.

[-fad]

Greetings Paul- and thanks for the freebie!

best regards
-fad

[Daesun]

Originally posted by suginami
Torque is a measure of hp available at a given rpm. High amounts of hp that are not available at low rpm's is not usable in everyday situations, unless you like flogging your engine at 8,000 rpm's to get the most of its power.

Quite the opposite. HP is a function of torque and engine speed. Torque is a measure of force exerted, while HP is a measure of work done. Moving your torque band around (e.g., hotter cams, free flowing exhaust) will modify your HP curve accordingly.

Low end torque is certainly handy for everyday driving. However, for performance applications, it is preferable to make most of your torque at higher engine speeds, as this will result in much greater HP output (i.e., more work done = better performance). In my experience, Mercedes engines are tuned for extremely flat torque curves, esp. the newer 3-valve designs. This results in ultra smooth power delivery at the cost of some WOT performance. Note that MB motors typically have higher torque ratings than HP.

[suginami]

I stand by my statement.

It is exactly presented that way by the technical editor of Car and Driver magazine in a technical article on hp and torque, and I quote, "torque is a measure of hp available at a given rpm."

[Daesun]

Originally posted by suginami
I stand by my statement.

It is exactly presented that way by the technical editor of Car and Driver magazine in a technical article on hp and torque, and I quote, "torque is a measure of hp available at a given rpm."

It must be a typo. When a car is put on a dyno, the only thing measured is torque at the wheels. This number, along with engine RPM, determines HP. I am 100% certain of this.

[Glen]

Some light reading...
http://www.vettenet.org/torquehp.html

[yhliem]

fad

my source is my dad who happens to be a Diplom Ingeneur from the University of Stuttgart. he is a maschinebauingeneur. In english, he holds a Master's Degree in Mechanical Engineering specializing in industrial machinery.

I've had this discussion with him several times in the past re: the difference between hp and torque and the relationship between the two.

though the details in my post may be a little off (yes, sugi, i know the formula is not correct, it was just a VERY simplified version and i stated that i didn't know what the actual coefficients are) i was just trying to illustrate the relationship.

I stand by my original post as it's written. minus some of the uncertainty

Sugi.

Sorry Bud, you've got it backwards. or rather the article you've sourced has it backwards. torque is the traditional measurement of applied force.

THIS is what is measured on a dyno. hp is not a measured number, it is a calculated number and there DOES exist a formula for the conversion. i'm just too lazy to look it up :p

hp is actually a measure of the rate of change of torque. whenever you introduce a measurement of time into the mix (in this case rpm) you are measuring the rate of change with respect to time. similar to how distance is a measure of displacement and speed is a measure of the rate of change of distance and acceleration is a measure of the RATE OF CHANGE of speed/velocity.

btw, i have a background in physics and mechanical design. just never went for my engineering degree...took business instead stupid me. i should have gone into engineering. or at least stuck with physics.

Glen

thanks for the article. i'd read that one a coupe of years ago. looks like my simple formula was pretty close. i just didn't have the constant.

in general, the magnitude of hp and torque are not as crucial as where in the rpm range these peak values are reached. for race cars, they spend most of their time at full or almost full throttle. therefore one would want the peak hp & torque to be pretty high up in the powerband; however, in a daily driven street car, you'll be working the engine all over the place in the powerband, so the engines are designed to provide torque over a broader, more useable range of rpm. that's where the term "broad torque curve " comes from