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Discussion Starter · #1 ·
This is an estimate, let me know if you disagree with some of it that materially affects the outcome:


  • From multiple internet calculators, for a car of the R171 SLK55's weight, going from 315 whp (N/A with headers/tune) to 410 whp (supercharged) has a 1/4 mile gain of 1.1 seconds ... for simplicity and conservatism, I'll just use one second.
  • When the faster car crosses the finish line, the other car is 1 second away from finishing, and (the slower car) averages about 110 mph over that last second.
  • 110 mph = 161 feet per second
  • the SLK55 is 161 inches long
  • 110 mph for one second is thus 12 car lengths, which is how far behind the slower car is when the faster car crosses the finish line

I want to know how much difference there should be between the two cars, and the above seems like a good estimate, unless I'm missing something big.


I realize the price of the supercharger package, etc. Please only comment about the numbers involved or if you have witnessed a comparable race. Thanks!
 

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When I first looked at the figures it didn't seem right but after checking you are correct .
12 car lengths seemed a lot over 1/4 mile. I think for the money I would rather install a 150hp NOS kit.
 

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1/4 mile

Some factors are missing. What is the top speed of the faster car in the 1/4. If both cars continue to pull thru the entire race the 110 will be a millisecond. if they both started the race at 110 and whatever the faster car runs at for the entire race then maybe 12 car lengths
 

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Discussion Starter · #7 ·
Some factors are missing. What is the top speed of the faster car in the 1/4. If both cars continue to pull thru the entire race the 110 will be a millisecond. if they both started the race at 110 and whatever the faster car runs at for the entire race then maybe 12 car lengths
The speed of the faster car in the 1/4 mile is irrelevant to the question posed, which was how far behind is the slower car when the faster car finishes.

It wouldn't matter if the faster car doesn't move for 12 seconds and then finishes instantaneously, or vice versa.

It would matter what the acceleration curve of the slower car looked like, but I think it is reasonable to assume a normal acceleration curve without explicitly stating it.
 

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I think a 410 rwhp assumption is too low for a blown SLK55- assuming the basic other accompanying mods like a full exhaust system, LSD, and tune are present. I had mine tuned with the prior blower @ 95 octane (the latter blower design that came out a bit later didn't put out as much power....from what I hear....but 410 rwhp still seems too low). As a general rule of thumb is 1 car length for every .1 seconds in the 1/4 mile, so the above "math" in prior posts aligns with with my understanding as well ;o) My RX-7 is a mid 10 sec car....its the only car that has pulled our SLK. The SLK is pretty quick - especially on a roll (it can't get solid traction until ~ 70 mph but its still pretty fun).
 

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Notwithstanding any of the technical figures and working purely on your assumptions, I think the slower car will be nearer 14+ lengths behind:

Using your figures:
Assume 110mph is 161 ft/sec.
161' = 1932"
Assume SLK is 161" long.
1932/161 = 14+

No?
 

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Discussion Starter · #10 ·
I think a 410 rwhp assumption is too low for a blown SLK55- assuming the basic other accompanying mods like a full exhaust system, LSD, and tune are present. I had mine tuned with the prior blower @ 95 octane (the latter blower design that came out a bit later didn't put out as much power....from what I hear....but 410 rwhp still seems too low). As a general rule of thumb is 1 car length for every .1 seconds in the 1/4 mile, so the above "math" in prior posts aligns with with my understanding as well ;o) My RX-7 is a mid 10 sec car....its the only car that has pulled our SLK. The SLK is pretty quick - especially on a roll (it can't get solid traction until ~ 70 mph but its still pretty fun).
yeah, I think the 410 is being conservative

Kleemann told me to only expect 1 or 2 car lengths in a 50-120 race of an N/A to supercharged. If that was the only difference, nobody would spend $10k+ on the supercharger kit.
 

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Discussion Starter · #11 ·
Notwithstanding any of the technical figures and working purely on your assumptions, I think the slower car will be nearer 14+ lengths behind:

Using your figures:
Assume 110mph is 161 ft/sec.
161' = 1932"
Assume SLK is 161" long.
1932/161 = 14+

No?
no, 1932/161 = 12

the 161 being in both pieces also makes it able to be calculated simply (12 inches in a foot) without converting one measure to the other
 

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Of course you are right..! I should not have done this one mentally..!
So, with your mathematics correct, it would be interesting though to see a comparison in real life that took into account the various factors involved.
 

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Of course you are right..! I should not have done this one mentally..!
So, with your mathematics correct, it would be interesting though to see a comparison in real life that took into account the various factors involved.
In real life, on street tires... And with both launching perfectly. It'll only be a car length ahead of the slower car in the quarter
 

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Based on what? Your hopes and dreams?
Based on physics. Let me know how "easy" it is for you to launch a supercharged slk55 from a stand still without burning rubber.

Then, let's say you're successful at doing the above... Next problem comes 2nd and 3rd gear. Where you can STILL accidentally burn rubber.

Street tires + lots of hp & tq + standing still + wanting to move forward quickly from standing still = moving forward slowly (unless of course you know how to feather the throttle through 1st, 2nd, & 3rd gear properly)

Now, go get some slicks and put them on the supercharged slk55. Now, you'll have a far greater lead on the stock slk55.





You see, this is where a turbo & a proper ECU that allows you to boost by gears would be great. On cars like the slk55 that don't weigh much. Because you can turn the boost down in 1st and 2nd gear then increase boost as you go into higher gears. Sadly, superchargers do not allow boost by gear. But they sure are fun :)
 

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Discussion Starter · #16 ·
you can't just claim "physics" lol

and you stated "both launching perfectly" not one spinning out ridiculously ... of course you would feather the throttle a bit at first, you have to do that even with mild upgrades (headers / ECU) or stock depending on conditions

I doubt there would be much difference from 0-50, but 50-120 there should be quite a bit of pull.
 

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Based on physics. Let me know how "easy" it is for you to launch a supercharged slk55 from a stand still without burning rubber.

Then, let's say you're successful at doing the above... Next problem comes 2nd and 3rd gear. Where you can STILL accidentally burn rubber.

Street tires + lots of hp & tq + standing still + wanting to move forward quickly from standing still = moving forward slowly (unless of course you know how to feather the throttle through 1st, 2nd, & 3rd gear properly)

Now, go get some slicks and put them on the supercharged slk55. Now, you'll have a far greater lead on the stock slk55.





You see, this is where a turbo & a proper ECU that allows you to boost by gears would be great. On cars like the slk55 that don't weigh much. Because you can turn the boost down in 1st and 2nd gear then increase boost as you go into higher gears. Sadly, superchargers do not allow boost by gear. But they sure are fun :)
Today's ultimate dry weather performance street tires practically stick like the drag slicks of yesteryear. I've got 275 width Goodyear asymmetric treaded rears meant for only DRY asphalt & I can assure you, like many other high HP/Torque sports cars that have under 11 sec 1/4 mile times, you will leave a stock SLK55 for dead with an additional ~ 100 rwhp at your beckon. An LSD is, in my opinion, a mandatory upgrade when increasing power. BTW, the SLK55 is not that light at ~ 3,400 lbs? It squats pretty well when the power is applied & the LSD also helps quite a bit - along with the sticky rubber ;o) My RX-7 is 2,750 lbs, that is what I would define as pretty light.
 
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