My 99 E430 "feels" like it accelerates significantly better in cooler weather, and demonstrates more induction noise while doing it.

While I know that a denser air load is supposed to help performance, I'm either surprised that I notice, or imagining the whole bit. I've only had this car for 6 months, four of them in sultry 90-100 degree Atlanta heat.. now at 60 degrees it feels like that car I bought back in the spring.

Can anyone help quantify this apparent effect? If I leap to the conclusion that the mass airflow sensor compensates for the denser air with more fuel and allows more power, would this be right.

Sorry about the voodoo science guesses.

I promise my next post won't be about the car going faster when cleaner.

Cheers,



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GParker
'99 E430

GParker,
Cold air is denser and hence gives more O2 to react with fuel. The electronics can adjust for this. The M113 engine doesn't seem half as sensitive as the previous generation M119 V8's when it comes to temp sensitivity. I've heard lots of figures thrown around but you could probably guesstimate about a 1% change in power per 10 degrees difference in ambient air temp. The colder and drier the air is the better it is for performance. (granted colder air can hold less moisture than warmer air but...) Also, if you don't have to run the A/C you are saving some significant HP right there.

I know exactly what you mean by variance in performance in Atlanta weather. I have timed the 500E from 6.4 seconds 0-60, 1/4 in 14.7@96.8 mph in 95+ degrees. I have also timed the 500E at 5.3 seconds 0-60, 1/4 in 13.6@107.1mph in about 70 degree weather. That difference has to be more than 3-4%. Bill Wood has an E430 and is also in Atlanta. You may want to ask him what kind of performance variance he notices in his car.

Happy Motoring....Lee

(though a bit happier in colder weather)

Cool Dense air has a "tighter' concentration of molecules per unit measurement.

Ever wonder why your voice carries farther in the winter?

Ever wonder why an airplane needs less runway to takeoff in the winter?

A lot more complicated and techy than that, but in plain english yes you are right.

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Chris Ecklund
98 300 DT

Appreciate the replies!

I do understand the science thanks to Boyle et al -- this is just the first time it was noticable in any car I have owned. I did not know, however, if the engine management computer was allowing the engine to take advantage of the denser air, or that it had such a significant effect. Lee's stats are astonishing (to me.) If I go back to my carburetor and big block days, I swear I got no such effect.

I'm off to find that friend with the 99 GS400 who I could only barely out run in the heat a few weeks ago. We'll see if O2 burned with rice creates the same effect!

Thanks again,
Greg

Most M.B. engines use an intake air sensor to monitor the incomming air. The timing can be retarded & the fuel mixture leaned out. Retarted timing can really slow down any of these cars.

Just how much horsepower can the aircon sap from a car? I would think a Mercedes would sap less hp than say, a 4 cyl. Honda.

I would like to agree that our MB should be affected less by having the air on than our Honda, but this doesn't seem to be the case. We have an 89 Prelude and an 89 190E 2.6. On the Honda you can hardly tell by performance and mileage that the AC has been on, but on the 190 it's very noticable. In fairness, I should say that the AC has always been very noticable on my BMW as well.

My understanding of the power loss is that it is a percentage loss. If you are losing some percentage on a Honda or other economy car you are not losing much. Compare that to a similar percentage of say a 500E's output.

Plus I'd bet good money there is more going on in the engine management systems of a M119, M104, or M113 than your average honda motor. There is some kind of temperature (both ambient and engine temp)/performance issue going on with the DOHC MB cars that isn't readily apparent.

Lee