30-70 MPH times

[Sagaris]

Have you ever timed your 30-70 MPH acceleration? I find it to be a pretty decent performance benchmark. 30 to 70 acceleration applies well since it represents what you might be doing exiting a corner on a racetrack or releasing all your rage when grandma is camping out in the left lane and its time to pass her.

0-60 is typically the benchmark for automotive performance but launch technique and traction can make a 0-60 time vary quite a bit, not to mention having a car that hits 60 in 3rd as opposed to one that hits 60 in 2nd.

Anyways. I wanted to compare numbers to see what some of you guys are running 30-70 in your E30's. Here is a list of what some other cars are running 30-70:

http://www.car-videos.net/performance/speed.asp?Speed1=30&Speed2=70

[nando]

30-70 either requires a shift from 2nd to 3rd or lugging it in 3rd gear. My 3rd gear doesn't even start breathing until 50, at 70 I haven't even reached peak HP and still have another 20mph of powerband. But I could give you a 50-80 time if you like. ;)

[Sagaris]

In my automatic I started in 1st gear
In my manual I started in 2nd gear. I know some people say the only correct way to do it is to stay in 1 gear and lug it but as far as im concerned its about doing it as fast as possible and if that means shifting once or twice then thats fine because thats how you would actually be driving the car in real life or on a track.

[nando]

but you're measuring shift times too, not the car's performance.

[jlevie]

If the goal is to compare engine performance you need to make the "pull" in one gear from 2500rpm to 6000rpm in a 325i. That will be about 34-82mph using 3rd gear, which on an empty section of 70mph Interstate is possible (though maybe a little risky). Getting the data this way eliminates the errors introduced by a shift or those in the speedometer and gathers data from the entire power band.

Since I don't know what the gear rations are in the automatic transmission I don't know what gear you'd want it in. The rpm band would be different (obviously) for an ETA engine.

[bimmerboy12]

82mph using 3rd gear, which on an empty section of 70mph Interstate is possible (though maybe a little risky).

In this case I am a very high risk driver

[nando]

hmm, I think I'll just do a pull from 2500 to redline in 3rd. it is what it is.

[LivingLegend06]

The stock speedometer is usually pretty optimistic, and therefore your times are too.

Try using a gps for the speed or do the math with the gear ratio, final drive, tire size and engine speed.

[CHIF8008]

a lot of variables go into this. you need a better system of trying to test

[Sagaris]

The stock speedometer is usually pretty optimistic, and therefore your times are too.

Try using a gps for the speed or do the math with the gear ratio, final drive, tire size and engine speed.

Not a bad idea, however a GPS will have error in how frequent the speed is updated , the tire size will have error due to wear or due to the instrument you use to measure the diameter. The raw calculations to determine what RPM you are at in 30 and 70 is not a bad idea but it presents the same argument about the speedometer. A GPS could be used to see how far off the speedometer is at 30 and at 70 though which would provide a correction factor. There is still error in the the person reading the speedometer and the stopwatch but thats life. The best way to do this would obviously be with a GPS data-logger but who has access to that type of equipment?

a lot of variables go into this. you need a better system of trying to test

Like what? Any suggestions?

[nando]

the error of the speedometer is a linear constant, about 5mph, which BMW probably added on purpose. I was surprised that with slightly larger tires, the dash speedo was a dead on match for a speedometer calibrated to my actual tire size. But with the stock size tires it's about 4mph off. If you do a readout on the OBC though (hold the "reset" button while on average MPH) it shows your speed without the added saftey margin.

[M-technik-3]

30-70 is a good tool for freeway merging. Nice way of seeing if your gonna be stuck behind the semi or not. Only time i have measured my times though have been at the dragstrip.

[KennyT]

Who cares if you are perfectly accurate? Speedo's will be roughly equal between cars as they are all optimistic. Shifting times are largely irrelivent, just mention what transmission and diff you have. I'm curious if any similarly modded engines are close with 3.25 and say 3.73 or 4.10 just due to shifting.

[Wh33lhop]

the error of the speedometer is a linear constant, about 5mph, which BMW probably added on purpose. I was surprised that with slightly larger tires, the dash speedo was a dead on match for a speedometer calibrated to my actual tire size. But with the stock size tires it's about 4mph off. If you do a readout on the OBC though (hold the "reset" button while on average MPH) it shows your speed without the added saftey margin.

The speedo error is not a constant, but it is roughly linear.

Who cares if you are perfectly accurate? Speedo's will be roughly equal between cars as they are all optimistic. Shifting times are largely irrelivent, just mention what transmission and diff you have. I'm curious if any similarly modded engines are close with 3.25 and say 3.73 or 4.10 just due to shifting.

Actually rolling diameter will make a difference (for example 195/60R14 is about 4% shorter than 195/65R14) as will user error. The only way to reliably do this is with GPS logging.

[nando]

it seems to be 4mph off with stock sized tires no matter how fast I'm going. My theory is the error is in the dial face, the actual speed read from the diff and calculated inside the cluster doesn't curve away from the true speed like many people believe. At least that's what I'm seeing by logging the VSS signal directly.

using gear/RPM/tire diameter should be just as accurate as a GPS, providing that's inputed correctly. It's not rocket science. :p