how accurate are self timed 0-60 times???

Sure it's not.
Accuracy requires GPS/laser technology
And anyway, acceleration times are impossible to reproduce...unless of course you don't care about your clutch, or you have a slushbox

 

Things like the g-tech pro are always off by a fraction of a second. If you want tenth-of-a-second precision, those are only good for relative comparisons to other times you have recorded with them, ie improving your performance with the car. I have used one in an autocross and at a roadcourse event (the "RR" unit) which was helpful in analyzing the best way to set up a term by comparing relative speed and braking information gathered by the unit.

I'd take any kind of straight line acceleration data produced by the G-tech with a grain of salt, especially something as highly variable as a 0-60 time. My guess is that it is accurate to within .3 seconds. Considering the unit isn't even connected to the engine at all (only connected via cigarette lighter), I'd say that is pretty darn amazing! But to take numbers detailed to a decimal point and preach them as fact would be skewing things slightly -- way too many variables involved, user calibration being one of the largest.

I'd also add that, having driven a 996 Turbo S myself, (many times/very hard) as well as other cars much faster, I have serious doubts that it can cut a 0-60 time quite that low. The car (as you've mentioned) weighs a good amount more than a sports car should, and regardless of how many people talk about the non-existence of lag in the turbos...well, it's mostly certainly there. It makes a lot of torque...but not that much torque, and not that low.

My 2¢ ...

 

I was talking to one of my friends that has a wrx which is heavily modded and hes really into testing his car so to speak... He installed a dash camera and taped the speedo and then played it back on his computer to try and get an accurate reading...

not a bad idea, pretty cool to watch, not very accurate though

 

The problem here is that you are once again relying on an instrument that is not very precise. Porsche speedos have been known to read higher than the average speedo which means you may be measuring your 0-55 time with amazing precision but, again you just don't know unless your using gps to calibrate.

 

A G-tech is an accelerometer, right? Why does anything need to be connected to the engine to measure acceleration? RPM isn't an issue with 0-60 times so the trick with reading revs through the lighter is moot.

It seems to me the biggest variable would be orienting the unit correctly. But, oriented correctly it should measure acceleration pretty accurately. That data plus a little math/physics will give you 0-60 times. Ain't digital stuff grand? ;-) No need to tie into the engine or speedo.

As for hand held stuff, I'd agree there are way too many varables involved to get anything very accurate. Reaction time on starting and stopping the watch, measuring the speed, reading the speed, etc...

 

Car and Driver test of inexpensive timers:

http://www.caranddriver.com/article.asp?section_id=4&article_id=9380&page_number=1

They're listed in price order, from lowest to highest, but when you look at the features and accuracy, The Passport looks like the one to get.

 

Spot on. The G tech or any good timer will give you accurate 0-60 times, within a hair of actual. I have found these timers to be accurate. (particularly the G Tech)

 

I tried the stop watch method once.

It was on a 4 speed 240D.

Got to 55 in about 50 seconds and then there was a slight rise on the highway so I never quite got to 60.

 

Yea, same here.... I pretty much swear by my G-Tech. I have tracked it as well, to test it's accuracy. Had mine for about 6 years now and still tickin!