Some Gtech numbers.
 

I did a few runs with the Gtech last night. I was really easy on the launch, way too easy. I was doing 0-60 in a pathetic 7.8 sec (if that tells you how easy). But even with that horrid launch I got a 1/4 mile of 14.6 @ 109 MPH. Nothing to write home about but take the granny launch into the equation and it looks promising. I was able to get 5.5 sec 0-60 last year with hard launches so thats certainly possible now. Anyone know what times I should be running at 109 MPH?

A 109 trap speed is pretty darned high. Your car must pull like a freight train through 2nd and 3rd gear.

Wow len, that car must accellerate like a rocket to be doing 109 at the end of the quarter mile!

Before I took out the 2.7 in my '75 to do the turbo swap, it ran consistent 5.9 0-60 times. I was surprised a 2.7 car was so fast (but it was very lightened and had SSIs).

I suspect my turbo engine may not be that much faster in the 0-60 range. Can't wait to test it out though!

I thought that was a high trap speed but I didn't want to gloat till I was sure:) Yes, once it hits boost in first from there on it is quite a ride! It pulls real hard in second I mean REAL hard, I was giggling like a school girl on the first couple runs. Tonight I will see if I can get a real launch! Any advice there? I mean I don't want to side step it, but should I slip it to bring on load/boost? Or just mat it right away with a normal clutch release?

In my old days...(5 years ago) I had a big block Dodge Dart that I drove on the street some and I was running 12.20s @108mph. on street tires with full exhaust. (Denver altitude no less)

With a 60-foot launch time of 1.7 seconds (not 0-60mph) I suspect that my 0-60mph times were in the high 4's somewhere.

As a side note, these cars are funny on acceleration. I mean the G's it pulls in late first gear don't compute in my head. What I mean to say is that you feel like you shouldn't be able to keep traction. I did blow the rears away on one of the runs, but only one. Any front engined RWD car would definitely not be able to put it to the ground.

Len what did your recent problem turn out to be? You were thinking it was something serious...? Glad you're back on the road.

Keep in mind that although gtechs are very consistend if you use them right, they tend to be a little optomistic on the trap speed, by about 2-3 mph. You're probably running 106-107 mph trap speeds (still hauling butt!)

109...wow, can't wait to see what my girl can pull!

Slider, thanks for the info. I am well awarew that I will not see mid 12's let alone low 12's with this setup as you simply cannot launch a 930 that hard(if you care about it), therefore my 60 ft times will always suck and thats a huge part of it. I will be happy with low 13's. No I am not huge into drag racing, but it is fun sometimes, and is certainly a good measure of performance mods.

Colin,

It was a vacuum leak at the pressure outlet pipe from the turbo. An oring was chunked.

Lenndaddy,

You are very wise in your attempts at getting the car rolling, launching one of our cars like I did with my drag car would be catastrophic to say the least.

The best way that I have seen a 930 launched is to just let the clutch out gently at just barley above idle and then hammer it. Slipping the clutch to bring it up on boost is just asking for more problems later down the road.

Most of the speed contests that I have seen between Porsches (very few because I hang out at the road race tracks now ) :D were from a rolling start anyways.

The G-tech trap speeds are accurate... and higher than a proper drag strip trap speed. If you check out the G-tech's web site they explain why... to paraphrase (if I remember correctly):

1) A drag strip trap speed is not the actual trap speed at the spit-second end of the quarter mile. But, it is an average taken over the last few yards (I can't remember how many).

2) The G-tech trap speed is the actual speed your car is going at the split second the 1/4 mile is reached... and therefore is not based on an average, so it will always be a few mph higher than a real track trap speed.


As for NA 2.7's... even though my owner's manual says 0-62 mph in 7.8 seconds, my (stock) 77 911S is clearly way faster than that. Car and Driver got a 0-60mph in 5.9 secs for the US-spec 2.7 liter 911S Targa. However, I don't think my car could do that, mainly because the 1-2 shift is too slow... although, it's probably in the high 6 second range.

-MAS

I wouldn't trust a G-Tech farther than I could throw it.

An accelerometer suction cupped to the windshield is not the most accurate of instruments for distance travelled, especially when you concider how the harsh ride of the porsche throws a lot of noise into the accelerometer.

I never owned one but I borrowed one from a friend one time and its numbers were awful.

Everyone I know who has taken one to the track or who knows their HP from multiple dyno runs has never gotten a number that is even close.

I would say from my and other experiences that a g-tech can easily be over 10% off in its readings that are time averaged (power, quarter mile).

For these reasons I concider the g-tech nothing more than an overpriced toy for those people who don't want to go the drag strip or a dyno.

Blah, your quarter mile times will always suck using this method.

While you are correct that a slipping 930 clutch will never have a chance to grab once the boost is on, the secret is to master a reasonable clutch engagement between 4 and 5 K RPMs so you can use the momentum of that heavy flywheel and crank and the reasonable unboosted power at that range to get the car out of the hole then get the clutch fully engaged in the very short amount of time you will have before the boost kicks so you can drop the hammer and fly down the strip.

The biggest enemy of the 930 in a drag race is the tall gearing, especially with the ***** of a first gear you must deal with if you have the four speed.

Since autobahn gearing has been my biggest enemy at the track and strip and I do not see much of a need to go past 160 MPH I just bought the 8:39 ring and pinion from andial.

If my calculations are correct this one change alone may allow me to dip into the high 11s or low 12s easily once all my mods are complete.

350,

My suggestion on launching is based on minimal damage to the drive train, not the quickest launch method.

I used a G-Tech to test the estimated HP in my 87 Carrera after I did an exhaust and MAF uprgade. I used an average over a number of runs (10 I recall) and got something like 207 to the wheels. I then had to dyno tune the MAF for smoothness across the RPM range and to check air/fuel ratio. The car dynoed at 207 to start and 209 after we tuned it in. It seems like the G-tech works to me. Many, many people have also reported taking it to the track to cross check 1/4 mile times and everyone I have talked to have reported that the G-tech is uncannily accurate.