Noticed the new ZR-1 gets to 60 in just 1st gear in 3.4 sec. Engine has 638 HP (6.2cc, supercharged) with 604 torgue. Porsche tt with manual gets there in 3.7, while the auto makes it in 3.4sec. Sure would be nice to lengthen out first gear a bit....seems like the rev-limiter kicks in about the time you decide it is not time to shift and acceleration time is lost big-time. With a manual, if is focus 100% to remember that first shift because you have about two-three seconds or get zapped with the rev-limiter. This problem alone will be worth maybe switching to the auto-2-clutch maual that just made its appearance in non-turbo porsches this year and should be on the tts by next year.

There is an equation available that shows a rear axle ratio of about 2 would let the tt make 60 in first gear, but I think porsche keeps the rear axle at 3.44 to get the turbos going. At low rpm, the turbo's are worthless.

the equation: mph = [RPM x (Td) x 3.14] divided by [(GR) (1050)]


Where Td = tire diameter in inches
GR = overall gear ratio (gearbox ratio x axle ratio)

Fitting in values: 60 mph = [(6800rpm)(19) x 3.14 ] divided by [(ra)(3.818)(1050)]


where ra is equals rear axle ratio and from the equation, ra comes
to around 2.0.

However, with such a low rear axle number, the rpms would have to be substantial off line when the clutch is lifted.

I noticed the automatic has 3.6 ratio for first with a rear end ratio of only 3.06, wheras the manual uses a 3.818 first gear with manual final drive 3.44. Big difference in overall gear ration 13.3 manual with 11.0 for auto.

IF you use the equation to match 1st gear near redline speeds for the manual vs the automatic, looks like in 1st gear, the manual tt redlines at about 5-6 miles per hour lower than the auto-trans. Which translates to a 1st gear shift in the auto tt around 42-43 m/h. Never have driven a tt auto. Can someone with an auto-tt let me know if the autotrans shifts at 42-43 when at redline???
Trying to see if the above equation really extrapolates to the real world.

Any other ideas out there to get a tt to 60 without a shift????
Eq..ref "Tunning for power and economy by A Bell."

 

tym is looking at gear sets to get me to 60 in first gear. it definitely helps that my redline is 7800 rpms as well. my car did 0 - 60 in 2.54 seconds on the drift box. tym thinks we can hit 2.0 seconds flat if we can hit 60 mph in first gear!

 

What is your speed in first gear when your tt reaches 7800 rpm?? I was thinking of moving the rpm cut off to 7500, but experts tell me that the turbo just runs out of accelerating punch after 6800, so the extra rpm does not mean much with respect to acceleration because you still need to shift. Don't you think there may be engine problems at that rpm?? I wonder how high the rpm cutoff can go with tt engines and still keep the engine under safe limits??Do you have a simple means to return the rpm back to 6800 if in for warranty issues??

 

his car is a highly modified monster, so warranty issues don'd come into play there.

 

the optimal shift point on my car is around 7000 rpms. these is where i shift from 1st to 2nd, 2nd to 3rd, and 3rd to 4th. i simply hang it out to 7800 rpms in 4th to try to complete the 1/4 mile without another shift. i don't think i would run the stock motor above 7800 rpms and only do this to complete a drag pass. but i had a different gear set, i would make 1st and 4th taller. there is a pretty big gap between 1st and 2nd. and 3rd is fine. so i would leave 2nd and 3rd alone.

 

You could always start off in second.

I agree that 1st is way too short...it bugs me. It's hard to shift fast enough when the power hits and it's way too easy to hit the rev limiter.

I wish the rev limiter was well north of 7000rpm. Seems like the only way to get that is with an engine rebuild...chips at best offer a few hundred rpm bump. I dont think that going with a different gear set willl actually make the car faster...it would only improve the 0-60 measured time but nothing else.

 

How about the GT2 gearing with that 7800 shift? i think the GT2 can do 15-20mph more than the TT in first

 

Due to the turbo lag I'm not sure that hitting 60 in 1st is the right answer for what you're looking for (which seems to be just a fast 0-60 time). That said, increasing your redline in combo with a taller first would be the right direction if that's what you want to do.

I'm geared to 59 mph in 1st for autocross and track use (not a TT). I've got a 13:41 first gear ratio in the G50, and have the GT3 motor redlined at 8500. Depending on tire diameter it would be easy enough to get to 60. If I was going to try and do a similar thing with a TT I'd focus on raising the power band and rev limit. This is certainly possible- on an air-cooled motor the GT2 Evo turbo cams increased the RPM that peak power is made by over 1000 rpm (with proper turbos, etc), and I'm sure a similar cam is available for the 996TT. Not sure where the rest of the package revs to, though, but I'm sure tuners have figured that out the hard way if you ask around. To give you an idea in my last 993 motor I did cams, valve springs, titanium retainers and rod bolts and was able to safely increase the redline by 800 rpm.

Before you go through all of that, however, I'd suggest you simulate the various options.
The basic version of Bosch Lapsim is available free here:
http://www.bosch-motorsport.com/cont.../html/3589.htm
Once you get the car set up, which does take some time (you'll need vehicle dimensions, gearing, dyno, etc) you can virtually drag race it, make changes and drag race it again. You'll find that simply changing 1st gear to hit 60 mph will actually slow you down, but you'll be able to look at other options that will help.

 

What is your car speed in mph when you shift at 7000 rpm in 1st gear and then car speed in second gear when shifting at 7000 rpm???

 

the GT2 definitely has some taller gearing. ideally, i would love to have a gt2 gearbox in my tt.

 

At 7000 rpms, i can hit about 40 mph in 1st gear and 74 mph in second gear.

 

Thanks for info, looks like 1-1.5 m/h (1st). and 3-4 m/h in 2nd gain at 7k rpm over what is seen at the factory 6700-6800 redline.

 

this exactly what i always tought...!!!

but the question is if our turbine can keep pushing the car with the same power after 6800!



ABOUT 60mph(aprox 100km/h) in first, is imposible! BECAUSE TURBO LAG...

IMAGINE you in a roll from 15km/h with a turbo car that goes 60 in 1st... the car will just start to push after 40-50km/h

RIDICULOUS, before 40-50 km/h NOBODY HOME!

 

so you are running 900 hp on a stock manual gearbox ?!

 

yes. stock gearbox and stock internals. bolt-ons only.