JohnJL

Chip,
I'm still stuck on your "Psychology of the Butt Dyno."

Sounds like a great read.

LOL

Jean

Sonny1

Thanks for the suggestion, I forgot they existed! I will check it out, any tips or clues about pricing would be very helpful.

Chip, Pfeww, first one to tell me it actually can make sense. Thanks.

Hey Mike, no I did not make it, but due to hechtic business schedule. You're back to civilization I guess and none less than in Spain, quite a drastic change, it is my home country as well you know, I know you're having fun! I hope next time we meet.

OK, I might be ready to exchange my 993TT gearbox for a G50/20. I will post separately if so. Just waiting for some final advise.

Jeff96-993

Jean,

What's the model number on your tranny (G64/51? G50/54?).

I'd like to see a similar assessment of your transmission on an NA car... if it's positive then you may have a G50/20 donor!

914und993

I know what I'm talking about, since most of the time my head is up my... well we won't go there.

Chip

akolodesh

What an excellent thread - exactly the kind of stuff that helps everyone of us "addicts" continue on our quest of the slippery slope of mods. I am very interested in the relationship between the infamous "butt dyno" and the actual numbers. I have driven in the passenger seat of a close ratio geared 993 and it "seemed" significantly faster than my standard ratio tranny. If it really is not much faster than this may not be a cost effective mod for me. I would love to see real head to head numbers in different distances/speeds (0-60, 0-100, 30-60, 50-80, 1/4 mile, 1 mile, etc..) to get a better understanding of the real effect this mod has on the performance of the car.
I have heard (and felt) that the close ratio gearing add 50 hp on the "butt dyna". Some of the analyses on this thread would dispute this claim. Anyway that we can get some real world numbers to evaluate the different hypotheses?

Jean

Jeff,

The gearbox for the TT is a G64/51. I will run the numbers in a couple of hours no problem, dinner time here

Alex, I have always wondered the same thing. I have seen a friend with his 996TT Roock beat me on acceleration due to this (I beat 996GT2s with my 965 up to 130-140 mph). I was changing gears and he was still pulling ahead of me without changing gears, I could never catch him back after that. Roock also uses taller ratios. Their latest car puts out a claimed 3.1 seconds 0-60.

Jean

Ok, I have made some runs on a Carrera 4 comparing US vs ROW vs TT gearbox and the findings are that the TT and ROW gearboxes yield similar times all the way up to quarter mile ( Ihave not tested beyond that point). The gears are the same between TT and ROW with only the 4th, 5th, and 6th ratios being slightly taller on the TT. Obviously the other difference is that the TT gearbox is stronger.

Also, for information, I checked on the EKS RUF clutchless sytem, it is a great system apparently, the drawbacks being that it adds weight to the car and complexity. Also, for a correct calibration, the car must be at the workshop since it needs quite a bit of customization to the engine caracteristics, power curve etc.. Net net, not a viable option for non-stock cars from a distance.

Will revert with more news on ideal gearing after further research.

Jeff96-993

Jean,

I was hoping that you had the GT2 tranny... that could fit a normal Carrera plus it had some interesting ratios.

I don't think the 4wd gearbox would be the best solution for a NA car. It must weigh more, right? I'm sure there are other drawbacks that I haven't even considered.

Jean

Jeff,

Sorry I do not know the answers, but my guess would be that it does not matter whether it is a Carrera 2 or 4 as far as gearbox itself is concerned??? I converted my 993TT to a 2WD (have not driven it yet) and I have not done any modifications to the box, all the work was in the front.

I am not decided whether I want to swap or not, as we are assessing the best approach, but I have two TT trannies at home so I can afford exchanging one eventually, I will post about it separately if so.
Jean

993RS

The close gearing just allows you to rev up quicker. You feel as if your torque curve has been raised in the low to midrange. More fun to drive. Gives it kind of a TT feel... But once you are up in the powerband and accelerating fast, not much difference IMHO.

DJF1

While I have not done a numbers analysis like you, the only thing I know for a fact is that when I changed the gearbox I picked up consistently 5+ MPH of top speed before turn 1 down the long straight of TWS. I did not make any changes to the car other than the gearbox swap. While this is not scientific data by any means, the shorter box keeps the engine on the boil so to speak so most of the time you are in the "right" gear so to speak. The long US box presented many times a challenge when it came to 3rd or 4th gear turns. If I would stay on 3rd I would revlimit at the trackout and have a very twichy car , If I upshifted to 4th I would be off the powerband at track out for example. With the short box that challenge is not there.
I'm also a proponent of the "dyno butt". For me it feels like a 50HP upgrade

Just my 02...

Jean

DJ, it's what, 4:00 AM there?

I would like to clarify again, the ROW gearbox does show better response than a US, on a N/A engine. In straight line acceleration, the difference is very little though and even turns to a disadvantage at higher speeds., and a 10-15 hp increase on the US car would offset that advantage.

On a track, many parameters will make a difference, of which the ones you mentioned are the most important, if you fall outside your optimum powerband with the US box coming out of a turn, you can fix it with a ROW box. On longer turns however, it could be the other way around, as you might be forced to shift-up right in the middle of the turn while you can be carrying more exit speed with a US box since you have not shifted, you will not catch up the US car in straight line if he exits faster ahead of you. Do you agree?

As you know, on some tracks, you will fare better with a taller box, this is why I am focusing on street acceleration.

Many parameters.. I have never driven a US Carrera, and I don't feel the ROW to be that responsive, but one thing I feel needs calibration, your butt dynos guys! you are not following DIN requirements..

DJF1

Heh...close to it! I had to wake up really early this morning

At any rate, if you have not driven a N/A Carrera then the whole discussion is becoming a bit academic comparing the application for a monster TT like yours...
The difference on the NA is profound and very tangible. In your case with so much torque the higher gearing will nto be much of an issue and yes its probably better for what you need. On our cars it takes a virtual eternity to get on cam so to speak and that means a lot of time outside of the sweet spot with the G50/20. Varioram cars fare better here, but 95's like mine which don't have much of anything below 4 grand it becomes crucial IMO.

Regarding the track usually the shorter box on a single lap will be more usefull than a long one. Most tracks if not every track have slower corners or S type of corners just before their longest straights. There it is crucial to be on full torque at the exit in order to gain as much time on straight line so the benefits of a gearbox that can keep you on torque are tanglible and desirable...

I guess the question in your case should be what type of power and torque character your modified motor has, to match a gearset. If you were stock GT2 then the GT2 box I pressume would be what you want, but a modified motor makes up for a bit more head scratching...