What would be your choice for transmission gear ratios be with the GT700 engine upgrade? (six-speed)

I want to keep sixth gear at the stock ratio.

 

i am also very interested in this.

1st gear goes by *way* too fast.

- chuck

 

BigBadBen changed up his gears. I drove his car and they are awsome. He can give you some excellent feedback.

 

If you need a taller first gear, you will need to change 2nd and 3rd as well, it becomes quite costly.

In any case, if you need a good gearbox, this works very well (993GT2):

1st : 3:15
2nd: 2:00
3rd.: 1:44
4th: 1:133
5th: 0.969
6th: 0.75 (if you need to keep it this tall)

If you have a 7K RPM limiter and 315s you will get roughly these speeds.

1st : 48mph
2nd: 75mph
3rd.: 105 mph
4th: 134 mph
5th: 156 mph
6th: 185 or so

I have a 1st gear of 2.5:1 on my sequential, which gets me to about 62mph in 1st. and the rest of course are all consequently staged, but I would not recommend it for street.

If your target is quartermile, work out the gears to be just before the limiter in 4th at trap speed, whatever that estimated speed is, I would see the above 4th gear suggested as good.

 

Have a look at this Blue Bayou. What Jean said too.

Ben

https://www.6speedonline.com/forums/...ad.php?t=49012

 

Nice setup Ben. Did you get the CF torque tube done? I have hard bushings as well and the car is indeed loud (very). I am buying a couple of boxes of Dynamat Extreme padding and filling-in the tunnel area under the car, as well as from the inside under the carpet. I have straight cut gears and it is no fun on the street. My 6th gear tops at about 160mph!

While in-gear acceleration is much better, I would think that your 0-130mph will be hurt?

 

Jean,

Thanks....

The CF tube should be here very shortly, its been made, torque tested and balanced so I am just waiting on it to be shipped to me, I will report back my finds as to how it changes the resonance from the steel driveshaft to the CF one. As CF has a higher resonant frequency it should fix my drive line resonance, from the gear box slap, LWFW and Wevo triple disk.

Yes, I did the Dynamat thing (carpet side) about two months ago. I completely stripped the car out to the front seats as I was installing my new Recaro Sport Toplines and it was the best time to do it, it made quite a difference.

As far as the gearing it concerned, it is a huge improvement over the stock gears. I noticed a huge lag IMO when shifting from 2nd to 3rd (stock gears)... That has gone completley now. I have to be really aware of each gear as they all have about a similar amount of time between shift points...you know..bang bang bang WOT etc. I sometimes wish 6th was a bit taller...I just came back from a 1K road trip and several times was looking for a 7th gear...now big deal really, the missus was with me this trip that's why.... It's funny I can be tootling along in 5th (4K plus RPM) and stamp on it and the thing just bloody takes off, even in 6th it's like that...I just am gob smacked at the acceleration of this car in each gear, I laugh my head off. Being in the sweet spot RPM (turbos are always nicely spooled) wise in each gear is the business, yes she whines a bit more but don't you just love that sound all the way up to redline..OMG it's so damn intoxicating, I can't get enough of it....I pitty the poor soles behind me when I let rip, it's friggin loud.

160 top gear OMG and I am complaining about 180 ... . I am itching to do the cams and raise the redline to 7600 or 8K but I know it's a big job that I don't have the tools for otherwise I could tackle it myself.... Chads car is 8500 I believe, (yours is?) now that would be something to see....I would be close to 60MPH in first I think.

I am such a believer in doing the gears on these GTXXX cars, it makes the power way more useable..the only snag is, it's not an inexpensive proposition.

One thing Brian Copans did tell me is that I will never break his gearbox, it's built like a tank now with only the best Porsche Motorsports gears, steel syncros/parts etc. I told him, I wanted the best he could get, no expense spared as I only wanted to do this once..so far so good...no issues at all. Brian knows his **** and I really appreciated his candour when we discussed this modification.

 

Ben,
Thanks, so it sounds like the Dynamat option is worth trying.

As you rightly said, and as far as gear staging and ratios are concerned, the biggest benefit of course is in the reduced RPM drops between shifts, which translates into faster shifts and always remaining on full boost.
With your gearbox, the RPM drops would be as follows with a 6800RPM limiter (this is approx of course):

1st-2nd: 4,317 RPMs
2nd-3rd: 5,304 RPMs
3rd-4th: 5,409 RPMs
4th-5th: 5,479 RPMs
5th-6th: 5,637 RPMs

You are therefore keeping your revs between max torque and max HP, optimizing acceleration.
I do think that 6800RPMs is a bit on the lowish side of the rev limiter, you can go to 7200RPMs quite safely.

My engine (993 not 996) has a rev limiter of 7150RPMs, but my gear ratios are taller, giving me a 1st gear of 62mph or so at 7100RPM. My gearbox was built by Holinger Engineering in NZ and then later modified further by Ricardo in the UK (F1 and Veyron builder). It is an undestructible sequential 6 speed gearbox. Cup gears are very strong but for high performance turbo engines, or cars running enduros, they can fail, I am guessing Brian used something else, there is nothing he wouldn't know anyway.

Worth mentioning, I have reduced my gearshift time by about 0.2 seconds per shift with this gearbox (on datalogs), extrapolate that to a full lap with an average of 40 shifts and do the math Obviously you will not be gaining 0.2s in each shift, but you can get a 4-5 second advantage per lap, which is by far the best mod on a track car. What is more important, my long G's don't drop into negative territory between shifts, meaning I am almost always accelerating.

 

Has anyone done a sequential for a 996TT?

 

Certainly, some 996 Cup cars have a sequential gearbox, so do the 997 Supercup cars, however the internals are not as strong.

This same gearbox fits the 996, it needs minor adjustment in terms of a custom bracket and conversion to cable shifter instead of rod if one prefers. The 996GT2 gearbox internals are derived from the early 993GT2s. They are not easy to get by though and rather expensive. The bracket that you see at the left is made to fit a 996 in fact, which is what the seller thought I had..

 

Jean, My redline is 7K now so are you saying Todd at EVO could program to 7,200 without doing the cams?

Ben

 

Ben, I would not know, they (the builder) are the only ones to be able to answer that, what I meant is without damage to the valvetrain, although it is safer to upgrade. I have mechanical rockers instead of hydraulic.

 

thanks guy for an awesome thread.

jean, could you explain your statement above a little more?

bigbadben, any way to get your hands on a datalogger so we can compare a normal gt700 acceleration vs yours?


- chuck

 

Jean qould you quite corrupting 996TT guys lol? For real though, Chuck is right, one of the reasons I like the tip is the gearing is siginificantly better down low over the 6speeds.

 

Chuck, it is basically painful teeth-grinding noise. I have to put some sound padding in there. However the beauty is that it takes about half an inch of shifter movement (front and rear only) to change gears, and no need to lift the gas pedal.