Gear ratios yet again

[ultimad]

Folks,

I have had confirmation that a final drive ratio change for the Getrag is possible. I have the choice of 2.83 or 3.10 final drive.


3.10 final ratio gives :

Gear 1 2 3 4 5 6

MPH 48 83 119 147 176 213


Estimated torque at wheels :

At the point of changing from 5th to 6th: 1365
At top speed in 6th : 1137

2.83 gives :

Gear 1 2 3 4 5 6
MPH 52 91 130 161 193 234
Torque at wheels (5th and sixth gears) 1241 1028


At the point of changing from 5th to 6th: 1241
At top speed in 6th : 1028


The above is based on the top speed/torque spreadsheet that has done the rounds. My AS dyno report incicates 562 lb-ft @ 4800 RPM and 611 BHP @6954 RPM. Top speed is based on 7200 RPM (engine Dyno print runs to 7500 RPM but power drops off a lot after 7200).


Any thoughts as to which would be more suitable ?

[LuckyP]

Go lower. Higher and you'll be in my boat - yet with more power

[GTWayne]

If, like P above, you are hell bent on seeing 200+mph then the first option is as P suggests, more likely to tick the box but reading between the lines and the fact that I have a 70mph first gear with 650bhp @ 6,800rpm, shift point @ 7,200rpm, I find that it is well up to the task and in effect gives me a much more usable first gear and if I am right you do seem to like your track days, go for the second option, better to have 5 x usable gears in normal circumstances and a nice long 6th for economic cruising to and from the track

[San Diego GTR]

"Suitable" for what purpose? What is your goal? I think we're all assuming you want 200+ but maybe not? My G50/52 has 3.44 which takes me to something like 211, but my car (with me driving) will never test that math.

Edited by San Diego GTR on Thursday 6th September 15:23

[GTRCLIVE]

2.83 every time

[CanAm Dave]

Hi Andy

I would go for the 2.83 final drive. Any forecast on when these will be available. I would like to fit one to my car also.

Have you gone any further with your plans to supercharge?

Regards Dave

[kylemrushall]

Defo the later.

[ultimad]

CanAm Dave said:

Hi Andy

I would go for the 2.83 final drive. Any forecast on when these will be available. I would like to fit one to my car also.

Have you gone any further with your plans to supercharge?

Regards Dave

Hi Dave,

Roger Brown didn't say when in his latest correspondance (he was just telling me his manufacturer has come back to him and said it's feasible), although his original estimate was for Sep/Oct.

On the Supercharging front - I don't think I can afford Fuel Injection, lowering Compression ratio and then Supercharging and water/meth injection (especially if I do the Final Ratio change too) , so I'm currently looking into the fesibility of a blowthru carb Procharger unit using current engine compression ratio and buying gauges to give me feedback on things like A/F ratio and Exhaust Gas Temp. And before anyone comes back with a quip like 'it's cheaper than a new engine' it does appear quite safely achievable if I keep boost low, just a lot of work for me setting up/tuning. I've started by ordering a Holley Carb book recommended by one of the guys on here - in reality I think I would have to do the carb jetting etc. work myself and if I decide not to do it in the end, the knowledge should come in handy.

P.S I want it all - 200mph + and ridiculous acceleration coz I'm a total head case

[nickmpower]

what ratio are the 6 speeds supplied from the factory?

[ultimad]

nickmpower said:

what ratio are the 6 speeds supplied from the factory?

Getrag 6 Speed 3.820 2.200 1.520 1.220 1.020 0.840 3.444

(the last one being Final ratio)

[kylemrushall]

CanAm Dave said:

Hi Andy

I would go for the 2.83 final drive. Any forecast on when these will be available. I would like to fit one to my car also.

Have you gone any further with your plans to supercharge?

Regards Dave

I too would be interested in a 2.83, perhaps we can get a bit of discount if we order a few??? What sort of money will they be??

cheers Kyle

[ultimad]

kylemrushall said:

CanAm Dave said:

Hi Andy

I would go for the 2.83 final drive. Any forecast on when these will be available. I would like to fit one to my car also.

Have you gone any further with your plans to supercharge?

Regards Dave

I too would be interested in a 2.83, perhaps we can get a bit of discount if we order a few??? What sort of money will they be??

cheers Kyle

I dunno - I'll ask. Let me know who is is REALLY interested then and I'll go back to Roger with the numbers ? So far I have :

-Me
-Dave
-Kyle

[kylemrushall]

With my basic schoolboy maths i have just worked out that...

with the 2.83 final drive at 70mph we should see 2468rpm as opposed to 3000rpm with the current factory final drive!!! that shouls give much better cruising speeds and help with MPG!!

come on you Getrag boys lets see if we can get a nice big discount!!!

[kylemrushall]

Apparently it is even better than 2400 (thanks can am dave) it is

2100 RPM at 70 mph and not much more than 3000 RPM at 100 mph (not that i have ever gone that fast Officer!!!!)

That has got to be a cost effective mod for anyone with a GETRAG box???

[Chewy]

I would like the 2.83 final drive.
However I thought it was said that they would not produce this as they could not guarantee it.
Therefore the 3.1 final drive was the only reliable option.

[kylemrushall]

I have just spoken to a mate of mine (Master tech with Audi) he does quite a lot of work with Audi transaxles and they use a lot of Getrag Tranys!! He thinks if it is similiar to an Audi box it should be a straight forward job (changing the final drive that is). Porsche may of made it more difficult to change but manufacturers ie Getrag tend to build boxes the same way??

[ultimad]

Chewy - we were waiting on CMS's manufacturer to confirm faeasibility of a 2.82 ratio.

Roger's latest communication :

"At last, the final pricing from manufacturing:

996 Getrag G96/00 series 6 speed crown wheel and pinion sets 2.82 or 3.10 @ $3000.00 USD per set. They would be available by the end of the year. The 3.10 will be stronger and I think will work better overall for you versus 2.82."

I have asked him why he thinks 3.10 is a better option and whether a group discount applies and will let you know when he replies. I also asked him about strength compared to stock.

[kylemrushall]

ultimad said:

Chewy - we were waiting on CMS's manufacturer to confirm faeasibility of a 2.82 ratio.

Roger's latest communication :

"At last, the final pricing from manufacturing:

996 Getrag G96/00 series 6 speed crown wheel and pinion sets 2.82 or 3.10 @ $3000.00 USD per set. They would be available by the end of the year. The 3.10 will be stronger and I think will work better overall for you versus 2.82."

I have asked him why he thinks 3.10 is a better option and whether a group discount applies and will let you know when he replies. I also asked him about strength compared to stock.

Any more news on this