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-   -   5spd vs 8 speed tranny (http://www.jeepgarage.org/f97/5spd-vs-8-speed-tranny-46939.html)

davidl13 09-02-2012 10:52 AM

5spd vs 8 speed tranny
 
the biggest difference i can see that will help is the new tranny has a .67 reduction final gear where the 5spd has a .83 reduction...

i test drove the 2012 srt8 yesterday and i noticed that i was at 2700 rpm @ 80mph... which is very high by todays standards....

so by my calculations , the new tranny should bring the highway rpm down to 2056@80mph... this should make the car quieter and fuel consumption lower....at cruising speed... of course the paddle shifters can eliminate the weakness if need be...

this is assuming the rear gears are the same...and the efficiency of the tranny is the same... if the new tranny is far more efficient as claimed, then the rpm may be lower still....

i think this will be a very positive change....and much needed lower rpm on the flat highway....


someone let me know if my research is accurate

5sp

http://i668.photobucket.com/albums/v...rannyspecs.jpg


8 spd

http://i668.photobucket.com/albums/v...22-12-00PM.jpg

Scottina06 09-02-2012 12:56 PM

Re: 5spd vs 8 speed tranny
 
the ratios for the 8 speed...did you get the hp45 or hp70 ratios

davidl13 09-02-2012 01:15 PM

Re: 5spd vs 8 speed tranny
 
8hp70

http://i668.photobucket.com/albums/v...22-12-00PM.jpg

Scottina06 09-02-2012 02:37 PM

Good numbers!

Scottina06 09-02-2012 02:38 PM

I'm gonna go drive an 8 speed LX on Tuesday to see how that tranny is......

davidl13 09-02-2012 03:35 PM

Re: 5spd vs 8 speed tranny
 
i currently drive a 69 plymouth barracuda convertible with a 225 slant six (super six) and at 80mph i am doing about 3000 rpm with a 3 speed auto tranny and (either 2.92 or 2.76 rear gears, i can't remember)...and it will drive all day, but with a big v8, you just don't need the rpm's up that high for flatlands... i am sure the srt8 will drive all day as well, but with today's technology, 2700rpm @80mph for the srt8 is significantly too high for a comfortable cruising speed/rpm.... i guess they designed the gears for traffic lights, because the 5.7 doesnt behave that way.... but the 5.7 takes way too long to find its power band...

but hey my boat cruises at 4-5k rpm... so i guess its a matter of perspective... and certainly at 2700 you have instant power on tap....

i personally am torn, i really dont want to wait or pay the premium...but the OD gearing is something i will have to deal with everyday...

not sure if i can wait it out....

http://i668.photobucket.com/albums/v...CudaAdd011.jpg

Scottina06 09-02-2012 03:55 PM

Re: 5spd vs 8 speed tranny
 
Im the same...Im not waiting 6-9 months and then paying $70k

HAMMMERHEAD 09-02-2012 08:52 PM

Re: 5spd vs 8 speed tranny
 
No way that much disparity. 2300-2400 RPM's at 80mph max. You would have to get in the .50 range for that kind of RPM drop.

curio 09-03-2012 03:57 AM

Re: 5spd vs 8 speed tranny
 
So for the Touareg with 8spd, ts 3000rpm at 119mph... :)

Happy Day

Achim

davidl13 09-03-2012 09:40 AM

Re: 5spd vs 8 speed tranny
 
here is the math....

if you are at 2700 rpm at .83 reduction , that would mean you are at 3253 rpm at 1.00 or zero reduction (x (.83)=2700)

therefore

3253 (zero reduction) minus .67 reduction would translate to 2180....@ 80 mph...

3253 rpm (.67 reduction) = 2179 rpm


not including any extra efficiency that the new tranny may offer.... and this can be significant,... there can be as much as 10-15% slippage....but i really don't know that figure, allpar states that the new tranny is 98% efficent....which will translate into higher mpg...although i am not certain about rpm... i would think once the torque converter locks up...all is equal...


Quote:

Originally Posted by HAMMMERHEAD (Post 678460)
No way that much disparity. 2300-2400 RPM's at 80mph max. You would have to get in the .50 range for that kind of RPM drop.


Mongoose9400 09-03-2012 11:09 AM

There is nothing wrong cruising at 80ish mph in the 2700-3000 rpm range. Just pay a little more for fuel. The WK1 SRT8 rev higher than the WK2 SRT8 at the same speeds. Many WK1 SRT8 with high mileage, the rpms won't harm the Jeep. Hell, I've put 14k highway miles on my WK2 SRT8 and my highway speeds are 80+ mph. Even drove it 30 hours straight one trip. The Jeep can take it no problems.


Sent from my iPhone 4S

davidl13 09-03-2012 12:02 PM

Re: 5spd vs 8 speed tranny
 
true that, it is just more comfortable at a lower crusing rpm for longer trips.. (mpg, noise, vibration etc...) ... my 69 barracuda can do it all day long at 3000 rpm and that is a pretty old engine....all original, no rebuilds...


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