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3.90 Rear Gear performance enhancement


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#1 Truth

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Posted 20 December 2003 - 10:42 AM

since my friend with his 97 Mustang GT got those 3.73 gears, and i saw how much of a difference it made, i have contemplated buying some 3.90's for my quest.  the only thing i have a problem with is availability, and what rpms will i be running doing about 60mph?
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#2 Shelby

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Posted 20 December 2003 - 11:36 AM

now  UL if you  follow the same reasoning   with say mods  like  you have done, the diff is further  enhance'd , one thing to  keep in mind along with the lower top rpm/spd  is the time need'd to abtain that rpm,, you  will have less time  during  each gear shift  for the engine to work, so the importance of the engine  tune'd state becomes more  and more important ,as will the time to  actualy make those shifts ,
thus  with  realy  low rear  gears it is almost  a must to go to an auto car so the shift time is reduce'd ,  we're not machines and doing the same perfict  shift time and time again  is some thing not many  can do , now of course  road raceing  and  ralley  raceing are a diff thing  entirely , here guys like the choice of haveing more gears to chose from

now  changeing out the  rear gearing is not  something for every one,it is only  for the serious   racers ,if mpg is  of   intrest to you  don't even think about it, unless you  want to do a swap  of  diff  in and out  for a special event
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#3 UltimateLurker

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Posted 20 December 2003 - 05:00 PM

Agreed, I certainly won't be putting the 4.22's in my car, the powerband is only from 3-5K.

My ultimate goal is a 13.5 ET, and I believe wholeheartedly that a Super 16G and 3.90's will get me there.
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#4 long4boost

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Posted 20 December 2003 - 05:59 PM

SIGN ME UP! dude im all about quick accerlation, really top speed does nothing for me at all, acutly to be quite honest it scares the shizzle out of me, for what can happen, and how fast it can happen.  So tell me you smart a** mofo ul (not meant darogatory, meant meaning that your freakin smart) where would one go to get something like this.  and then could i use my stock diff, and just change out the that gear?  Because i could swap a diff out in a few hours (done it enough hehe) and after christmas i will have the right tools so doing something like that wouldnt take long for ME, but for others it might take more time..  sooo where would i get one? and then just one other question,  say @80 in 5th would would my curzing rpms be?

peace
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#5 Boosted_One

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Posted 20 December 2003 - 06:00 PM

QUOTE
.

My ultimate goal is a 13.5 ET, and I believe wholeheartedly that a Super 16G and 3.90's will get me there.



I agree on that one!

My goal is to hit mid 12's on street tires.  ;D
Mike K

#6 Lizzord30

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Posted 20 December 2003 - 06:19 PM

QUOTE
Agreed, I certainly won't be putting the 4.22's in my car, the powerband is only from 3-5K.

My ultimate goal is a 13.5 ET, and I believe wholeheartedly that a Super 16G and 3.90's will get me there.


If nick can get constint 13.6's on Small 16g and stock gears (i think he would get at lest a 13.5 now with the head ported and HD springs). I hope you can get 13.5 with a larger turbo and gears.
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More info here: http://www.starquestclub.com/forum/index.php?showtopic=130169
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#7 UltimateLurker

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Posted 20 December 2003 - 09:44 PM

Ted: I'm checkin' on that right now, at the moment you can get them HERE for $510, but if I can find out exactly what to look for in the Junk Yard that'd be a LOT cheaper ;D.

Luke: I didn't know Nick's times with mods, thanks for tellin' me smile.gif.  All I know is that it gets harder and harder to shave time the faster you get, and I'm not looking to kill my car, just enhance it.  If I run a low 13 I'm be more than happy, all I'm looking for is 13.5.
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#8 Technology

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Posted 20 December 2003 - 10:26 PM

i'm looking for 11's ...mid 11's.

that'd be pretty nice. i could own pretty much anyone.

#9 Ratmtattat

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Posted 21 December 2003 - 01:18 PM

I remember talking with Shelby about this a long while back and wondering why no one was doing this, since it has the ability to enchance the accleration of the car to a greater degree than almost anything.   But now you guys are making me so happy that you're going to do it. Maybe a kit will come out eventually and even a poor college kid like me can even afford it.  :)
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#10 UltimateLurker

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Posted 21 December 2003 - 02:05 PM

We already know the part # (MB185461), now all we have to find out is exactly what to look for when we go to the junk yards and we're set, I don't think this is an expensive endeavor Jason.
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#11 UltimateLurker

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Posted 21 December 2003 - 02:21 PM

Edit.
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#12 Shelby

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Posted 21 December 2003 - 03:23 PM

smile.gif  in most  cases the  use of a set of 3:90 gear will give  the  average  guy a lower ET , esp if he goes to the track  with his every  day tires , any  gain in the last half of the track will be ate up from wheel spin ,at the  first 60 ft ,  all these coments about  my 1st and 2'd gear are useless  due to wheel spin, if you haven't figure'd it out yet it's your tires not  the fact  you have  400 hp ,the car weigths 3k lbs that more then enought  to get traction with a good set of tires , one  ride arround the  block in drag radials and  all that  wheel spining  crap will be  gone you'l think some  one detune'd  your   pride and  joy while you weren't looking , or you may be looking for the rest of the drive shaft pieces  hehe

gear ratio playing is  just like  every  thing  else,  doing one thing  may mean the   need to do some thing else , like valve springs, it'l be a manditory  fact  they will have to be in good shape , cause that   5or6k  rpm  will be there  faster then it is now ,

UL  you  say the 1-2 shift  will  be with in the 60 ft,, one thing your  not  counting on is the  fact that with out  wheel spin the launch is at a much lower  rpm then  when the  tires are spining  and going  no where , so you  guys thinking about this gear swap  be prepair'd  to buy  drag  tires of some type , you every day tires are gona be useless , that is if you  realy want to see the  advantage of  what they  can do for you , the higher the number the  more tire  you'l need

you auto  guys  will love the  gear swap tho more so then the 5 spd  guys  for you the add'd   tourqe off the line under boost  will realy  kick it in the   rear ,with the proper tire 's ,  speaking of the auto's we're gona have to have  some one  get  to work on a stage'd boost controler to  limet the boost untill after the 1-2 shift , one that will  do it on it's own

the next yr or two, we   can  realy be in for  some  fun
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#13 UltimateLurker

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Posted 21 December 2003 - 05:46 PM

Shelby, I was actually talking about the 0-60 MPH bracket, not 60 ft wink.gif.

And do I sense another chance at a shameless plug for the mighty Yoko's?

http://gallery.s2ki....mageview/67833/

Ah, I feel much better ;D.

Trust me, I'll make good use of the 3.90's ;D.
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#14 Shelby

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Posted 21 December 2003 - 06:05 PM

;D ;D ;D ;D ;D ;D yepper's  good time  for a pic
oh and 60 ft , 0 to 60 mph don't you think they  relate to each other clock  is  running on both right  ;)
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#15 chiplee1

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Posted 21 December 2003 - 07:16 PM

QUOTE
Changing to the 3.90 gears will require 2 shifts to 60, which will most certainly eat away at their theoretical .7 advantage, but they should still make the car quicker in the 8th and the ¼.

.


it already required two shifts to 60 unless you're driving some hybrid.  But if you were actually talking about 60ft when you posted that I'd have suggested launching in 2nd, which I may try with the stock rear gears.


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#16 Boosted_One

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Posted 21 December 2003 - 07:41 PM

QUOTE
 all these coments about  my 1st and 2'd gear are useless  due to wheel spin, if you haven't figure'd it out yet it's your tires not  the fact  you have  400 hp ,the car weigths 3k lbs that more then enought  to get traction with a good set of tires , one  ride arround the  block in drag radials and  all that  wheel spining  crap will be  gone you'l think some  one detune'd  your   pride and  joy while you weren't looking , or you may be looking for the rest of the drive shaft pieces  hehe



I've found since I swapped to the larger turbo in I have a lot more 1st gear. I seem to get a little more load on in 1st gear.

Positive byproduct? Perhaps.
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#17 Shelby

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Posted 21 December 2003 - 08:08 PM

Chip,, hehe  last  few guys that try'd 2"d gear lauchs are still bicking up pieces and parts  :)
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#18 chiplee1

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Posted 21 December 2003 - 08:29 PM

QUOTE
Chip,, hehe  last  few guys that try'd 2"d gear lauchs are still bicking up pieces and parts  smile.gif


comes highly recommended from several experienced racers locally.  Desktop dyno says it's the only way my car will see even a high 12 second pass.  2nd gear launch was a full .7 sec faster in the quarter than the 1st gear launch.  If your recommendation is against it I'll take that under serious consideration, as I'm not really interested in breaking, but I was under the impression it was rather common.  And with the 3.90 gears it shouldn't be as hard on parts.


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#19 Shelby

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Posted 21 December 2003 - 08:45 PM

the 2'd gear is a 2:08 , a better bet would be an older  D50 with a  2:36 1st , all the  gears are a  bit taller even 5 th, may not last long with  the power you're puting  out tho , but  should hold for a few  runs , ours is a 3:36   1 st ,  with the old tranny i could almost  get 60 mph out of it  in 1st with the  3:54 rears
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#20 jinx

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Posted 22 December 2003 - 01:14 AM

I wouldn't get rid of my 3.54 stock gears, especially for a moded car.
Its much easier (and cheaper) to try a shorter, smaller diameter tire and test it at the strip before commiting to a 3.90 or higher.
Once you have considerably more torque available, 3.54 are fine imo.
I remember a handful of GN clubmembers brought over those traditional hot rod practices and swapped out their 3.42s for shorter gears. Sure the car 'felt' more responsive, but guess what happened to their ET?
Turbos love load




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