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3.90 Rear Gear performance enhancement


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#21 UltimateLurker

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Posted 22 December 2003 - 09:31 AM

QUOTE
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.


???, terminal speed in 2nd is 61 mph, and although that's at 6K and the power leaves at 5K, 60 mph still only requires 1 shift.
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#22 chiplee1

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Posted 22 December 2003 - 12:16 PM

QUOTE
???, terminal speed in 2nd is 61 mph, and although that's at 6K and the power leaves at 5K, 60 mph still only requires 1 shift.


oh you're right, I was thinking two gears.  I took what you said to mean that with 3.90s you'd have to shift into 2nd to get to 60mph, but with 3.54s you wouldn't.  That explains alot, as I was starting to wonder about you thinking you could get 60mph out of first gear.  ;)  Good post by the way, on the original topic start.


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#23 artinist

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Posted 22 December 2003 - 12:35 PM

guys, part number MB185461 is replaced by MR325565 $393.58 according to mitsubishi.

i also heard back from Bill and he said that the gear info on his website is 3 years old and the pricing is off. he is charging $250 labor plus parts.
parts being> gears, seals and bearings if necessary.

as for used gears, i took a trip down to the junkyard yesterday and started looking around. seems like the trucks with G54 engines have a 3.54 gears like a stock starion. its is the 4G63 engine trucks that seem to have the 3.90s,

one thing that was anoying is that the D50s have a plate under the hood that just says mitsubishi motors and no info no gears, so i was only able to find out about the gears on mitsu truck that have that info on that plate.

does anyone know how to find the gear info on the D50? i plan to pull a set of gears out a mitsu truck this saturday. if this works, then there is plenty of used gears to go around.
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#24 UltimateLurker

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Posted 22 December 2003 - 01:03 PM

Excellent work Art!
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#25 heefner

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Posted 22 December 2003 - 01:38 PM

a lot of good points brought up on this post.  Art, I know some american cars and truck would have gear ratios stamped right on the rear.  Any chance the Japan did that also?  As for 3.90's shaving a bunch of time off in the 1/4, it might not look as good on the track as it does on paper.  Some of you guys shifting around 5200 and 5500 may have to go into 5th befor the traps which will cost you a few tenths.  Chip, I honeslty haven't tried launching in 2nd but I would think that would put a lot of ware and tare on the clutch in order to get the boost up enough to not bog off the line.  I may have to experiment a little to see how it works.

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#26 artinist

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Posted 22 December 2003 - 01:54 PM

since i put a lot of miles on the car, I drove a good distance in 4th at around 80mph to see how it will be to have 3.90s, its definetly not an issue for me.

Heefner, even with a 5500rpm limit 4th gear will have plenty of rpms left in it for the 1/4, and for the racers, their engine will have more room to rev so the faster speeds still will not be an issue.

launching in 2nd gear??? its not THAT much of a difference between the 3.90 and 3.54. this will also be impossible for the fidanze owners.
anyone who plans on doing that, should also have a bottle of A1 ready for the BBQ party.
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#27 haztoys

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Posted 01 January 2004 - 03:28 PM

Theres a sticker on the back of the rear end housing that will say what gears are in it .

At least out west there still there on most Mitsu rear end ,truck or Quest . In the rust belt states I do not know?

If the stickers white its a open diff if it yellow its a LSD.

3:90 WILL say 3:909 i "think" 3:45 says 3:545. 4:202 is 4:20. So just drop the last number

I'll try to explane this  I do not write that good so here go's

To find out what gears are in a rear end (any rear end)
-----------------------------------------------------------------------------------------------------------

If its a "open" diff

Get "one" wheel off the ground ! LEAVE ONE WHEEL ON THE GROUND!!!! or have some one hold one wheel!!

Mark the drive shaft yoke with chok

Turn the wheel "TWO" turns .

If the driveshaft "turns"  allmost 4   turns thats 3:90

If the driveshaft "turns"    3 1/2  turns thats 3:54

If the driveshaft "turns"    4  and a little more thats 4:20

If the  driveshaft  "turns"   4 1/2 plus a little more thats 4:62

________________________________________________________________

If you have a LSD like a Quest

GET "BOTH" WHEELS OFF THE GROUND

AND TURN THE WHEEL "ONLY" ONCE AND DO NOT HOLD THE OTHER WHEEL!!!!

And look at the number of turn on the shaft just like a open diff . The count on the driveshaft is the same as above.

__________________________________________________________________

Doe's anyone under stand what  I've wrote??

Car MUST not be in gear at the trans!!!!!!

I hope this is OK to post here?

 David

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#28 marksweet

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Posted 02 January 2004 - 02:41 PM

Interesting post! The 3.90 rear would cruise less rpm's than the 3.54 in 4th gear as the OD with the 3.90 yields a 3.31.
Mike I believe you will have NO trouble running mid 12's except for the street tires, though with practice launching you could do it. Slicks/11's!
Back when I was younger I was a Buick driver, GS models. Skylarks with big blocks. Most had 2.92's or 3.08 rears and a Chevelle rear wit 3.55's made an impressive difference. These cars really need more of a drop from 4th to 5th or an automatic that will hold up.
Gears have been the way to go fast all long. Having them streetable was the problem. New vettes have a .50 drop in 6th gear. That would drop our 4.22's to a 2.11!!! That's how those vettes can make nearly 30mpg cruising.
Shelby has had his share of big block mopars. The Hemi of those days really needed the 4.11's to really move the 4000lb. cars they were in. I rode in a 3.54 equipped R/T Hemi and it was not as impressive as I expected.
Looking foreward to your thoughts UL when you get the 3.9's. Personally due to my 6'2" frame and a multi surguried back I will try to find an automatic that will last. 4.22's would bce just fine with an auto/OD with their big drop in OD, usually just 68% of the rear gears. 4.22's bececome 2.86's!! in OD. The possible drawback at the track would be dropping into OD before the finish!!
Certainly gearing has been overlooked with our cars and UL may get us going in that direction. Mike are you going to 3.90's also?  

#29 ZPI28

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Posted 14 January 2004 - 07:53 AM

Id consider the 3.90s or even the 4.20s with my auto. Wonder how much longer my Auto tranny would last with lower gears and more boost?

=
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#30 marksweet

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Posted 14 January 2004 - 10:31 AM

I think the 4.22 rear and an auto would be great. Kevincar1 is working on a stronger auto for his quest and he will post results. The stock auto is just not strong enough even for a stock quest. I bought my quest from the 2nd owner, both females. The auto had to be rebuilt at 61K I bought it at 71k and burned it up in 5k. Admittedly I ran it hard. I will foreward Kevins email to anyone who wants to see his plans and contact him if you like. A strong auto with 4.22s would be very quick not lose boost between shifts and still cruise at less rpms than a 5speed with 3.54s. Mark

#31 Shelby

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Posted 25 January 2004 - 12:18 PM

for the auto tranny cars theres two things i'd recomend, first the  oil cooler has a  tmp  control valve on it , this can stick and  not alow the fluid to  flow thru the  cooler,,not  good , i'd sugest a  swap or  switch over to an after market   tranny cooler  with a larger   capasity , this  has alway been a requirement for  auto's when  toweing, so  the same applys to   drag raceing , and may explain  many of the  auto tranny failure over the yr's ,esp  some of the multi  failures

another thing i can say from personal experiance that  installing  3:90's in an auto   makes the  OD gear  ratio the same as the  5 spd  cars in 5th  gear at road  speed,
doing so in a 5 spd tranny car will  increase the 5th gear  rpm  by  500 rpms at any  given speed so the 5spd  would see more of a gain  then the  auto  cars ,but the drop in top  mph will be no problem  for the guys with  biger then  oem   cams , cause of the extra  top end  rpms  gain'd from the use of the cam
this will  cause the  1-2 shift  with  any cam to be a little earlier , but  if you have  500 to  900 more rpms on the top end , you may end up  shifting at the  same point  in the  frist part of the launch meaning if you are past the  60ft mark with the  3:54 gears  you should also be with  the 3:90 gears  with the extra rpms  avaiable , the  lower tourqe load put on the  engien will alow  a little more rpms  unless you get into vave float
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#32 marksweet

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Posted 25 January 2004 - 01:08 PM

Shelby a quest with an automatic could go to the 4.22's and once in OD it would still turn LESS rpm's at a given cruising speed than the 5-speed with the stock 3.54's. Too bad the stick in OD(5th) runs at 85% of the rear gears while the automatic is only at 68% of the rear gears.
The stick in 5th has in effect dropped to a 3.00 ratio (with a 3.54 rear) while the automatic car with 4.22's drops to 2.87.
A strong enough auto tranny would be a blast with 4.22's and some boost! Remember how some of those Road Runners and GTX's with autos and a shift kit would leap forward a car length when they shifted from 1st to 2nd? It would be wild with 18psi from even a Big 16G plus the 4.22's. There is a SQ member working on a auto that he feels will hold up. He told me that 87-92 Montero's with V6's had a Toyota A44D tranny. And with a 4 cylinder bellhousing could bolt to our G54B and still have a lock-up converter. The part about a proper tailshaft is the next to be solved as these tranny's were not rear wheel drive tranny's? We'll see what he comes up with!

#33 Shelby

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Posted 25 January 2004 - 01:23 PM

>Remember how some of those Road Runners and GTX's with autos and a shift kit would leap forward a car length when they shifted from 1st to 2nd? It would be wild with 18psi from even a Big 16G <<  


yep sure do  i had an  11sec road runner with the  383 engine
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#34 marksweet

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Posted 25 January 2004 - 02:02 PM

i RAN A '66 bUICK sKYLARK gs WITH THE "NAILHEAD" 401". i DID HAVE A BUDDY WITH A '69gtx-440 THAT RAN MID 12'S WITH AN OCCASIONAL STREET RUN/hang on!! MAN DID THAT REV QUICK!!

#35 Starcon88

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Posted 02 February 2004 - 09:23 AM

Question, can we do a speedometer correction? Since its going to be off.

  Kurt
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#36 marksweet

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Posted 02 February 2004 - 09:41 AM

The speedometer would read faster than the car was actually going so a different speedo driven gear would be needed. Fuel injection specialities should have the appropriate gear availale or part # since they offer the ring and pinion upgrade. Mark

#37 spoolinturbo

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Posted 02 February 2004 - 11:07 PM

sounds like a lot of work to me... ??? interesting though...
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#38 marksweet

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Posted 03 February 2004 - 06:29 AM

Jeff I aqgree. Unless your car is spending most of it's time on the track I do not believe the expense is worth the results. 3.54's aren't slouch gears and the money spent to go to 3.90's would reap greater benefits if applied elsewhere on the car. Just my opinion. Mark

#39 Shelby

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Posted 09 February 2004 - 09:35 AM

guys if  you  have never personaly   try'd swaping  gear ratio's  while drag  raceing please   say so  so  we can tell if your speaking from personal experiance or   hear -say
that said if you have  no more  rpms to work with other then the stock  valve train ,   lower gears  may not help you , but if you  have  the  upper  rpm range to  be able to get to  6.5 and 7 k  then your  going to  need them
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#40 KT

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Posted 10 February 2004 - 09:20 PM

Hey Chip,

Someone earlier mentioned you would need to shift at 6K, but we run out of power at 5K.  I find it hard to believe that a MPI won't make power past 5K.  Any input?

KT
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