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Storm Transmission Modifications

With the Open differential, the storm constantly would lose traction launching or in turns, and torque steer was at the verge of being dangerous. Most of my launches at the track were one-wheel burnouts, and just accelerating on the highway turned into a battle to stay somewhat straight as the oscillation of power from wheel to wheel would pull the steering wheel left and right. A group of us decided that we needed to get a group buy going and contactd Quaife in the UK and have a custom ATB LSD made for our transmissions. The group consisted of 32 individuals around the globe, including the UK, Netherlands, Singapore, and the US. These people all shared one thing in common, an Isuzu built tranny. The vehicles included the Geo Storm, Isuzu Impulse/Stylus, Lotus Elan M100, and the Chevy Cavalier. The Quaife LSD retailed for $1600US + shipping, but when you have a group buying a bunch of them all at once, it dramatically lowers the price! I ended up paying $750 + $33 shipping, not bad considering what the Quaife LSD does.
Quaife Limited slip differential
Installed into the Storm GSi transmission
Quaife LSD installation
Once installed into the Storm, there is an immediate difference noticed in launching and torque steer, and an even greater difference noticed while making turns, specifically high speed/power turns. With an open differential, turning would usually make the car respond by pushing you out of the turn. With the Quaife though, you actually feel the car being pulled into the turn, with no wheel slip. It is quite an amazing feeling, and well worth the $750 I spent on it.

Here is the Quaife marketing blurb on the Automatic Torque Biasing LSD:
Quaife LSD cutaway
The QUAIFE Differential powers both drive wheels under nearly all conditions, instead of just one.
With an ordinary open differential, standard on most cars, a lot of precious power is wasted during wheel spin under acceleration. This happens because the open differential shifts power to the wheel with less grip, along the path of least resistance.
The QUAIFE, however, does just the opposite. It senses which wheel has better grip, and biases the power to that wheel. It does this smoothly and constantly, and without ever completely removing power from the other wheel.
In cornering, while accelerating out of a turn, the QUAIFE biases greater power to the outside wheel, reducing inside-wheel spin. This allows the driver to begin accelerating earlier, exiting the corner at a higher speed.
The QUAIFE also controls loss of traction when the drive wheels are on slippery surfaces such as ice and snow or mud, providing the appropriate biased traction needed to overcome these adverse conditions. The QUAIFE Differential provides constant and infinitely variable drive.
Power is transferred automatically without the use of normal friction pads or plates seen in other limited-slip designs.
The QUAIFE'S unique design offers maximum traction, improves handling and steering, and puts the power where it is needed most. A definite advantage whether on the track or on the street.
The QUAIFE is extremely strong and durable and since the Quaife is gear operated, it has no plates or clutches that can wear out and need costly replacement.
The QUAIFE is great for street driving or racing. Racers don't have to put up with locking mechanisms or spools that tear the steering wheel out of their hands when cornering. Because it behaves like an open differential during ordinary driving, street drivers will have trouble telling it's there until pushing the cars limits.
The QUAIFE has been proven in everything from SCCA Rally to Formula 1. It provides autocrossers with such an advantage, it has become "required" equipment for a winning effort.

Geo Storm/Isuzu Impulse/Stylus/I-Mark Transmission Specifications

Transmission 1st Gear 2nd Gear 3rd Gear 4th Gear 5th Gear Reverse Final Drive
Base Geo Storm SOHC 2+2 3.727:1 2.043:1 1.448:1 1.027:1 0.829:1 3.583 3.833:1
Stylus S SOHC 3.727:1 2.043:1 1.448:1 1.027:1 0.829:1 3.583 3.578:1
Geo Storm GSi / Isuzu Impulse XS / RS 3.909:1 2.150:1 1.448:1 1.027:1 0.829:1 3.583 4.117:1
1992 XS (maybe 92 GSI too) 3.727:1 2.150:1 1.448:1 1.027:1 0.829:1 3.583 4.117:1
Lotus Elan M100 3.333:1 1.916:1 1.333:1 1.027:1 0.829:1 3.583 3.833:1

I-Mark "S" or Sunsport 1.5 Carby 3.727:1 2.043:1 1.333:1 0.923:1 0.744:1 3.583:1 3.578:1
I-Mark XS 1.5 F/I 3.727:1 2.043:1 1.448:1 1.027:1 0.829:1 3.583:1 3.578:1
I-Mark LS 1.5 Turbo 3.500:1 1.916:1 1.333:1 0.923:1 0.744:1 3.583:1 3.833:1
I-Mark RS 1.6 DOHC N/A 3.727:1 2.043:1 1.448:1 1.027:1 0.829:1 3.583:1 4.117:1

Automatic Transmission Ratios
89-91 Base
(3-speed Mazda F3A automatic)
90-91 GSi
(4-speed Jatco F403E automatic)
92-93 Base
(3-speed Mazda F3A automatic)
92-93 GSi
(4-speed Jatco F403E automatic)
First 2.841 3.027 2.841 3.027
Second 1.541 1.619 1.541 1.619
Third 1.000 1.000 1.000 1.000
Fourth - 0.694 - 0.694
Final Drive 3.526 4.015 3.526 4.015
Part #s amd price list for replacement syncros and forks for the transmissions:

1st - 2nd syncro = 94335056 $111.79
1st - 2nd fork = 97015681 $ 34.66

3rd - 4th syncro = 97109769 $127.31
3rd - 4th fork = 94464752 $ 28.94

5th syncro = 97109770 $160.68
5th fork = 94109002 $ 28.46 lists two part numbers for the 3-4 and 5th gear synchros, they're the same ones listed for the Fiero.
I ran a pretty cool simulation with the different transmissions. these numbers are with stock HP numbers...except for the Turbo Storm applications :-D
Geo Storm Isuzu transmission comparison

Other LSD options available

Well, you only have 2 other options for the Isuzu Transmission; weld the differential spider gears in place or install the Phantom Grip LSD.
Welding the spider gears in place is about the cheapest way to get power to both axles at the same time, the down side is that making turns can really put a lot of stress onto the transmission, axles, CV joints, wheel bearings.
But if all you need to do is go straight for drag racing, this would be the way to go.

Another option you have is to install a Phantom Grip LSD kit. (Model# 910-GOLD $300-$349+shipping)
I did a little research into the Phantom LSD. . .it is a Limited Slip Differential conversion kit, that you install into your non-lsd, open differential.
I read a lot of opinions out there, and they all say that if you get it, get the Gold springs(Street/Race), or the Green springs(Full Race/Hard Core). The red springs only have 20lb/in, the Gold springs are 60lb/in and the Green springs are 120lb/in.
The base model comes standard with the Gold springs, and the Green springs run $29.95 extra.
Here is what you get from Phantom Grip:
Phantom Grip
Installed on the left:
Phantom Grip installed
here is a good article with benchmark test on a Nissan Site:
Nissan Performance Mag

There are a couple people that have installed it and did not notice any difference in performance, some of them are producing well over 350hp. I did read one article that the Phantom grip did cause some damage to the spider gears, so take that into account if you do decide to go this route. In my opinion, if you just can't afford to lay down a ton of cash for the Quaife LSD, or aren't building up a monster engine and just need a little bit more performance out of your transmission, then the Phantom Grip would probably be your best route, but don't expect it to perform like an Quaife LSD will, they just work differently. There are stats to back up the pluses to installing one compared to the stats of people that haven't seen a difference or have experienced a failure. All parts break, if you do it right, and I have broken many parts. In the end, it is your decision, and money!

Geo Storm isuzu impulse performance parts