Drivetrain

Clutch
Most of the clutches available for Geo Storm use an unmodified 1.8 liter 4XF1/Impulse RS Turbo 4XE1 pressure plate, and an upgraded disc. Common discs are a stock sprung hub with ceramic or Kevlar lining (full circle), a sprung hub with star shaped disc and ceramic or Kevlar pucks, or a solid hub with a full circle disc or star shaped disc with pucks.
A sprung hub will engage and disengage more smoothly, while an unsprung or solid hub will be more abrupt and will cause more shock through the drivetrain and chassis.
It is important to note that when the clutch is engaged, the drivetrain has the disc’s friction surfaces clamped between the pressure plate and the flywheel, and the power is not being transferred through the springs of the hub. The springs act only to hold the puck when the clutch is disengaged. So there is no enhanced power handling aspect of using a solid hub clutch disc.

Isuzuperformance first set up Broward Clutch to manufacture Geo Storm and Isuzu clutches.
After Broward Clutch closed, Isuzuperformance set up Clutch Specialties to make clutches for Geo Storm and Isuzu.
Isuzuperformance has more recently been building their own billet aluminum pressure plate assemblies for use with a proprietary ferro-carbon sprung hub disc.

Avoid clutches marketed with buzz words like “Stage 1, Stage 2, etc.” and “”Level 1, Level 2, etc.” These are marketing schemes to distract the buyer from looking at the materials, features, and power handling ability of the product, which determine the actual durability and quality.

Stiffer Pressure Plate from RWD Impulse Turbo
Among the Japanese Isuzu Gemini FWD and AWD owners, it has become popular to use the OEM pressure plate from the rear wheel drive 1985-89 Isuzu Piazza Turbo (1985-89 Impulse Turbo in the US market). The bolt pattern, diameter, and offset are the same, while the clamping force is at least twenty-five percent higher. This is partially due to the use of a hydraulic clutch in the RWD Piazza/Impulse, which greatly reduces pedal effort to operate the heavier clutch. (The Geo Storm and 90-93 Isuzu cars use a cable operated clutch).
One word of caution would be to be very careful that the added strength of the pressure plate does not pull the end of the clutch cable through the firewall. This was a common problem with the previous generation R-Body car, the 1985-89 Chevrolet Spectrum and Isuzu I-Mark. While the firewall was redesigned and strengthened for the Geo Storm and 90-93 Isuzu cars, there is a limit beyond which the cable will pull through the firewall.


Aluminum Flywheels
The flywheel is the heaviest rotating item attached to the engine. An aluminum flywheel with a steel friction plate will drop 6 pounds from the rotating mass, and provide a durable surface for the clutch to ride against. The power improvement is very noticeable. However, feathering out the clutch becomes more difficult and requires more concentration. The engine speed while letting out the clutch will need to be increased slightly, and the window between killing the engine and spinning the tires will become smaller.

Mueller Fabricators
Isuzuperformance commissioned Mueller Fabricators to make flywheels for Geo Storms and Isuzu engines, and paid all of the research, development, and tooling costs in exchange for exclusive sales rights. Mueller did not honor that promise, and made the products available for wholesale purchase to everyone, without any compensation to Isuzuperformance for paying to have the products produced to begin with. Mueller made a very good product, but the company closed around 2006.

Fidanza Engineering
After Mueller Fabricators closed, Isuzuperformance then commissioned Fidanza Engineering to do the same, and paid all of the research, development, and tooling costs a second time. Fidanza promised Isuzuperformance exclusive sales rights to the Isuzu and Geo Storm applications. Fidanza did not honor that promise, and made the products available for wholesale purchase to everyone, without any compensation to Isuzuperformance for paying to have the products produced to begin with. After a year or two, Fidanza had run out of their shelf stock that was paid for with Isuzuperformance’s R&D and tooling fees, and Fidanza asked Isuzuperformance to pay for another production run, or sell stock back to Fidanza to fill orders they had accepted for products they could not supply. Isuzuperformance declined the request. Fidanza then discontinued the products for Geo Storm and Isuzu engines, instead of paying their own production costs to make the product themselves.

Aasco Motorsport
Aasco is not a product manufacturer. Aasco purchases flywheels from Fidanza, and sells them under their own name. Like many online retailers (THMotorsports, Andy's Autosport, etc.), Aasco has fed all of the part numbers from one of Fidanza’s out-of-date catalogs into their website, and they accept orders for everything that they have a part number for. There is some pretty good evidence backing this up:
1. Aasco’s product listings always use stock photos of Fidanza products.
2. Aasco’s part numbers are identical to Fidanza’s part numbers.
3. Aasco has never successfully delivered a flywheel for an Isuzu vehicle (because Fidanza discontinued those items).
Once Aasco, or any retailer selling Fidanza flywheels, accept an order for an Isuzu application (Isuzu Impulse, Isuzu Stylus, Asuna Sunfire, Lotus Elan, etc.), and charge the customer’s credit card, they check if they can actually get the product from Fidanza, and upon learning that the product has been discontinued, they send the customer a short note stating that the product is no longer available, and they refund the customer’s money.

Isuzuperformance
After two choruses of paying all the costs to have two other companies make aluminum flywheels, Isuzuperformance has developed their own line of aluminum flywheels, with better clearance around the oil pump, lower weight, and incorporating a crank angle sensor for sequential fuel injection when used with the Isuzuperformance Programmable Computer System.

Limited Slip Differential / LSD
The differential in a car allows the inside and outside wheels on the driven axle(s) to travel at different distances as the car goes around a corner smoothly. Open differentials, such as the original differential used in the Geo Storm, will allow one wheel to spin freely, and the other to loose power, if traction is lost.
Limited slip differentials solve this issue, by forcing power to both wheels. A clutch pack type differential uses friction and a locking mechanism to accomplish this, but in FWD cars, the action is not smooth and the torque steer can be excessive. A gear driven torque biasing mechanism is more desirable, as the action is smoother and the mechanism will actually send more power to the wheel with traction, as long as the slipping tire does not lift completely off of the ground.
Limited slip differentials improve acceleration in both a straight line and also at corner exit.
Phantom Grip - Junk
The Phantom Grip is a spring loaded assembly that installs in the stock differential cage. Springs apply pressure against the blocks, which press on the side and/or end gears of the differential. It is supposed to act like a spring loaded clutch pack differential. As the differential moves within the transmission, the metal blocks are move on the shafts and "lock" against the spider gears to lock the differential. "Locking" is actually jamming against the gears within the differential, inevitably leading to damage to the gears, breaking the differential, and scattering broken pieces of gears, plates, and springs throughout the transmission, which will quickly destroy the transmission.
The slip limiting action of the Phantom Grip is negligable at best, quickly wearing and acting as a completely open differential with no slip limiting at all. By any and all measures, the Phantom Grip is a waste of money.
Quaife
R.T. Quaife Engineering sell automatic torque biasing limited slip differentials. Quaife subcontacts manufacturing to GKN Visco Drivetech, whose manufacturing facilities are in India and China. The steel used in the differentials is not the best quality and the case is not heat treated. The internal machining is sloppy. Chalk is used as thread lock on the bolts. (This is an indication of third world manufacturing and assembly). Though they are sold as “zero maintenance”, the mechanism will become loose over time.
Bill’s Inc. and Isuzuperformance purchased exclusive North American distribution rights for the Quaife product line and was granted exclusive rights to the use of the brand name and trademark. Isuzuperformance developed and commissioned applications for GM/Chevrolet/Pontiac/Saturn, Chrysler/Dodge, Mitsubishi, and Ford vehicles, as well as Isuzu and Geo Storm. Isuzuperformance dropped the retail price of the product line from $1200 per unit to $900 per unit. Very quickly, Isuzuperformance became the final step in manufacturing Quaife products, performing final inspection and quality control, correcting an increasing number of manufacturing errors and defects, preparing differentials for final installation, manufacturing installation parts and kits, and performing all warranty repair work.
Unfortunately, Quaife also sold exclusive North American distribution rights to several other companies, and multiple legal battles ensued. Eventually, Quaife was forced to purchase distribution rights back from Isuzuperformance, and the Isuzu applications were retired/discontinued as part of the settlement. Quaife lost a great deal of money, nearly lost their trademark rights, and essentially disappeared from the US market. The apparent “winner” of the multiple-exclusive-distributor debacle, Autotech, lost their authorized importer/dealers status in 2008. At that time, Autotech lost all authority to purchase, import, resell, distribute, service, etc., any and all Quaife products. Autotech did not receive a buy-back, and has been attempting, rather unsuccessfully, to unload product inventory as an unauthorized seller, in a never ending inventory reduction sale, since 2009. Some might observe out that Quaife made the wrong decision. Others might point out that Isuzuperformance was the only one to extract themselves from the situation without hundreds of thousands of dollars in losses.
Quaife discontinued the Isuzu and Geo Storm differential applications, and raised the prices of the rest of their product line up to $1,600 per differential.

Tracmax
Tracmax make automatic torque biasing limited slip differentials, in the United States, using top quality materials and with much cleaner machining.
Tracmax products for Geo Storm and Isuzu applications are available exclusively through Isuzuperformance.

Transmission Ratios
The Isuzu 76 mm transmission used in the Geo Storm was used in a number of different vehicles with a relatively wide range of ratios. However, for racing use, the ratios used in the DOHC Storm GSi, Impulse, and Stylus XS/RS, provide the lowest and most closely spaced ratios which are most desirable for acceleration.
The Base or SOHC transmission can be directly swapped with the DOHC transmission, providing stronger acceleration.

Convert to AWD from Impulse RS AWD
Transplanting the drivetrain from an Impulse RS AWD Turbo engine into a Geo Storm is simple and straightforward, just as described above under the engine swap section. The chassis are the same, so everything bolts directly into the vehicle, but everything in the system must be swapped, as very few of the pieces are shared between the two.
Again, as described above in the engine swap section, this is best accomplished with the donor car parked next to the recipient car, shop manuals for both vehicles, and transplanting all of the drivetrain directly from one vehicle to the other.
This will involve changing:
• The transmission.
• Transfer case.
• Front axles.
• Lower cross member.
• Steering rack.
• Power steering pipes.
• Rear engine mount (Transfer case mount).
• Driveshafts.
• Rear suspension cross member.
• Differential.
• Rear struts.
• Rear spindles.
• Rear axles.
• Rear wheel bearings.
This is best done with the turbocharged engine, as the drivetrain losses through the all wheel drive system make response rather dull with anything less than 160 HP of engine output.


DOHC Axles, Spindles, and Front Wheel Bearings for SOHC
The spindles, front wheel bearings, hubs, and axles of the GSi model are heavier duty than the Base model 12 Valve. The GSi right side axle is two piece, with a bearing and support that bolts to the back of the engine, creating an equal axle length for the left and right side, to minimize torque steer.
The parts can be swapped easily and without modifications. But they must be swapped as a group, because the individual pieces are not interchangeable. The GSi outer end spline (at the hub) is a larger diameter. The GSi front wheel bearing is larger in outside diameter and inside diameter.
Do not ever use a SOHC 12 Valve axle in a GSi spindle. The axle will spin inside the hub, stripping the splines from both, and destroying them in the process. This is a particular hazard when exchanging axles for rebuild, because many rebuilders are unaware that there is a difference between the two.

Engine Mounts / Transmission Mounts
The stock engine mounts in the Geo Storm were designed with a primary concern for reducing engine vibration. The soft material, large air voids, and 20+ years of wear and tear, leave them soft, if not cracked and broken. Good, solid engine mounts will reduce engine movement, provide more control to the driver, and improve performance. The tradeoff is an increase in engine vibration through the body of the vehicle.
Glue, caulk, and silicone are not a solution, as these are not strong enough and do not provide repair and structure where it is really needed.
The front and right side mounts are designed facing sideways to the direction of movement, so the entire load of the engine is placed on the side surfaces of the engine mount bracket and the flat surface of the chassis mounting tabs. The vehicle manufacturer placed rubber pads between the bracket and side tabs. You’ll notice a lot of wear to those pads, because they are the only thing resisting the twisting movement of the engine. Gluing or caulking around the core of the original bushing, or cutting a rubber cylinder to replace the part of the bushing within the round bracket, does nothing to reduce engine movement which is resisted only by the rubber side pads.
The only true solution is a molded, top hat shaped bushing, which fits tightly against the edges of the bracket and faces of the chassis mounting tabs.

Isuzuperformance
Isuzuperformance is the only company offering molded engine and transmission mount bushings for Geo Storm. Their bushings are an exact fit to the stock brackets, and go a step farther with stainless steel center sleeves which, unlike the original mild steel center sleeves, won’t rust to the engine mount bolts. The bushings are offered in two different hardness levels, medium for street use, and hard for racing use. Isuzuperformance also makes engine mount bushing brackets, including racing versions of the right side and front brackets. These brackets feature a flanged edge that increases the side surface by 2 ½ times over the area of the original brackets, providing more surface for the bushing to rest against to further resist engine movement.

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