Porsche 993 & 964 Resource Notes & Words of Wisdom Page

This page contains resource notes beyond the over 100 other 993 buying, servicing, repair, and upgrade topics in this blog that just make owning, servicing, and getting parts for a 993 or 964 easier and less costly. It is a work in progress and will have entries added going forward so check back here from time to time.

CD-ROM or download .pdf Porsche Parts Catalog:

 The 993 & 964 CD-ROM parts catalogs are in some respects a re-part numbered appendix to earlier model catalogs. For this reason many smaller subassembly part numbers are just plain missing. For example, the broken-out component list for the rubber shift coupler is listed in an earlier catalog with inexpensive part numbers for purchase where only the entire assembly, an expensive part is listed on the 993 CD-ROM.

Shift Coupler

Another example is the BOSCH distributor that shares many of the same parts as earlier single head designs. The drive gear, seal, and shear-pin needed to service the internal belt on a 993/964 distributor is listed for the single head BOSCH distributor in the '80s Carrera catalog these parts are most likely completely interchangeable.

Another example is the listing of electrical harness replacement plugs, sockets and other terminations most of which can be found in a setion of the 964 catalog listed at the bottom of this page. and not to be found in the 993 catalog.

 The Factory 993 Parts Catalog and its earlier Model iterations can be found online with a little searching.

For example: 

 https://www.porsche.com/usa/accessoriesandservices/classic/genuineparts/originalpartscatalogue/

  

The Factory Shop Manual in binders or as a .pdf:

Similar to this the Porsche Factory Shop Manuals for the 993 & 964 act in many ways as an appendix to earlier 911 shop manuals and is missing entire subject areas covered in depth in earlier model shop manuals. For example, the sunroof mechanism design goes way back to very early cars. An early-year shop manual has a complete section on the disassembly, adjustment, servicing, and reassembly of the sunroof. This is not to be found anywhere in the newer  model shop manuals. This page includes some select sections from ealier shop manuals that apply to the 993 & 964.

The factory shop manual and its earlier 911 model iterations can be found online with a little searching: 

For example :https://www.carpdfmanual.com/porsche/ 

Items that save a lot of aggravation while owning and servicing your 993 or 964:

• 

  
  

  A long-reach low-profile hydraulic floor jack, similar to what is sold at Harbor freight, is something you will bless the day you purchased it every time you change your oil or do most any wheel end or under-car servicing.
  
• Porsche specifies that the 993 be only lifted by the factory jack points to do this with jack stands involves subjecting the car to significant twisting forces when lifting from a single jack point, say when servicing a wheel end.  Using a product called LiftBars in conjunction with the two jacking points on each side of the car eliminates this twisting force and is discussed in the middle of this page.
• 

• 
  A pressure bleeder for when changing the brake fluid. Something I found to be a golden item to have on hand making one-man brake bleeds a no-brainer.

• The Original Equipment Emergency Jack, the jack that comes with the 993 Carrera is compact, lightweight, and extremely unsafe to use on the side of the road. 

  

  Original Carrera
  Emergency Jack

  Swapping it out with a  light alloy scissors-style Porsche branded jack that came with the Turbo is an option. It is referenced under several Porsche part numbers for example; 000.721.711.05 or 996.721.711.00. It can be purchased new at the dealer, from Pelican Parts, or used on eBay or from a Porsche dismantler. It seems this jack has been renumbered and superseded several times in the catalog so if you purchase it without seeing the actual jack have the seller verify the jack is the scissors type with the 993 alignment stud for the 993 body lift points.
• An inexpensive steel scissors jack from Walmart, Amazon, or really most auto parts stores is an option. In this case, one will need to modify the jack by adding a  short bolt with washers and nuts forming a stud that interlocks with the hole on the lift point of a 964/993. This modification is very important as it protects the car from slipping off the jack during an emergency jacking event.

Porsche Scissors
Emergency Jack

Generic Scissors Jack with
nut, bolt & washers stud added

• A 1.5 to 2.5 Amp float/charger that fits into your cigarette lighter or one with an adapter cord that does. A lifesaver if you left your lights on and your car won't start. Plug it in and 4 hours later your 993 will start right up.
• A basic $50~$100 On-Board Diagnostic (OBD) reader such as an Autel AL519 handheld reader or even an advanced one that can read the Porsche Specific manufacturer codes and running data. Something very useful when sorting out why the Check Engine Light is lit on your dash. 

With the basic reader and even if you have no intention of ever servicing your own vehicle reading out the trouble codes is as easy as using a pocket calculator and a quick Google search will tell you what the codes mean and what various folks did to clear them and the attendant Check Engine Light. This alone is very valuable for when you visit your local servicing entity you will know if the remedy they propose makes sense avoiding unnecessary work or upselling.  More on this subject here.

• A .pdf copy of the Porsche 993 & 964 parts catalogs, discussed above.

Parts & Information one should always have on hand in their 993/964:

• A complete set of  the three belts for the alternator/fan/AC compressor; 
• Three spare pulley capscrews (

  900.976.004.01) 

  & 
  

  

  Compressor Nut

• Three AC compressor square mounting nuts (964.126.311.00); 
• Consider keeping all the individual tools to replace the belts stored in the frunk. Belts can break without warning on a,993, especially if not tensioned using a gauge and you may end up not having a  servicing shop along the road to replace the belts, having this stuff on hand will get you back on the road without drama. Here is a resource to help in identifying these items;

The two biggies! Always have a backup; 

• A 993 or 964 DME Relay (

  993.615.227.02 for the 993)

   A failed DME relay is the number one reason by far that folks get stranded when their  993 won't start.
• Window switch (

  964.613.621.01)

   in one of your door pockets. The window switch is so one doesn't find one's self out in the rain with a window that can't be rolled up. Also, be aware there are two switches for the passenger side window that are linked together and after swapping one out you may find the offending switch was the other one on the other door. 

  

  DME Relay

• Key stalk, cut for your car in your wallet, and an extra 
• Electronic fob, if your car came equipped with one, in the frunk with a fresh battery. If you lose your key or your fob fails this will save you from what will at least be an overnight stranding to get a replacement. 

• Keep a printed-out copy of the 993 fob programming instructions including your immobilizer code in your owner's manual in the frunk. This, in a pinch, will allow you to start your car even if no electronic fob is available. This does not supersede keeping a working spare fob in your frunk as well. Fumbling through an unfamiliar procedure for the first time in some parking lot can be a real challenge potentially drawing the interest of a local police cruiser. Also, the programming process can be problematic for some to complete due to problems with electrical noise internal to the ignition switch or other reasons and you don't want to find out you can't start your car due to a faulty fob while away from home.
• If one has only one working remote entry fob it is asking to get stranded. The dealer-supplied fob has gotten astronomically expensive however, a direct replacement aftermarket fob for the 993  is available through Specialized ECU Repair or EZ IMMO BLOCK . Be sure to order the 315Mhz one for all USA-delivered cars 1995-1998 or the 433Mhz one compatible with cars originally delivered in Europe with the same Drive-Block alarm/immobilizer system. There are a few exceptions to this rule, for example, Australia-delivered cars and certain early production vehicles so look at your fob's FCC license label or look up the part number in the Porsche parts catalog to verify which of the two will be compatible with your car. 

The Specialized ECU Repair and the EZ IMMO BLOCK fobs use a modern button battery, whereas the OE fob's canister battery /contact arrangement has proven to not be perfectly reliable. I have been carrying around and using the above aftermarket fobs as daily users for several months now where they are exposed to moisture and lint in my jeans pocket and have proven to be 100% reliable to this point.

EZ IMMO BLOCK also offers a new fob that can be used to clone its configuration from any working fob. avoiding the factory programming sequence some find difficult to complete. Here is a page that discusses programming fobs, mating them to one's 993. 

• This is sort of an odd item, get rid of the one anti-theft wheel nut on each of your wheels. Replace all four of them with a fresh standard nut purchased online or from the dealer. The original keyed security nut is prone to stripping and failing. When this happens you can get stranded at the side of the road with a flat tire that you are unable to change. Besides few, if any of our car's wheels are stolen these days as the 993/964 have been around long enough that used wheels are cheap and plentiful to buy on eBay vs stealing them off of your car. Also if a professional thief wanted your wheels any wheel security nuts are just a minor nuisance.

• Here is a comprehensive discussion of junk you should consider having in your frunk.

Porsche branded, Porsche's OE Supplier branded, and generic aftermarket branded parts:

There seems to be a lot of confusion as to the relationship of quality (durability) to a brand. For example, durability differences between Porsche branded premium priced parts versus Original Equipment manufacturer (OE) supplier branded, like BOSCH versus third party branded parts, such as URO when purchasing replacement parts for our cars.

Keep in mind the below definition of Premium Pricing as you read on: 

"Premium pricing is a strategy that involves tactically pricing your company's product higher than your immediate competition. The purpose of pricing your product at a premium is to cultivate a perception in the market of your product being just that bit higher in quality than the rest."

First of all common service parts such as rotors, pads, struts, links etc were never designed or manufactured by Porsche to begin with. Their design, testing and manufacturing was left to Porsche's tier-one suppliers, Sachs, Bosch, Marinelli and others. So buying the Premium Priced product in a Porsche branded box at a 40% or more premium price vs buying it in the original manufacturer's branded box represents a poor value. Bosch makes fuel injectors, oxygen sensors and every component of the Motronic engine management system, Porsche never did. 

The reason why dealers prefer to sell parts purchased through the Porsche distribution network is that they are mostly used in in-warrenty work where the published retail price is not relevant and the captive financial relationship between the dealer and the parts source is, how should I say, a lot less than arms length. Also higher Premium prices improves margins on out-of-warrenty work for customers who believe servicing should be done at a dealer.  

Having higher Premium aftermarket retail parts prices is also attractive to the dealer's Independent (jobber) import car servicing customers because the higher retail price translates into higher margins when sold to you as part of a repair. In essence folks who buy parts to service their vehicles on their own (Do It Yourself) are simply not the dealer's core parts customer and for this reason dealer pricing seems, many times, to be irrationally high to the DIY folks. 

It is interesting that the margines are so good on retail dealer parts and labor that an entire industry of independent service contract/extended warrenty providers has sprung up making good money by negotiating reduced pricing on dealer parts & service. These are the same folks that have your cell phone on speed-dial that are constatly phoning you about your expired new-car warrenty, go figure?

Parts sold through the dealer network or independent distributor are referred to as Service New parts. Universally, they are not subjected to the same level of quality control as the same part supplied to Porsche at car assembly. Most testing is driven by warranty periods. Many Service New parts have been through what is euphemistically called a "Quality" program to take manufacturing cost out of the part while still being durable enough to survive the reduced aftermarket warrenty period.  

Aftermarket parts warranties, through the dealer or a distributor generally don't come close to those offered with the car when it was new so many of the now down graded parts simply don't last as long. This is especially true when a part has long been absent from a current production vehicle, in many cases its manufacturing has been handed off to a lower-cost, low volume manufacturer as most parts on a 993 or 964 now are. In a way, there is a perverse incentive in the entire aftermarket parts industry to make Service New parts less durable resulting in the opertunity to sell them to you more than once. 

Porsche sources its aftermarket Service New dealer parts from the same manufacturers used by independent import parts distributors, referred to in the industry as Warehouse Distributors. So the same part, of the same quality in most cases, came off the same assembly line with the same quality controls regardless of who's box it is in. This is particulary true for parts where the current manufacturer originaly supplied the part to Porsche at assembly.

Porsche branded vs original manufacturer branded tie rod end

 Sometimes there is no attempt made to hide who made the part 

as here is what appears to be a co-branded oil filter that came in a Porsche box but is clearly made by MAHLE:

Certain parts are an exception to this rule. 

Performance Market parts: 

Those supplied by by botique high performance parts distributors, for examle some of the items offered by StopTech who cater to those who race their cars or like the idea of installing race inspired parts on their car. They are usually limited to wheel end and suspension components and clutch & engine enhancements. These parts usually include cosmetic or functional enhancements and can have durability the same as or even better than run of the mill Service New part.

 

Low-Value, Low-Tech parts: 

 Some parts are manufactured by multiple entities under differing conditions at times using different designs of varying quality/(durability). They are usually low value. low-tech, easy to manufacture higher volume parts. 

For example, the window switches in a 993/964 if manufactured in Germany or Eastern Europe are similar in design to the original factory-supplied part. The same part purchased under the URO brand and now even the Porsche branded part manufactured in Taiwan, although they look very similar, are an entirely different design internally and suffers functionalproblems that become apparent when attached in series to a second switch as is done for the passenger side window with switches on each door. So, for small incidental parts be observant of the manufacturer as printed on the actual part and/or its country of origin unrelated to what branded box it came in. The original switches supplied with our cars typically last 15 years or more and for the DIY inclined can actually be repaired and stored in one of the car's door pockets for emergency use.

As an experiment I recently researched where 993 Porsche branded verses manufacturer branded windshield glass comes from for a 993.

It turns out this is easy to do because to be sold in the US automotive glass must be labeled with a US DOT number that identifies the specific factory of origin and also the country of origin. Turns out Porsche branded glass with the Triangle-P logo comes from the same two factories in Germany as all aftermarket windshields for our cars. The only difference is the added Porsche branded logo on the Porsche dealer sold glass. So any premium price one pays for the dealer part is purely to get the logo.

Hunting for the best value in Service New replacement parts:

Many times a part will seem to be a "Dealer Only" part because the original manufacturer's part number is difficult to obtain. Many online auto parts distributors list multiple part number cross-references for a part that can be looked up and may result in a less expensive source of supply. Also, many times the original manufacturer's part number is actually printed on the part and when searching for a part using that number may result in a significantly lower cost source of supply.

For example;

The Denso supplied sensor blower part on the back of the

Climate Control Unit (CCU) discussed in the "What is that buzzing behind the dash?" section on this page. When looking at the part the original manufacturers part number is printed right on it.  Where conducting an internet search under the Denso "173000" and excluding the car make extension -0410 it turns up several inexpensive alternative automotive branded part numbers in the $50-$75 range versus the Porsche dealer part that is several hundred dollars. The alternate part number may come with a different mounting frame however the frame and, if needed, the electricl plug can be harvested from your original unit.

 Another example is when a part is only available at a lower price through a dealer,

just not a Porsche dealer. For example the vacuum actuators on the Varioram intake manifold, Porsche part number is 99311046202 discussed on this page. On the part is printed the supplier Pierberg's part number 7.14242.07, see the picture to the right. This number crosses to the BMW part number 11617786961. This part if purchased under the Porsche part number is $103 under the BMW part number it is $46. There are three of these on the Varioram manifold so the savings adds up rather quickly. This cross was discoverd by reading the manufactuer's part number off 

the part in a picture at a distributor's web site and then searching

for a cross on an internet distributor's part number lookup.

Remanufactured Parts:

Remanufactured parts such as alternators, starters & calipers are highly variable in the quality (durability) of the finished product. First of all the condition of the used part from which the rebuilt part is finished out has a big impact on part quality. The used part is referred to as a "core" in the industry and the remanufacturer really has no control over the condition of the cores he receives. 

Each remanufacturer has their own standards for an acceptable core. In all cases, the standards doesn't in any way approach that of the new part when it was installed on your car at assembly. This is why some reman calipers exhibit loose bleeder screw casting threads that strip right out of the box. Also, a reman core may have been installed, used, and through the remanufacturing process more than once due to some unidentified failing. A failing you are now installing on your car.

Once a core is in hand the remanufacturer decides what testing is done, what parts are replaced or reused. This also explains the wide variability of durability and short warranty on these parts. Reman alternators due to their complexity are an example where durability varies widely even from the same rebuilder.

The best way to get a reman part with potentially better durability is to always remove the part from your car and have that specific part rebuilt versus one purchased on-exchange made from the cores the rebuilder has on hand. This is extremely important on parts where the supplier has a very limited source of good quality cores or the core is a precision or a complex part to begin with. It also may minimize the risk of installing of a reman part that is not configured exactly as the originally installed part. See this page for how this can be an issue.

In our cars the big one is the steering rack where rebuilder core availability is very low, core quality is just plain bad and the one recently taken from service from your car is the best bet for a durable remanufactured part hands down. Also when working with a rebuilder directly you can discuss the rebuilding process and what sub assembly parts you require to be refreshed. This is very important in the case of alternators. Luckily there usually is an electric motor/alternator/starter rebuilder with knowlegable service counter men in most cities of any size to do the work on your original component. If you have the interest here is a DIY on how to remove and reinstall a 993 steering rack.

Here is a page that lists my favorite go-to pages for parts for my 993 and also for a 964 information and parts supply. 

The difference between 964 and early 993 1994-1995 Non-Varioram OBD-1 vs. and a 1996-1998 Varioram OBD-2 Carrera

OBD-I vs OBD-II

The 1995 and early 993 and the 964 OBD-I cars have a single oxygen sensor located before the catalytic converter (CAT) that is used to evaluate and adjust the engine to optimize performance while minimizing emissions. It captures data only on the exhaust emanating from the engine that can trigger a Check Engine Light (CEL), not the downstream emission components. Since it has only one oxygen sensor before the CAT it does not evaluate the effectiveness of either cylinder bank of the engine individually or downstream components such as the catalytic converters nor does it evaluate the performance of the Supplemental Air Injection system (SAI) at start-up. For these reasons, it reports fewer issues that will trigger a CEL and so will have fewer issues that will cause it to fail a state emission inspection. To identify a car as an OBD-I vehicle look under the rear bumper at the rear center of the engine one will see a single oxygen sensor screwed into the catalytic converter hanging down in a protective shroud as seen below.

Location of the oxygen sensor on an OBD-1 equipped car.

The 1996 and newer 993  OBD-II car has four oxygen sensors located before and after each catalytic converter segment these are used to evaluate and optimize the performance of the engine, the catalytic converter (CAT), and the air injection system. Since it has two before CAT and two after CAT  oxygen sensors it evaluates the performance of the catalytic converters as free-standing devices and the performance of the supplemental air injection system at start-up. For these reasons it reports a greater number of issues that will trigger a CEL and so more issues that will cause it to fail a state emissions inspection in most states. 

The key service issue with the later 993 is that the emission OBD monitoring system will capture:

• The SAI air pump's electrical supply wires have insulation that fails from heat exposure. Getting to the wires to repair them is not easy with the engine in the car and so they should be addressed if the engine is removed from the vehicle for other service reasons. The pump itself is a very expensive part and rarely fails as it only runs for a few moments at the startup of an engine from dead cold. For this reason, if your shop suggests the pump needs to be replaced due to a Diagnostic Trouble Code you may want to prevail upon them to just replace the pigtail wires leading to the blower motor.
• The SAI system has a check valve that can throw an OBD-II code as it has a relatively short service life due to internal corrosion and should be replaced every two to four years.
• The SAI ports to the exhaust path can clog throwing an OBD-II code. This is the biggest gripe with the OBD-II vs the OBD-I car by owners. The most cost-effective method to clear the clogs is to remove the exhaust manifold and snake the ports out with a wire, This known issue has caused a debate in the 993 community as to its cause being; 

• The overfilling of the oil; 
• Leaking of oil around the valve guides or; 
• Both. 

Although the prevalence and to the extent each contributes to the issue is still open to debate generally, once the ports are cleared and the check valve replaced this cause of a CEL seems to not return. 

Here is a little more information on the subject of the Air Injector system's known issues including the above: Emission Control Systems - The Horror of the Check Engine Light!

964 & 1994-1995 993 Non-Varioram vs. 1996-1998 Varioram

To be clear owners of the earlier non-Varioram and owners of Varioram cars are generally happy with the performance of their vehicles. The Varioram cars breathe a little easier. The theory, I understand, is much like the valves on a trumpet where changing the air path lengths changes the frequency at which the instrument wants to oscillate. The Variorum system changes the effective length of the intake manifold runners so the air intake pulses maximize cylinder intake air charging at specific RPM ranges. This in conjunction with the larger intake valves produces slightly higher torque and horsepower at certain points along the rpm range. The varioram car is identified by a large bright cast metal intake manifold sitting over the top of the engine, see below.

Location of the Varioram intake manifold on cars so equipped.

The Varioram concept was originally implemented for the 993 in the Carrera RS as a way of increasing performance and was later added to the standard normally aspirated engine. The performance enhancement is small and incremental. On the negative side, there are more vacuum actuators on the engine to actuate the valves in the intake manifold and by now they are all suspect and should be tested for leaks in their internal diaphragms, The testing procedure is in the middle of this page. 

Model Year and DME differences, my understanding is that:

• MY 1995 and earlier 993/964 OBD-1 BOSCH Digital Motor Electronics (DME) Electronic Control Unit (ECU); 
• Its simpler intake manifold is better suited to certain intake modifications such as adding a supercharger. 
• It tests fewer emission issues and so reports fewer Check Engine Light (CEL) events.
• The 993 1996 OBD-II BOSCH DME ECU;
• BOSCH ECU Panumbersber ending in 008 (Carrera) and 758 (Turbo) in the US market.
• Unique, being the first model year where OBD-II regulations were implemented and; 
• Can not, as originally configured, have its memory reflashed to alter its intake maps.
• It can be internally modified by adding a daughter board to allow for reprogramming by Specialized ECU Repair at  https://www.ecudoctors.com/. See my comments on the advisability of doing this in the "Gotcha" section below.
• It also does not report the five non-continuous tests' individual emissions-related OBD Readiness statuses as they flip from "Not Ready" to "Pass" or "Fail", just reporting the individual results when all the tests are complete. More information on what readiness tests are can be found here;
• All readiness tests must be completed in a single-engine running event or all tests revert to a not-ready state and the drive cycle will need to be repeated. This may be why some owners of these early OBD-II cars experience frustration getting all the flags to a "PASS" state for an emission inspection after having their battery disconnected for service or replacement.
• The  993 1997- forward OBD-II BOSCH DME ECU; 
• BOSCH ECU Part numbers ending in 649 (Carrera) and 377 (Turbo) in the US market.
• Can, as originally configured, have its memory reflashed to alter its intake maps. See my comments on the advisability of doing this in the "Gotcha" section below.
• These cars report the status of the five readiness statuses individually for each non-continuous test as they are completed and retain this information even if the ignition is turned off before all the tests are complete. More on readiness tests and OBD reporting can be found here.

993 & 964 "Gotcha" Common and sometimes ill-advised upgrades and servicing:

• 
  Installing a lightweight flywheel. I regularly see posts on cars exhibiting stall-out or excessive noise issues with this modification. A recent quote from Rennlist "The RS lightweight clutch and flywheel is great on the track, but a pain in the ass on the street." typifies the words on this modification. More on this topic can be found here. Also replacing the dual mass flywheel with one not implemented with this feature accounts for the "excessive noise" comment above. 
• 
  Upgrading to Porsche replacement radio with navigation. The screen is too small and the radio placement in the dash is too low to make it an effective replacement for your cell phone with Google Maps or Waze installed. An alternative to consider is a;
• Dash Clock Smart Phone Mount can be found on this page. 
• Alternative popular radio solutions can be found at the bottom of this page.

• Any modification to the Motronic ECU to defeat the Immobilizer or remap the engine ignition. All these modifications involve a vendor altering table values in a compiled program or "black boxing" what programmed functions
  
  in the ECU are and how and why they function. The remap only changes the performance envelope very slightly as the factory ignition maps are well optimized from the factory for performance using the readily available grades of pump gas at service stations. If one wants to address the immobilizer function here is how to do it without an invasive modification or reflash to the Motronic ECU.
• Servicing the Climate control unit (CCU). When having the CCU serviced by ECU doctors they swap out the original guts for
  
  their solution. The CCU controls or monitors 21 major functions related to the HVAC & the engine and is complex even by today's standards.  It is generally very robust and if you prefer to retain the original internals  others will service and repair your CCU if needed, including bergvillfx.com
• Swapping out the stock black calipers with 'Big Reds". A very expensive upgrade that offers no performance or brake-feel advantage for a street-driven car. Upgrades to consider are to be found here. 
  
  Better to just paint the faces of your existing calipers red like the souls on French-Egyptian fashion designer Christian Louboutin's shoes if you are looking for a fashion statement.
• Installing RS engine mounts. Many folks who installed them love them giving a more precise feel to shifting. Others have viewed them differently "the motor mount created an increase in vibration that just made a buzziness in the cabin. Things that never vibrated did a lot over 4k rpm." ("clib" a Rennlist member)
• Something called a "Top-End" rebuild on a 993, commonly proposed by an enterprising service shop but actually rarely needed,  more on this topic can be found here.
• Regearing the transmission to shorten up the gears. Although regearing
  
  can enhance the driving experience for some by moving the shift points to shorten the gears, it is an expensive modification. One may be better off learning to value the virtues of the stock, tall 2nd & 3d gears when driving in traffic.
• Having steel synchronizer rings installed in the transmission at servicing for a street-driven car may not be a good idea. First of all the steel racing synchro teeth geometry is designed to provide very strong positive gear locking for race applications so the shifter doesn't slip out of gear. This feature in a street-driven car is not relevant and makes for a significantly less than smooth shifting experience.  Having worn synchros replaced on my 993 I can tell you from observation it's not the synchro teeth that are subject to significant wear it's the friction surfaces. Gear lubricant GL-4/GL-5 attaches a sacrificial coating to the steel gears in the transmission so the coating wears instead of the gears. This property vastly increases the service life of the gears in the transmission. The standard synchros are a yellow brass or bronze alloy, a nonferrous metal, and impart smooth shifting. I suspect another reason why steel is not used in the standard rings may be how the brass gears interact with the gear lubricant differently than with steel over time.
• Swapping out the fan and alternator belts for a single belt arrangement. The factory belt arrangement seems to work just fine for street use and the belts have a reasonably long service life if the correct belts are used and are tensioned properly with a tensioning gauge. The aftermarket single belt arrangement is expensive to buy, and have installed and results in unintended consequences discussed here. The factory service manual recommends inspecting the standard V belts every 30K miles for retentioning or replacement. In practice, I would inspect the belts every 15K miles and just replace them every 30K, one of the inexpensive and easier DIY servicing items.
• Shy away from any exhaust updates that involve removing or replacing the factory Catalytic Converter. Do you plan to drive the car legally from an emissions standpoint? If so consider modifications after the CAT(s) only. There are lots of options.
  
  Any comprehensive exhaust change only improves engine performance very little, if at all, and the weight saving is probably only material if one races their car. This is not to say thoughtful aftermarket muffler modifications downstream of the CAT(s) such as those done by Fister or others don't enhance the symphony the engine produces. 

In any event, save all the original exhaust parts as when the car is sold finding replacement parts to put back may be problematic and expensive. In the case of the stock CAT the value of the internal Platinum/Pladium catalyst compounds have skyrocketed as of late and the used converters in older cars such as ours contain a lot of it where the street value for the internal catayst alone is aproaching $1000. For this reason , I suspect a lot of the take-off ones will be chopped up for their content. This may, in a few years, make finding a good functional used one at a reasonable price a problem.

• Swapping out suspension or brake components for ones intended for race applications. For example, non-DOT brake hoses with non-crimped terminations are a brake failure waiting to happen unless you are prepared to inspect the lines after every few hours of operation as is done with race cars. 

Another is swapping out the cast suspension arms for adjustable race arms such as those sold by Tarett and others. Again these features being easily adjusted for race applications also make them easy to go out of adjustment for street applications.

Finally replacing rubber suspension components for harder resin or metal such as bushings and strut hats. These transmit noise and vibration to the car and in some cases have been implicated in sudden glass failure when used on a street-driven car. If your car is being developed as a track weapon, go for it, otherwise, I would shy away from these sorts of upgrades.

• Adding wheel spacers to push the tires out closer to the edge of the wheel well. I view this as a case where someone is overruling function for fashion. Doing this diminishes the available tire travel without the wheels rubbing the wheel well liners. this can be a problem on public roads. Also, the use of wheel spacers increases cantilever forces on the wheel-end suspension components. In some cases, it will require replacing the wheel studs.
• This is not a don't-do, more of a consideration. When changing out components such as the radio head, suspension springs or other major components keep the originals as having them is important to some buyers when you go to sell your car.
• Getting one's 993 wrapped. This is a common enthusiast discussion Item. Don't do it! The manufacturers of the film 3M & others openly admit it has a shelf life of two years. If you ever decide to remove it several years from now, after it has dried out, be ready for a job similar to removing the stone guards from your car, but on a much larger scale. Some have experienced paint pulling off with the film, a real nightmare. Also see this page: Fender Guards, Body Wraps
• Swapping out the factory wheels for larger diameters up to
  
  18-inch original option wheels or even larger aftermarket wheels used in conjunction with very low-profile tires have become a fashion statement of late. Larger wheels are really not the right thing for the vast majority of drivers. For street use 17" wheels are somewhat harsh on a 993/964, and optional 18" 993 wheels can be downright jarring. For years 15" to 16" were standard on the 911 and gave a reasonably compliant ride. For proper suspension geometry on the  993/964, the total diameter with rubber-mounted are all the same regardless of wheel size, just the height of the tire wall gets shorter as the wheels get bigger. 

A taller tire in conjunction with a smaller diameter wheel gives you some tire tread roll-over feel as you get near the edge of the tires' grip in aggressive turning

16" vs, 18" Wheel

while driving.  Roll-over is a feeling in the steering as the front tires begin to displace horizontally and the edge of the tires begins to distort or roll-over. In my experience the 18" low profile tire gives almost no warning before letting go and sliding, 19" probably no warning at all. For nonprofessional drivers, the margin of safety given by the roll-over tread steering feedback provided by smaller rims with higher profile tires before sliding is a welcome and significant safety communication. 

Finally if one peruses the catalog of documents in this blog via the list found in the top left-hand column of this document (when viewed on a desktop or laptop computer) it will provide somewhat comprehensive education on the workings, servicing, and upgrading of a Porsche 993 and many subjects that also apply to the 964. 

If you found this page informative return to the main page and bookmark it for future 993-related servicing, repair, and upgrading guidance & information. If it saved you some coin consider a donation through the button on the top left margin of this page.

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