Bill Gregory, CVR

Well, here we go again. Bought a 1993 964 C2. Stock.  Just waiting for preparation for track usage, in addition to being a daily driver.  But before getting into upgrades, let's spend a little time on 964's. The prices have been recently getting into a more affordable range, particularly on the earlier 89-91 years.

By way of background, the 964's were introduced in 1989 in all wheel drive, or C4, configuration, whose drivetrain was evolved from the fabled 959 program in the mid-80's. Porsche said that around 85% of the parts in the C4 were new, with notable changes like a 3.6L engine, coil springs instead of torsion bars, ABS brakes, airbags, power steering, a retractable rear spoiler, and a new heating and air conditioning system that worked (!). Significant work was done on the body aerodynamics, and the 3.6L M64 engine was the first Porsche engine that was produced as a single engine for all worldwide markets, with 247hp. The manual transmission was an updated version of the G50 5 speed introduced in 1987. In 1990, the rear wheel drive version, C2, was added.  During the 964 program there were coupes, targa's, cabriolets, speedsters, and turbo looks, plus the limited run America Roadster, RS America (US only), and Carrera RS (non-US). models.  964's replaced 944's in the then 4 year old Porsche Cup racing series, and were used from 1990-1993.  45 964's were also prepared for a US race series that was cancelled, with the cars mostly being returned to street guise and sold.  In the US, upwards of 13,000 964's were sold.

At this point, the 964 line is pretty well shaken down, and there are some things to be aware of if you're considering buying one. Early engines were built without a cylinder head gasket, and in a small percentage of engines, can leak. Porsche fixed those that were found leaking at that time, with leaking being defined as wet to the touch. In 1991, Porsche updated the production engines by adding a cylinder head gasket, redesigning the cylinder head base, and installing all steel head studs. The 1990-on 964's use a dual mass flywheel, which helps isolate drivetrain vibration, however, the early Freudenberg units proved unreliable.  In 1992 Porsche changed to LUK-manufactured units, which have stood the test of time. In late 1993, Porsche added a vent kit for the distributor, to help prevent the dual distributor rubber belt from breaking due to ozone concentrations. There is a $10 kit to add this to earlier 964's. 1989-1991 964's need different spacers on the steering rack if you want to fit 17" wheels. The rear suspension geometry was changed in 1991, which is important to know if you make any rear suspension upgrades. At around 50,000 miles you should replace the dual distributor drive belt. As a Digital Motor Electronics (DME)-based Porsche engine, you should consider carrying a spare DME relay (993.615.227.00, around $22) in your glovebox.


Some people aren't keen on the 964 C4 all wheel drive system (as compared to the different and improved system of the 993, for example), so be sure you're OK with it before buying one. C4's have a high pressure (up to 180 bar or 2,600 psi) non-vacuum, hydraulic-based brake system, as opposed to the more conventional system with vacuum assist. This is important if you bleed your own brakes, as it's difficult, if not impossible, to properly bleed the 964 C4 brakes without a Bosch 9288 system tester, aka "hammer", or, it's replacement, the KTS-500. These tools run $3,000-$6,000, and Bosch no longer supports the "hammer".  C2's and RS America's use a vacuum-assisted brake system and can be bled at home (2 bar or 30 psi on your pressure bleeder). If your interests involve the track, the RWD 964's may be the better choice  Of course, have a pre-purchase inspection done, so you know what you're getting and that you negotiate the best price for it's condition.

So what's it like to drive a stock 964? It's more quiet and isolated from the road and environment than earlier 911's.  The 3.6L engine, with it's additional horsepower,  is a joy.  It's heavy at around 3030 (C2) to 3250 (C4) lbs, the suspension is basically what you'd expect, although it plows, or understeers. The heating and a/c system really does work better than earlier 911's.

So, with this background on the 964 line, next month we'll look at modifications to enhance  safety and performance at the track. If there are any questions, I can be reached at

Last month we overviewed the 964 line, covering history and buying considerations. This month we want to look at can be done to improve a 964's performance at the track. Note, since the 964 we're using as an example is also a daily driver, modifications that would be used for track-only, or racing, usage aren't included in the discussion.

First, let's look at the interior. Rollbar, seats, harnesses, floor.  For the rollbar, I used one from Doughterty (DAS), which is a removable bar, i.e., bolted in, not welded. What's nice about this bar, which fits both 964's and 993's, is that it has a support bar that attaches to each side of the body at the stock seat belt take-up spool locations. I like to think this adds some small amount of stiffness to the body, and it's a good place to mount your fire extinguisher. Stock seats were replaced with Recaro SRD's, which include a hole for the sub belt. Both 964's and 993's share a body made for all wheel drive, so we have to deal with large center tunnels and limited-to-no space to install the seats. However, with a dremel tool and some Porsche and Brey Krause parts, it can be done. Rear harnesses are run through the seat, over the rollbar, and down to eyebolts at the rear seat belt mounts. A drivers seat back brace is also used.  Last, floors. In a 964, there is a thick bundle of wires running off center on both the drivers and passengers floors. To prevent the insulation being chewed up at the track (with floor mats removed), 2'x2' ribbed .032" aluminum sheets were cut into pieces shaped essentially like floor mats, which are secured by a few screws. Others, including the factory,  use thin plywood as an alternative.


Next, mechanicals: suspension, brakes, tires/wheels. The stock suspension is marginal for track usage. Alternatives abound, from various lowering and stiffening springs to heavy duty shocks to spring/shock combinations to adjustable sway bars. I chose to stick with a Porsche solution, and installed the suspension used on the non-US Carrera RS. You can read an article discussing the installation, with pictures, at The only non-Porsche part was a larger rear adjustable anti-sway bar (21mm vs stock 18mm). An alignment and corner balance was done after the suspension upgrade, and a Brey Krause strut brace is used up front. Brakes are quite good on the 92-94 C2's and all C4's. 90-91 C2's used a dual piston rear caliper, versus the C4's quad piston caliper.  So, on the brakes, the front and rear brake backing plates were removed, cryogenically-treated front (also slotted) and rear rotors are used, with Pagid Orange brake pads. I also added a Porsche brake cooling kit (an available Tequipment part) which routes air from cutouts in the fog lamps via a hose to the wheel well. Mike Shaw, as well as others, also makes a similar brake cooling kit. The brake bias valve was upgraded to the Turbo 60 bar valve, which adds stability under heavy braking. For tires, 225/45x17 and 275/40x17 Kumho Ecsta V700 DOT "R" rated tires are used on track wheels. The flat oil line in the right wheel well was made a bit flatter, for tire clearance.

Finally, to protect the exterior, Armourfend was applied to the hood, front bumper, front light rims, front lights, rear view mirrors, side sills, and the panel in front of the rear wheel wells.

And how is it on the track? Nice. With the adjustable sway bars, the general balance is tuned towards a neutral position. The progressive springs, however, are a compromise for dual purpose usage. On the street they are fine, firmer than stock, but not harsh.  The downside to them is that, in high load turns, like the downhill at Lime Rock, the suspension has to move through the progressive part of the coil before it gets to the more rigid part of the spring, for the chassis to take a set in the turn. Brakes are fine.  Aerodynamics can use a little help, so a rear RS America/Carrera-style wing and front valance extension are next on the improvements list.

If there are any questions, I can be reached at

Written by Bill Gregory for the "Challenge", monthly publication of the Connecticut Valley Region, Porsche Club of America