How to Convert the PORSCHE 924 / 944 to V8 power

gt1scca Mon Jun 22, 2009 10:10 pm

HOW TO CONVERT THE PORSCHE 924 / 944 TO V8 POWER

Driving an 80's Porsche model 944 or 924 can be one of the liveliest and entertaining experiences anyone can have. With near perfect 50/50 weight distribution, due to the engine in the front and transaxle in the rear, these cars were very fast and nimble for their time as well as today. However, since the 80's and 90's these models have seen major maintenance bills and strife due to their four cylinder engines. Whereas one person pays these bills to keep the car stock and completely "Porsche," others tend to think outside of the box.

The Porsche 924 and 944 share a common feature; a four cylinder engine with a degradable rubber timing belt, and pistons that do not clear the valves if the timing belt breaks. After so many years, the timing belt must be replaced along with its tensioner, rollers and other related items. This is no small task as well as quite expensive. Nevertheless, many of these cars have been scraped simply because of this kind of incident.

Another issue included the mere price of performance modifications. There was never a high demand for aftermarket support in the way of engine internals which made it hard or even impossible for most to compete with others such as Chevy and Ford. What's more, the Porsche engines had a limit as to how high horsepower and torque numbers could go reliably.

The 924/944 series models have a 4 cylinder slanted engine mated to a driveshaft (torque tube) and then to a transaxle in the rear of the car. This set-up is also seen in the C5 Corvettes and Saleens. The weight distribution allows for easy high speed cornering with little roll as compared to other cars where the transmission is directly behind the engine. Although these cars were not designed for straight line drag-racing, they handle twisty-turning roads quite well. If you intend to drag race this car, you will be disappointed as most cars designed for that have solid rear axles or CV joints connected to a differential. Moreover, the ring and pinion in the transaxle of these models are prone to explosions from wreckless take-offs and drag racing which often costs the owner a lot of money to rectify.

Chevrolet eight cylinder engines are very reliable, cheap to maintain and upgrade. They have loads of horsepower and torque in their stock form, and have extremely high aftermarket support. It is no surprise that this would become the answer for some who wish to keep their 924s and 944s on the road when replacement engines are unobtainable or highly cost ineffective.

The conversion is pretty straight forward and easy to accomplish by do-it-yourselfer's in as little as a weekend’s time. Cost is a very constant question when contemplating such a drastic move and there is no real answer. A typical conversion, assuming you already have one of these models, is roughly 6-18 thousand dollars. This also assumes that you yourself will be doing all the work. However, having a local garage do the work could range between 10-21 thousand dollars and up. This is all subjective in that different people want different things from their car, for example, where one would just want the bare essentials i.e. no air conditioning, no power steering, or stock horsepower and torque numbers, another may want all of the above as well as 500 horsepower and a supercharger. Another point is that whenever you go from a 130 horsepower 4 cylinder engine to a 300+ chevy V8, you have to think about other changes such as brakes, shocks, coolers, etc. So the price could fluctuate quite a bit.

The first thing to do when considering an engine swap is to find the resources that allow you to do so. A fair amount of fabrication could be done to accomplish the transplant in a 924/944, and some aftermarket conversion parts are still available for the 924/944 small block conversion. Anyone wanting to do this conversion with the LSx series V8 from Chevrolet can easily source the required parts, or have the custom pieces fabricated. These engines feature aluminum blocks, as opposed to the earlier V8's that were cast iron blocks, and are all fuel injected. These engines produce a large sum of power in stock form and with simple cost-effective upgrades (i.e. cam shaft) can easily see upwards 450-500 horsepower, which makes this engine a very easy choice for a swap.

WHAT YOU'LL NEED If you decide you are ready to do an engine swap, you will need to obtain a conversion kit, or you may choose to purchase or fabricate the parts individually. You will also need to purchase an engine. Small block V8 engines are still plentiful and inexpensive, as are the LT1 engines. A complete LT1 with PCM and harness can be had for as little as $500. LSx engines are also readily available for a decent price. Typically, one could find a complete (includes a long block with all accessories) pull-out for around $1,500-$3000. The 5.3L GM truck engines have also became popular, and are around $500 complete. For hood clearance, the LSX intake must be used on the 5.3L. To adapt these engines to the torque tube, you will need a special bellhousing that bolts to the V8 block, houses the clutch components, and then to torque tube. QuickTime Inc. offers a spun-steel bellhousing that fits well inside the 944 tunnel. As of now, the '97 up Corvette C5 bellhousing and a custom adapter for the torque tube is the most cost effective solution. Another option is the stock GM SBC bellhousing, and fabrication of an adapter plate system developed by 944Hybrids Board members. These bellhousings are still readily available, and can be had for as little as $25. Obtaining an engine of the LSX variety requires a little more work as many came with the 4L60 or T56 transmissions where the bellhousing is not useful. However, you can buy an earlier bellhousing from a C5 Corvette to bolt to the LS engine and then have a plate machined to fit between the end of the bellhousing and the mating surface of the torque tube. The clutch components are plentiful, cheap, and readily available from any parts house. The Porsche 924/944 driveshaft splines match that of many vehicles including early Mopar. Basically you are going to be looking for are 1" x 23 spline 10.5" or 11" diameter disc, 153 tooth flywheel and a pressure plate to fit accordingly. The LSX engines utilize the stock GM flywheel and clutch components.

MOUNTS The mounts are pretty basic. There have been many different configurations made by lots of do-it-yourselfers. A tubular mount has been used with great success, however, you may just decide to fabricate your own that attach to the engine block and then to the OE cross-member.

EXHAUST The LT1 and LSX OEM headers that may come with the engine do not lend themselves well to retrofit. They have been found to clash with available space in the 924/944 engine bay. For LT1/4 engines, the headers part number CC90 driver side and CC2 passenger side from Sanderson Headers are the perfect fit (Paul Mellor). The headers should run into a 3" exhaust to a 3" converter and all the way out for best performance. The LTX and LSX engines all use OBDII computers which require 4 oxygen sensors, with the exception of earlier LT1 engines that utilize OBDI and 2 O2 sensors. However, on the later 96+ LTX/LSX engines, 2 of them can be successfully programmed out, unless your local state laws prohibit this type of modification. As well, the emissions system may also be programmed out if allowed by your local laws.

ELECTRICAL The electrical system part of the conversions scares most people from attempting such a swap. However, this need not be the case. With the support of companies such as Painless Wiring, lt1swap.com, and PCMforless.com, etc., the factory GM harness is can be successfully modified. The factory Porsche engine harness is completely eliminated. No need to splice in here or there. The Chevy harness is close to stand alone where a mere 9-10 wire hook-up is required for fuel pump, tachometer, oil psi, water temp, AC, and other related functions. The wiring should take very little time at all with the use of the service manual from GM and Porsche together.

TRANSMISSION Many will say that the transaxle should be replaced with a Chevy transmission, or that the stock Porsche transaxle will not take the abuse of a V8. This is simply not true. However, the 924 transaxle is weak, and should be replaced with the 944 unit. The 924 torque tube is also a point of weakness, although some have used the 924 TT without incident. The gearing of the transaxles used in these cars is very usable. The NA (normally aspirated) and turbo version transaxles are said to hold a reasonable 400lbs. of torque. Whereas there have been a few people who have transplanted various Chevy transmissions into their 924s or 944s, it is rare and very difficult to accomplish/justify. The NA transmission allows for a very fast take-off with the right clutch action. For increased drivability and strength, the turbo LSD transaxle can be retrofitted with the N/A 5th gearset.

BRAKES Brakes should remain a great concern here. When increasing the pure power the car generates, stopping that power is just as important. The energy the engine produces is transformed to heat from the brakes. If the brake pad area is too small or the brake system is faulty, you could be looking at major damage to property or death. The 924/944 NA brakes are considered too small for even mild V8 power and should be converted to the bigger and stronger 944 turbo versions. However, the inner and outer spindle diameters on all 944s prior to 1987 are the same and became a source of minor problems (fracturing) with the heaviest brake set up from '83 to '86 which was on the '86 944 turbo. This issue became more prevalent when '86 turbo owners upgraded the front brakes to larger calipers and rotors WITHOUT changing the spindle to the post '86 version. This change also requires going from the "short version" of the front suspension A-Arm to the "long version" that was stock on all 944s after '86.

If you own a 924, many will explain that in order to build a fast, fun, and safe V8 car, you should sell the 924 and buy a 944T. This makes sense for the fact that the brakes and suspension as well as the transaxle gearing and strength is perfect for V8 power. If you decide to keep your 924/944 NA for this conversion, you may be paying what you would in difference just to convert it to 944T specs.

If you own a Normally Aspirated 944, many will explain that in order to build a fast, fun, and safe V8 car, you should sell the 944NA and buy a 944 Turbo. This makes sense for the fact that the brakes and suspension, as well as the transaxle gearing and strength are perfect for V8 power. If you decide to keep your 944NA for this conversion, you may be paying what you would in difference just to convert it to 944T specs. However, you can simply upgrade the brake system with 993TT brake calipers, pads, and rotors (requires 17" and up rims), or one of the custom brake setups being developed by 944Hybrids members.

- 944-LT1