Jun 8, 2009, 7:42 pm · #1
Revised 3-5-11
I want to give fairness to all the engines we discuss on this forum, since all these engines have their strengths and weaknesses... Perhaps I need to show the good and the bad about them, and let us discuss it more point-by-point.
S12 Engine Swap Guide
(scroll down for the FAQ section)
OVERVIEW
Mainly I will be discussing 4-cylinder swap options, because the majority of S12's around the world have 4-cylinder powerplants (and the engine crossmember to support them). The swaps discussed below are almost always a direct bolt-in for the engine, with your choice of motor mounts... stock mounts native to the choice of swap, aftermarket mounts, and even custom jobs such as the "hockey puck" mount.
TRANSMISSIONS
The transmissions are a different story. Given your car is an earlier "Mark I" chassis (1984 through early '86), your manual trans S12 came with the "B" transmission. Generally speaking, you will be swapping to the transmission associated with the engine swap choice you decide on. In most cases, this means a modified transmission mount, and modifying your trans tunnel (in the unibody) to accommodate the new shifter location. S13 and S14 transmissions have their shifters located approx. 5 inches further back than S12 transmissions. The advantage to this is that you get a more comfortable reach for the shifter, but the disadvantage is you absolutely have to modify the hole in the trans tunnel to accommodate this. You will also have to resolve the driveshaft issue.
The driveshaft on most Nissan RWD vehicles is a two-piece design, with a carrier bearing in the middle, mounted to the chassis. If your car was a five-speed "B" trans, you can use the front half section from an S13 together with your rear section from your S12, and the driveline will work. Since each individual shaft section is balanced from the factory, you should be fine. As far as can be seen, the automatic trans S12's have a different front shaft, but using an S13/S14 transmission with an S13 front section should resolve this as well -- the carrier bearings appear to be in the same locations for both MTX and ATX S12's. An alternative to this would be a one-piece custom driveshaft from a driveshaft shop. This will run you anywhere from $150 to $250 (USD) depending on where and how it is produced. It will also require exact specs -- front shaft specs from an S13, and rear specs from an S12. The advantage is that you can have a U-joint on both ends. The hybrid S13/S12 shaft combination leaves you without a U-joint on the front (S13) section. It is debatable if this is important. On one hand, the carrier bearing houses a joint to allow the shaft sections to flex, but others have concerns that the front of the S13 shaft should also have flex. To date, nobody has confirmed that the combo shaft route has any issues, and a number of people have been running on the S13/S12 hybrid driveshaft combo for some time now with no complaints.
If you have a later "Mark II" chassis (1987 and '88) and some later 1986 Mark I cars, and you have an MTX car, you have the S12 "C" transmission. This transmission is often confused with the S13/S14 transmission. They are not the same. While of similar design, they do not share the same trans case, the shifter is different, and the bellhousing is also different. What they DO share is bellhousing interchangeability with the S13/S14 transmissions. This means that S12's with the "C" trans have the option to KEEP their transmissions, and simply swap to the bellhousing for the engine they want to go with (provided the engine swap choice has a compatible bellhousing). SR, KA, and CA DOHC are perfect examples of this. Choosing the bellhousing swap route means avoiding the need for a custom trans tunnel or messing with the driveshaft issue. You can keep your stock interior, because you don't need to move or modify your center console, either.
On some cases (FJ engines for example), you can utilize the "B" transmission in this way, too. However, FJ swaps are uncommon because the engines themselves are becoming increasingly rare.
ENGINE SWAP CHOICES
SR20DE is nice if you want an NA build. It's a very well balanced engine, with a girdled bottom end and a fully-weighted crank. High revving, plenty of aftermarket, and highly tunable with many different routes. There are also many different fuel maps already charted for various stand-alone engine management systems, so this is a great engine for those of you who want a hard-core NA beast. Possibly the best route for NA, with the FJ20E (mentioned later on below) a close second).
For those of you simply looking for a peppy, responsive engine, while keeping your costs low, and parts availability high, the best choice IN NORTH AMERICA seems to be the KA24DE. While not as high-revving as the SR20DE, it still manages to keep things spinning in a good powerband. Finding these engines in North America is easy, although if you're on the opposite side of the world, you might not have the KA series as an option (in which case the SR20DE is the natural choice for NA). The nice thing about the KA24DE is the cost. Complete motorsets can be picked up with transmission and ECU/harness for anywhere from $600-800 (USD). While still tunable, it lacks the larger variety of the SR20DE in aftermarket. Still, there are aftermarket options for things such as cams, tuning, and bolt-ons, but again, these are limited to only a few vendors, whereas the SR series is possibly the widest-supported Nissan engine in the world. The KA24DE also has a girdled bottom end for strength, but only has a half-weighted crankshaft. This engine will not be as rev-happy as an SR, but its price, availability (in North America), and displacement still make it one of the top choices for both NA and boosted configurations (discussed next).
An alternative to the KA24DE is the KA24E, it's single-cam predecessor. Less power in naturally aspirated form, but they seem to take very well to boost, and even without turbocharging, a healthy KA24E is still a major improvement over a CA18ET (and especially a CA20E). Again, like the KA24DE, these are primarily found in North America.
If you want to build an all-out boosted monster, I think the KA24DE+T (i.e. turbo'd) is the better choice. Pound-for-pound, a fully-built KA24DE longblock has more displacement than the FJ series, and benefits from similar modern computer control and engineering as the SR. Add boost to the mix and you can take into serious scary power territory with the right internals. Your only drawback is you are limited to only a few avenues for tuning, and the engine will prefer a lower powerband than the SR series.
If you want moderate power levels, easy install, stock-looking appearance... all of those traits and more describe the SR20DET. An all-in-one package, it's robust enough to offer good growth with just stock internals, and it's highly tunable with a large variety of paths to take. Like all RWD SR's, it has a girdled bottom end, and its fully-weighted crankshaft helps it reach higher RPM's safely. It's a great engine to tune, but if you want to get really high AND reliable power out of it, you will still need to build the bottom end... and the expense would be better spent on an all-out KA turbo build -- if that engine is available in your region.
If you want bang-for-buck, and still some tunability, you can run with a CA18DET. Your head will flow nicely, and this engine takes to moderate increases in boost. Another distinguishing point is for "purists" who want a performance engine that was indeed found in S12's -- In Japan, some 1987 and 88 S12's were indeed equipped with CA18DET engines, so swapping in one of these is technically chassis-correct. This might appeal to the hard-core S12 enthusiast who wants both a tuner car and a show car that he/she can claim is "100% authentic". While the CA18DET is tunable, it's trickier than the SR, and its lack of a CONSULT port and its direct ignition means you will have some additional things to tackle, but it can be done and with good results. This engine is great for people who want a cheap swap with mild performance growth. It also has a girdled bottom end, and a fully-weighted crankshaft, allowing the engine to safely use higher RPM ranges to squeeze more power out of the motor. However, if an all-out boost monster is in your plans, you are still probably better off putting the money into a KA24DE+T, or if that isn't available in your region, going with a built SR20DET.
The FJ20E is a great NA engine. It's head flows better than all the previously-mentioned engines, and if you want to work on the bottom end, the block is WAY underbored. Boring it out isn't difficult, provided you get custom pistons to match with the new cylinder bores. The FJ20E is actually derived from the FJ24, a carbeurated version. The FJ20E is just an underbored version of the FJ24, so naturally the block walls are REALLY thick! The rods have been likened to Chevy 350 rods in size, and the main caps are the same as those found in the venerable L-series inline six cylinder Z engines. The FJ's are probably the STRONGEST 4-cylinder engines ever produced by Nissan. The only drawback is the increasing scarcity of these engines, and new replacement and upgrade parts sources are limited to a handful of vendors around the world. The same is true of parts for it's turbocharged version, the FJ20ET, only you need not do much at all to these engines, other than slap on a huge turbo, tune gently, and let the stock longblocks take you easily past 500 hp. Another bonus... as with the CA18DET, the FJ engines are "chassis-correct", as they were offered in Japanese model S12's from the factory. Like with the CA18DET swap, an FJ swap can hold appeal for both the tuner and the showcar owner alike for the reason that the car can remain 100% all-S12.
Some of you are wondering, "What about my CA18ET or CA20E?"
The CA20E is the base-model engine offered in most S12's around the world. While 2 liters like the SR and FJ, its bottom end is much weaker, and its rods are much thinner. The walls of the block are also thin. This is a single cam engine, designed for economy. In some countries, it had an 8 spark plug head designed for better emissions. The same head used only four plugs in other regions, but the port geometry is the same regardless. It has a very mild camshaft, and small fuel injectors. The head flows poorly compared to the dual cam engines discussed initially. On the other hand, arguably no Nissan four cylinder engine is as common as the CA20E, so parts are both plentiful and cheap. Maintenance is also simpler. And paired with an automatic transmission, it gets amazing mileage on cheap gas. If you're looking to save money, and don't care about power output, this is a great engine. If you want more power, forget it -- they don't yield more power easily.
The alternative choice to the CA20E was the CA18ET While similar to the CA20E, it has a shorter block deck. The rods are the same thin design as the CA20E rods, but are shorter, and are less-prone to bending or breaking. Still, they are toothpicks compared to the dual cam engines. And the block walls are thin, like the CA20E. The difference here is BOOST makes them a bit more peppy. Some people have wrenched decent power out of them, but to get them in reliably higher ranges usually requires extensive internals and other work. For the cost, you could go with any one of the dual cam 4-cylinder engines and run safe, reliable power levels higher than with the CA18ET. It's a decent engine, but I would never put it on par with even a KA24DE.
Worth mentioning is that some people have managed to bolt on the CA18ET hardware (turbo, manifold, etc.) onto the CA20E with varying success -- thus creating the "frankenstein" motor "CA20ET". It can be done, and initially you will end up with more power than a stock CA18ET. A little more displacement and a little higher compression are the reasons, but such a combination will not be very tolerable of anything higher than 7 psi. Of course, you could install custom forged rods and pistons, a custom head gasket, and hardened fasteners for the head, rods, and crank mains. But the money would of course be better spent on swaps that offer more power initially, and plenty of room for growth well beyond the limits of a CA20E+T.
Some of you in North America have the VG30E in your car... a 3.0L naturally-aspirated V6 that was also found in the first 300ZX's. In of itself, it's solid, and in stock power levels puts down a respectable amount for such a light car. The VG30E is sometimes called "bulletproof" by those who support it, but I would say that's not quite true. It's strong, but spinning bearings on aging VG's is a common occurrence. Still, a fresh rebuild does wonders, and a freshened engine can even handle mild boost. Some have dreamed of putting in the VG30ET found in the turbocharged version of the 300ZX, but due to specific differences between the S12 chassis and the 300ZX, this is not possible without extensive (read as: expensive) modifications to motor mounts, driveshafts, and other details. It seems far simpler to just turbocharge the existing VG30E found in the S12's with a custom system -- either a remote mounted setup or a front-mounted setup. A remote mount setup is for now the most researched and documented system, but a front mount system has been tried as well. In theory, a supercharger from a VG33ER (Xterra) might be possible as well.
OTHER CHOICES THAT AREN'T AS PRACTICAL
Since I've mentioned the V6, I might as well cover a couple other occasionally-discussed options.
The VG30DETT was found in the last-generation (Z32) 300ZX. A twin-turbo version of the 3.0L VG series, it has been successfully fitted into a few S12's. While clearing both firewall and strut towers, it can be said of the fitment that it is tight at best, and while it has been achieved, it most certainly must be difficult to work on (much like it is in the Z32 300ZX). Similarly, the NA version (VG30DE suffers from the same issue, but again should fit in the engine bay. Like any VG series engine, you must possess the VG crossmember for an S12. Those of you who's S12 came with the VG30E (the "SE" model) already have this crossmember, but for those of you who started out with a four-cylinder engine, you will have to locate one, which is becoming increasingly difficult.
Lastly, we have the RB series, most notably the RB20DET and the RB25DET. The RB's are inline-six engines, with dual-came heads. They employ progressive electronic systems, and the RB20DET's head design is similar to the CA18DE/DET's. They are stout, and pushing great amounts of power through one via a large turbocharger is not uncommon nor difficult. Mounting one in an S12, however, is indeed difficult, and requires customization of mounts, driveshafts, and other details. While a novel achievement, I would never consider one of these engines to be cost-effective or simple in the execution of a swap. Nevertheless, there are lots of reasons why someone might want one... I would think most of them have to do with the aftermarket options available for the RB series engines, or even the novelty of an inline-six in an S12 chassis. On the other hand, there is both engine weight and the distribution of that weight further past the front wheels, which may adversely affect the front to rear weight ratio of the car (think extra oversteer tendencies).
This should cover the entire scope of discussed engines, their pros and cons, and provide some thoughts on the choices available. While there have been talks of other engines, some oddball Nissan offerings, some V8 swaps, and even an occasional discussion of rotary-based powerplants in S12's, the above engines represent the available choices *at this time*.
ENGINE SWAP FAQ
Q. Is a swap for these cars difficult?
A. Not really. Most of the engines discussed above are a direct bolt-in, and the modifications for the transmissions are minimal. In some cases, you only need to swap the bellhousing (if you have a later Mark II S12). Your only real difficulty will be wiring, and the documentation for the SR and the KA series engines is out there. If you are patient, intuitive, and don't mind reading, you should be fine.
Q. Can I use a FWD engine (such as an SR20DE from an Infinity G20, or a FWD version of a KA24DE from an Altima)?
A. The simple answer is no. The distributors and other details are in the wrong location, and would not clear the firewall for a RWD setup. You must stick with a RWD engine for your swap.
Q. What is the best swap choice for my S12?
A. There isn't a "best choice". It will depend on what you want from it immediately after the swap, what you want from it in the long term plans, and how much you want to spend. It will also depend if you're interested in a naturally-aspirated setup or a turbocharged one.
Q. Which engine has the most power out-of the-box?
A. In stock form, the SR20DET, and for naturally-aspirated engines, the SR20DE and KA24DE are similar in power output, with the KA24DE a bit more powerful than the SR20DE.
Q. Which engine swap has the most power potential?
Anything turbocharged or that can be turbocharged. In most cases you will have to build the internals with stronger aftermarket parts -- forged rods, forged pistons, hardened fasteners (head studs, main studs, rod studs), and probably a copper or even steel head gasket. Only the FJ20ET can take you well into 400+ horsepower on a stock longblock *safely*.
Q. Which engine swap will be best for a naturally-aspirated (or "NA") build?
A. Probably the SR20DE, because it loves high revs, and there is plenty of aftermarket for both mild and extreme NA builds, including such crazy setups as high-compression setups, crazy timing advance tricks, and even individual throttle bodies (ITB's).
Q. Which engine swap is the cheapest?
A. If you're in North America, the KA series hands down. If you're elsewhere in the world, probably the SR20DE.
Q. Which engine swap is the most available?
A. In North America, again the KA engines. Elsewhere, again the SR20DE or SR20DET.
Q. Which engine swap has the best fuel efficiency and will be easiest to maintain? (I'm not into power)
A. Probably an SR20DE or KA24DE. Both offer a smooth running engine, easy maintenance, and decent fuel economy, with the SR probably more efficient than the KA.
Q. Do I need to do wiring or an ECU swap, or can I use my original stuff?
A. Yes, you need the wiring harness and ECU (engine control unit, or "the computer") associated with the engine you are swapping in. It is best to get a clean, uncut harness, but with enough wiring skill and experience, you could take a hacked harness and rebuild it the way you want it.
Q. Is a swap legal in my State/Country/Region?
A. Please consult your local laws for this answer. In most places with emissions laws, it is not legal, but test locations are often most concerned with tailpipe emissions. If your swap is clean, and doesn't have lots of bling, you may be able to get by. But regardless, it is still probably illegal in such locales, however some locations with emissions laws have provisions for swaps provided that they are 100% complete and compliant with the emissions standards for the car the engine came from. Most specifically, California is possibly one of the strictest regions in the world for emissions, however California does allow swaps within certain limitations, including that it meet the standards for the car the engine came from (among other requirements). Again, consult your local laws for further information.
Q. Do I need to change my transmission as well?
A. It depends. If you have an earlier "Mark I" S12, in most cases yes (the FJ and CA DOHC engines are the exception). If you have a Mark II, your "C" transmission can be kept as long as you swap the bellhousing.
Q. Which is better, the S12 "C" transmission, or the S13/S14 manual transmission?
A. The S12 "C" transmission doesn't require you to modify your car if your car came with it, but the S13/S14 transmission has the shifter relocated in what some feel is a more comfortable, closer reach length. Both transmissions are much more stout than the earlier S12 "B" trans.
Q. I want to use the S13/S14 transmission. What do I need to do to adapt this to my S12?
A. You need to modify the trans tunnel to accommodate the new shifter location. You need to modify the transmission mount. You also need to use an S13/S12 combo driveshaft, or a custom one-piece shaft.
Q. Can I swap a VG series V6 into an S12 that came with a 4-cylinder? OR, can I swap a 4-cylinder engine into an S12 that came with a V6?
A. To use a 4-cylinder engine, you need a 4-cylinder style engine crossmember. Likewise, a V6 engine needs a V6 style crossmember. If you are planning to switch from one to the other, you will also need to obtain the appropriate crossmember. This is easy when switching from V6 to 4-cylinder engines, because the 4-cylinder crossmembers are easy to come by, but the V6 crossmembers are more difficult to find. From what we know, only North America received S12's with V6 engines in them. If you wanted to change from 4 to 6, or from 6 to 4, and you can't find the right crossmember, you *could* conceivably customize your original crossmember, but this means you will need the fabrication skills or access to someone who has those skills to do the work for you.
Q. Can I swap an inline-6 or a V8 from another Nissan?
A. You will need custom motor mounts, often times you will have clearance issues with the radiator fan when working with inline-6 engines in S12 chassis. In most cases you will be dealing with a transmission that requires the same kinds of modifications the S13/S14 transmissions do, and you may not be able to run a combination shaft (meaning you are limited to only a custom one-piece unit). These kinds of swaps are not documented as well as the more common choices, so technical assistance will be lacking at best.
I want to give fairness to all the engines we discuss on this forum, since all these engines have their strengths and weaknesses... Perhaps I need to show the good and the bad about them, and let us discuss it more point-by-point.
S12 Engine Swap Guide
(scroll down for the FAQ section)
OVERVIEW
Mainly I will be discussing 4-cylinder swap options, because the majority of S12's around the world have 4-cylinder powerplants (and the engine crossmember to support them). The swaps discussed below are almost always a direct bolt-in for the engine, with your choice of motor mounts... stock mounts native to the choice of swap, aftermarket mounts, and even custom jobs such as the "hockey puck" mount.
TRANSMISSIONS
The transmissions are a different story. Given your car is an earlier "Mark I" chassis (1984 through early '86), your manual trans S12 came with the "B" transmission. Generally speaking, you will be swapping to the transmission associated with the engine swap choice you decide on. In most cases, this means a modified transmission mount, and modifying your trans tunnel (in the unibody) to accommodate the new shifter location. S13 and S14 transmissions have their shifters located approx. 5 inches further back than S12 transmissions. The advantage to this is that you get a more comfortable reach for the shifter, but the disadvantage is you absolutely have to modify the hole in the trans tunnel to accommodate this. You will also have to resolve the driveshaft issue.
The driveshaft on most Nissan RWD vehicles is a two-piece design, with a carrier bearing in the middle, mounted to the chassis. If your car was a five-speed "B" trans, you can use the front half section from an S13 together with your rear section from your S12, and the driveline will work. Since each individual shaft section is balanced from the factory, you should be fine. As far as can be seen, the automatic trans S12's have a different front shaft, but using an S13/S14 transmission with an S13 front section should resolve this as well -- the carrier bearings appear to be in the same locations for both MTX and ATX S12's. An alternative to this would be a one-piece custom driveshaft from a driveshaft shop. This will run you anywhere from $150 to $250 (USD) depending on where and how it is produced. It will also require exact specs -- front shaft specs from an S13, and rear specs from an S12. The advantage is that you can have a U-joint on both ends. The hybrid S13/S12 shaft combination leaves you without a U-joint on the front (S13) section. It is debatable if this is important. On one hand, the carrier bearing houses a joint to allow the shaft sections to flex, but others have concerns that the front of the S13 shaft should also have flex. To date, nobody has confirmed that the combo shaft route has any issues, and a number of people have been running on the S13/S12 hybrid driveshaft combo for some time now with no complaints.
If you have a later "Mark II" chassis (1987 and '88) and some later 1986 Mark I cars, and you have an MTX car, you have the S12 "C" transmission. This transmission is often confused with the S13/S14 transmission. They are not the same. While of similar design, they do not share the same trans case, the shifter is different, and the bellhousing is also different. What they DO share is bellhousing interchangeability with the S13/S14 transmissions. This means that S12's with the "C" trans have the option to KEEP their transmissions, and simply swap to the bellhousing for the engine they want to go with (provided the engine swap choice has a compatible bellhousing). SR, KA, and CA DOHC are perfect examples of this. Choosing the bellhousing swap route means avoiding the need for a custom trans tunnel or messing with the driveshaft issue. You can keep your stock interior, because you don't need to move or modify your center console, either.
On some cases (FJ engines for example), you can utilize the "B" transmission in this way, too. However, FJ swaps are uncommon because the engines themselves are becoming increasingly rare.
ENGINE SWAP CHOICES
SR20DE is nice if you want an NA build. It's a very well balanced engine, with a girdled bottom end and a fully-weighted crank. High revving, plenty of aftermarket, and highly tunable with many different routes. There are also many different fuel maps already charted for various stand-alone engine management systems, so this is a great engine for those of you who want a hard-core NA beast. Possibly the best route for NA, with the FJ20E (mentioned later on below) a close second).
For those of you simply looking for a peppy, responsive engine, while keeping your costs low, and parts availability high, the best choice IN NORTH AMERICA seems to be the KA24DE. While not as high-revving as the SR20DE, it still manages to keep things spinning in a good powerband. Finding these engines in North America is easy, although if you're on the opposite side of the world, you might not have the KA series as an option (in which case the SR20DE is the natural choice for NA). The nice thing about the KA24DE is the cost. Complete motorsets can be picked up with transmission and ECU/harness for anywhere from $600-800 (USD). While still tunable, it lacks the larger variety of the SR20DE in aftermarket. Still, there are aftermarket options for things such as cams, tuning, and bolt-ons, but again, these are limited to only a few vendors, whereas the SR series is possibly the widest-supported Nissan engine in the world. The KA24DE also has a girdled bottom end for strength, but only has a half-weighted crankshaft. This engine will not be as rev-happy as an SR, but its price, availability (in North America), and displacement still make it one of the top choices for both NA and boosted configurations (discussed next).
An alternative to the KA24DE is the KA24E, it's single-cam predecessor. Less power in naturally aspirated form, but they seem to take very well to boost, and even without turbocharging, a healthy KA24E is still a major improvement over a CA18ET (and especially a CA20E). Again, like the KA24DE, these are primarily found in North America.
If you want to build an all-out boosted monster, I think the KA24DE+T (i.e. turbo'd) is the better choice. Pound-for-pound, a fully-built KA24DE longblock has more displacement than the FJ series, and benefits from similar modern computer control and engineering as the SR. Add boost to the mix and you can take into serious scary power territory with the right internals. Your only drawback is you are limited to only a few avenues for tuning, and the engine will prefer a lower powerband than the SR series.
If you want moderate power levels, easy install, stock-looking appearance... all of those traits and more describe the SR20DET. An all-in-one package, it's robust enough to offer good growth with just stock internals, and it's highly tunable with a large variety of paths to take. Like all RWD SR's, it has a girdled bottom end, and its fully-weighted crankshaft helps it reach higher RPM's safely. It's a great engine to tune, but if you want to get really high AND reliable power out of it, you will still need to build the bottom end... and the expense would be better spent on an all-out KA turbo build -- if that engine is available in your region.
If you want bang-for-buck, and still some tunability, you can run with a CA18DET. Your head will flow nicely, and this engine takes to moderate increases in boost. Another distinguishing point is for "purists" who want a performance engine that was indeed found in S12's -- In Japan, some 1987 and 88 S12's were indeed equipped with CA18DET engines, so swapping in one of these is technically chassis-correct. This might appeal to the hard-core S12 enthusiast who wants both a tuner car and a show car that he/she can claim is "100% authentic". While the CA18DET is tunable, it's trickier than the SR, and its lack of a CONSULT port and its direct ignition means you will have some additional things to tackle, but it can be done and with good results. This engine is great for people who want a cheap swap with mild performance growth. It also has a girdled bottom end, and a fully-weighted crankshaft, allowing the engine to safely use higher RPM ranges to squeeze more power out of the motor. However, if an all-out boost monster is in your plans, you are still probably better off putting the money into a KA24DE+T, or if that isn't available in your region, going with a built SR20DET.
The FJ20E is a great NA engine. It's head flows better than all the previously-mentioned engines, and if you want to work on the bottom end, the block is WAY underbored. Boring it out isn't difficult, provided you get custom pistons to match with the new cylinder bores. The FJ20E is actually derived from the FJ24, a carbeurated version. The FJ20E is just an underbored version of the FJ24, so naturally the block walls are REALLY thick! The rods have been likened to Chevy 350 rods in size, and the main caps are the same as those found in the venerable L-series inline six cylinder Z engines. The FJ's are probably the STRONGEST 4-cylinder engines ever produced by Nissan. The only drawback is the increasing scarcity of these engines, and new replacement and upgrade parts sources are limited to a handful of vendors around the world. The same is true of parts for it's turbocharged version, the FJ20ET, only you need not do much at all to these engines, other than slap on a huge turbo, tune gently, and let the stock longblocks take you easily past 500 hp. Another bonus... as with the CA18DET, the FJ engines are "chassis-correct", as they were offered in Japanese model S12's from the factory. Like with the CA18DET swap, an FJ swap can hold appeal for both the tuner and the showcar owner alike for the reason that the car can remain 100% all-S12.
Some of you are wondering, "What about my CA18ET or CA20E?"
The CA20E is the base-model engine offered in most S12's around the world. While 2 liters like the SR and FJ, its bottom end is much weaker, and its rods are much thinner. The walls of the block are also thin. This is a single cam engine, designed for economy. In some countries, it had an 8 spark plug head designed for better emissions. The same head used only four plugs in other regions, but the port geometry is the same regardless. It has a very mild camshaft, and small fuel injectors. The head flows poorly compared to the dual cam engines discussed initially. On the other hand, arguably no Nissan four cylinder engine is as common as the CA20E, so parts are both plentiful and cheap. Maintenance is also simpler. And paired with an automatic transmission, it gets amazing mileage on cheap gas. If you're looking to save money, and don't care about power output, this is a great engine. If you want more power, forget it -- they don't yield more power easily.
The alternative choice to the CA20E was the CA18ET While similar to the CA20E, it has a shorter block deck. The rods are the same thin design as the CA20E rods, but are shorter, and are less-prone to bending or breaking. Still, they are toothpicks compared to the dual cam engines. And the block walls are thin, like the CA20E. The difference here is BOOST makes them a bit more peppy. Some people have wrenched decent power out of them, but to get them in reliably higher ranges usually requires extensive internals and other work. For the cost, you could go with any one of the dual cam 4-cylinder engines and run safe, reliable power levels higher than with the CA18ET. It's a decent engine, but I would never put it on par with even a KA24DE.
Worth mentioning is that some people have managed to bolt on the CA18ET hardware (turbo, manifold, etc.) onto the CA20E with varying success -- thus creating the "frankenstein" motor "CA20ET". It can be done, and initially you will end up with more power than a stock CA18ET. A little more displacement and a little higher compression are the reasons, but such a combination will not be very tolerable of anything higher than 7 psi. Of course, you could install custom forged rods and pistons, a custom head gasket, and hardened fasteners for the head, rods, and crank mains. But the money would of course be better spent on swaps that offer more power initially, and plenty of room for growth well beyond the limits of a CA20E+T.
Some of you in North America have the VG30E in your car... a 3.0L naturally-aspirated V6 that was also found in the first 300ZX's. In of itself, it's solid, and in stock power levels puts down a respectable amount for such a light car. The VG30E is sometimes called "bulletproof" by those who support it, but I would say that's not quite true. It's strong, but spinning bearings on aging VG's is a common occurrence. Still, a fresh rebuild does wonders, and a freshened engine can even handle mild boost. Some have dreamed of putting in the VG30ET found in the turbocharged version of the 300ZX, but due to specific differences between the S12 chassis and the 300ZX, this is not possible without extensive (read as: expensive) modifications to motor mounts, driveshafts, and other details. It seems far simpler to just turbocharge the existing VG30E found in the S12's with a custom system -- either a remote mounted setup or a front-mounted setup. A remote mount setup is for now the most researched and documented system, but a front mount system has been tried as well. In theory, a supercharger from a VG33ER (Xterra) might be possible as well.
OTHER CHOICES THAT AREN'T AS PRACTICAL
Since I've mentioned the V6, I might as well cover a couple other occasionally-discussed options.
The VG30DETT was found in the last-generation (Z32) 300ZX. A twin-turbo version of the 3.0L VG series, it has been successfully fitted into a few S12's. While clearing both firewall and strut towers, it can be said of the fitment that it is tight at best, and while it has been achieved, it most certainly must be difficult to work on (much like it is in the Z32 300ZX). Similarly, the NA version (VG30DE suffers from the same issue, but again should fit in the engine bay. Like any VG series engine, you must possess the VG crossmember for an S12. Those of you who's S12 came with the VG30E (the "SE" model) already have this crossmember, but for those of you who started out with a four-cylinder engine, you will have to locate one, which is becoming increasingly difficult.
Lastly, we have the RB series, most notably the RB20DET and the RB25DET. The RB's are inline-six engines, with dual-came heads. They employ progressive electronic systems, and the RB20DET's head design is similar to the CA18DE/DET's. They are stout, and pushing great amounts of power through one via a large turbocharger is not uncommon nor difficult. Mounting one in an S12, however, is indeed difficult, and requires customization of mounts, driveshafts, and other details. While a novel achievement, I would never consider one of these engines to be cost-effective or simple in the execution of a swap. Nevertheless, there are lots of reasons why someone might want one... I would think most of them have to do with the aftermarket options available for the RB series engines, or even the novelty of an inline-six in an S12 chassis. On the other hand, there is both engine weight and the distribution of that weight further past the front wheels, which may adversely affect the front to rear weight ratio of the car (think extra oversteer tendencies).
This should cover the entire scope of discussed engines, their pros and cons, and provide some thoughts on the choices available. While there have been talks of other engines, some oddball Nissan offerings, some V8 swaps, and even an occasional discussion of rotary-based powerplants in S12's, the above engines represent the available choices *at this time*.
ENGINE SWAP FAQ
Q. Is a swap for these cars difficult?
A. Not really. Most of the engines discussed above are a direct bolt-in, and the modifications for the transmissions are minimal. In some cases, you only need to swap the bellhousing (if you have a later Mark II S12). Your only real difficulty will be wiring, and the documentation for the SR and the KA series engines is out there. If you are patient, intuitive, and don't mind reading, you should be fine.
Q. Can I use a FWD engine (such as an SR20DE from an Infinity G20, or a FWD version of a KA24DE from an Altima)?
A. The simple answer is no. The distributors and other details are in the wrong location, and would not clear the firewall for a RWD setup. You must stick with a RWD engine for your swap.
Q. What is the best swap choice for my S12?
A. There isn't a "best choice". It will depend on what you want from it immediately after the swap, what you want from it in the long term plans, and how much you want to spend. It will also depend if you're interested in a naturally-aspirated setup or a turbocharged one.
Q. Which engine has the most power out-of the-box?
A. In stock form, the SR20DET, and for naturally-aspirated engines, the SR20DE and KA24DE are similar in power output, with the KA24DE a bit more powerful than the SR20DE.
Q. Which engine swap has the most power potential?
Anything turbocharged or that can be turbocharged. In most cases you will have to build the internals with stronger aftermarket parts -- forged rods, forged pistons, hardened fasteners (head studs, main studs, rod studs), and probably a copper or even steel head gasket. Only the FJ20ET can take you well into 400+ horsepower on a stock longblock *safely*.
Q. Which engine swap will be best for a naturally-aspirated (or "NA") build?
A. Probably the SR20DE, because it loves high revs, and there is plenty of aftermarket for both mild and extreme NA builds, including such crazy setups as high-compression setups, crazy timing advance tricks, and even individual throttle bodies (ITB's).
Q. Which engine swap is the cheapest?
A. If you're in North America, the KA series hands down. If you're elsewhere in the world, probably the SR20DE.
Q. Which engine swap is the most available?
A. In North America, again the KA engines. Elsewhere, again the SR20DE or SR20DET.
Q. Which engine swap has the best fuel efficiency and will be easiest to maintain? (I'm not into power)
A. Probably an SR20DE or KA24DE. Both offer a smooth running engine, easy maintenance, and decent fuel economy, with the SR probably more efficient than the KA.
Q. Do I need to do wiring or an ECU swap, or can I use my original stuff?
A. Yes, you need the wiring harness and ECU (engine control unit, or "the computer") associated with the engine you are swapping in. It is best to get a clean, uncut harness, but with enough wiring skill and experience, you could take a hacked harness and rebuild it the way you want it.
Q. Is a swap legal in my State/Country/Region?
A. Please consult your local laws for this answer. In most places with emissions laws, it is not legal, but test locations are often most concerned with tailpipe emissions. If your swap is clean, and doesn't have lots of bling, you may be able to get by. But regardless, it is still probably illegal in such locales, however some locations with emissions laws have provisions for swaps provided that they are 100% complete and compliant with the emissions standards for the car the engine came from. Most specifically, California is possibly one of the strictest regions in the world for emissions, however California does allow swaps within certain limitations, including that it meet the standards for the car the engine came from (among other requirements). Again, consult your local laws for further information.
Q. Do I need to change my transmission as well?
A. It depends. If you have an earlier "Mark I" S12, in most cases yes (the FJ and CA DOHC engines are the exception). If you have a Mark II, your "C" transmission can be kept as long as you swap the bellhousing.
Q. Which is better, the S12 "C" transmission, or the S13/S14 manual transmission?
A. The S12 "C" transmission doesn't require you to modify your car if your car came with it, but the S13/S14 transmission has the shifter relocated in what some feel is a more comfortable, closer reach length. Both transmissions are much more stout than the earlier S12 "B" trans.
Q. I want to use the S13/S14 transmission. What do I need to do to adapt this to my S12?
A. You need to modify the trans tunnel to accommodate the new shifter location. You need to modify the transmission mount. You also need to use an S13/S12 combo driveshaft, or a custom one-piece shaft.
Q. Can I swap a VG series V6 into an S12 that came with a 4-cylinder? OR, can I swap a 4-cylinder engine into an S12 that came with a V6?
A. To use a 4-cylinder engine, you need a 4-cylinder style engine crossmember. Likewise, a V6 engine needs a V6 style crossmember. If you are planning to switch from one to the other, you will also need to obtain the appropriate crossmember. This is easy when switching from V6 to 4-cylinder engines, because the 4-cylinder crossmembers are easy to come by, but the V6 crossmembers are more difficult to find. From what we know, only North America received S12's with V6 engines in them. If you wanted to change from 4 to 6, or from 6 to 4, and you can't find the right crossmember, you *could* conceivably customize your original crossmember, but this means you will need the fabrication skills or access to someone who has those skills to do the work for you.
Q. Can I swap an inline-6 or a V8 from another Nissan?
A. You will need custom motor mounts, often times you will have clearance issues with the radiator fan when working with inline-6 engines in S12 chassis. In most cases you will be dealing with a transmission that requires the same kinds of modifications the S13/S14 transmissions do, and you may not be able to run a combination shaft (meaning you are limited to only a custom one-piece unit). These kinds of swaps are not documented as well as the more common choices, so technical assistance will be lacking at best.
