Putting a big-power engine into a hum-drum body is the time-honoured way of achieving performance. A heart transplant can revolutionise performance in an achievable (and affordable!) way.
But it's all very well to see what others have done - but how about doing it yourself? We'll assume here that you're working on a rear wheel drive car, not front wheel drive (or all wheel drive) machine.
Before doing any DIY development work, make sure that there's not an adaptor kit already available off the shelf. New engine mounts, bellhousing and clutch bits might be yours with the plonking down of some dollars - saving you a huge amount of time. For example, sticking a Big Block into an early Holden (like the one shown here) has been done so many times that everything's available off the shelf.
Making Sure It Will Fit
The first thing to do when considering an engine swap is to check that the engine will actually fit in the car. Obviously, if you're prepared to do major surgery, pretty well anything can be fitted into anything! But here we're assuming that you still want to keep the inner guards, firewall and chassis rails pretty much the same as they looked when the factory made them.
There are three vital dimensions to measure: the distance between the chassis rails, the height of the engine, and its length.
If the engine is wider than the space between the chassis rails you're basically stuffed! But make sure that you actually do the measuring, though. Some cars are a lot more roomy in this dimension than you'd first think - and some are the other way around. A Mazda RX-7, for example, has got very wide chassis rails - even though the factory engine is physically quite small. Cars that came out with V6s and V8s (not necessarily in your market) are likely to have wider engine bays than those bodies available only with in-line fours and sixes. This Ford Zodiac is happy to take a V8 transplant - but that's not the story with all cars!
The height of the engine is probably the least important of the three measurements. If the engine is too high then a bonnet scoop or bulge can often be used to cover the carb or injection plenum. Alternatives also include lowered engine mounts. However, the length of the engine is important if it's to easily fit in. If it's a matter of 5-10cm or so (not 20 or 30!) the radiator can be moved forward and thin electric fans used.
The other area to measure is the size of the transmission tunnel - but this is best done by trial fitting the engine and tranny.
Test Fitting
Because there are so many dimensions that need to line up, after you've concluded from some basic measurements that the engine's likely to fit, it's then best to do a trial-fitting.
Unless the new engine bolts straight up to the tranny (pretty unusual but not unknown!), it's best to slot both a new engine and transmission into place as one unit. If you're fitting a much more recent engine (like this RB30 into a FC!), you'll want to use the late model trans anyway. Sometimes helps to first remove the cross-member (that's the hefty pressed-steel piece that the engine mounts bolt to). With the engine and tranny in place (suspended by an engine hoist) you need to decide what you're going to line everything up from.
Let's say that the transmission length is pretty close to original. That means that the tailshaft length is going to be darn near in length to stock. You might decide then to get the powertrain into the position that allows you to use this stock tailshaft length. Everything then gets worked out from there - the position of engine mounts, gearbox mounts, and so on. But if getting the tailshaft factory in length puts the engine halfway through the firewall you can scrap that idea!
The things that you can line up first and then work from are:
- the engine mounts;
- the position of the engine in the bay;
- the gearbox mounts;
- the position of the gearbox lever
- or, as stated, the tailshaft length.
Taking each of these as the starting point has advantages and disadvantages - but get at least one thing to line up, or you'll have to adapt them all!
It can be helpful to put a block of wood on top of the (re-installed) cross-member, and rest the engine temporarily on that. If you use a block of the right size the engine can be located in close to its final position, allowing the checking of all the clearances: bonnet to carb or plenum, firewall to engine, fan to rad, and so on. From a handling point of view, the best position for the engine is as close to the firewall as practicable.
Engine and Gearbox Mounts
Unless you're dead lucky, it's unlikely that the new engine's mounts will bolt straight to the old cross-member. That means that new mounts will need to be fabricated - and it's an area where some people do horrible things!
First up inspect both the new and old engine mounts. Can the old mounts be used with the new engine? Can the rubber block from the new engine's mounts be used with the old engine's metal bracket? Check all of the possible mixing and matching options using factory-produced mounts first. But if they won't fit, you need to make or adapt your own.
Let's say that the new engine's mounts are further forward in the engine bay than the old cross-member's bolt holes. One approach is to simply use a piece of flat steel, bolting this to the cross-member mounts and then bolting the new engine's mounts to it. But this is not a good idea: the piece of flat steel will be subject to big bending loads whenever you floor the throttle! I once saw an adapted engine mount that had a staircase of pieces of flat steel welded, one on top of the other. The mount ended up being something like 15cm away from the original point! Failure was inevitable.
Better in this situation is to heat and bend the original steel, so that the new off-set mounting position is held in place with straight (but angled) flat steel. In other words, there is a straight load-bearing path between the engine and cross-member. Some gusseting (triangular reinforcing pieces) welded into the corners will give this sort of bracket immense strength. If fabricating from scratch, use at least the same gauge material as in the new engine's mounts. At the gearbox end, the story's much the same. Either carefully adapt the factory mount or make a new one from heavy gauge steel.
Gear Lever Position
If the tranny location will move the gear lever position that's probably not a big deal - with some provisos. A matter of a few centimetres will make stuff-all difference: you probably won't even need to cut the hole any bigger in the tranny tunnel. However, if you're talking maybe 10 cm then mods to the tranny tunnel and console will be needed. You might also want to sit in the car and pretend to drive with the gear lever this far removed in location from standard. If it's always gonna be a pain in the butt (or arm) then maybe putting it there isn't a good idea.
If the tranny tunnel does need to be cut, a metal-cutting blade in an electric jigsaw will give the neatest final result. Don't forget to file away the sharp edges, and then paint the raw steel with a rust preventative. Making the console then fit back into place can be difficult - one easy way is to fit a larger gear lever boot that covers both the original and the extended opening.
Exhaust
Generally custom-made extractors will be needed to fit the new contours of the engine/body combination. This can be bloody expensive, but there's no way around this. On turbo cars, a single dump pipe out of the turbo is generally easy to fit in. Talking about turbos, if there's a turbo version of your car's engine available, that's one of the best (and easiest) engine swaps you can make.
Radiator and Fan
The new engine and the old radiator probably don't have a good relationship going when it comes to coupling - the water hoses that is. If the rad has the outlet (or inlet) on the wrong side, have a radiator shop change it over - a heap neater than running long cross-over hoses. When sourcing hoses, bend up a guide of what's needed from welding wire and then go to a big auto parts shop that will let you browse through their selection of hoses. A moulded hose that fits is so much better than one of those 'universal' convoluted hoses that scream "bodgy engine swap!" whenever you open the bonnet...
Most factory cars have got an engine-driven fan up close to the radiator, all surrounded by a shroud. They do this 'cause it works pretty well! If the new engine has a viscous-coupled fan, it makes sense to leave it in place rather than fit new fans. However, it's quite likely that the old shroud won't fit any more. Searching through a wrecker's yard or modifying the old one to fit are two options: don't leave it off.
Legality
We've not covered the legal implications of an engine swap here - but you'd better. Ring your local registration authority to find out what needs and/or what can be done - almost certainly a brake upgrade will be a requirement.
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