CONVERTER
Engine Conversions

By Martin Donnon
(c) Copyright Express Publications. Reproduced under expressed permission. No copying permitted

Engine conversions. Shoehorning the power plant, or even complete drivetrain, out of one car and into another. Regardless of how you look at it, or how easy it seems, swapping engines isn’t straightforward. There's this problem, particularly with swapping factory engine management systems between cars - I've never been able to accurately pin-point. I call it conversion disease. I've written about it often, but, even after all these years, I still find it hard to put a finger on the cause. The problem is that no matter how professionally, or diligently, you swap the components between, say, front cut and existing car, the engine never seems to run as factory. Sometimes they run too rich, other times they won't idle properly. It's a mystery. Whether it depends on interfacing speed sensors properly, or the location of engine bay air feeds et cetera, there is some mysterious gremlin that creeps in and usually compromises the installation, if only slightly.

Many wouldn't bother with these small hiccups and so accept them as part of the process, simply fitting aftermarket engine management, if the problems are too steep to live with. Then you get the problems of making aftermarket management run the engine as well as a factory system, in all the light-load and cold-start areas. It's not as easy as you might think it is, that's for sure. Some get it right and have the near-perfect result, but they are the exceptions to the rule. They are the ones that spend countless hours finessing the job, making sure everything is perfect, and they are the ones that have a fair smattering of DIY skills, in the first place. The problem with finishing a conversion to near-factory standard is that it takes a lot of time - and the problem with time is ... it costs money.

 

It all comes down to responsibility, though, as there is no way I can guarantee you that $5000 is going to be enough to properly install an SR2ODET into a Datsun 1600. We can't foresee the problems - and therein lies the dilemma. You will notice we usually suggest you purchase the car that has the right hardware under the bonnet in the first place. It's the fairest thing we can do. It's not all doom and gloom, though, as amongst the conversion nightmares there are some reasonable jobs. Slotting a B16A into a first-gen CRX, for example, makes much sense, as does putting a turbo rotary engine into a Series IV atmo. Why do these conversions make sense? Mainly because the rest of the car is up to the task.     Conversely, contemplate putting 200kW worth of modified and turbocharged SR20DET engine into a Datsun 1200. Sure, it can be done and be made to run fine. On paper, the whole concept even sounds pretty good. The reality, though, is that most of these conversions drive like the dangerous deathtraps they are. It doesn't matter whether you have updated to the 200B disc brake front end, or even better suspension - ultimately, these elderly chassis simply weren't designed to handle anything like this sort of power.

Which brings us to the basic premise that, there is more to the overall behaviour of a car and, more to the point, its ability to handle 'uprated' power loadings than the mere sum of its parts. Four-spot brakes, coil-over sus-pension and strut tower bars can't undo the work that was initially done by the factory engineers. If that work was to build the cheapest and lightest car possible then you are never going to make the thing drive right with these sorts of bolt-on power aids. Another interesting point is that changing the driveline of an older, small-displacement vehicle to something later and more powerful - and, no doubt, heavier - also upsets the basic balance of the chassis. Suddenly, you may have gone from having 150kg over the front wheels to more like 220kg, altering the static weight distribution of the car massively. You might not notice this driving along the street, but pitch the thing into a corner, or - more importantly - attempt some type of swerve and recover procedure and you may well end up in a heap of trouble. That's the reason for the lazy and less adventurous route of buying a car engineered for the engine of your choice.

 

That is, the factory model isn't such a bad idea. It gives you a base that is not only safe, legal and more predictable to drive, but also something that, ultimately, will cost you less in the long run. Hopefully, if you go the other way, that cost is only a financial one.

 

(c) Copyright Express Publications. Reproduced under expressed permission. No copying permitted