Engine and cooling
There is a lot of scaremongering about Turbos and their reliability. Most of it is wrong. Treated with respect and some degree of mechanical sympathy, the Turbo is a reliable engine unit. A lot of the issues come from historically abused examples by people not understanding the early Turbo tech.
The first thing to note is that the S2 and S1 engines are not the same. There are many changes between the two but enough similarities to mean incorrect parts get substituted from one to another.
The S1 has an oval-shaped throttle body and boost duct. The S2 has a round one. Each then has a different intake manifold to accommodate the correct throttle body and boost duct affecting the vacuum hoses used and even the throttle cable.
The breather on an S1 goes from the Purolater to the airbox. On the S2 from the Purolater to the fuel/air meter unit.
The compression ratio on the S1 is 7.5:1 on the S2 it is 8.5:1. The turbo used in each type is different despite being a K26. The S1 is K26 2470 6.10, the S2 is K26 2664 4.10. As they are so similar they often get swapped in, especially in the past when the cars may have been run on a shoestring budget. The wrong turbo on the engine might still run, but not at the optimum. The S1 turbo is larger for the lower compression ratio and to give more boost.
The two engines drive differently too. The S1 is more “laggy” and an S2 would have the bester off the line acceleration. However once on boost it has the legs on the S2; what it loses 0-40 it makes up for at anything above this speed.
S2s have a DITC box behind the centre console/radio. Put your hand in there and you’ll find it. There should be a square loom connector on top of the engine’s loom leading into a rubber grommet- just to the right hand side of the coil. Through this grommet there is a boost signal pipe from the back of the plenum to the DITC box. Some rough running or boost problems can occur when these connections fail.
S2s also have a crank sensor on the top of the bell housing. These have been unobtainable for some time. There are few solutions to fix this and second hand parts are rare.
S2s have a connector on the front left wheel arch above the small black ignition amplifier. Also note there should be no vacuum/retard diaphragm on an S2 distributor.
S1s do not have an ECU and have a round engine to loo connector instead of the square one. There is no large rubber grommet nor is there a signal pipe at the back of the plenum. The signal amplifier is silver on these cars and has no wired connector above it. There is no crank sensor (which is good news given their scarcity) and the distributor has a large round vacuum/retard diaphragm housing.
The Turbo shares the bottom end with the NA. The head and turbo ancillaries are squeezed into the bay tightly though meaning some parts, like the starter and alternator are in different places.
The head is unique to the Turbo. Valve stem seals can fail, over time, indicated by a smoky engine. Its design means the engine becomes an interference one though so timing belt failure is a big problem on this car. Check when it was last done. It is not an overly tricky job but gets neglected.
High quality synthetic oil is a must for the Turbo. In period the oils available were not up to the stresses of the heat generated and quickly broke down, leading to premature failure. Regular oil and filter changes will look after the turbo much better. If buying a Turbo, see how the owner switches off the engine. The turbo needs time to run at idle speed to cool and allow oil flow. A red hot turbo not allowed to cool down will prematurely fail.
Look for smoke on start up and through the rev range on a turbo. Ideally, on the test drive, get someone to follow you to see what comes out of the exhaust. A turbine seals failing will use a lot of oil as will valve stem seals.
Due to the heat generated by the engine, check all electrical connections and wires in the engine bay carefully- they lead a hard life and shorts here can cause intermittent running faults.
If you treat the Turbo for what it is, an exotic engined sports car, and maintain it well there is no reason it shouldn’t be reliable. Be aware though that unique parts will be pricey and you may have to wait to source one. Non-running Turbo engines need to be treated with extreme care. A full rebuild can run into many thousands of pounds.
