It seems to make sense to explain what fits what with the Abarth 500 series of cars.
There are two production turbos, actually three, but two types. The IHI which can be safely coaxed to 165bhp, but not much more - the exhaust wheel and the 30mm hole it sits in are just too small. The other production turbo is the Garrett GT1446 in early or late form, which can be coaxed to 200bhp but every time we have tried to go beyond that we have snapped the turbo shaft, again proving that the exhaust wheel and the 34mm hole are just too small.
So with Geoff Kershaw at Turbo Technics, the S260 was designed, it uses a bespoke turbine housing that externally is the same size as the GT1446 but internally is much bigger, 42mm, allowing the exhaust gasses to get out. If we are talking about the volume of exhaust gas that can flow, the S260 is more than double the IHI. The turbo core is a proven unit and the compressor is something like a Fiesta ST, but made by TT. We originally thought that we could get up to 285bhp from the S260, but with 440cc injectors and race fuel we see 300bhp at 1.55bar of boost with a standard engine.
What we didn’t realise when we started looking for more power from the Abarth 500 engine was just how ‘det limited’ the engine is. Now that we are racing it is obvious. The engine has a knock sensor fitted to the cylinder block to stop the pistons being destroyed by detonation. First, a textbook explanation:
Knocking (also knock, detonation, spark knock, pinging or pinking) in spark ignition internal combustion engines occurs when combustion of some of the air/fuel mixture in the cylinder does not result from propagation of the flame front ignited by the spark plug, but one or more pockets of air/fuel mixture explode outside the envelope of the normal combustion front. The fuel-air charge is meant to be ignited by the spark plug only, and at a precise point in the piston's stroke. Knock occurs when the peak of the combustion process no longer occurs at the optimum moment for the four-stroke cycle. The shock wave creates the characteristic metallic "pinging" sound, and cylinder pressure increases dramatically. Effects of engine knocking range from inconsequential to completely destructive.
What we are seeing is the engine running at 10 degrees ignition advance when relatively cold, but moving to no advance at all when very hot. Modern race engines have a knock sensor for each cylinder. For the Abarth, we can have a knock-on one cylinder that is affecting them all, so one lazy injector and the power comes down.
The Trofeo race series ran with 102 octane Panta fuel and that was at 188bhp, pump fuel dropped the engine to below 180. In our brief power tests we see 285 on pump fuel and over 300 on 102, but that is before the temperatures go up.
The car that finished second in Turbo Tin Tops in the 40 minute race at Silverstone in October 21st was running at 1.45bar of boost to keep the temperatures down, and Andrew Marson set his fastest lap 11 laps into the race, which backs up our theories.
The race cars run standard intercoolers. We have found that a front mount puts the water and oil temperatures up too much and thus reduces the power more. The production side mounts have air flowing through them into the wheelarches, just as Ferrari and Porsche do on their GT3 cars. Bigger side mounts would be good but they will be expensive and need better pipework.
S260 and fitting kit.
The S260 turbo and fitting kits are available from Turbo Technics in Northampton, 01604 705050.