Monday, December 10, 2012

The Day of the Dyno

There is some debate about the desirability of a thermostat in a race car engine. Some say that it restricts flow and that it is a bad thing, others say that without it, the engine will be slow to reach its ideal running temperature. Often they are removed in the hope of reducing engine temperatures that are close to the limit, rather than addressing the underlying problem.

I can now state quite categorically that thermostats are a Good Thing. When Mark Adams found that, contrary to my recent experience, the Beast was running hot at a fast tickover, he started investigating. And he discovered that we had no thermostat. However, in the LS2 engine, the thermostat and ‘stat housing design is such that without one, around 50% of the water flow from the pump will be immediately short-circuited back to the pump infeed, without going anywhere near the radiator! This is clearly a Bad Thing, and one more legacy of the original (rather questionable) build quality. He also found a blanked off bleed tube, which is there to release any air trapped in the highest point of the water jacket back to the radiator. Without this, hot-spots can develop where the air has displaced the coolant.

A quick trip to the helpful guys at Al Ghandi resulted in a shiny new ‘stat and housing, and after some re-jigging of the coolant pipework by Robbie the Fabricator, normal cooling was restored!

None of the garages where the Beast was serviced had noticed these problems. We’ve gone down the road of solving overheating through bigger and better radiators and fans, without understanding the fundamental problems. With these addressed, we can now put the Beast under the stress of a dyno run, which has been delayed accordingly. So before we even get to the tuning, Mark has earned my gratitude.

So finally, we get the Beast on the 4x4 dynamometer at 1000 Dunes Garage, where Sam has built his reputation on tuning Evos. As suspected, Mark finds issues with the mixture as well as the timing, which are addressed as the mapping is progressively refined over the course of some ten dyno runs. The final result (with restrictor) is a maximum 213 bhp at the wheels, coming at around 4700rpm, and a peak torque of 277 ft/lbs with a very flat torque-curve. The mandatory FIA restrictor (37.2mm) is costing us around 15 bhp, but the torque is actually slightly increased – go figure. All figures show an improvement over the original mapping, but more importantly the re-map should provide increased engine reliability and durability.

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