Thanks to Leigh from Deshele performance we've come to the conclusion it's valve to valve contact that's done it. I've always thought the engine was slightly noisier after my drag strip visit but until now just though I was imagining things.

Something Leigh said (without knowing about the noisier engine) has confirmed my suspicions. We think it's valve float when hitting the limiter that's done it.

On the drag strip I hit the limiter in 4th at 135mph about 10 meteres before the line. I think this has been the point where the inlet and exhaust valves have hit each other and bent slightly. Then they've just fatigued over time.

I'm not going to buy supertech again. I've read a few posts by some quite serious engine builders who have switched to Ferrea valves as they tend to just bend rather than break.

I'm also going to raise the limiter from 7800rpm to 8500rpm. That will get me across the line without limiter bashing. It's not the rpm that's done this it's the float when the limiter kicks in.

Block is possibly salvageable, bottom end looks to be good too apart from the pistons of course. Ill know for sure when i split the block later.

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605whp
Quarter Mile in 10.9 seconds @ 135mph /217kph
0-100 kph 3.2 seconds