LPG burns hotter than Petrol . This study evaluates the difference on a Nissan 1500cc car. My interpretation of the screenshots below is that while the car would likely run all day at 2800 revs 120km hour the lpg exhaust temperature would be much higher at the same speed. Dropping the lpg speed to 100km hour would produce exhaust gas temperatures similar to petrol at 120km with similar effects on valves maybe.
If interested the full study can be read here https://www.slideshare.net/ucsp/exp...s-of-lpg-on-spark-ignition-engine-performance
If interested the full study can be read here https://www.slideshare.net/ucsp/exp...s-of-lpg-on-spark-ignition-engine-performance