There has been a lot of discussion on adding gas here (and a search will find it). But looking at your question objectively, increasing boost and fuelling is in theory unlimited until something breaks. Increasing fuelling, either injected or gas, can only be done to a limited extent before there is insufficient air to burn properly, and further increases are inneffective.
It is claimed that small amounts of gas give more efficient combustion, plus the advantage that gas is cheaper than diesel, but for the reason given, you will not get a dramatic increase in power, which you can with increased boost and fuelling. The other method of increasing power is to reduce the temperature of the intake air - i.e. a bigger intercooler, which will have the same effect as increasing the boost, plus the advantage of slightly improved cooling.
As far as the overall stress on the engine goes, no you cannot say they are the same because the horsepower is the same. Remember that the horsepower is only the maximum power; the stress on the engine will depend on the rpm at which this is developed, and the stress may be most critical at, for example, maximum torque, which will be when the highest peak pressure and hence greatest stress on the mechanical components exists. Then there is the question of thermal stress, both localised (which depends very much on the rate of combustion) and overall, which will depend on the relationship between cooling effectiveness and waste heat; consider that the cooling effectiveness and power both increase with rpm, but certainly not at the same rate.
You can be certain that whatever you do to increase power will increase the stress on the engine, effectively using up some of the manufacturer's safety margin. How much of this you use with any power boost is not very predictable and impossible to measure by any practical method. About all you can say is something like "quite a few people have done 'X' without any problems showing up, so I ought to be able to copy them". But you need to make sure you copy them exactly - if you do not you are doing something that does not have this assurance.
John
John
JDNSW
1986 110 County 3.9 diesel
1970 2a 109 2.25 petrol
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Originally Posted by brianwood
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