rkillpack said:
I just talked to an engine shop and they said to lower the compression for propane. Everyone else says increase it. Say the compression in the motor is 8:1 now what should it be to take advantage of propane? Everyone with a propane motor speak your mind please because I am confused.
Thnks.
The machine shop isn't really concerned about the compression ratio, it's more about the flame front and flame travel, propane doesn't ignite the same way that gasoline does, it isn't a suspension of fuel in air, it is actually a gas, which means it will have an almost random flame front because of differences in thermals within the engine. It isn't a bad thing, but I would advise either lowering the compression ration - I wouldn't go to 8 9.0 - 10.0 is good, then you could run pump gas and still have good power should you change your mind, or getting a coated forged hyperutechtic piston, it will be able to take any increased forces.
It is a common misconception that propane runs at above 100 octane, the truth of the matter is that first there is no ocatene in propane. Second, in actuallity it could be compared to more like 84 octane - pound for pound. the reason that it "feels" like 100+ ocate is because of the cooling effect of the gas as it evaporates on the intake charge of air, creates a cooler more dense charge of air-gas which equates to more power. Propane is more susceptible to detonation then gasoline mostly because it is poorly regulated, it also tends to lean-burn slightly. polishing the combustion chamber and removing any ridges - you said big block so remove the wedge ridge and polish it, also stainless valves and cooler plugs will go a long way for reliable performance, and increasing engine life.
I know this post is getting long, but I have done a significant amount of research on this, and this may be helpful.
another thing to consider is that there is no lubrication in propane, and it tends to pull lubrication off the fire ring, so slighty larger ring gaps are a good idea too. or it's a chevy, just don't change the valve guide seals, works the same, or use a hybrid system gas - and - gasoline, and use them both.
) so that I don't need to worry about longer trails but I will need to refill eventually. Thanks for any input and suggestions.