Propane plus the addition of a module, tuner or chip is still well within the limits of what the engine can handle assuming there are no pre-existing defficiencies. Propane actually provides a complete burn of all the fuel you are already injecting into the cylinder plus of course since it is also a fuel there is a moderate increase in power due to its own ignition. A properly tuned propane system poses no threat to the engine in their factory settings. Turning the flow rate up on the system while running a tuner chip or module that has already advanced the fuel timing can contribute to predetonation. If this is the case, it is still possible to have your tuner or chip loaded with a custom tune that takes the advance back out of the fuel timing and just adds fuel, whereupon predetonation is no longer an issue. I have never read of or heard of any engine failures related to propane that were not due to either a home made system(no safeguards for flow rates) and or people just cranking the propane up to its highest setting. For the purposes of the original poster, he probably doesnt even need a custom tune just for towing... You mentioned you blew your engine running a chip and water....?? I read your post where you said you were running a 60/40 methonol to water ratio with a chip or a tuner I cant remember which. You also stated you were doing a top end prolonged run @ 130mph without guages and I would probably be correct in assuming you chip or tuner was on the highest setting. No offense, but you were trying to blow your engine!! I would venture to say even if both systems propane or water/meth were used responsibly, the propane would be safer and the only reason to need to 0 ring the heads in either case is if you were going to push 35-40+PSI consistantly. The propane along with a chip/tuner will yeild 35 max. BTW sorry about your engine. The twin turbo stroker you are building is gonna be awesome, good luck with it!