Propane RX-7
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Joined: Feb 2006
Posts: 211
From: Tucson, Arizona
My dad and I are converting my RX-7 to propane. Do you guys think it would be worth it? Another thing we're wondering, is how would we put 2-cycle oil in the engine, since they say that you should put 2-cycle oil in with every fill up. Is there any contraptions out there that let you do it? Or do I have to make it myself?
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Joined: Sep 2002
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From: teh frozen nort
If you leave the stock oil metering pump in place, the oil injection will take care of itself. Just make sure to check the oil every few hundred miles. Propane likes a LOT of compression, so I suspect you will find performance will not be very good. Unless you turbocharge it 
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Joined: Feb 2006
Posts: 211
From: Tucson, Arizona
We were planning on putting an electric supercharger on it, so I'd get more power out of it. I'm not worried about power right now, I just want it to have the guts behind it to move quick enough. I'm going to be putting a 3-rotor engine in it later on, Once I have the money saved, and the time to do it. We're also going to be making a body-kit for it, just to see how well I can design the stuff.
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From: olympia wa
actually on performance wise. we were discussing this last week at a tech day. with the right amount of propane( meaning you would have to have bigger injectors for the propane to compensate the fuel) you might only see 5hp difference. good luck and i'd like to see how it turns out.
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From: Tucson, Arizona
Originally Posted by kettlman' post='802622' date='Feb 18 2006, 09:20 AM
actually on performance wise. we were discussing this last week at a tech day. with the right amount of propane( meaning you would have to have bigger injectors for the propane to compensate the fuel) you might only see 5hp difference. good luck and i'd like to see how it turns out.
5hp difference (increase or decrease?) if I put in a standard propane carburetor, or 5hp difference if I get a faster-flow propane carburetor? We're ordering the carburetor today, so we can figure out how much modification we have to do to to get it to fit the mount on the engine. I'll post some pictures of it, once we have everything put together, and have it running good enough, which is gonna take a month or two, once we install the carburetor.
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From: olympia wa
was talking about a decrease. and adding more propane cause of the cfm management or something like that. i don't know that much about it, yet they were also talking about the octane in propane is much better and it's colder than gas. so when they do it most likely they will BOOST the hell out of it. the guys at pineapple racing were the ones talking about it.
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From: Tucson, Arizona
Originally Posted by ryderx' post='802656' date='Feb 18 2006, 01:24 PM
isent propain a lot cheeper than gass?
Yes, which is one reason why I'm converting to propane. Out here, in Tucson, gasoline costs anywhere between $2.23 to $2.49 a gallon, whereas propane costs $1.39-$1.59 a gallon. That's almost a dollar difference per gallon. That means I'll save more money in the long run.
Originally Posted by kettlman' date='Feb 18 2006, 03:57 PM
was talking about a decrease. and adding more propane cause of the cfm management or something like that. i don't know that much about it, yet they were also talking about the octane in propane is much better and it's colder than gas. so when they do it most likely they will BOOST the hell out of it. the guys at pineapple racing were the ones talking about it.
Okay. Yes, you are right, propane has a higher octane in it. I think its around 105-110 octane, compared to gasolines ~80 octane (I think). You can also get more propane in the same volume container, than gas, because propane can be compressed, because it is a true gas, whereas gasoline is a liquid, and cannot be compressed.
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From: Choctaw, OK
We were planning on putting an electric supercharger on it, so I'd get more power out of it.
Also, from http://www.consumerenergycenter.org/transp...fv/propane.html,
One gallon of propane contains less energy than a gallon of gasoline (82,485 British thermal units [Btu] for propane, versus 115,400 Btu for gasoline.
Propane also requires more air to burn. From http://www.iangv.org/files/IANGVREPpart2final.pdf, Table 2.1 (on page 4) we see that gasoline requires 14.7 parts air to each part fuel, while propane requires a 15.6:1 mixture. The last column is your relative energy density. Propane has a relative energy density of .96 compared to gasoline's 1.00
To relate to this, Nitromethane is a great racing fuel because its relative energy density is exceptionally high. Nitro has less than 1/3 the BTUs per pound as gasoline, but its stoichiometric ratio is 1.7:1. (http://www.smokemup.com/tech/fuels.php) You will lose power running propane.
The upside is if you do decide to run a forced induction setup. Propane has a significantly higher octane and can allow more boost. http://www.importpoweronline.com/propanecontent.html (this website is selling boosted propane setups, so take that into consideration when evaluating their information).
