Humor me: Propane and compression

64starfire · May 10th, 2009, 08:58 AM

So I get these new fangled, crazy ideas because well at the moment, I'm pretty bored. So just for the sake of discussion, does anyone have any helpful info.

So....converting my High Comp 394 to propane. It's already got the high compression, but the secret to power in propane is compression. And since this is a good ol fashioned iron block and heads, I bet it could handle more.

Note: for those who have gotten this far and think I'm crazy, the odds of me actually doing this coversion are pretty slim. No need to get too worked up.

It would be nice to get a few more points but every engine has it's limits. Propane would really like 15:1, but in a factory NA motor, I'm willing to be more realistic. So we all know the several methods:

Milling the heads-easy cheap, have to mill the intake too, but that is a point of return. Plus gonna have to change the push rods (hm would a previous motors' rods work? 303, 324? maybe? anyone? Bueller?)

Thinner head gasket- yeah, unless it's custom made- good luck. Does anyone know of a place that makes custom thin gaskets? Actually this would be nice due to the increased cylinder pressures.

Longer con rods- costly and labor intensive, especially since they very well might be custom. I did come across an article where someone found that the 425 rods were the same. Food for thought.

pistons- again costly and labor intensive unless anyone knows of a piston that would work, maybe from another motor?

One of the questions I have early on are- what is the exsisting valve/piston clearance? Is it already that tight or is there room to play via milling the heads?

So if you're as bored as I am, or like the idea of alternative fuels, or have some info that might help, I'd be interested in hearing from you. Thanks

Warhead · May 10th, 2009, 09:26 AM

Mill the heads? You can not mill enough out, without causing piston to valve clearance issues, or gasket fitment issues, or pushrod length issues, or manifold fitment issues.
WILL NOT WORK.
Longer connecting rods will not give you the higher compression ratio you are looking for, they will only cause a need for shorter pistons, just to clear the head.The long rods ONLY increase dwell time at TDC (increase tranference of mechanical power to crankshaft), will NEVER, EVER, EVER increase compression, unless, with the new pistons, head clearance is diminished. Still will not be much increase.
WILL NOT WORK.
Thinner gasket will not give enough compression increase.
WILL NOT WORK.
You want a 1 or 2 point increase in compression, and that means custom PISTONS.
Fact. Figure around $500 to start.
The only other alternative is if there is another cylinder head that fits the 394, and has a much smaller combustion chamber. Being for the 394, I do not know what would work in this instance.
Ask Norm.
Jim

64starfire · May 10th, 2009, 10:23 AM

Yeah at that point, with custom pistons, I'd want to think long and hard before really wanting to go that route.

Texascarnut · May 10th, 2009, 01:15 PM

I indulged in this exercise of mental masturbation a number of months ago. Got real fired up over the idea until I realized all of the associated costs of conversion and inconvenience of propane availability far outweighed the benefits I perceived propane might have. The first stumbling block being with the State of Texas and the annual payment of road use taxes at the time of registration renewal. An amount estimated on anticipated fuel consumption and ordinarily paid at the pump with gasoline. The bookkeeping alone can become more of a hassle than I wanted to maintain to keep from paying excessive taxes in future years.

Conversion units for dual fuel usage have been employed for years trucks (usually government owned) and motor homes. Find someone with a dual fuel motor home and ask them if it is worth the trouble.

May 10th, 2009, 08:58 AM	#1 (permalink)
64starfire Registered User Join Date: Mar 2009 Posts: 55	Humor me: Propane and compression So I get these new fangled, crazy ideas because well at the moment, I'm pretty bored. So just for the sake of discussion, does anyone have any helpful info. So....converting my High Comp 394 to propane. It's already got the high compression, but the secret to power in propane is compression. And since this is a good ol fashioned iron block and heads, I bet it could handle more. Note: for those who have gotten this far and think I'm crazy, the odds of me actually doing this coversion are pretty slim. No need to get too worked up. It would be nice to get a few more points but every engine has it's limits. Propane would really like 15:1, but in a factory NA motor, I'm willing to be more realistic. So we all know the several methods: Milling the heads-easy cheap, have to mill the intake too, but that is a point of return. Plus gonna have to change the push rods (hm would a previous motors' rods work? 303, 324? maybe? anyone? Bueller?) Thinner head gasket- yeah, unless it's custom made- good luck. Does anyone know of a place that makes custom thin gaskets? Actually this would be nice due to the increased cylinder pressures. Longer con rods- costly and labor intensive, especially since they very well might be custom. I did come across an article where someone found that the 425 rods were the same. Food for thought. pistons- again costly and labor intensive unless anyone knows of a piston that would work, maybe from another motor? One of the questions I have early on are- what is the exsisting valve/piston clearance? Is it already that tight or is there room to play via milling the heads? So if you're as bored as I am, or like the idea of alternative fuels, or have some info that might help, I'd be interested in hearing from you. Thanks

May 10th, 2009, 09:26 AM	#2 (permalink)
Warhead Registered User Join Date: Mar 2008 Location: Phx, AZ Posts: 311	Mill the heads? You can not mill enough out, without causing piston to valve clearance issues, or gasket fitment issues, or pushrod length issues, or manifold fitment issues. WILL NOT WORK. Longer connecting rods will not give you the higher compression ratio you are looking for, they will only cause a need for shorter pistons, just to clear the head.The long rods ONLY increase dwell time at TDC (increase tranference of mechanical power to crankshaft), will NEVER, EVER, EVER increase compression, unless, with the new pistons, head clearance is diminished. Still will not be much increase. WILL NOT WORK. Thinner gasket will not give enough compression increase. WILL NOT WORK. You want a 1 or 2 point increase in compression, and that means custom PISTONS. Fact. Figure around $500 to start. The only other alternative is if there is another cylinder head that fits the 394, and has a much smaller combustion chamber. Being for the 394, I do not know what would work in this instance. Ask Norm. Jim Last edited by Warhead; May 10th, 2009 at 09:36 AM..

May 10th, 2009, 10:23 AM	#3 (permalink)
64starfire Registered User Join Date: Mar 2009 Posts: 55	ok thanks Yeah at that point, with custom pistons, I'd want to think long and hard before really wanting to go that route.

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May 10th, 2009, 01:15 PM	#4 (permalink)
Texascarnut Geezer Join Date: Jun 2008 Location: So. Central Texas Posts: 269	I indulged in this exercise of mental masturbation a number of months ago. Got real fired up over the idea until I realized all of the associated costs of conversion and inconvenience of propane availability far outweighed the benefits I perceived propane might have. The first stumbling block being with the State of Texas and the annual payment of road use taxes at the time of registration renewal. An amount estimated on anticipated fuel consumption and ordinarily paid at the pump with gasoline. The bookkeeping alone can become more of a hassle than I wanted to maintain to keep from paying excessive taxes in future years. Conversion units for dual fuel usage have been employed for years trucks (usually government owned) and motor homes. Find someone with a dual fuel motor home and ask them if it is worth the trouble.