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Interpretting Vacuum Gauge Data
https://slantsix.org/forum/viewtopic.php?t=37728		 Page 2 of 3
Author:  coconuteater64 [ Sun Nov 01, 2009 6:15 am ]
Post subject: 
That plug gap thing assumes a stock ignition system if I read it correctly. Still seems to me a bigger gap would be better, and an MSD ignition could more than make up for the increase in gap.

As for burns hotter I again don't get it. Doesn't propane have fewer BTUs than gasoline? :shrug:

I am very curious about this propane stuff as a fuel. My lawn mower is propane and it seems to run cooler than a similar motor on gasoline. Our aircraft tugs are also propane and don't seem to even need to warm up on cold days, just turn the switch and go. Butthe temp gauge stays in the cool range all day.
Author:  Roelof [ Sun Nov 01, 2009 6:27 am ]
Post subject: 
I used to have the same problem with my propane-burning slant.

I installed a Remflex-gasket and it got a lot better. After re-adjusting the valves (were too tight) and turning the mixture a little richer it went away. I use standard electroninc ignition (new coil, leads, box) and plugs with standard gap.
Author:  Daddiojoe [ Sun Nov 01, 2009 6:49 am ]
Post subject: 
Roelof--

what is a Remflex gasket and where does it go?

Coconut--

As I understand it, BTU is a measurement of energy capable of being released that is contained within a certain mass/measureable quantity. So, the British Thermal Units contained in a cubic foot of propane compared with the equivalent in gasoline would be less. While releasing the smaller amount of energy, though, the propane may indeed burn hotter.

Maybe like horsepower vs. torque?

Some engineer please correct me.

Thanks for all the responses, I'll do more work today and get back w/ you.

Joe
Author:  Daddiojoe [ Sun Nov 01, 2009 9:27 am ]
Post subject: 
OK--

With vacuum gauge hooked up to the base of the carb--19.5-20" at idle and an unsteady 13" when in gear.

Anything I can surmise from this?


Also, bought some Champion long-reach platinums, same application as the NGKs, and they make a bit of a difference. Champions are made in the U.S.

I installed the Champs at .035" gap. Made some difference, but not enough. Late will go back and see if gapping them at .030" makes the difference I'm looking for.

When I removed the Autolites, half of them were fouled. I got a refund. They were new two weeks ago.

I am able to replace the Champions if they go bad in three years.


Short of breaking down and taking it in to get scoped out, is there an easy way to determine if my problem is electrical or fuel related?

Thanks again for all of the help.

Joe
Author:  SlantSixDan [ Sun Nov 01, 2009 9:50 am ]
Post subject: 
Champion spark plugs are poorly-made trash. Get NGKs. What's being said about gaskets is that it is very much worth your while to get the good gaskets for the manifolds-to-head and intake-to-exhaust junctions.
Author:  FrankRaso [ Sun Nov 01, 2009 10:53 am ]
Post subject:  Re: Interpretting Vacuum Gauge Data
Quote:
As per the advice of a propane-guru, the plugs are gapped at .030. WHAT DO YOU THINK ABOUT THIS PLUG GAP?
The reason that the gap is reduced when burning propane (or natural gas) is that a propane fuel mixture has a higher ionization energy than a gasoline fuel mixture. To reduce the voltage required at the spark plug, the gap is commonly reduced. However, I've run higher gaps in my engines and have not experienced any problems. You can increase the gap but the rest of the ignition system must be working perfectly. Closing the gap to 0.028" - 0.035" gives the ignition system a bit more reliability (with electronic ignition).

Incidentally, I am using the OEM sparkplugs (0.060" gap) in my 2003 Impala. Technocarb recommends 0.040" gap with propane but I have not experienced any misfires at 136,000+ km. I'll replace them with 0.040" gap plugs closer to 160,000 km.

BTW, I emailed Franz today and he still suspects you have a ignition-related problem. Do you know of a local shop that has a scope and understands how to read it?
Author:  Daddiojoe [ Sun Nov 01, 2009 11:05 am ]
Post subject: 
Thanks Frank. Looks like I may have to go to a shop.

Dan-- yep, I've got the good big Australian gasket, and Dutra casting front exhaust manifold and chopped stock exhaust manifold in the rear (fwiw). Guess I never paid attention to the brand name.
Author:  FrankRaso [ Sun Nov 01, 2009 11:10 am ]
Post subject:  Propane Conversions
Quote:
As for burns hotter I again don't get it. Doesn't propane have fewer BTUs than gasoline? :shrug: .
Propane does have less BTUs/gallon than gasoline (84,500 BTU/gal LHV vs 116,090 BTU/gal LHV). See US DOE AFDC Properties of Fuels.

Copied from an old Woodward Streamline catalog:
Quote:
CNG has a peak flame temperature of 1790°C/3254°F which is 187°C/337°F (9.5%) cooler than the peak flame temperature of gasoline at 1977°C/3591°F. The peak flame temperature of LPG at 1991°C/3614°F is only 13°C/23°F (less than 1%) higher than gasoline.
People often ran their propane engines too rich and often the spark advance curve was not optimized for propane. This would often cause burned exhaust valves because the fuel mixture would still be burning when the exhaust valves opened. If anything, a propane engine would tend to run a bit cooler because the converter would absorb some heat vaporizing the fuel.
Quote:
Our aircraft tugs are also propane and don't seem to even need to warm up on cold days, just turn the switch and go. But the temp gauge stays in the cool range all day.
Gasoline engines need a warm intake manifold to keep fuel in the airstream. Propane is always vaporized and engines will start easily (provided the battery can crank the engine) down to -40°F. Your tug's engine is probably running cool because 160°F thermostats are often installed as part of a conversion.
Author:  Daddiojoe [ Sun Nov 01, 2009 4:36 pm ]
Post subject: 
Re-gapped the plugs to .030" and it makes a world of difference. Actually running pretty good now.

So obviously my ignition system isn't optimal. I'm running a blue ECU, electronic distributor, and an MSD hi-po coil. Any suggestions on a better coil, etc?

Thanks for all of the help. I'm looking forward to running it more later in the week and seeing if the improvements hold up.

Joe
Author:  SlantSixDan [ Sun Nov 01, 2009 5:34 pm ]
Post subject: 
Quote:
So obviously my ignition system isn't optimal. I'm running a blue ECU, electronic distributor, and an MSD hi-po coil. Any suggestions on a better coil, etc?
MSD coils are now made in China. :-( How 'bout an HEI upgrade?
Author:  coconuteater64 [ Sun Nov 01, 2009 6:30 pm ]
Post subject: 
Frank, thanks for the patient explanation. Now I get it. I do love the fact a cold tug will fire up right off the bat and work hard immediately. Didn't think about the thermostats being cooler. They have big ol' Ford straight sixes and they are some kinda tough!
Author:  Roelof [ Sun Nov 01, 2009 9:45 pm ]
Post subject: 
A standard (bluestreak) ignition and coil should run just fine with propane. But it all has to be in good working order. If your ignition is ok now, buying a new and more expensive ignition might not solve your problem.

Be sure there are absolutely no vacuum leaks and your valves are properly adjusted. You might try a very loose valve setting to find out if your idle improves.
Author:  FrankRaso [ Mon Nov 02, 2009 12:24 pm ]
Post subject: 
There is no need for anything fancy. Propane systems were installed on points & condenser systems but work better with electronic ignition. I'd give the NGK ZFR5N a try when you're due for new plugs.

The GM HEI is a good alternative to the Mopar electronic ignition.
Author:  Charrlie_S [ Mon Nov 02, 2009 7:42 pm ]
Post subject: 
Quote:
Well, now I'm even more curious: Why does propane warrant narrow plug gaps?
My comment, was not about using a narrow gap plug, but not opening up the gap, to .040-.045, from .035, with a stock Mopar ign system.

I'm glad, Frank answered, this question. I had/have done some reading on Propane conversion, and remembered this recommendation, but couldn't remember the technical reason, and I haven't had time to look it up.
Author:  Daddiojoe [ Wed Nov 04, 2009 8:16 pm ]
Post subject: 
Dan--

Read about the HEI upgrade. I just bought a new MSD hi-po coil. Don't have the model name at the moment, but it is cylindrical--old style coil.

Would it be worthwile to just switch to an HEI ECU and get rid of my blue box, or do I need a new coil as well?

My truck is running better, but still pretty rough.


Thanks,
Joe
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