Spark Plugs for Propane 300 six [Archive] - BB.BC4x4.COM

: Spark Plugs for Propane 300 six

August 18th, 2007, 03:56 pm
I cannot seem to find any literature about the proper plugs for a 300 six on propane.

I've been told by others to just use the normal plugs, but to tighten the gap up to .030 or so.

The plugs in my engine when i got it were Bosch Platinum DR9BPX.
I don't usually like platinums in OHV engines, so I went to Lordco.

They had a specific LPG listing for a copper core Bosch plug, which turned out to be DR10GC0.

Looks like a heat range difference there, not sure which is colder or hotter.. higher numbers hotter??

Any info people have about this would be much appreciated.

August 18th, 2007, 04:35 pm
ok, found some info on

it is suggesting a .044 gap (just like the gassers) on the lpg plug as well! i don't think it would run with that gap! i tried .037 when i installed the coppers originally, and it didnt want to run at all.

bosch doesnt even suggest a platinum plug for lpg. the platinum's i found in the engine were gapped at about .030.

still trying to determine what the best setup is with this. the engine is tight, good compression and oil control, and is otherwise stock, beyond the hardened valves for propane.

any insight or experiences ppl have in this area would be appreciated. not having any real trouble, just want to run this as efficient as possible.


August 18th, 2007, 06:18 pm
Theres always confusion with regards to what a hotter plug is and what a colder plug is.

Nobody can decide which is which. I have some 80's vintage propane installation books from Impco and it says
"a hotter spark plug runs cooler, a cooler spark plug runs hotter"

which is in complete contrast to Wikipedia

"A spark plug is said to be "hot" if it is a better heat insulator, keeping more heat in the tip of the spark plug. A spark plug is said to be "cold" if it can conduct more heat out of the spark plug tip and lower the tip's temperature. "

Propane burns a low slower than gas, so you want a spark plug that can throw a better flame front, which means you're looking for one heat range different that will give you more exposed electrode. You can get away with this in a propane engine because theres no carbon deposits to foul the plugs

Get yourself an aftermarket coil and some really good spark plug wires, it takes more power to fire a plug on propane for reasons that elude me, I think it has something to do with the lower combustion temperatures

Hope that helps. Myself I've changed plugs both ways, adjusted timing back and forth, changed my mixture form one extreme to the other, and it still runs rich at idle and gets bad mileage.

August 18th, 2007, 08:15 pm
On my Fords especially the 460s on propane nothing but NGK V power and its what I used to run in my 300-6 on reg gas.

I used NGK spark plugs untill I went to diesel and haven't had to change plugs for almost 8 years.

The worst plug on the planet is Crappion I never had any luck with them along with many others.

August 18th, 2007, 09:45 pm
the ngk V power is about the worst plug available
when half the V is missing everytime you pull them you gotta wonder where the little pice of steel is

gap them tighter then gas motors
lpg doesnt get a cooling wet charge of fuel, it is dry and hot, run a plug that will allow some of the heat to get out

and it still runs rich at idle and gets bad mileage.

an impco with a dead idle diaphram and worn guide?

August 19th, 2007, 04:26 pm
yeah, i've seen some funny stuff.

one manufacturer uses higher numbers for the cooler plug, another has lower numbers = cooler.

I never decided anything about it, but my take from reading general info via google is that hotter plugs help prevent fouling, in cases where there might be bad oil control, or rich conditions.

considering that, bosch plugs no matter the variety number their plugs in a manner such that: the higher the number = the hotter the plug. i will try a little hotter, to see how it runs, and beyond that, i guess i'm not too worried about it.

neither of the plugs types i was using seemed to foul up, and the truck doesnt seem to run any different either way.

i like the idea of an aftermarket coil and good wires though, i 'll try to get more voltage to the plug, so that i can open the gap a little and burn the fuel more efficiently.

August 19th, 2007, 07:12 pm
We ALWAYS use stock plugs with propane. I have NGK plugs,MSD wires and blue streak cap and rotor on my 460 with propane. I set the gap the same as gas. Propane burns cooler then gas and is dry so no carbon. Propane is also hard on ignition parts so I check the pluges every 20 000 km. Never use platinum plugs you get small backfires through the intake. Not a problem with metel ones but the plastic on newer trucks and boom the intake blows up. I have done 5 on different trucks for that problem. If you have any problems or need a set up I have a 4 gas analizer and my boss is been doing propane for 20 years. So PM me and I will give you my numbers and we can work somthing out. Propane always runs a little rich at idle and smells a bit. That is normal to have. Good luck with it.

August 19th, 2007, 08:01 pm
Use NGK plugs UR6 with a .030 gap.

August 19th, 2007, 08:19 pm
I never had any problems with NGK plugs and when I had propane powered 460s they were recommended by people with propane powered trucks.

August 20th, 2007, 03:30 pm
I like the idea of NGK plugs. I will switch to those, and will upgrade to aftermarket coil and wires. From there I will try to run a .044 gap, and if no dice, will close the gap a bit.

Thanks for the tips guys.

August 20th, 2007, 05:31 pm
If you have the stock Duraspark I would consider looking at a hotter ignition and the best plug wires you can buy.

August 20th, 2007, 06:41 pm
the ngk V power is about the worst plug available
when half the V is missing everytime you pull them you gotta wonder where the little pice of steel is

gap them tighter then gas motors
lpg doesnt get a cooling wet charge of fuel, it is dry and hot, run a plug that will allow some of the heat to get out

an impco with a dead idle diaphram and worn guide?

Hmmm, worn guide.......

I replaced the idle diaphram in both of my impco 425's and with the idle screw turned nearly all the way out I can just barely keep it on the high side of the scale of the gas analyzer.

so, what is this guide you speak of? servicable or do I buy new mixers?

Acutally its a progressive system so the rear mixer does nothing until 3/4 or more throttle, so its idle circuit is irrelevant, perhaps that one isn't worn out like the front one, maybe I'll switch them around. only problem its about ten gaskets between the mixers, adapters and throttle body lol.

August 20th, 2007, 09:17 pm
Well while we are talking about propane....does it run hotter than gas? I just bought a 86 with a 351 on propane and during my run to van and back the coolant never got over heated (was on the O of normal) but damnit when i checked the oil in pemberton i couldnt touch the valve covers and the engine bay was cooking. Also which is the hotter plug the one that has the shorter nose or the longer (how far the electrode comes from the plug) I had Autolite 42s(cant remember what the first numbers are but the emissions tag under the hood recommends 32s) in there and they had white deposits all over and broken insulators and discoloration on the outside of the plugs....i swapped in a set of plugs in the correct heat range and the electrode was further away from the end of the plug and there was more insulator showing.


August 21st, 2007, 07:26 pm
Now Hayes, would you suggest I keep the stock module and go with something like an Accel coil and wires? Or would you go further?

August 22nd, 2007, 07:58 am
MOnty, if you do not tune the mixer it will make the exhaust manifolds white hot.
if I were you I would try and richen the main jet by a bunch until you temps under control.
lordco was selling wideband innovative o2 sensor kits for just over $300 a couple of months ago. less in Canadian funds then I payed in US funds for mine.
I consider it an indispensible tuning tool for propane conversions.
next time I will buy the in dash one and leave it installed.

Craig I am not sure why you are trying to run big plug gaps.
the duraspark fires lpg just fine stock but when you start making it more difficult by spreading the gap a hottoer coil might be required.
you aent going to gain anything with yellow wires over other colours.

August 22nd, 2007, 06:20 pm

I am under the impression that a bigger spark will help me burn fuel more efficiently.
i'm certainly not worried about under-hood appearance or wire colours! hehe

August 22nd, 2007, 09:07 pm
It all depends on how much money you want to spend. The duraspark ignition is one step above points. I never had any problems with duraspark but I have had the modules fail on me.

Putting a higher voltage coil on the engine really won't benefit much if you have a old distributer that can't take the juice.

If you replaced the whole ignition system with a higher output you may or may not see some benefit.

Cheapest option is replace the oem stuff with new oem stuff that is better quality so you are getting maximum output from the stock parts.

August 23rd, 2007, 08:51 am
I do not believe that the Yellow stuff is any improvement over what ford put in.
if anything it looks like offshore junk.

if you want to get fancy with ignition I can point you to some cool stuff, DIS adaption from new fords with programmable ignition curves.
the control box is around $200 and you source the rest from wrecking yard fords.
no more caps and rotors to buy, just wires and plugs.

fords DIS system is really cool, modular design that begs to be adapted and there is a module on the market for cheap to do it.

August 23rd, 2007, 04:05 pm

I may be interested in a DIS system, if it is the best way to get an ideal timing curve for propane.

This has spurred me to check out what centrifugal advance is currently in the dizzy I have.

Baby steps!

My fuel mileage has dropped markedly since I took the engine and fuel system from 4200 lb truck with 4.10, 235/75r15s and a T19, and placed them into my 5500lb Highboy with 4.10', an AOD and 31 inch tires.

(go figure)

I've gone from 1200 - 1400kms -mostly city - from 200 litre tank, to about 800-1000kms of mixed city / highway.

I do know the weight difference plays a role, as well as having the AOD absorb some horsepower...

So now I try to maximize efficiency. :)

I think my exhaust is a little restrictive.

August 24th, 2007, 12:05 am
you can get an ideal curve with a duraspark but you can make any curve with the DIS
search for megavoltJr or megavoltlite
one of those is the DIS controller

there is very little to be found in ignition systems.
they either light off the mixture or they don't

August 24th, 2007, 02:46 pm
The truck does run well, and I do figure reasonable timing characteristics have been achieved by whomever built the engine.

It has an OHG X1 mixer, and it seems to be a decent unit.

There is a kink or two in my 2 1/4" exhaust that narrows it to 2" or 1 3/4" or slightly less in places, so I figure I should take care of that. Thinking about going to EFI manifold dual exhaust setup. :welder

I'm hopeful that I can make a few well considered adjustments and changes that will allow me to see a bit better mileage.

Engine was taken out .030 when it was rebuilt. I have no idea how many CFM the intake is moving into the engine, nor what diameter exhaust is ideal to complement intake.

I'm guessing if the propane system passes 300 CFM or so, that 2" single exhaust with quiet muffler is enough, or 1 3/4" dual with quiets.

I'm keen to do what I can to make this work well. Right now I'm getting about 4-5km to the litre. 11-14mpg wont cut it.

Even though I am happy about less weight in the front end, ease of maintenance and the reliability of the six, I'll go back to a small or mid-sized Eight ....if that's the kind of mileage I'm gonna get.

I'm starting to think I should have started a thread asking about efficiency tips for a six on propane.. heh.

August 26th, 2007, 11:32 am

Determined that my vaporizer is an OHG X-1, and the TB is an OHG X-450.

Does anyone have any specific experience or links related to these? I'd like to know how to adjust or determine if adjustments are required.


August 26th, 2007, 01:30 pm
weld an oxygen sensor bung into the exhaust
test with a wideband meter
there is no better way

August 26th, 2007, 05:40 pm
good idea. i'll look into that.

August 27th, 2007, 02:41 pm
I want to point out a fantastic source of information to help anyone with propane tune their setup. Google up "Diagnostic Guide to Alternative Fuels" by Franz Hoffman.

I definitly agree with Michael that the O2 sensor and wideband tester are a real necessity to help calibrate the fuel systems; now that I've read into it a bit.

The sensors seem cheap to get ahold of, the tester might be another matter.. still looking..

Check out as well. I was amazed to discover a seeming abundance of engineers and professionals on this site, carrying on a number of threads with in-depth, and in most cases properly cited conversations regarding fuel mileage improvements, propane or gas. It isn't just limited to six cylinders, btw.

Was also surprised to read on a propane association newsletter, that there is now a patented process for lowering the compression on diesel engines, and running them on straight up propane... check it out:

Thanks for all the advice everyone offered me here, as I clumsily found my way around to the resources I need to make my setup work the best it can. I still have a lot of work ahead, but now I know where to start!

August 27th, 2007, 06:32 pm
I have an Innovative wideband
Lordco had them on sale for far less then I paid a few months ago

if you weld a sensor fitting into your exhaust we can meet on a weekend and you can see where you are at.

does your mixer have a large bolt near the 1" Gaan hose inlet? newer ones are set at the factory but the older ones had adjustment.

personally I think Franz is full of ****te

August 27th, 2007, 07:02 pm
It has a large nut for power adjustment, looks like a jam nut on it too.

Mine also has two vacuum lines, both entering the TB near the idle mix adjustment screw.

I am thinking of plumbing my regulator parallel with the heater core, as opposed to in series..

I will need to get ahold of my own wideband sensor, as I'm in Halifax for the summer.. we drove it here two weeks ago with 3500lbs of cargo. We got 800km from each 200litre fill. Not bad, considering.

But I'll look into the model you mention, maybe I can get ahold of one at a reasonable price..

thanks again. the engine is running rather well at this point, and I'm thinking that any adjustments to idle, power mix and timing will be minor in nature. I'm hunching that my exhaust pressure should be an equally important thing to address in this situation, as I think it's a little restrictive due to some kinks.

I intend to do a compression test at some point, and would like to check the total timing, and maybe adjust initial a bit, which I have fairly advanced right now. I do have good vacuum at idle, and load readings seem right.. gonna take a look at recovery..

then i'll try to get a sensor and tester geared up before I attempt much of anything with the fuel metering/ air fuel mixture..

can't forget to put a fresh tstat in there as well, and a fan shroud. I'm using a 460 4 core rad, (not the huge one) as well as a 5 blade fan from a 460, but it still gets a little hotter than I want when idling in traffic.

August 27th, 2007, 08:21 pm
I bought the LM1 handheld meter but next time I will go with an in dash guage
my new 425 was very lean across the board and really lean at WOT
still not as rich as I would like at WOT and nothing I do really effects the light throttle cruise, hovers around 15:1 guage reading (guage reading is stoich at 14.7 as it reads in Lamba and has a conversion to stoich for gasoline)

August 27th, 2007, 10:06 pm

I've gone from 1200 - 1400kms -mostly city - from 200 litre tank, to about 800-1000kms of mixed city / highway.


What????? Dude I need to hire you to tune my truck. I get 450 km's to 200 liters of propane

I have a portable gas analyzer that I use to tune my cruising mixture, its pretty much ideal as far as all the information I've got from alternate fuels website, and my mileage still continues to suck

of course its 6200 lbs with a 460 ....

August 28th, 2007, 11:52 am

In Dash Gauge?!! Wow.. That would be really neat... do tell.. I'm gonna look up the tester as well.

Hey Dan,

Yeah, as more time passes, and I as I learn a little more about how this engine and fuel system of mine have been put together, I'm more impressed. (stuff like the regulator and mixer being directly connected) I think whoever put it together knew exactly what they were doing, and anything I do will be more along the lines of maintaining and adjusting, as opposed to real changes; beyond my exhaust system.

Is your power adjustment correct for throttle tip in, load and such? What about your total advance, what rpm is your total advance achieved by?? Beyond all that, gearing and tranny choice make a huge difference for mine.. I'll never go without overdrive again.. My AOD build/upgrade cost over $2000.. If she blows before 5 or more years; I'll go ZF and never look back.. heheh

I've heard the lore of 20mpg achievable with a stock 460, but I dont know if I buy it.

August 28th, 2007, 05:36 pm
this is the one I have
but they have since come up with a lot more
if you do not want to data log then this is theway to go I think

August 29th, 2007, 06:15 pm
Thanks .. I now have some new items on my shopping list.. gonna do some research on this one, to make the right choice at the right price..

May 1st, 2008, 05:37 am

May 1st, 2008, 08:16 am

I've gone from 1200 - 1400kms -mostly city - from 200 litre tank, to about 800-1000kms of mixed city / highway.


What????? Dude I need to hire you to tune my truck. I get 450 km's to 200 liters of propane

I have a portable gas analyzer that I use to tune my cruising mixture, its pretty much ideal as far as all the information I've got from alternate fuels website, and my mileage still continues to suck

of course its 6200 lbs with a 460 ....

I get about the same but mine is a 5.8 with a np435 with gear splitter.
I recurved my dist to give full mech advance about 2500 rpm total advance is 38deg (mech+vac) if I recall. I have a hotter coil with the factory gap on the plugs the Hotter coil makes a big differance over the factory ford fodder.

May 17th, 2008, 07:01 pm
I am also using a stepped up coil, and it works well.

after starting this thread; has been a place I've used extensively over the past several months to discuss propane efficiency.

Jay Storer's Book, and Franz Hoffman's Guide to Propane Performance have been very good for information.

38* total advance might be a bit too much still, barracuda

here is a good link to recurve:

your total is your static/initial plus your centrifugal. Your vacuum advance is adjustable, and should be tinkered with to fit your needs best, there is no defined rate for any vehicle, you need to find it for yourself. (i havent even got to that yet with my own rig)

for the record, i still am at 12mpg. it is the same, regardless to how i drive. I am blaming the beefed up AOD for a portion of it. Even though my truck weighs 5500lbs, and has 4x4 drivetrain further lowering driveline efficiency (remote case at that) - i still feel a ZF or other standard with ideal cruising rpm combo factored in - that i could get about 17 mpg with this beast.

Still haven't definitively tested a/f ratio either.

i have started using an efi shortblock with rebuilt / shaved head, good for a total CR of 9.2:1, over the 7.5:1 ratio I had. Much better power, but still same 12mpg.

Intake / Exhaust mods are in order, plus cam timing advancement.

i have very little vacuum at 110 km/h, at 2100 rpm, 3/4 throttle.. 0-5"... engine working hard.

Propane is 1.25 / 1.29 per litre in Halifax. I have a vested interest in getting over 12mpg. Bought an 85 F150 2WD Np435 w 3.08 gearing and 20mpg to allow me to get the highboy off the road to get into the more involved mods. (efi exhaust, modified efi intake to accept the ohg x-450, and an offset crank key to advance cam timing 4*. all stuff i have already, just no time to do..

and along the way, i'll get an afr gauge, and o2 sensor, so on so forth

i better win the lottery first.