dedicated cng 300 build

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cng f100
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dedicated cng 300 build

Post #1 by cng f100 » Tue May 24, 2011 9:59 pm

Long time reader first time poster. I'm building a ford 300 that will run on CNG (compressed natural gas ) only. I have a 1986 block, 352 piston, 240 head shaved a 10th of a inch with very mild port and polish, Clifford 4 bbl intake, and a impco 425 mixer. It will go in a 1969 f100 long bed with a t85 overdrive transmission. The truck will be used for everyday driving in the city of Houston only no trailering.

My question are
What camshaft should i use?
What rear end gear should i use?
How to tune a distributer for CNG?
and all around things i did not think of.

Right now i have a 1976 300 with Clifford intake and EFI headers running on CNG in the 1969 f100. It feels way under powered compared to my 1980 f250 long bed extended cab with a stock 300 in it.

My goals are to improve performance wile keeping good fuel economy, while taking advantage of CNG 140 octane.

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Re: dedicated cng 300 build

Post #2 by cng f100 » Thu May 26, 2011 10:06 am

I am also looking for some remote gauges.
3600 psi to 0
200 psi to 0
1 psi to 0 or a gauge that reads water column inch


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Re: dedicated cng 300 build

Post #3 by woodbutcher » Fri May 27, 2011 12:22 am

:) Hi cngF100.IIRC from previous threads,the engine must be purpose built for the CNG.
Compression should be in the neighborhood of 12 or 13-1.(If I am wrong here,someone PLEASE correct me).That is just a beginning.
I am sure that someone with more knowledge than I will be along to provide a more in depth
listing of how to build a proper CNG engine for long life and good economy.
Have fun.Good luck.And welcome to the I6 family.
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Re: dedicated cng 300 build

Post #4 by coreybrenner » Mon Jun 27, 2011 9:48 pm

I've been looking at something like this, too, but for propane.

One of the biggest factors will be cam timing. You want to boost your dynamic compression ratio as high as you can (as close as you can get it to the static compression ratio.) This is done by closing the intake valve earlier. The Isky Mile-a-More cam I just read about might be a good place to start, and then grab your degree wheel and some sort of adjustable timing setup (offset woodruff keys or somesuch, perhaps) and go to town.

The idea would be to get the intake valve closed as soon as possible after bottom-dead-center. Then, you will build maximum cylinder pressure, and can put the 140 octane equivalent of the CNG to work for you. Gasoline motors typically close the intake valve much later, because of the horrible quality of today's gasoline.

You'll definitely want high compression to start with, and then cam for maximum cylinder pressure.


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Re: dedicated cng 300 build

Post #5 by 80broncoman » Mon Jun 27, 2011 9:57 pm

so you want performance with good MPG.
How high of Rpm are you going to twist this engine??
My thinking is to stay with the smallest cam you can to get there.
is it going to work as a truck (towing and or hauling) ??
If so set the timing up doing just that. If you crank it up empty and dump a ton of sand in the bed you might just melt the engine.
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Re: dedicated cng 300 build

Post #6 by Harte3 » Tue Jun 28, 2011 8:52 pm

Check with the folks that make the CNG/Propane mixers...they may have suggestions.
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Re: dedicated cng 300 build

Post #7 by 6bangerwanab » Wed Oct 05, 2011 10:49 am

if your still not sure about the ignition, and not afraid to use a computer, a megajolt/EDIS system will let you program any timing curve you desire, and changing/tuning the timing curve is alot easier.
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Re: dedicated cng 300 build

Post #8 by 300Six » Mon Dec 12, 2011 5:47 am

There are a few things about automotive fuel that are very difficult to overcome. Diesel fuel contains about 30% more energy per gallon than gasoline and if I recall CNG has about 30% less. Unless you are willing to burn considerably more fuel to overcome this energy deficiency you're basically stuck. Taxis and commercial fleets in Canada were big on natural gas (dual fuel engine conversions through gov't subsidys ) in the mid 70s until drivers became aware of the noticable loss of power whenever they switched to CNG. That fad died out fast once the funding dried up.

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Re: dedicated cng 300 build

Post #9 by Thad » Mon Dec 12, 2011 8:19 pm

Basic performance mods work with CNG, LNG, Propane, etc. Very high effective octane rating so more compression can be ran. This is one point many miss when converting, purpose built that can be avoided. Has a faster burn rate would require less ign adv. Intake is basically dry flow when compared to a gasoline engine so an OEM efi intake manifold could be modified to use the CNG "carb" and get the benefit of the ram tuning of the longer runners. And just as gasoline 300 benefits from head work and bigger valves so would one using gaseous fuels.
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Re: dedicated cng 300 build

Post #10 by 62RatRod » Wed Jan 04, 2012 9:26 am

All points given are true. I built a natural gas Chevy 350 in my diesel tech class and we had bigger valves pun in, bigger cam, 13.5:1 compression, and a factory hei distributor. We did advance the timing slightly with the distributor but set the cam at o degrees timing. That was the best sounding fastest revving 350 I've ever heard. I think putting a 240 crank in and bumpin up your cam size and getting it bored like .060 over then get ur head ported n polished with bigger valves and you would have a fast revving, pretty torquey motor. It would last forever too having a shorter crank and longer rods your piston wouldn't deflect as much every power stroke and it would be more balanced. You can't utilize that long of a stroke anyways because of the low BTUs but we know it will rev quicker and we can take advantage of the high octane.. If you have any more questions about the setup I'd b happy to answer

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Re: dedicated cng 300 build

Post #11 by J.R. » Thu Jan 05, 2012 1:32 am

A head from a 240" motor may or may not have stellite valve seats; you'll want 'em with CNG or propane. As has been said, good-flowing head work with lots of compression works best, and adding a knock sensor/retard device could help keep from beating it up if you're working it hard. Lots of industrial Ford 300s have been set up to run on propane or natural gas, for 24/7 powering of pumps and generators, operating constantly for years. Even though the oil in an LPG- or natural gas-fueled engine generally looks cleaner than that of a gasoline or diesel engine, it does get thicker over time, so it still needs routine changes for the best engine lubrication and longevity.

B-W's T85N w/overdrive is a nice combo in a half-ton pickup. You probably already know that the R-11's o.d. ratio is 27%, not 30% like the light duty R-10 unit. Using that number, the RPMs for the best torque range based on your cam selection, the rear tire size you want, and what speed(s) you want to cruise at, you can usually find your 'ideal' rear axle ratio, especially for the good ol' Ford 9-incher. Might even get some decent fuel mileage numbers out of it. Have fun.


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Re: dedicated cng 300 build

Post #12 by bubba22349 » Thu Jan 05, 2012 2:20 am

I happen to have a Propane head that I picked up and installed on one of my 300's. The casting is made different than the standard truck head casting.
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Re: dedicated cng 300 build

Post #13 by clintonvillian » Sun Nov 25, 2012 4:24 pm

What happened to this build?

Reason I ask my state (WV) is now looking into setting up stations and doing conversions.

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