i bought a 1977 ford f-250 4x4 crewcab with a 400 for an engine and a 4 spd trans. i was wondering if someone could switch the truck to propane with out the normal sounds of a propane engine, but has a good sounding custom exhaust and power with good mpg for a 400?

 

Guy, sure it can be done. It will cost a bit to do a nice job, however. Propane likes compression, and the 400 doesn't have much. You'd need to use flattop pistons, maybe from a 351C, maybe mill the heads some too. You'll want something like 11 1/2 or 12 I believe. Hard seats under the exhaust would ensure the seats don't burn out- propane is a 'dry' burn. Your machinist will want to cut the valveseats wider than normal as well.What are the propane sounds you are hoping to avoid, and why are you wanting to switch ? Is propane cheap where you live ? DF, @ his Dad's house

 

come to the 335 forum and follow my build- I am right in the middle of it- big time

btw: the 400 is not a M. the 351M came from the 400 which came from the 351C.

 

The 400 may not be the best choice for a propane engine. It was produced solely as a low compression engine for the '70s era polution control emissions. Putting flat top pistons and shaving the heads down about 20 mils will give you in the high 9's to 10:1 compession, if my calculations are correct. Any more shaving than that and you will run into fit problems with the intake manifold.

 

"The 400 may not be the best choice for a propane engine. It was produced solely as a low compression engine for the '70s era polution control emissions."

NO!!! IT WAS NOT. It was designed in the 60's and produced initially as a torque producing clelveland for large cars and trucks. It was 'sacrificed' by ford for smog purposes.

 

You'd think they would have gotten rid of it for it's gas mileage. :-)

 

mileage was very adversely affected by the smog crap. Folks that re-build it right with rv type grind, performer intake, 4bbl, straight up timing etc get better mileage and 400-420 ftlbs with about 300hp (thats not bad for an rv grind-((ie stroked cleveland)). I'm building mine specifically for propane with roller cam, full roller rockers, closed chamber heads and the highest compression I can run with a semi rv grind (214/218 duration @ .050) and still get dynamic compression below 9:1 for a semblence of longevity. Looking at close to 400hp 430+ftlbs and, hopefully, decent mileage. well see. It's odd with operating compression similar to race engine but with mileage cam...love that octane.

 

and...flat top pistons...very important...

 

RD, what are you doing for a transmission. I am considering propane for my 78 crewcab. My truck is being built for recreation, not a daily driver, but I would like the economy of an overdrive. So, what are you planning to put behind your engine?

 

i was going to keep the 4spd trans but i would like to put a nv4500 if i had the cash for it.

 

I would run a longer connecting rod, should put the piston up higher in the cobustion chamber. Mill the block and run some 6.8-7" rods. may put the top of the piston sticking out of the block but with those giant combustion chambersand a low valve life .450 or less it should be fine.

 

using c6- may go with overdrive once my pocket fills back up again- in fact will likely go with overdrive or look at 4 speed auto options which kindof exist.

Money it takes to get longer rods for this motor is $$$ prohibitive. not a lot of options for the 400. can get cleveland pistons but have to bush rods...on and on. My static compression ratio (10.5) is right where I need it for the cam I'm running and, again, if you get into the 9:1 DYNAMIC compression ratio and above the motor may have a dramatically lower life regardless of octane. So my 10.5:1 bled down to 8.75:1 (or so) by rv roller cam seems to be the best option/compromise. Another $$$grand in pistons etc would only give me a bit better quench and thats a maybe as we are not sure how quence affects propane.

I have all my parts now except hei distributor/elec fan and a few minor things. The block is being prepped for the retro roller cam and then I will start building...I am also still porting my oz heads. I have assembles some of the best parts money can buy for this build and am getting excited- still trying to finish up my sons bronco-argh!

 

Every one seems to forget the 400 from '71 and '72 that had some muscle.

 

The 1971 400 was a great engine. They dumped the compression to around 8.5 (sources vary) in 72 tho. From personal experience I can tell you they were dogs compared to the 71's.

 

I am going to build a 390, and if ehanol does not catch on I may put on a propane carb, and run digester gas.