compression ratio's

[jct842]

I have committed to building a henry ford plumbing parts engine. I am baffled as to the size of the combustion chamber. I know what I like is about 6 to one ratio. I am thinking that the pounds per square inch would work out to atmospheric pressure X 6.

am I correct in assuming that I would have about 85-90 lbs pressure at the spark plug hole?

This afternoon I bored out a 3/4 black iron pipe nipple to a few thousands under 7/8. I intend to have a stroke of around 1 1/2". I will be using instead of a T, a 4 sided fitting with a spark plug in the top opening. I am going to use some well aged 1 1/2" thick maple instead of iron to support crankshaft and cam shaft. the maple is as hard to mill as 6061 and thin pieces can not be bent easily. I would appreciate any comments, thanks john

 

[John Rudd]

The volume of the comb chamber is a function of the cylinder swept volume and the compression ratio..

Example, picture a cylinder and its combustion chamber with the piston at the bottom of its stroke containing 100 cc of air (90 cc in the cylinder plus 10 cc in the combustion chamber). When the piston has moved up to the top of its stroke inside the cylinder, and the remaining volume inside the head or combustion chamber has been reduced to 10 cc, then the compression ratio would be 100:10, a 10:1 compression ratio.

So from that you can work out the cylinder swept volume based on diameter and stroke, you know you want a CR of 6:1, then work out the cylinder volume from manipulating the numbers...

Does this help?

 

[cfellows]

There's another fellow who built a smaller version of the Henry Ford engine, I believe it was Gary Hart (ghart3). He had to insert an extra length of plug into the cylinder head space to raise the compression ratio enough for the engine to run. I think if you can get a compression ratio of about 4:1, the engine will run OK.

Chuck

 

[jct842]

Thanks, I think I can find out the volumes once I get it partly together. I think I will get a syringe and fill with water measuring as I go. I have though of making plug's too in case there is too much volume in the pipe fitting. John.

 

[jct842]

today I did some measuring with water and a syringe. I don't know how ol henry got his to run, the volume of that pipe fitting is huge. What I plan to do is get a friend to melt aluminum and fill the fitting after I put plugs in all the holes but one. I can then carve out a suitable compression chamber with the mill. It will still have the crude look of the pipe fitting but be a little easier to work with. Thanks for the compression explanation guys. John

 

[Generatorgus]

I had the same question when I built my half scale Ford. The compression was not at all good, but I found later it was valve related. The pipe fittings for the valves make up a large amount of volume that also factors in. I made plugs to fill some of the voids in the valve bodies as well as the top of the cylinder head. Turned out the engine ran much better without the volume reducing improvements I made in the to the valve fittings. When I made the first cylinder assembly, I didn't like using the design that the cylinder stopped just short of the intake holes, I felt it left to much volume in the head. The second cylinder I made runs thru the tee fitting, stopping about an eighth short of the front end. I made an aluminum plug to fit and and fill most of the volume ahead of the piston, grooved and fit with an O-ring to seal it. The intake and exhaust fittings were drilled and tapped thru the tee and the pipe. The engine ran until the valves failed.

 

[vascon2196]

I have been trying to get my Full-Scale Ford engine to run for over 4-weeks now. I have played with the timing, the gas, the exhaust valve, and have put lead in almost evry crevice I can think of. The engine "poofs" once or twice and offers nothing else except a "poof"....no power...nothing.

I can't figure it out.

Chris