Force pushing on the cylender head question

so im building a new type of engine, just sketching it now but before i go on i need to find out how much force is put on a cylinder head when a combustion takes place??? maybe im over looking terms but i cant seem to find an answer anywhere. The engine is based off a 350chevy so i guess stock force is what im looking for but i'll take anything you got tho. I'm sure someone will point this out right in front of my face but maybe thats all i need.
Thanks

 

about 13 ounces give or take

 

really not even a pund i would have thought like 10 pounds, WAY off

 

i used a slide o meter and a doppleganger addomatic and that's what i got.

 

One way to get a rough estimate is to assume that each cylinder is producing torque at a time, the torque out put is about 350 lbs-ft, the "arm" of the crank is 1.74" or .145 ft, so the force exerted by the rod on the crankshaft is about 350/0.145 = 2400 lbs. The area of the top of the piston is the same as the area of the head, so that's the force pushing up on the head too.

This is a very rough average, peak force will be higher.....that's why they have 5 each 7/16" high strength bolts around each bore.

 

Let's see - if your compression is let's say 150PSI then you have 150 pounds PER square Inch - on a 350 - (4" bore) A=pi r "squared" - so 3.1415 times 4 = approximately 12 -1/2 - so compression alone is good for 12-1/2 times 150 = 1875 lbs. Now add the extra force from combustion and I'd venture to say it's gonna be a heck of alot more than you guys are figuring. There's a reason for all them haed bolts!!!

Of course all these numbers are subject to engine specifics.


EDIT: Squirel types FASTER than me.

 

Suggestion #1 :
Search the net for BMEP , then multiply by the area of the piston,
to get the total pressure per cyl.
Peak pressures are higher, but that will give you an idea.

Suggestion #2:
If your design is really "new", build a single cylinder test motor
to develop your design.A lot quicker, easier, and less expensive.
Most of the F1 teams do that.

 

BMEP stands for Brake Mean Effective Pressure, it's also an average, and won't tell you the peak pressure. It's a lot higher at the time of combustion.

 

Well Diesel engines use high pressure injection to force the fuel in against combustion pressures and they can be in the thousands of psi. So, um yeah...figure alot.

 

Compression on a Ford Powerstroke diesel is about 400 PSI.

 

Yeah, but that's just the compression pressure. I think he is asking about the pressure in the cylinder during combustion. In that case we are talking well into the thousands of psi.

 

Good Luck!

 

If you REALLY want the answer to this, look at this link. This is much more complicated then the suggestions above and everything from Compression ratio, to timing to volumetric efficiency along with many other factors come into play.
http://www.hcs.harvard.edu/~jus/0303/kuo.pdf

 

I'm doing some rough figuring and going by the tensile strength at the root of the threads of the five bolts holding the cylinder head on, I figure the five of them together can handle about 96,000 pounds max before the cylinder head pops up off of that cylinder. For a 3-1/2" diameter combustion chamber, that's a force of about 1000 pounds per square inch on the bottom of the cylinder head for each cylinder.

If you drove around on really crappy gas, with the engine pinging constantly, towing a trailer up Pike's Peak all day long, you would probably eventually fatigue the head bolts to the point that you blow a head gasket. I think a pinging engine probably puts more stress on those bolts than a normally running engine where the gas is burning instead of exploding. So a pinging (or detonating) engine is probably the worst extreme.

 

Good luck on your engine design, my only suggestion is if your in doubt it's better to over build it than under build it as far as strength goes.

Here's a little bit on Rudolph Diesel inventor of the diesel engine, and what could happen if it's not built strong enough.

Rudolf Diesel was born in Paris in 1858. His parents were Bavarian immigrants. Rudolf Diesel was educated at Munich Polytechnic. After graduation he was employed as a refrigerator engineer. However, he true love lay in engine design. Rudolf Diesel designed many heat engines, including a solar-powered air engine. In 1893, he published a paper describing an engine with combustion within a cylinder, the internal combustion engine. In 1894, he filed for a patent for his new invention, dubbed the diesel engine. Rudolf Diesel was almost killed by his engine when it exploded. However, his engine was the first that proved that fuel could be ignited without a spark. He operated his first successful engine in 1897.

Be safe, and be careful!

 

I just happen to have some info from a friend who use to do testing for Felpro gaskets the examples he gave me from their testing was 5.0 L Ford 160 hp normal combustion pressure 900psi
225hp high output 1100psi
Nascar 355 [700+ hp] 1300-1400 psi
That's normal combustion pressure now if the engine experiences pre ignition the pressure increases 2to 3 times that and if it detonates 20 x that

 

Gold, as others have already said, the peak combustion pressures are way higher than any average pressure you can measure. You then need to design the head fixing bolts or studs so they will not stretch or move under the very highest peak pressures. Your best bet is to look at the designs of similar engines, taking into account the cylinder bore, and if it is diesel, gasoline, supercharged, or whatever. Engineers have been designing engines for well over a hundred years, and they have all evolved along similar development lines. So take note of how many bolts or studs there are, and their size, and copy an existing successful design. If you try to work it all out yourself from first principles, and you get a very different answer from what you are seeing on popular engines, then you have almost certainly made an error somewhere. And good luck with your project. Don't let the Forum morons discourage you.

 

A 350 Chevy has 7/16" bolts torqued to 65 ft-lb, generating a clamping load of 8900 lb each. 5 per cylinder = 44500 lb.

A 351 Ford has four 1/2"-13 bolts per cyl torqued to 100 ft-lb, for a total clamping force of 48000 lb.

So figure 45 - 50 K to keep a gasket in place.

 

Hmm,a SBC has 7/16 inch head bolts,18 per head,right? What also matters is the ability of the block and heads to resist distortion no matter how many fasteners are used.

 

That's some good info right there.

 

I think Warren Johnson and some of the other Pro Stock guys have done plenty of research on this subject with some sort of pressure transducers in the cyl heads during dyno runs.

May have published some of the info, if I remember right.

Call the Professor or better yet, wander up to him at the races sometime, bet he would tell you all. Those guys always a chatterbox at the track

K