Can someone explain to me why manufacturers including the one who made the engine in my truck has chosen to use 4 valves per cylinder instead of using two LARGE valves? If it's due to space requirements, why not use oval shaped valves or what ever shape is needed. I'm sure I am missing something simple here but I'm also sure someone here will be happy to point that out.

 

I believe valves need to be round so they rotate when opening and seat in a different place each time they close. Oval valves would seat in the same place every time and would be difficult to impossible to grind and lap. They would burn out very quickly IMHO.

 

What he said ^. Also, putting the injector dead center in the cylinder helped emissions a bunch, that was the main reason Cummins did it. Further benefits (the main ones for gassers) are more flow than two big valves, you can get more area with 4 small ones. Also less weight to allow higher RPM without valve float.

 

also less likly to burn a valve ( less aera )

 

There are many reasons that drive the choice of how many valves an engine has. It seems like lately it is more of a marketing ploy than engineering.

At low valve lift, flow area is basically the circumference of the valve x lift. For a given valve area, two small ones gives more circumference than one large one. So for an engine that won't see a lot of valve lift, four valves is better.

For high rpm engines, four smaller valves means less valve train inertia for the valve springs to overcome. Smaller (lighter) valves mean a higher rpm potential. (IIRC, Formula 1 cars, running up to 19,000 rpm use pneumatic valve springs. )

As I said, though, most of this technology, while having a basis in engineering, is just marketing. Although the Toyota Formula 1 car needs dual overhead cams, five valves per cylinder, and pneumatic springs, the Corolla surely does not. Nor does the 5.9 Cummins, although big Cummins engines have had four valves per cylinder at least back to the NH220 (circa 1940?).

FWIW, Top Fuel rails and Funny Cars run two (count 'em--two) valve heads. So you can make some serious power (6,000+ on nitro) with two valves.

 

Great reply! Thanks.

 

A major advantage of having the 4 smaller valves is that you come closer to a symmetric combustion room and get better economy on less nitrous oxide emission. (all other advantages stated before are valid too)
The swirl pattern of the air entering the cylinder can be controlled better with the 4 valves, or the 3 valves like some smaller toyota engines in the past. Since valves flow by area and the cylinder content goes by a cubic relation to size bigger cylinder engines do profit more from more valves for the same engine speed. Therefore even very old diesels can be found with multi-valve designs, whereas the trend to more valves for small engines is relatively young. (and some marketing hype too, since for joe user the hp/pound of engine and efficiency are much more important than cc and number of valves- even though it makes a good topic for bar discussions)

AlpineRAM

 

Also a1/4 mile machine is a completely diff. animal .At a hundred grand a run they do not give a rip about a valve lasting any further then the finish line!

 

don't them new fraud f150's have their v8 gassers with 3 valves?

 

Yes, that is correct. However I don't know how its setup.

2 intake, 1 exhaust or
1 intake, 2 exhaust

I don't know. Time to research. Be back shortly.

 

Ok, I'm back. It's 2 intake valves and 1 exhaust.

 

naturally it will be 2 intakes and one exhaust- bigger pressure differential for the exhaust and also a much less viscuous gas (because it's hot) than on the intake. All "modern" engines use a bigger inlet valve. (or more valves)

AlpineRAM

 

cp was on it, so was alpine ram.....each valve weighs less, more flow, less lift...FWI on the valve rotation....this is dictated by RPM and keeper groove design. Some have more grooves than others allowing the valve to rotate at different RPM ranges. All depends on the engine and application. I won't go into all of the possible designs.

EDIT: forgot to mention that cp is also correct on the valve springs. There are some serious harmonics and velocities going on here that some people do not realize or have not seen/studied.

2 intakes 1 exhaust...several manufacturers are investigating/playing with this idea to reduce the cost of the expensive exhaust valve material. China is killing us now on the steel prices. Our vavle materials are going through the roof.

 

Some Ferraris and lamborghini's have 5 valves a cylinder.

 

Guys,

You cannot group engines like you have. The example I am talking about is the top fuel dragsters, its a Hemi, it is designed to be a two valve head. The valves are in line with the exhaust and intake ports so the flow path is straight through, very unique. Most gas and diesel engines have the valves laid out lenghtwise with the head, thus the flow goes into the intake through the valve and must turn and go out the exhaust valve and port. Obviously not as efficient as the Hemi. Thats why EVERYONE uses the HEMI-Designed by Dodge-in their cars!