Whisper

iTrader: (12)

Just a random question I thought up, and I do not know enough about the mechanics of an engine to know myself.


Also, with the 4 valve per cylinder heads made for pushrod motors-how are the extra valves actuated?

rubin

its possible, very possible. I believe the vw bug motors were pushrod and they were flat 4. Not sure if you know how an engine works at all or just the pushrod mechanisms. check out the howstuffworks.com article on engines. heres a good video also heres a good diagram of a pushrod cutout


with 4 valve pushrod engines the pushrod pushes the rocker which actuates 2 valves instead of 1, very simple. only issue is the pacjaging and extra weight.

HOHN

Sure-- almost anything is possible.

With pushrod 4V engines, there is usually a "bridge" that is triangular in shape, with the peak of the triangle resting under the rocker arm, and the lower two points pushing against the valves.

Justin

Old SStroker

Pushrod OHV engines can have any bank angle from 0° (inline) to 180° (flat or HO). Most radial aircraft engines are pushrod OHV.

One pushrod operating 2 valves usually uses a Y or fork-shaped rocker arm. Because the arms are quite heavy, they tend to limit rpm, just the opposite of what you usually think multivalve engines are good for.

Torovair

Air Cooled VW, Chevy Corvair, early Porsche, Continental aircraft and Lycoming aircraft are all Horizontally Opposed, OHV engines.

There is one difference from convention. In all but the Lycoming, the camshaft is located underneath the crank and the valve angle points outwards/downwards. Makes for some different intake and exhaust port configurations.

Whisper

iTrader: (12)

Wow, thanks for all the great info guys. I usually just think **** up at work to help pass the time and creating cars in my head is just one form. The reason I was thinking of a flat OHV engine is because it would have the weight advantage of a pushrod motor and a lower center of gravity over that of a V configuration. The same with the 4 valve idea. Could the arm weight be overcome with a stronger alloy? Or does the added weight also adversely affect gas mileage and durability?

A-man930

iTrader: (2)

fun thread...

Old SStroker

The arms shown in the photo are beefy steel which have a mass almost 3 times that of a steel LS1 rocker. You can often reduce the mass and moment of inertia of rocker arms by putting material only where it does the most good. The problem is figuring that out. Finite Element Analysis (FEA) is a good computer method of doing that, but not everyone has access to it.

Interestingly, more and more ultra-high performance rocker arms are being done in steel vs. aluminum. Also, some of the best moderately high performance rockers are steel. Comp's ProMags, for example.

As far as CG height being important in a race car, look at the Daytona Prototypes (DP). They use mostly V8s like Pontiac (a 5.0L short-stroke LS6), Ford 4 cammer, BMW 4-cammer, Lexus 4-cammer and one 4.0L flat 6 4-cammer from Porsche. Everyone but the Porsche has engine restrictions and rpm restrictions. The Porsche is given a few thousand more rpm and less overall vehicle weight. Notice that the only pushrod engine (Pontiac) does much of the winning.

One bit of advice: you never know who reads these forums, so admitting that you daydream a lot on company time may come back to bite you. It would if you worked for me, unless we were in the racecar design business. If you were, you'd not have any time to daydream.

Whisper

iTrader: (12)

Lol, this is a summer job until I go back to college in late August. And its manual labor, so its not like they're losing any production out of me anyway.

Old SStroker

Intertesting work ethic.