It seems that only american manufacturers still build and use OHV(pushrod) engine(am I right?) while other manufacturers have given up and build SOHC or DOHC engines instead. What's the advantage and disadvantage of OHV to OHC engine?
Why would an OHV be cheaper to produce? (unless you have an extreemly long production run) it has more parts.quote:
Originally posted by MAJA:
The pushrod design has some advantages. First it is cheaper to produce. It is probably easier to "time" and keep in "time".. The chain or gear to drive the cam would be closer and more direct, compared to an overhead design with the cam on top of the head(s). With the cam being directly attached, no tensioners are needed to keep the belt or chain tight. The chain or gears on a pushrod design are always lubricated with the oil, whereas overhead designs usually are exposed and not lubricated. The chain or gears for the cam rarely wear out in an overhead design, as opposed to an over head cam which needs the belts or chains replaced or retensioned from time to time. A pushrod design is also easier to hop-up cheaply in the aftermarket, by changing different cam designs, or different rocker arm ratios to produce more lift which could require differing springs and or valves. Also the overall width and height of a comparable pushrod design will be more compact, helping packaging. Hopes this answers most of your questions.
Ahem! The Cadillac Northstar V8 is quad cam, four valves per cylinder with VVT. Check the GM Powertrain site if you'd like proof. Scroll down a litte farther and read about the Global V6, also a quad cam, VVT motor.quote:
Originally posted by cryptokid:
i think american companys are generally cheap and also slow to adapt compared to the europeans and asians.
heres an example:
look at briggs and stratton, they still make flathead lawnmower engines (and ohv too, but mostly flatheads) . where as honda makes belt driven SOHC lawnmower engines. honda hasnt made a flathead mower engine is 20 years. their lowest economy model engine still features overhead valves, which is only somthing that high end briggs motors have.
briggs and stratton could of made a ohc engines decades ago if they wanted to, but they are cheap and wanted to milk the flathead profits.
i think this is a similar problem with american automotive companys. they like milking the old designs to get maximum $$$ out of them before switching onto somthing new. you can see this "milking the design" in everyting from engines to suspensions.
almost any american company could produce a quad cam v8 with 5 valves per cylinder but they never will. its too advanced and american companys like to progress is small steps so as to milk current designs for all they are worth.
IIRC, the Toyota design is to be able to compete in some racing class that only allows pushrod engines.quote:
Originally posted by ekpolk:
Sure, there are plenty of disadvantages to the pushrod design, but it's not near as bad as some would have you believe AND it's not an "old" design vs. a "new" (OHC) that Detroit refuses to adopt. Rumor has it that Toyota is even working on a racing engine that is a ... pushrod V-8!
No, they don't make mostly flatheads. The only flatheads they still make are the very low end, low HP disposable lawnmower engines. The only reason they're still flathead is that they need to stay dirt cheap, that's their market. Without them there would be no $99 walmart lawnmower. The vast majority of their engines are OHV.quote:
Originally posted by cryptokid:
look at briggs and stratton, they still make flathead lawnmower engines (and ohv too, but mostly flatheads)
crypto,quote:
Originally posted by cryptokid:
[QB] look at briggs and stratton, they still make flathead lawnmower engines (and ohv too, but mostly flatheads) . where as honda makes belt driven SOHC lawnmower engines. honda hasnt made a flathead mower engine is 20 years. their lowest economy model engine still features overhead valves, which is only somthing that high end briggs motors have.
briggs and stratton could of made a ohc engines decades ago if they wanted to, but they are cheap and wanted to milk the flathead profits.
So he can cut the grass really really fast.quote:
Originally posted by Shannow:
just what do you need a belt driven OHC in a garden mower for anyway ?
So does it mean a larger displacement pushrod engine can possibly be smaller than a smaller displacement OHC engine in size(weight and dimension)?quote:
Originally posted by Ryan00TJ:
Take the old 5.7L LS1 OHV vs Ford's 4.6L DOHC motor.. The LS1 is vastly lighter and smaller than the 4.6L
Assuming you are talking about equal performance from pushrod vs OHC with weight held constant and displacement allowed to vary....That's a good question, because there are no displacemnt classes on the street.quote:
Originally posted by hungdynasty:
So does it mean a larger displacement pushrod engine can possibly be smaller than a smaller displacement OHC engine in size(weight and dimension)?