valvetrain systems and engines?

[pyry]

not exactly formula related but what is the difference between SOHC and DOHC valvetrains. also, what is a flat and opposed engine configuration?

[Monstrobolaxa]

DOHC - Double Over Hear Cam (2 cams work the valves and they are placed "ontop" of the cylinder)

SOHC - Single Over Head Cam (1 cam activates all the valves and it is placed "ontop" of the cylinder)

Well about the flat and the opposed I'm not sure (cause it has also raised some questions in my head)....

But flat and opposed configuration is the position of the cylinders, opposed cylinders means that there is 180º between both cylinder banks.....flat configuration is the same as the opposed but the name is diferente (this second part about the flat raises some questions because I've read in one or 2 places that it isn't 180º but 0º and in other places they say it's 180º....for me it's 180º)

[Tomba]

hmm well knew that hehe
but what are the basic advantages of DOHC and SOHC, and why would anyone prefer to use one above the other?

Anyway, I suppose you would like a perfect timing between both cams in DOHC configuration, so are they linked directly to each other and why (not)?

[Monstrobolaxa]

Well with a single cam all the valves have to be in more or less a line.....with 2 cams you can put each 2 valves in a line and the other 2 on the oposite side of the cylinder....in terms of valve size and shape the DOHC is better. But in terms of timing it is harder to calibrate it because the valves have now 2 variables (2 cams) while with one cam...it's all down to the cam design.

[tempest]

that is true, but with Sohc it is impossible to get variable valve timing, since the only variable you have is the speed of the camshaft, and the relationship between the intake and exhaust valves is fixed.

SOHC is a lot cheaper for this reason, but pretty average for performance cars.

[schumiGO]

Last year our team used Dohc, then regulation were changed, and this year we had to use Sohc in the same engine like last year.


Whe lose nearly 20% of the engine power 'case the intake sistem can't put the same mass of Gas in the cylinders per cycle.

Engine 4 cyl 1600, 8 valve.
Intake sys like Dallara 99.

[sharkie17]

that is true, but with Sohc it is impossible to get variable valve timing, since the only variable you have is the speed of the camshaft, and the relationship between the intake and exhaust valves is fixed.

SOHC is a lot cheaper for this reason, but pretty average for performance cars.

lol... next time do some research before you post...

Ferrari Modena... 400 hp, 274 ft lb of torque, DOHC V8- 12.7 mpg.

C6 Corvette... 400 hp, 400 lb ft of torque, SOHC v8 - 21 mpg.

your "lowly" and "cheap" SOHC Corvette engine not only has more torque, it gets lot better gas mileage...

[tempest]

lol... next time do some research before you post..

Ferrari Modena... 400 hp, 274 ft lb of torque, DOHC V8- 12.7 mpg.

C6 Corvette... 400 hp, 400 lb ft of torque, SOHC v8 - 21 mpg.

your "lowly" and "cheap" SOHC Corvette engine not only has more torque, it gets lot better gas mileage...

Ok, C6 corvette is a 6 litre engine vs 360's 3.6. That expains the torque.
It makes its power from burning more fuel per stroke rather than revving hard.
c6 is geared a lot higher. Tremec t56 is the crappest 6 speed ever invented, 6th gear is a fuel saver for the highway, top speed is in 5th. 6th in the ferarri is much more usable. The torque in the C6 is made at 4000rpm vs about 4800 so you change up a bit earlier in normal driving.

C6 is not a SOHC engine anyway, it has its cam in the block, not the head. It is pushrod, same as my commodore. I love that engine, it is seriously cool for getting around, and is untouchable hooked up to an auto. But for true tuning performance i'd take a jap or euro any day.

More to the point rev the corvette hard and grimace, rev the faz and grin. If SOHC could do the job as good as DOHC, then why do no limited capacity race cars use it?
[/quote]

[guest]

oh my god sharkie17 are you serious? you take two engines with the same horsepower the other being sohc and the other dohc, and you make your assumption based on that on the whole technology. you really are a complete idiot. and 21mpg with a american crapengine? give me a break. my friends dad has one and as carefully as you drive it, its nearly 20l/100km. if you want an indication of an economic car, comparing to a ferrari sportscar hardly gives you that much ground, the look at audis 1.4lfsi dohc engine, it can do 100km on 2.4l of fuel.

[Guest]

I thought corvettes use OHV

[sharkie17]

lol.. i love starting up a great dialogue... especially when a guest comes in and call someone a complete idiot and spew information that is CORRECT but NOT relevent to the discussion and point at hand...

the POINT was that he stated (whoever i quoted) that SOHC had crappy power compared to DOHC... (which isnt true).

i did NOT even consider the technological aspect of the engine design or anything... YES, i compared 2 engines with different capacity, BUT the point i was making was that OHV or SOHC engine could have JUST as much horsepower or more than a DOHC design.

and guest, next time and register before you call someone a complete idiot.. unless you like hiding behind your big brother (internet).

[Monstrobolaxa]

I thought corvettes use OHV

The do use OHV - over head valves......technically you are correct "guest". OHV means that the valves are ontop of the cylinder....but in order to activate the valves you need cams....OHC (Over Head Cam) now you have to know how many SOHC (Single OHC) or DOHC (Double). There are also other ways of activating the valves: pneumatic (but don't know any road car that has it already) and "arm" activation (don't know the tech name) like used in the old Star-engines for the old airplanes...where the cam is in the middle of the star and activates an arm that goes to the top os the engine block and activates the valves (though this technology i quite old and heavy...not vey suitable for amost any kind of engine....I think that only boats and engines for power plants use it).

So as you see there are quite a few diferent names....but analysing them you'll see that they're inteconnected.

[tempest]

Monstro, the type of engine you are talking about is called the pushrod engine, where the cam is in the block just above and to the side of the crankshaft and pushes rods (hence the name) up through the block to the heads. These push 'rockers' which are levers to convert the upwards motion of the pushrod into downward motion of the valves. While no euro or japanese cars have it anymore, all small block V8's (like in corvette etc) are still this type. It is not very advanced, but is cheap and effective if you have a large capacity behind it.
Like I said before the engine in my road car is this type (3.8L buick made v6), and although it was made in 1991, it was phased out 2 months ago in australia and is still availible on new cars in the US.

Sharkie, the point i was trying to make Re performance engines was that VVT is such a wonderful thing for making the most of limited capacity, not that there were not other ways to make power, the easiest of which is to simply increase displacement like Chevrolet has just done with the LS2.

[Monstrobolaxa]

Thanks tempest....didn't know it was still used (like I mentioned).

About the increase of power....usually displacement increasement will increase torque....to increase torque you can increase the bore or the stroke (displacement)! To increase power you usually decrease the stroke, and make it as small as possible.....Mario Theissen (BMW) gave an interesting interview about engine development in a 2001 Racecar Engineering magazine, where he explains this.

[sharkie17]

lol.. wasnt that so much better than just calling each other idiots