i dont understand this, on a dohc is there just one camshaft just for intake valves, and the other cam for the exhaust valves? If thats so, why do that when you can just have one cam with intake and exhaust lobes??

 

becasue with two cams you can have more valves ie, more air in, more exhaust out. Also you can adjust your cam timing independantly. A sohc has 12 valves and a twin cam has 16.

 

My old sohc f22 had 16 valves.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Tmack &raquo;</TD></TR><TR><TD CLASS="quote">becasue with two cams you can have more valves ie, more air in, more exhaust out. Also you can adjust your cam timing independantly. A sohc has 12 valves and a twin cam has 16.</TD></TR></TABLE>
Hellooooo!? D16A6, D16Y8, D16Z6, etc? All 16 valve. And to the original poster....it doesn't really make much difference despite what someone may have told you.

 

it makes alot of differance. whats the record horsepower on a sohc zc turbo compared to a gsr turbo. and it would make more sense if it had more valves but the sohc and dohc honda engines have 16 valves

 

whoa nelly! **** my bad peeps, ok they have 16 valves, and come to think of it my moms accord does have 16 valves. Ive been up for 20 hours and im at work so cut me some slack. You can still adjust valve timing independantly. PLUS with twin cam you can run bigger valves due to the larger head.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by torqueless &raquo;</TD></TR><TR><TD CLASS="quote">it makes alot of differance. whats the record horsepower on a sohc zc turbo compared to a gsr turbo. and it would make more sense if it had more valves but the sohc and dohc honda engines have 16 valves</TD></TR></TABLE>That is almost entirely due to the fact that one is a d-series and the other is a b-series, NOT due to the extra cam. Compare sohc zc to dohc zc, i.e. apples to apples. They're about the same.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by tjbizzo &raquo;</TD></TR><TR><TD CLASS="quote">That is almost entirely due to the fact that one is a d-series and the other is a b-series, NOT due to the extra cam. Compare sohc zc to dohc zc, i.e. apples to apples. They're about the same. </TD></TR></TABLE>
oh, ok that makes more sence. but still if you were to fully build w/gurbo the sohc zc and the dohc zc, the dohc would make more power, and still dont understand why.

 

everyone knows 2 is better then 1.


Sorry i cant help

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by TurboEM1 &raquo;</TD></TR><TR><TD CLASS="quote">everyone knows 2 is better then 1.


Sorry i cant help </TD></TR></TABLE>

2 is not always better than one

 

hey! you can't compare a sohc to a gsr. not even a b16. The b series have a bigger cam and higher compression. put the same size cam, same compression they should be at the same power level.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by torqueless &raquo;</TD></TR><TR><TD CLASS="quote">oh, ok that makes more sence. but still if you were to fully build w/gurbo the sohc zc and the dohc zc, the dohc would make more power, and still dont understand why. </TD></TR></TABLE>OK, here's "THE DEAL", and I'll go into it in a little more depth this time. Keep in mind that the following is what is typical and often true, but not always true! Most car manufacturers usually make their economy car engines sohc because it is cheaper, and their sports car engines dohc because of the perception of their performance. As such, sohc engines usually come from the factory tuned more for economy and dohc engines come from the factory tuned more for performance.

This being the case, you could build two generic (i.e. not specifically Honda) engines, one sohc and one dohc, with the same compression/camshaft profiles/crank/rods/pistons/valves/ports/ecu/etc. and they would make *exactly* the same power. Think of it like this: if you hid the top of the cylinder head from view, you wouldn't be able to tell the difference. The air flowing into and out of the engine doesn't care if it has one camshaft or two, because it will see the same ports, valves, valve timing, and compression and will therefore make the same power.

Now, as far as Honda d-series engines go, there are some *slight* differences between the sohc's and dohc's. The dohc's usually have slightly larger valves, slightly larger ports, and a slightly hotter tuned ecu. Those are about the only significant differences, and obviously you could build a sohc equal to (or better?) than a dohc with some head work and ecu tuning. So you see, the benefits of the dohc engines comes from two places... 1) the factory tuning, and 2) some stunna who has a dohc and wants to brag about it, which really doesn't count. All the rest is hype. Please bookmark this so you can tell the next 100 people who ask this question. DO IT NOW!!! Thanks!

 

DOHC should benefit from lower reciprocating mass in the valvetrain, which lets you go to higher rpms. But then you've got more sprockets & bearings up there, too, so there's friction losses. Then there's the positions & angles of the valve stems that are possible/impossible with SOHC vs. DOHC.

But like tjbizzo says, that's not as important as having a more agressive cam profile, & all the rest of the choices that the engine-designer makes.

 

hehe, there is a little more differences than the ones noted.
as sayd above the sohc engines are usually built with economy in mind, as where as the dohc with performance in mind.
dohc heads have a lot simpler valvetrain than the sohc, making it possible to rev higher (valsprings aside) because of lighter mass..
ports are different size as so are valves/ port angles.
you would have to do A LOT to a d-series head to be able to flow the same as lets say a pr3 head.

As far as the block there is of course also design differences because of the different ''expentancy'' for the motor.
As rod ratio/ bore/ stroke are diferent. sohc's usually have bigger stroke for grocery hauling around town and smaller bores.
dohc have smaller strokes and bigger bores for rev abilities and power band placement.

if you compare lets say a d16 and a b16 (d16 being 75mm x 90mm and the b16 being 81mm x 77mm) displacement is almost the same, but 2 totally different type of characters...
if you were to make the same power with both engines you will find out that the d16 power band will die a lot sooner than the b16, but it will eat the b16's low and mid range power.
they do what they are design to do.

edit: damn jim you beat me to it.

 

Ok. So lets pretend that the d16 is a "d18", it has the exact same displacement, lt. everything is identical to the b18c1, except the "d18" still only has on camshaft, will it still make as much power as the dohc?


p.s. How do i book mark this thread?

 

This 'D18' would have to have the same bore & stroke as a B18C1. Then the valves (& ports) have to be made the same size & position. Then the cam profiles would have to be made to match the B18C1, including the vtec. Then intake & exhaust manifolds, then... etc.

That's a lot of other stuff that has to be changed, all of which will make it more & more like a B18C1. Somewhere down this road, you'll have to figure out how to get the redline up to 8k rpm without floating the valves.

But I hope you get the idea. It's not actually FUNDAMENTAL to the SOHC vs. DOHC, but there's so much other stuff that has to be done.

Let's pretend we want to go the other way. Take a B18C1 shortblock & design a SOHC head. Give it the same valve sizes, seats, ports, & all that stuff. Make it accept the same intake & exhaust manifolds. Hope there's enough room to put the sparkplugs in the same place, while the camshaft is *-oops-* the camshaft is in the way... It's those kinds of details that'll prevent you from making 'everything identical'.