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DOHC

G

Goosemaster

Lifer
It has come to my attention that the Ford Lightning's 380hp is a SOHC engine...

I was under the impression that such a powerful engine, or at least stronger than normal, would use DOHC's. Wy doesn't it? Does it have bigger valves or something;doesn't need four vavles per cyclinder?


Thanks
 
SOHC or DOHC does not imply that it has more valves, simply that the intake and exhaust valves are controlled by either a single cam or dual cams (one for intake, one for exhaust).
 
Originally posted by: J0hnny
SOHC or DOHC does not imply that it has more valves, simply that the intake and exhaust valves are controlled by either a single cam or dual cams (one for intake, one for exhaust).
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yup

but i am curious tho, is there a V8 out there that is 4 valves per cylinder??

i can't think of one of the top of my head.
 
Just a quick couple of things, A) Don't assume that SOHC can't have 4 valves per cyl (though I know the Lightning is a 2v engine)
and B) There's plenty of 2 valve motors that make lots of power, back in the day, many V8's made much more than 380HP from pushrod 2 valve motors. 🙂

but i am curious tho, is there a V8 out there that is 4 valves per cylinder??
Click to expand...
Sure, there's many out there...off the top of my head I know the Northstar V8 is , and I know Ford has a 32V 5.4
 
Platinum: I can think of MANY.

Ford's DOHC cobra.
GM's (now obselete) LT-5
BMW's V8s
Mercedes's
Lexus's
...


Edit: typo.
 
It's all about variable valve timing buddy! Now that we've learned so much about fluid dynamics, we can control the flow of gases in the engine for better efficiency and horsepower.

Anyway, I've always wondered why DOHC is considered better than SOHC. If you have a single cam that can control both intake and exhaust, wouldn't that be better? Oh well.
 
I am having trouble imagining four valves with only one cam, but I'll take your word on the subject.

One last question......what are the advantages of having dual cam's when you have such powerful single-cam engines?

I would assume control in timing.....fuel efficiency....power etc...?
 
j0nny, it's better cost wise, but having two separate sets of cams makes variable valve timing possible, it also makes it easier to tune intake/exhaust valve timing separately if you're into modifying. Plus I'm sure that there's an advantage to not having one cam actuate 16 valves, but rather only 8 a piece.
 
DOHC is better than 4V SOHC for the same reason why SOHC is better than pushrods. Less reciprocating mass and better valve angles.
 
Originally posted by: Demon-Xanth
DOHC is better than 4V SOHC for the same reason why SOHC is better than pushrods. Less reciprocating mass and better valve angles.
Click to expand...

Omg, that slipped me...and I'm a mechanical engineer too.....
 
Originally posted by: Goosemaster
I am having trouble imagining four valves with only one cam, but I'll take your word on the subject.

One last question......what are the advantages of having dual cam's when you have such powerful single-cam engines?

I would assume control in timing.....fuel efficiency....power etc...?
Click to expand...

DOHC engines can be easier to tune for efficiency.

However, maintenece and parts are usually more expensive. Alot of people consider SOHC engines "old technology" and shun it just for that.
 
Originally posted by: Demon-Xanth
DOHC is better than 4V SOHC for the same reason why SOHC is better than pushrods. Less reciprocating mass and better valve angles.
Click to expand...

less reciprocating mass per cam, but not neccessarily less overall mass, right? You'd actually have *more* reciprocating mass with two cams, no? Or does that not count the cam's motion, rather just the valvetrain?
 
Goosemaster: consider that the 24V Cummins in the Dodge Rams have 4V/cylinder, and are still pushrod.

Why there are tradeoffs between DOHC, SOHC, and pushrod:
Cost: in a V8, DOHC has 4 cams, SOHC has 2, and pushrod has one.
Physical size: from the crank to the top of the head, OHC engines are MUCH taller than pushrod. And DOHC is larger than SOHC. This makes for some wide V8 engines. (we're talking bigblock width small blocks).
Reciprocating mass: In a DOHC arrangement, the cam pushes a lifter and a valve. In a SOHC, the cam pushes a rocker against a lifter and the valve. In a pushrod, the cam pushes a lifter, rod, rocker, and a valve. They all have one valve spring.
Valve lift: Pushrods can get better valve lift numbers due to the size of the rocker. SOHC and DOHC engines are more limited.
Valve angle: DOHC engines can get excellent valve angles. SOHC engines aren't bad, but it's awkward to get good valve angles on pushrod engines (check out a 426 Hemi's rocker arrangement, or a Chevy w/ splayed valves vs. normal)
Number of valves: DOHC is better suited to having 4, or even 5 valves/cylinger. You can do it with a SOHC or pushrod (as in the case of Cummins or these babies but it's not as easy or cheap.
 
I don't think anyone has brought it up, BUT the new Ford Truck motor has 3 valves per cyl. They also use a Variable valve timing on it also. BUT since it only has one cam, the V.V.T works BOTH exhust and intake at the same time. So not as good as each having their own timing specs, but a MUCH improvment over the old motor/head setup.
 
Originally posted by: geno
Originally posted by: Demon-Xanth
DOHC is better than 4V SOHC for the same reason why SOHC is better than pushrods. Less reciprocating mass and better valve angles.
Click to expand...

less reciprocating mass per cam, but not neccessarily less overall mass, right? You'd actually have *more* reciprocating mass with two cams, no? Or does that not count the cam's motion, rather just the valvetrain?
Click to expand...
The cam is not reciprocating mass. The rockers (absent in most DOHC layouts) would be.

 
WOW! You guys are awesome!

I understood most everything you wrote too😀


I am still a little hazy as to the benefits of the third valve on the lightning...why have a third valve if any timing changes will be applied universally anyways....?


More fuel delivery?
 
because it's domestic 😛

they usually seem to use pushrod older style engines...

heh. like the GM 3800.... pushrod iron engine, but reliable!!

DOHC isn't always better though. it's easier to tune a single CAM. at least in my experiences with SOHC and DOHC 2.0 Neon motors.
 
Originally posted by: Goosemaster
WOW! You guys are awesome!

I understood most everything you wrote too😀


I am still a little hazy as to the benefits of the third valve on the lightning...why have a third valve if any timing changes will be applied universally anyways....?


More fuel delivery?
Click to expand...
*Anything* you can do to make your pump(engine) breathe better will improve efficiency(and therefor power, etc).
 
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