SOHC and DOHC

[unrealman]

what'z the diffrence between them. would like a technical and a dummies discription. con sidering a car and was wondering what engine would eb better prefoprmance.

[flash4master]

SOHC = single overhead cam = 1 cam per head.
DOHC = dual overhead cam = 2 cams per head.

single overhead engines commonly have only 2 valves per cylinder, with the cam running both exhause and intake...this has one cam in the middle of the head.

dual overhead motors have 4 valves per cylinder, one cam runs 2 intake valves per cylinder and 2 exhaust valves per cylinder...this has a cam centered over each set of valves.

[randy48]

Well done Flash!

[unrealman]

so the DOHC is a better engine? right? well the car i'm loking at is a chrysler 300M the engine is a SOHC 24-Valve 3.5 liter v6 maxes out 250 horsepower at 6,400 rpms. what is a cam because this has 4 valves per cylinder too?
would a 2.7 liter 200 horsepower DOHC 24 valve v6 be better? i'm thinking no because of the horsepower.

[This message has been edited by unrealman (edited 02-13-2001).]

[flash4master]

hehe, im not only edjumacated in 'puters

[flash4master]

a dual cammer will allow better airflow into the cylinders...more air equals more power...if i were to get a new car, i would choose the dual cammer (unless i got an older pushrod motor, but we wont get into that here)...what kind of car are you looking at?

[flash4master]

ok. some sixes have 4 valves...read what i just posted above, with the exception of one cam...a cam is what "pushes" the valves open and closed.

[unrealman]

well there is the chrysler 300M and a sebring the reason i'm asking is becauswe the sebring has a 200 horsepower engine with DOHC and the 300M has 250 horsepower with SOHC.

[Marty]

Every dohc or 4valve per cyl engine I have seen is an absolute nightmare as far as servicability goes. I know people want the power for bragging rights but down the road it will cost you, more parts, more expence,more often.
On the other hand us mechanics need the extra money to pay for these computer upgrades, so we can have bragging rights.

[unrealman]

well that i know of chrysler don't make a car with anything but a v6 with 24 valves. except the cruiser and that has a 4 banger in it

[justy]

Hehe, There's a better margin for over clocking in DOHC motors!

All the best, Justy.

[struggles]

1.There is no substitute for cubic inches.
2.Go for the Horsepower!!

[unrealman]

the 300M it is. i like silver hehehe anyways. have you guys tried the auto stick feature on chryslers???? it'z really nice not having to mess with the clutch. hehe

[wyvrn]

My mechanic loves DOHC because he makes more money fixing them.

[samwichse]

The number of valves per cylinder is not necesarily related to the number of cams a car has. For instance, they are pretty rare, but certain cars have had 3 or 5 valves per cylinder. Also, just because a car has 4 instead of 2 doesn't mean that the engine will be better ventilated. Two large valves will provide just as much fuel/air mix and exhaust. However, a DOHC engine with 4 in each cylinder will have a more even torque curve and be more efficiant at high RPMs than a DOHC with 2 per cylinder due to the capability to have different overlap and whatnot on the cycle.
As for what makes more power... struggles is right that there's no substitute for more cubic inches, but then you drive to the end of the block and find you're out of gas. If you're looking for power, best to get the most for the least. Of course my car is a VW with a 1.3 liter pushrod driven valve system, so I suppose I shouldn't be talking.

[samwichse]

And if you're a do-it-yourself kind of person, then you can do a little computer chip upgrade. Try JC-Whitney for a chip for your car's computer with more aggressive ignition timing and fuel injection.

[Andy_L]

DOHC should allow higher RPM's with lighter valvesprings, but have more rotating mass. There are cars with sohc and 4 valves (actually very common), but the linkage is more complicated.

[Szech]

My friend who works for GM told me that the benefits of DOHC is that you have a dedicated cam for both intake and exhaust. You get more power this way, but the disadvantage is that you have a higher chance of failure, and repair is harder (twice as many parts). SOHC relies on one cam to control both intake and exhaust, which yields less power, but is more reliable.

[JimmyJamed]

and if you bust a timing belt with a dohc, your chances of kissin' a valve are alot higher...

[struggles]

Quote

***For racing, the more valves & cams the better***

hehe...Bring one of those fancy cammers to da track sometime, but dont forget to bring a box for all those parts laying on the ground.

A good pushrod roller motor will smoke it! And stay in one piece.

Quote
**In spite of owing a Plymouth, I wouldn't own a Chrysler product if it was my only car.**

????????????????What the hell does that mean? Sorry cad but your confusing me, (which isnt to hard to do.)


[This message has been edited by struggles (edited 02-15-2001).]

[samwichse]

I wouldn't buy a Chrysler either, even if it wasn't my only car. Why buy an american car to last you 150,000 when you can buy a Honda and get 300,000 (or more).

[desmocat]

Or for another flavor, try desmodromic valve actuation..NO VALVE SPRINGS..:0
Both my Ducs use this system, it's very good for high rpm use, because you will not get valve float, because it uses another cam lobe to close the valve.
This system was brought about by the poor metallurgy available to the designers back in the 40's &50's. The metal available just plain sucked for valve spring material,and had probs makin' it last in racing applications. (Fatiuge,strength,etc..)
I think Mercedes pioneered this technology in their racing program and had some success, then moved on to bigger and better things.
Only when Ducati picked back up on the idea to use in their engines did it gain attention again. If you ever get a chance to look in a Duc engine's top end, it's kinda cool to see all the engineering that is involved.
(I try not to think about all that stuff whirlin' around in there when I'm wailin about 10,000 rpm in the boonies, far from home http://sysopt.earthweb.com/forum/smile.gif )
short lesson,
Diesel parts=$$
marine parts=$$$$
Italian engine parts=(*&^&^*!!$$$$$$$$$$$$$$!

[skai]

The Chrysler engine is probably a Mitsubishi,or bitsamissin as we call them in the trade,one of the advantages of twin cam engines is the inclined angle of the valves, this allows a wedge type combustion chamber with the spark plug at the apex and a straighter port configeration.multi valve engines are getting easier to recondition due to the replacement of adjusting shims with inbuilt hydraulic tappets in the cam bucket

[RayH]

The Chysler engine you want is a 440 Magnum! Period!

[Toadman]

Cams? We don' need no stinkin' cams! http://sysopt.earthweb.com/forum/biggrin.gif
<IMG SRC="http://www.geocities.com/toadmeister2k/spinrotor.gif" border=0>

[Rat]

nice wankle toad.....

rat...

[Undertow]

YAY!!! Somebody brought up rotaries! Screw SOHC, DOHC, pushers, hell anything with the akward motion of a piston. I had a RX-7 with the 13B in it and it was the best motor I've ever rode hard and put away wet. Try gettin' one of those crankers up to 14,000 RPM, you'd have metal flyin everywhere. As for the sealing problem? My rotary had 130+ thousand miles on it and the guy I sold it to, a rotary guy, said it had every bit of power in it that it should. I think piston engines are very primitive in design compared to rotary and I **** Mazda for not putting it to better use, they could at least let someone else make use of it. Unfortunately, they rotary's only practical use would be in a sports car or a small truck, where lots of low-end torque and high-revvin horses are needed. These engines are no bigger than a motorcycle engine, mine was 78 CID!! You could easily fit one in just about anything. So what's wrong with them? They never did quite master the apex seals, but they at least made them last for 150K miles. Oh yeah, don't forget the 10-15 MPG. But hey, how else you going to get 250 HP out of a 78 CID motor?