Car Forums  

Go Back   Car Forums > Vehicle Specific > Asian Imports
FAQ Search Today's Posts Mark Forums Read

Reply
 
Thread Tools Search this Thread Display Modes
Old 06-16-2005, 02:45 PM   #1
Accord_Man
CF Addict
 
Accord_Man's Avatar
 
Join Date: Mar 2005
Posts: 345
DOHC and SOHC

Whats the advantage of an engine with two cams when comparing it to a single cam engine with the same number of valves and the same displacement, and the same compression ratio. Thanks.
__________________
Accord Man

Accord_Man is offline   Reply With Quote
Old 06-16-2005, 02:54 PM   #2
ChrisV
The Big Meaney
 
ChrisV's Avatar
 
Join Date: Mar 2004
Location: People's Republic of Maryland
Posts: 3,714
Quote:
Originally Posted by Accord_Man
Whats the advantage of an engine with two cams when comparing it to a single cam engine with the same number of valves and the same displacement, and the same compression ratio. Thanks.

The ability to time the intake and exhaust separately. That's it.
__________________
I'm not mean. You're just a wuss.



www.midatlantic7s.com
ChrisV is offline   Reply With Quote
Old 06-16-2005, 04:08 PM   #3
thunderbird1100
CF dB-o-holic
 
Join Date: Jul 2004
Location: LSU Campus
Posts: 3,260
Quote:
Originally Posted by Accord_Man
Whats the advantage of an engine with two cams when comparing it to a single cam engine with the same number of valves and the same displacement, and the same compression ratio. Thanks.

What chris said...and in the real world it usually means a smoother powerplant that can possibly rev higher.
__________________
1990 Honda Accord LX Sedan
Mileage Ticker: 232,400 Miles
Stereo Mods: Coming soon...

~Blow your mind~

thunderbird1100 is offline   Reply With Quote
Old 06-16-2005, 04:19 PM   #4
Accord_Man
CF Addict
 
Accord_Man's Avatar
 
Join Date: Mar 2005
Posts: 345
Quote:
Originally Posted by ChrisV
The ability to time the intake and exhaust separately. That's it.
Thanks, valve timing was the only thing I could think of.
__________________
Accord Man

Accord_Man is offline   Reply With Quote
Old 06-16-2005, 05:01 PM   #5
Inygknok
El del Supra
 
Inygknok's Avatar
 
Join Date: May 2004
Location: Puerto Rico
Posts: 1,863
not to mention that SOHC designs arent as balanced as DOHC (in terms of the camshafts, not the engine itself). its all due to the position of the camshaft in order to operate the valves. cant put it into the right words right now.
__________________


Supra: To surpass or go beyond.
Inygknok is offline   Reply With Quote
Old 06-25-2005, 05:59 PM   #6
nissanTFsx
CF Enthusiast
 
nissanTFsx's Avatar
 
Join Date: May 2005
Posts: 136
DOHC is heavier than SOHC
__________________


"Being slow is NOT a crime..."
nissanTFsx is offline   Reply With Quote
Old 06-25-2005, 08:50 PM   #7
TurboLag
CF's Bonafide Sonbitch
 
TurboLag's Avatar
 
Join Date: May 2005
Location: Morgantown, West Virginia. WVU stand up
Posts: 699
more moving parts
__________________
-Alex

Quote:
I am crazy. But you know what else? I don't give a ****.
-Tupac
TurboLag is offline   Reply With Quote
Old 06-25-2005, 08:57 PM   #8
CarEXPERT
Banned
 
Join Date: Jan 2005
Location: Bay Area, California
Posts: 1,117
how do you say DOHC? do you say DOC or like letters D-O-H-C?
CarEXPERT is offline   Reply With Quote
Old 06-25-2005, 09:01 PM   #9
99integra
CF's Florida boy
 
99integra's Avatar
 
Join Date: Jan 2005
Location: Piqua, OH
Posts: 6,099
Quote:
Originally Posted by CarEXPERT
how do you say DOHC? do you say DOC or like letters D-O-H-C?

Just say dual overhead cam but you say it D-O-H-C
__________________
Current whip: walking
99integra is offline   Reply With Quote
Old 06-26-2005, 12:48 AM   #10
Wally
I Know More Than You
 
Wally's Avatar
 
Join Date: May 2004
Location: Oz
Posts: 2,564
Quote:
Originally Posted by Accord_Man
Whats the advantage of an engine with two cams when comparing it to a single cam engine with the same number of valves and the same displacement, and the same compression ratio. Thanks.


Generally they breath better and rev higher.

DOHC generally have multiple itake and exhaust valves/pot, but of course there are three valve heads and even two valve (slack engineers and accountants). For a two valve there is less deflection of the camshaft and better angles of attack through canting and pent roof designs.

Tackling four valve and higher:

There is are a myriad of advantages, but consider you have two valves doing the job of one. This reduces the displacement (acceleration) of the valve and mass. Both these factors are major considerations when looking at force (f=ma).

The valve is less likely to flex or bounce so the rpm redline is typically higher, thus increasing your top end power capability. The radius of the valve is smaller so less likely to deform and more likely to seat when under duress.

The valve train losses are less because of f=ma. Flanking and ramps of the cam lobes is more moderate. Spring tensions are less also, unloading the camshaft and resulting in less shaft deflection and wear. Point load is more evenly spread.

The head itself has a reduced localised stress, both through reduced valve train stresses and stress distribution via two camshafts instead of one. The mass of the individual camshaft is less, reducing rotating mass.
__________________
"She gave me a look only a mother could give a child."

Last edited by Wally : 06-26-2005 at 12:58 AM.
Wally is offline   Reply With Quote
Old 06-26-2005, 08:20 PM   #11
ChrisV
The Big Meaney
 
ChrisV's Avatar
 
Join Date: Mar 2004
Location: People's Republic of Maryland
Posts: 3,714
Well, yes, Wally. But there are a number of SOHC 4 valve heads, SOHC 3 valve heads, and quite a few DOHC 2 valve dsigns (of course, most of those are older, like the Jag 4.2 liter in my old XJ6 that had been around in one form or another since the late '40s, and the DOHC 2 valver in my Fiat 124)

Since the difference between DOHC and SOHC isn't necessarily predicated on the number of valves, it really comes down to the ability to tune each bank separately (which is hard to do with an SOHC setup, or single cam-in-block layout). While you might lighten each small valve, you still have double the frictive surfaces and up the total mass, using up power to contend with, as well as the added cost and complexity (especially in the mass and location of the cam drive assembly, be it belts gears or chains).
__________________
I'm not mean. You're just a wuss.



www.midatlantic7s.com
ChrisV is offline   Reply With Quote
Old 06-26-2005, 11:09 PM   #12
Wally
I Know More Than You
 
Wally's Avatar
 
Join Date: May 2004
Location: Oz
Posts: 2,564
Serves me right. I actually wrote more than what you see and realised I had explained why SOHC was better than OHV and followed it on with the DOHC. I then deleted out a few paragraphs including the cam timing, rockers, buckets, etc before running off down the coast.
__________________
"She gave me a look only a mother could give a child."
Wally is offline   Reply With Quote
Reply


Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes

Forum Jump



All times are GMT +1. The time now is 10:12 PM.

Powered by vBulletin Version 3.5.4
Copyright ©2000 - 2017, Jelsoft Enterprises Ltd.
Copyright 2002 - 2011 Car Forums. All rights reserved.