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Old 01-09-2006, 05:40 AM   #1
pik_d
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my neons engine

i've got a few questions about my engines that are somewhat obscure to the point that i dont even know where to look for the answers, except for hands on experience, but this is not the time nor place to get my first bit of experience, or asking on a message board...

the neon R/T's engine is an I4, 16 valve, SOHC engine.

now, the most basic of explanations pointing out differences between SOHC and DOHC state that DOHC allows for more valves per cylinder. but this engine has 4 valves on only one camshaft.

on first thinking, the most obvious thing about it is that they just have four cams in a line, so the two intake, and two exaust are just in a line (parallel with the camshaft). my first query is: is this thinking correct? and if not, what would be correct?

the second thing that comes to mind is that this seems to negate the most obvious advantage of the DOHC system. though a little bit of investigation comes up with the realization that such technologies as variable valve timing are dampened on SOHC engines (can only be applied to intake valves). but in engines without VTEC, VVT-i, or comparable system, am i on to something with the first statement in this paragraph?

and finally, if they can get 4 valves on one camshaft (per bank of cylinders, i should probably specify), how many valves can be acheived with twice the number of camshafts? space has to be taken into consideration somewhere, as only a limited number of valves will fit, but has anyone heard of anything exotic like 6 or 8 valves per cylinder on a DOHC engine? or is that just not feasable or practical?
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Old 01-09-2006, 05:55 AM   #2
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Quote:
Originally Posted by pik_d
i've got a few questions about my engines that are somewhat obscure to the point that i dont even know where to look for the answers, except for hands on experience, but this is not the time nor place to get my first bit of experience, or asking on a message board...
Okay.

Quote:
Originally Posted by pik_d
the neon R/T's engine is an I4, 16 valve, SOHC engine.
Yep.

Quote:
Originally Posted by pik_d
now, the most basic of explanations pointing out differences between SOHC and DOHC state that DOHC allows for more valves per cylinder. but this engine has 4 valves on only one camshaft.
Whoever told you that is confused.

Quote:
Originally Posted by pik_d
on first thinking, the most obvious thing about it is that they just have four cams in a line, so the two intake, and two exaust are just in a line (parallel with the camshaft). my first query is: is this thinking correct? and if not, what would be correct?
Huh?

Quote:
Originally Posted by pik_d
the second thing that comes to mind is that this seems to negate the most obvious advantage of the DOHC system. though a little bit of investigation comes up with the realization that such technologies as variable valve timing are dampened on SOHC engines (can only be applied to intake valves). but in engines without VTEC, VVT-i, or comparable system, am i on to something with the first statement in this paragraph?
Huh?

Quote:
Originally Posted by pik_d
and finally, if they can get 4 valves on one camshaft (per bank of cylinders, i should probably specify), how many valves can be acheived with twice the number of camshafts? space has to be taken into consideration somewhere, as only a limited number of valves will fit, but has anyone heard of anything exotic like 6 or 8 valves per cylinder on a DOHC engine? or is that just not feasable or practical?
There are lot's of engines out there with five valves per cylinder, and I've seen racing engines with up to eight valves per cylinder such as the mid '80's Honda NR500.

EDIT: Added links.
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Last edited by vwhobo : 01-09-2006 at 06:10 AM.
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Old 01-09-2006, 06:22 AM   #3
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hmm, i thought the advantage of DOHC engines was that it could accomidate more valves, which would inturn mean more intake and exaust airflow, and therefor higher preformance. if that's incorrect, or flawed, then what is the advantage of DOHC engines over SOHC?

based on said incorrect knowledge (false facts, anyone? ), i was having a bit of trouble understanding how all the fact fit togeather, which may have lead to the bits where vwhobo said "huh?" in response.

then i was trying to get a 3d visualization of how the camshaft, cams (or is it rockers, what is the correct term?), and valves all fit togeather. what i was envisioning was 4 cams (two controling the intake valves, two controling the exaust valves). the part about being parallel, i now realize wasn't as clear as it could have been... that part really isn't important though. just, is it 4 cams per cylinder? or are they somehow controling four valves with fewer then four cams?

the second think vwhobo said "huh?" to, largly had to do with the part that he said "Whoever told you that is confused.", so now i'm not so sure how important that part is too. basicly i was asking "if they can do 4 valves with SOHC, why do they do it with DOHC so often"?

EDIT: thanks for the links
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Old 01-09-2006, 06:26 AM   #4
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A camshaft is comprimsed of many lobes, the valves either follow the lobes of the cam directly (as in many DOHC engines), or there is an intermediate rocker arm that follows the cam lobe and transfers that profile to the valve. You're right, you are very confused.
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Old 01-09-2006, 06:26 AM   #5
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pik_d :- Going to be a bit hard getting 4 valves all lined up wouldn't you think? So do you suppose that DOHC may also allow elimination of rockers?
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Old 01-09-2006, 06:28 AM   #6
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Quote:
Originally Posted by vwhobo
There are lot's of engines out there with five valves per cylinder, and I've seen racing engines with up to eight valves per cylinder such as the mid '80's Honda NR500.

Very interesting, Honda has recently started dabbling with ovular shaped pistons again. As I recall they're looking at putting it in a Quad. I'd never seen that motor before.
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Old 01-09-2006, 06:32 AM   #7
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This is a representative picture of a DOHC head. There are differences between manufacturers.



The major reason for using a DOHC instead of SOHC is generally speaking you have better control over valve placement and angle, and lighter (but more) valvetrain components allowing higher revs. That explanation is general and basic.
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Old 01-09-2006, 06:33 AM   #8
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Quote:
Originally Posted by Bino
A camshaft is comprimsed of many lobes, the valves either follow the lobes of the cam directly (as in many DOHC engines), or there is an intermediate rocker arm that follows the cam lobe and transfers that profile to the valve. You're right, you are very confused.

yea, i had no idea what rockers are. and now i know what they do, but not quite what they are. that could be the main problem...

vwhobo-
thanks for that explanation.
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Old 01-09-2006, 06:41 AM   #9
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http://www.1stgencivic.com/phpgdv2/e...fo/Engine2.jpg

SOHC motor with rockers, the cam runs down the middle and the "fingers" of the rockers follow the cam profile, the other end of the rocker makes contact with the back side of the valve. This is an EB3 Honda Civic head.
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Old 01-09-2006, 06:43 AM   #10
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A SOHC BMW cylinder head with rocker arms. They are basically a bellcrank that transmits vertical motion from the cam to the valves.



.

An OHV Ford cylinder head with rocker arms. They transmit motion from the pushrods to the valves.



.

Old school rocker arms. They transmit your ass to sleep.

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Old 01-09-2006, 06:47 AM   #11
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Here's a single cam with rockers
Attached Images
File Type: jpg HCEengine2.jpg (74.0 KB, 13 views)
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Old 01-09-2006, 06:58 AM   #12
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thanks for the examples, i'll try and make more sense of it tomarrow when i'm more awake.

and hobo, i dont think i need that rocker to transmit my ass to sleep. i'm doing it well enough thinking of the semister starting tomarrow morning...
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Old 01-09-2006, 11:51 AM   #13
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Quote:
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my neons engine.

Well there's your problem. just kidding.
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Old 01-12-2006, 12:05 AM   #14
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Well there's your problem. just kidding.

waht r yuo tryin to say
my neon would kill ur intagra
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Old 01-12-2006, 12:32 AM   #15
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waht r yuo tryin to say
my neon would kill ur intagra
If this is supposed to be an impersonation of me, youre off to a good start. You can take over once I am done tonight.
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