SOHC vs. DOHC

[DriftMonkey]

this topic could've already been discussed and probably already has but i havent seen anything on it so......

i was talking to a friend and he asked me the difference between the 89-90 s13 and the 91-94 s13 and i told him that the major difference was that the 89-90 are SOHC and the 91-94 is DOHC.  so he asked me if the 91-94 s13's were faster and i said that i have no idea but i would assume so because they are DOHC but i havent seen this topic on the forum so i thought i'd bring it up...so that i could answer my friend with some intelligence behind my reasoning...

any ideas would be apprecited

[Fresh 240SX]

</span><table border="0" align="center" width="95%" cellpadding="3" cellspacing="1"><tr><td>Quote (DriftMonkey @ July 23 2002,12:39)</td></tr><tr><td id="QUOTE">i was talking to a friend and he asked me the difference between the 89-90 s13 and the 91-94 s13</td></tr></table><span id='postcolor'>
Your "friend" has alot of questions &nbsp;<img src="http://www.zilvia.net/f/iB_html/non-cgi/emoticons/tounge.gif" border="0" valign="absmiddle" alt=''>

Just busting your balls

[BRSTYLE240SX]

if you were willing to go to edmunds.com and look at the specs of a 89-90 and a 91 and up you would see that the SOHC engine are 140hp and 152 torque.. againt the 155hp and 160 torque of the DOHC.. which means that yes the DOHC is faster... it's not like a Civic agains a Viper... but it's a bit faster... correct if im wrong.. but i'd say .5 to 1 sec. difference in the 1/4? if both engines are well tuned... im just guessing tho...

by the way.. it's ok to ask questions.. but i also had a "friend" like that when I was a newbie...

Later!

[DriftMonkey]

thank you very much....and figured there was a difference and i figured that it wouldn't an enormous difference but 1 sec is pretty good. &nbsp;its just good to have numbers to back up the assumption i made...thanks again

seriously it is a friend but whatever i dont care...the question was answered and thats all that matters

[whateverjames]

no it's not a 1 second difference. <img src="http://www.zilvia.net/f/iB_html/non-cgi/emoticons/wink.gif" border="0" valign="absmiddle" alt=''> &nbsp;if that were the difference between 15 hp, if you added 15 horsepower to a DOHC, you'd be running 14's. my SOHC hasn't lost to a DOHC. but if i had a choice, i'd go with a DOHC if i had to do it again. more turbo kits.

[DriftMonkey]

so if its not a 1 sec difference.....then its just a little bit of a difference, but there is still a differnece.... right? does the DOHC perform better.. or what...why did they opt to switch to DOHC from SOHC if there isnt much of difference?

[BRSTYLE240SX]

on the numbers.. like i said i was guessing.. and the reason i'd say it because maybe that's the direction the whole world was going... just guessing again! I LOVE GUESSING! lolol

Later!

[chickenmanq]

Hey, I'll guess too! &nbsp;<img src="http://www.zilvia.net/f/iB_html/non-cgi/emoticons/smile.gif" border="0" valign="absmiddle" alt=''> &nbsp;I imagine the benefits for two cams instead of one is to better control the valves. &nbsp;You split the work effort, and allow the engine to breath better, and breath more differently with two cams instead of one. &nbsp;However, that's also extra weight with the extra hp, and extra complexity. (One more part to break) &nbsp;It may also have something to do with the number of valves, or the way they're configured. &nbsp;I don't think they differ between SOHC and DOHC (?), but largely engine configurments require different operating structures. &nbsp;It may have had something to do with monitoring emissions too. &nbsp;Lotsa variables for why they changed it. &nbsp;Could be just because people think more is better, so they added one. &nbsp;Any engine builders out there that have more info?

And yeah, the difference will be negligable in stock form. &nbsp;In modded, the DOHC may have a better high end depending on what lift and duration the cams have, however, they're still going to be remarkably close until you pass the base mod point.

In any case, SOHC's rule!!!!!!! &nbsp;Long Live Eleanor!

[AKADriver]

</span><table border="0" align="center" width="95%" cellpadding="3" cellspacing="1"><tr><td>Quote (DriftMonkey @ July 23 2002,9:45)</td></tr><tr><td id="QUOTE">so if its not a 1 sec difference.....then its just a little bit of a difference, but there is still a differnece.... right? does the DOHC perform better.. or what...why did they opt to switch to DOHC from SOHC if there isnt much of difference?</td></tr></table><span id='postcolor'>
The DOHC engine does produce more power, thanks to the extra valves. &nbsp;The real reason for the switch was NVH (noise, vibration, and harshness). &nbsp;The DOHC is somewhat smoother.

There are plenty of reasons to choose one engine or the other. &nbsp;I bought a SOHC because it was just plain cheaper and easier to find one. &nbsp;They also have a bigger aftermarket for N/A power.

[sykikchimp]

A couple reasons the DOHC motor is better is the Addition of an extra exhaust valve allows for a more free flowing exhaust tract. &nbsp;Works (sorta) like giving the motor a larger exhaust.. &nbsp;Does some other things for emmisions as well b/c it allows for a slightly cleaner burn - (better swirl, and easier evac of exhaust gasses). &nbsp;It also allows the Spark Plugs to be placed closer to the Center of the cumbustion chamber for a more effective burn. &nbsp;This is for better emmissions, as well as extra power. &nbsp;

I think with Proper head work the DOHC motor can be more efficient than the SOHC motor, but it is a more complex job than the SOHC motor.

[240 2NR]

Just to add, the SOHC is a twelve valve motor, that makes better low end torque. &nbsp;The DOHC is 16 valve and has a slightly better top end, at the expense of a little torque down low.

Although 15hp is not much, and given the fact that the DOHC cars all weighed more, it may still be possible for the DOHC cars to be significantly faster due to making better use of engine rpm (the higher redline, or at least power at higher revs) and gearing. &nbsp;It's also likely that these cars will be in a better state of tune due to being "younger" (though I'm sure there are DOHC's that re beat to hell that will get schooled by someone in a SOHC).