The SOHC heads out flow the DOHC heads, they also have longer intake runners which is most likely where the torque is coming from. Both are great heads. The DOHC heads are the same castings as the JDM sti heads, They are ported different but share the same basic mold. They make great turbo heads for this reason. older STI cams will bolt in and you don't need a special up pipe to clear them. They also have oil and coolant galleys that only need to be tapped for turbo feed lines.

The SOHC heads flow a bit better and have larger ports and are a more simple design. If I were going to build an N/A motor I would stick with the SOHC heads get cams and piston, up the compression to 11:1-12:1. They run 10:1, which is quite high but they run detonation free on 85 octane which means you can advance timing and or up compression run 91-93 octane for more power. this would really build a torque monster.

This is only how I would do it, and I am not knocking the DOHC heads at all, but I really think they are more suited for turbo motors than N/A.

 

N/A is too slow by the way. do you guys know where i can buy the cams than can make the SOHC motor more hp?

 

COBB, TWE, and Delta are the big ones. Delta are the least expensive. You pull you cams send them to delta they weld material on them then re grind the profiles on the lobes the send them back. They run 160ish + shipping, the others are in the 400-500 range.

 

Now that you've educated us....educate yourself with the search button....

N/A is too slow by the way. do you guys know where i can buy the cams than can make the SOHC motor more hp?

 

I know this is a bump, but are there any reliability differences between the dohc and sohc? I did find that they both have their pros and cons, but couldn't find much in the reliability field.

 

Wow... this thread being back up...

Well anyways, supposedly the DOHC is less reliable, from what I hear, mainly because they had more head gasket issues IIRC. They also made slightly less power then the SOHC engines, had lower compression ratio (9.6:1 as opposed to 10:1).

 

Generally speaking increasing compression 1 point from a starting range of about 8:1 - 12:1 gives only about 3-4% more HP.
Increase CR 1 point @ the 13:1+ range gives just 1.5-2% increases in HP.

So increasing the CR of the DOHC engine from 9:7:1 to 10:1 will not give you a huge power increase as you are increasing CR by .3 on a 165 hp engine.
I'd expect a 1-2 HP gain assuming timing can be advanced as much as it would be stock.
If the engine is a mutant & responds to the change 3 times as well as it is supposed to you'll get a whole 5-6hp....

That said a combination of mods (EL Header, exhaust, intake, cams,.....) should be able to increase HP from 165HP - 180HP without too much trouble @ all.

 

With cams, depending on which you get you will be pushing the 200 CHP envelope.

 

I can add from a performance aspect ... I notice the DOHC makes the max HP at a higher RPM where the SOHC is a bit lower in the RPM ...DOHC likes to rev a bit higher .....

But as an upgrade aspect goes , the same upgrades are out for both ... the advantage goes to the SOHC ....since you are only doing 2 cams instead of 4 ... and its an easy valve adjust .... save a bunch of $$ on a cam upgrade !!! And yea , with a slightly higher comp. and better flow ?? ..should make a tad more HP in the long run ....

I wanted a SOHC ... Got a DOHC only because It was an insane deal ... I am happy with the power ...No hot rod in any way ... but with the basic intake and exhaust upgrades its still fun !!

Headgaskets go bad on both ...DOHC are internal , SOHC are external ...