SOHC vs. DOHC....which gets more MPG?

[Zesty]

OK, sorry if this has been covered, I'm just curious.

I know the SOHC is less powerful, but I am wondering which gets better fuel efficiency.

Is it the same/comparable? Or does one have the edge over the other? Thanks.

[EchoOfSilence]

DOHC by a little

[Zesty]

Thanks for the quick response.

[neverlift]

kade better dual cams=more power=less throttle=less$ on gas

[EchoOfSilence]

that's not even the reason.
it's just a little more efficient

[wootwoot]

efficent in what sense?
Just trying to understand =)

[BigVinnie]

efficent in what sense?
Just trying to understand =)


1.) additional exhaust valve per cylinder adds for better flow, and scavaging.Creates larger curtain space and overall larger exhaust diameter, it helps to increase power and momentum(inertia). 16valve VS. 12valve, obviously in this instance more is better.
2.) higher compression than the SOHC provides greater use of power for optimizing the atomization of air to fuel. More power by compressing more air than a lower compression engine.
3.) 8bit mapped ecu tuning over 16 bit ecu tuning. UUUMMMM obviously 16bit utilizes better maps, and much more aggressive tuning than the old 8bitters.
4.) DOHC heads are ported larger in diameter than the SOHC's.

The only true disadvantage to the DOHC's is the knock sensor, using lower grade fuels lower than 91 octane can actually hurt and decrease gas mileage by retarding the timing to impending knock signals that would read higher than using a higher grade (91 octane). Sohcs you can use the crappy 87 octane and get the same gas mileage results as if you were to use 91 octane on the SOHC's.....

[EchoOfSilence]

how does one more valve increase scavenging, vinnie?

[BigVinnie]

how does one more valve increase scavenging, vinnie?


Diameter size is increased due to curtain space area. It makes stronger pulses than utilizing a single exhaust valve....
More area=more volume
more volume=stronger pulse

[Irukandji]

My sohc got 250-270 on a full tank
My dohc gets 300-350 on a full tank

I'm not trying to say my cars were prime examples to show mpg... but my Dohc gets suprisingly better gas mileage.

[sunnys14]

dohc wastes gas TWICE as much as sohc because it has an extra cam

[2forty]

iono, my sohc and dohc got similar mileage, but sohcs usually do worse because of bad conditions haha

[sunnys14]

i think ur wrong 2forty

[sunnys14]

im jk, 2forty is right though, DOHC i see get a couple more MPG than SOHCs

[EchoOfSilence]

My sohc got 250-270 on a full tank
My dohc gets 300-350 on a full tank

I'm not trying to say my cars were prime examples to show mpg... but my Dohc gets suprisingly better gas mileage.
pretty much. I fucking hate getting 250-270 a tank, while Evan's (nemeguero) dohc gets above 330 (when he was N/A). damnit.

[breakindrifts]

dohc wastes gas TWICE as much as sohc because it has an extra cam


:rofl: :rofl: sig worthy, but yea I can get around 300 miles to the tank on my sohc if I drive right.

[NIK90s13]

I'm in the 250/270 catagory. We just finished the dohc rebuild with the 91 exaust cam on the intake side. I just dont have the time to install it AAAAHHHHH!!!! It should go in in 2 weeks!!!!!

[Zesty]

Man, thanks for all the feedback. Pretty throughly answered my question!

So the DOHC is not as keen on the piss-gas as the SOHC is?

[BigVinnie]

So the DOHC is not as keen on the piss-gas as the SOHC is?

Yeah pretty much the only advantage the SOHC has over DOHC.
When ever lower grade fuels are used on the DOHC, cylinder temprature increases . As temprature increases from lower grade fuels, the knock sensor picks up knock (which is early signs of detonation). The knock sensor sends the signal to the ECU that the engine timing needs to be retarded in order to prevent early detonation. Retarding the timing decreases power output when the engine should of made optimal power at 20BTDC.
But even if the DOHC ran on crappier fuel it would still get better gas mileage than the SOHC. There are to many updated modifications to the DOHC engine that make it overall a better performer. The DOHC engine would probably lose about 1/2 mile per gallon using 89octane, and about 3/4mile per gallon using 87 octane, (or atleast this is what I figured going on long road trips and opening up the throttle). WOT also has alot to do with how much fuel is used. If you can keep the engine at or below 3000RPM you can pretty much use any grade fuel without sacrificing to much knock or gas mileage on crappier fuels. It is recomended for best performance to miles per gallon to use 91 octane on the DOHC engines.
But even on crappier fuels DOHC>SOHC.

[sunnys14]

:rofl: :rofl: sig worthy, but yea I can get around 300 miles to the tank on my sohc if I drive right.


it was just a joke :wiggle:

[sunnys14]

the most ive ever hit was 425miles on a s14 DOHC, bone stock. refilled with 16 gallons of 89 octane, so u can pretty much do the math.

(btw, the s14 has a huge gas tank, like 17gallons)

[BigVinnie]

the most ive ever hit was 425miles on a s14 DOHC, bone stock. refilled with 16 gallons of 89 octane, so u can pretty much do the math.

(btw, the s14 has a huge gas tank, like 17gallons)

16Gallons eeh and 425 miles????? How did you calculate anything so relative???

[Irukandji]

the most i've ever seen was 380 on a tank... 425 is crazy.

[EchoOfSilence]

i have to call it...
:bs:

[BigVinnie]

i have to call it...
:bs:


HAHA....Agreed someone is smoking too many trees..........

[Ricks15]

I guess all engines are different in the condition that there in anb the abuse they take from us I remember when i was running rich and full of engine problems a Full tank would only last 80miles, and this isnt bs People with SOHC kae's gota know exactly what im talking about.

[alienz]

hey my sohc has gotten 400 miles to the tank but im sure the dohc can get more...just depends on your driving. ive literally gotten 400 miles a tank then turned around and gotten 200 miles then did 400 again and back to 200...but its not fun driving trying to get 400 miles to the tank. must constantly fight urges and retards trying to run you!:x:

[BigVinnie]

I am still going to have to disagree. Weither it is SOHC or DOHC the bore and stroke of the engine leads to MASSIVE fuel dumping till about 1200RPM just to build enough power. Even if you did stay within 3000RPM and shifted properly on the standard s13 and s14 gas tanks that are offered, you will relatively get between the 300~350 at the maximum (weither SOHC or DOHC and how you drive). It is all supported by the EPA which has done alot of testing on all of these cars before approved for sale in the U.S.
Kinda makes you wonder the conspiracy of hybrid cars though doesn't it.
Anyways to get back on point we don't drive small bore and stroke Honda's that could probably conserve fuel a little bit better. We drive big bore and stroke engines that aren't very conservative when it comes to making torque.

[Pacman]

Doesn't the hemispherical combustion chamber of the DOHC get any credit for better MPG? I know the burn patter for a Hemispherical chamber is better then the others.

[ranisron]

S13 Fuel Tank, KA24DE, 15.9 Gallon, the best mileage I have gotten was 32 mpg to the gallon on 89 octane gas.

U13 (Altima) fuel tank, KA24DE (hello, same engine), 15.9 Gallon, the best mileage I have gotten was 35 mpg, 89 Octane (I have no idea how I did it).

Both cars run on 205 series tires, with the 240SX being lighter and healthier (I think). 240SX has higher tire pressures, which should results in better gas mileage. but I was getting some premature brake engagement so it tends to fuck things up.

Driving was done on the same highway, I-70, from Martinsville, IN to Cambridge, OH, which is about 28X.00 miles.

[2forty]

do some reading or something

[sunnys14]

i have to call it...
:bs:


umm... a s14 has a huge 17.2 gallon gas tank. i filled it up full before going on a long trip. i rode 425 miles on it before filling it up full again with 16 gallons (meaning i had about 1 gallon remaining). 425 miles / 16 gallons = 26.56 mpg! 26 mpg is about normal for a s14

u idiot, learn to do some freakin math before you open your mouth and say something stupid... dumbass :madfawk:

[S14DB]

S13 Fuel Tank, KA24DE, 15.9 Gallon, the best mileage I have gotten was 32 mpg to the gallon on 89 octane gas.

U13 (Altima) fuel tank, KA24DE (hello, same engine), 15.9 Gallon, the best mileage I have gotten was 35 mpg, 89 Octane (I have no idea how I did it).

Both cars run on 205 series tires, with the 240SX being lighter and healthier (I think). 240SX has higher tire pressures, which should results in better gas mileage. but I was getting some premature brake engagement so it tends to fuck things up.

Driving was done on the same highway, I-70, from Martinsville, IN to Cambridge, OH, which is about 28X.00 miles.
Drivetrain loss differences.

[Zesty]

^because the Altima is FWD and the 240 RWD? Or why?

[S14DB]

^because the Altima is FWD and the 240 RWD? Or why?
Yes, the drivetrain losses in FWD cars is alot less than RWD.

[neverlift]

so dohc wins this round?

[dct223]

dohc gets better gas milage....

most ive ever gotten was about 390 miles in a tank... that was all freeway from socal to norcal... made it in one trip without a fillup ahha..

[undesiredshoe]

i think the reason dohcs get better mileage than sohcs are because dohcs are newer than sohcs. Better technology? I dont know, just guessing.

[Project_Slipangle]

Doesn't the hemispherical combustion chamber of the DOHC get any credit for better MPG? I know the burn patter for a Hemispherical chamber is better then the others.


i know this post is really old but i cant believe noone flamed him for this! how would you ever fit four valves in a half a sphere? it would be nearly impossible to engineer a head with those kind of angles. every modern motor uses a pentroof configuration, with the exception of the new hemi motors which are less effecient. in addition to having less valves than the pent roof the hemisperical combustion chamber is also bigger in general. with the bigger chamber, you lose much more heat during combustion and also increase the distance the flame has to travel during ingnition. do some reaserch before saying something as ridiculous as that!

also having nearly identical motors but w diff heads, the dohc will always win out because its engineered better. tech progresses and so does effecency.

my question is would the dual cam motor be cheaper to run on crap gas or 91? how much does 91 increase mpg compaired to the cost of it?

[BigVinnie]

Doesn't the hemispherical combustion chamber of the DOHC get any credit for better MPG? I know the burn patter for a Hemispherical chamber is better then the others.


What do you mean by hemispherical? Don't you mean pentroof?
Nissan has used the Hemispherical design for almost all of there cross flow head designs since the birth of the FJ and (NAPS)Z series engines till about the late 80's with the CA18DE. SOHC utilizes hemispherical and is infact larger in volume than the DOHC (larger dome quench area). Hence installing SOHC pistons to DOHC engine increases the CR.

[Project_Slipangle]

no. wrong. its not hemispherical, or half a sphere. look at the head. its not round in the combustion chamber. its flat and goes up to a V. thats PENTROOF. thats the only way you can fit more than two valves. if it were round you would have the valves sticking out in four diff directions. but its pentroof, flat, so you can fit two valves for one cam and two for another.

[BigVinnie]

I never said DOHC was hemespherical. Did you see my question mark. Pentroof decreases surface area (quench) increasing CR, hense SOHC pistons on DOHC engine (my fault for not clarifying). Hemispherical design was used on older engines with single cams (8 and 12 valve nissan datsun engines). I belive the FJ also used hemispherical and was one of the only to use it as a DOHC head.
Also to the guy that stated earlier 35MPG.....B.S....

Quick thing to remember.
Nissan codes engine type and head type.
Any refrence at the end of engine type ending with E is a hemispherical head design (usually SOHC, but including the FJ DOHC). Any engine type ending with DE is pentroof ( and is always a DOHC head system).

[Phre0nBurn]

Haha, Dont feel bad guys...
I once got 40 miles to a full tank in my old Honda..
But it was cuz of a fuel leak...

And my truck I just sold... Ford F350 with a 12" lift, turbo diesel, i got about 230-250 per tank...

And the tank on her???
38 Gallons beeotches...
Beat that... haha
it sucked... I sold her cuz I couldnt afford to drive her...

[BigVinnie]

Comparison of Sohc to Dohc from the consumer guide.
Dohc gets one more mile per gallon freeway, estimated @28MPG, SOHC 27MPG. DOHC wins on the street mileage 22MPG, SOHC is 20MPG.....
DOHC does just as good with the automatic as well. Although automatic transmission degradated loss is @ 18%, while the 5speed stick degradated loss is 15%. On average the DOHC will get about 24.4MPG, from traffic stop and go freeway driving. SOHC gets relatively on average 23.1MPG, this is also calculated using a 5speed manual not an auto.
To all the fakers that claimed 35MPG......HAHAHA you are hillarious...
http://auto.consumerguide.com/Auto/Used/reviews/full/index.cfm/id/2218/act/usedcarreviewspecs/

[gripster]

why is it that my old 3.0L vg30e (sohc) maxima 5-speed got more than 400 miles to a tank going from norcal to socal on I-5 (or vice versa) and i'm having trouble getting 300 a tank on a smaller 2.4L motor?

I do a lot of freeway driving and noticed that keeping my motor around 3200 rpm gives me better mileage, and i have my tires at 40-45 psi. Just my .02

BigVinnie - i wanna talk to you about ka24e motor buildups.

[dct223]

size of the gas tanks????????

and its not always about size of the motor.. its efficiency...

[SochBAT]

I am thinking that people are forgetting other things, like wheel sizes to accurately read our and compare engine mileage.

At least we know we don't have a control (benchmark engine to compare to).

[SimpleSexy180]

ESPECIALLY when people put 17's on hatch or coupes.

[BigVinnie]

I should of also mentioned that cotton filters/intakes, and high flow CATS can increase gas mileage as well. I suppose 30MPG is possible on the KA24de with high flow CAT, CAT back exhaust and an intake system. A better breathing engine is a much more efficient engine. But don't quote me on that.