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

[2forty]

do some reading or something

[sunnys14]

Originally Posted by EchoOfSilence

i have to call it...

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

[S14DB]

Originally Posted by 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.

Drivetrain loss differences.

[Zesty]

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

[S14DB]

Originally Posted by Zesty

^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]

Originally Posted by 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.

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]

Originally Posted by 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.

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/U...arreviewspecs/

[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.