mourad

Guys,

Why would anyone running two cams WITH THE SAME NUMBER OF VALVES PER CYLINDER be better off than someone running a single cam? Isn't double parts double trouble, more maintenance, and more torsional resistance?
If Honda manages to squeeze 4 lobes per cylinder on a single camshaft, what would be the advantage of using only 2/cam and running dual cams?

Dyzee

Well, personally I think its a matter of how fat your wallet is...and how much your willing to let go here.

There is more potential with building a dohc, but you can buy a sohc for a fraction of the price of a dohc.

SOHC- cheap and uses more "knowledge to perform"

DOHC- easy swap, easy mods, parts readily avilable

Both are capable of ENOUGH power boosted...but DOHC is more capable N/A

dohc valvetrains are intrinsically lighter than sohc designs, motor more balanced, higher revs are possable, cams can be adjusted independantly of eachother to add/remove valve overlap,extra piston return tensile spring strength, longer closed exhaust outlet path diameter etc etc. I could go on but you get the jist of it.

mourad

I don't see how DOHC's can rev up higher given the fact that any cam profile you can achieve on a DOHC, you can theoretically match with a single cam.

All the other points you suggested though make perfect sense. I didn't think of the additional tweaking and flexibility you can get by playing with valve timing in relation to each other.

Any other good reasons to go with a dual setup?

imported_gatherer

well it's simple...

with SOHC when adjusting the cam degrees you adjust both at the same time... if you give the exshaust +2 degrees your giving the intake +2 degrees of timing as well... timing between exhaust and intake events is static, basicaly locked in when the sohc cam is made.

with DOHC you can give the exhuast +2 degrees of timing and the intake is not effected... this allows for a dynamic adjustability between exhaust and intake.

as for resistance and stuff like that I think it would stay the same... (however this is just an educated guess) see with a SOHC you have 4 valves per cylinder all 4 are following the one cam. with DOHC you have 2 valves per cylinder following each of the cams. this results in less resistance per cam. basically halves the resistance a single cam would feel because there's half the parts moving against it. but at the same time a DOHC has 2 cams so there even though each cam sees less resistance the total resistance hasn't changed.

I'd still run SOHC if I had a choice,....

mourad

You'd run SOHC? interesting.

The way I see it is, there is a total amount of resistance inflicted by 4 valves period. Whether you choose to inflict that resistance on a single cam or two, the resistance will not change. Now, by adding another cam however, you add the minimum "penalty" resistance in making the thing turn in the first place. ie: if the cams were not even touching the rocker arms and there was no resistance at all, then spinning two cams will undoubtedly cause more friction than spinning a single one. I'm sure it's very moderate and not worth mention in the first place.

Very simple indeed I didn't think of that. I guess if it comes to valve lift, you'd still have to buy two cams vs one though right?

imported_gatherer

no spinning 2 cams independant of a valve train would not cause more friction .. it would cause more rotational mass .. and the more mass you have the more energy it takes to get moving ...

I'd run SOHC because thats what they least expect

mourad

yeah good point about the friction issue. I meant more momentum, not friction.

I'm happy with my SOHC anyway, wouldn't trade it for the world (or about $1000)

zeeman

iTrader: (1)

SOHC

punkindrublic

two cams have a lot more inershia (sp) then one cam... they can both rev as high as one another...

the thing is honda builds a b16 a lot stronger then a d16... but match a d16 with equivelent parts as a b16 and i'd be suprized to see if theres much difference... the d16 has a lot more stroke so it might even be a bit more torquey then the b16 too

but pending my big plans work out i'll hopefully be spining a d16 to 9000 or so this summer...

punkindrublic

the only reason i think the b series are better is they do have two cams so your intake cam can have higher lobes and duration compared to the exhust cam... and also the bore on the b series is a lot nicer... cause a d16 has only 75 mm bore... and from looking at my block i wouldn't wanna make it all that much bigger....

i think the problem i'll come into with my build is that since the stroke is so long (90mm) that the piston speed at 9000 might be to fast and bad stuff could happen

but then again the piston speed on an s2000 at 8000 is actually faster then on hondas F1 engines... which considering they rev past 18 000 shows what stroke is all about

mourad

I think that's what gatherer was saying by rotational mass. Sure they have more inertia but it also takes more energy to make them move in the first place. All about momentum, kindda like having a giant 18-wheeler get up to highway speed, takes lots of energy. But once it's doing 120, you better watch out 'cause there's very little that will bring it to a halt.
That's why I'm thinking it's not worth having more mass/momentum in your valvetrain because you lose the ability to change rev'ing quickly and it would take longer to accelerate and decelerate. As an example, look at the rev limit of big V8's and how long it takes them to reach 6000rpm.

punkindrublic

well v8 powered cars have really long gearing so that they aren't reving high on the highway but also cause they make a lot of low end torque so there engines can handle the low gearing... but the reason those dont rev high is cause they are made in america... and america doesn't know how to make engines

but i think with the proper work a sohc can do just as much as a dohc... like if you could run the same bore and stroke on a d16 i'd really love to see the difference.....also the d16 are damn light motors so you save overall weight on the car too

mourad

I always assumed it is because they have more cylinders cranking more power overall. The smaller 4 banghers have to use their natural abilty to rev high to compensate.

Quote:

but the reason those dont rev high is cause they are made in america... and america doesn't know how to make engines

That holds true for most engines, but GM made a few fairly respectable v6 and v8 engines over the years. Their hit/miss ratio is still pathetic though. I think Bruno would have plenty to add to this topic.

Quote:

but i think with the proper work a sohc can do just as much as a dohc... like if you could run the same bore and stroke on a d16 i'd really love to see the difference.....also the d16 are damn light motors so you save overall weight on the car too

I concur

punkindrublic

its cause in america they deal with inches... while the rest of the world uses millimeters...


even there good engines like the 350 small block or even the hemi... they wont last to 200 000 kms... not by a long shot

dingus88

ahhhh I've saw 5.0 mustangs with very high km's...and lot's of 20 year old 350 blocks still running...probobly will outlast any thing honda can make seeing how they turn like 4 000 rpms's less...most honda motors can't break 200 000 anyway..I'd liek to see a b18c5 make it to 150 000 kms with real world usage (high rev's)....high rev's wear out motor's.....the only honda motors I've ever saw last are like granny driven SOHC's....

punkindrublic

haha come look at my motor... its got 303 000 kms and i drive the **** out of it... i bought it will 180 000 kms or so like 3.5 years ago and it still loves to redline... thats honestly why i'm doing the d16 build in a way cause a single cam valvetrain is way more reliable then two cams

dingus88

meh I've saw 25 year old 350's with unknown milage (scrape yard) get slapped into cars and gone racing for a couple seasons......and 10 year old motors 350's that have trailered race cars for 10 years and be a daily driver... (real high milage)and towing is not light on motors....so... ...lol

ya a sohc I can imagine but not a b16 or b18 lasting past 200 000 km's

imported_gatherer

Dingus has a point .... RPM while meaning revolutions per minutes sometimes gets coined as ruins peoples motors...

punkindrublic

hahaha i'll worry about that if rpm ruins my next motor and all the pretty stuff inside....

imported_mrchaos

d16!!! i thought you were going for the funny sound