why the dohc is alot better than sohc

[TomsMR2]

http://www.billzilla.org/2v4vpage2.htm#v8boughtscrol ldown a bit...Quote »First off I agree with most of what Bill has said, 4 valve engines simply allow better cylinder filling at all RPM, this translates to improved BMEP and therefore increased torque and BHP throughout the rev range. I would say that a 4 valve engine in aspirated form, developed properly will make about 90ft/lb per litre tops and can sustain most of this for around 50-55% of its rev range, an 8 valve engine developed properly will make no more than 82ft/lb per litre and can sustain most this for no more than 40-45% of its power band. This means that a stonking 4 valve engine will be far more flexible and have a wider torque envelope that an 8 valve.. end of story, where you choose to make that torque is up to you. Effective cylinder filling at high RPM (and therefore big BHP) comes at a price on an 8 valve engine, the price is wild cams and lots of overlap, these destroy low down torque. 16 valve engines have inherently better cylinder filling because of increased valve curtain area, to extract greater power requires less cam duration and less overlap than with an 8 valve, this allows better retention of the engines low down torque characteristics. I've run my current engine in 8 valve and 16 valve form, both times running relatively enormous cams (8v 326deg, 16v 302deg) with ultra big valve heads and 48 webers, the 16 valve version produces 70BHP more and comes on cam 1500RPM earlier, at 2500RPM the 16 valve has *twice* the torque of the 8 valve. Peak torque on the 8 valve was 155ft/lb, on the 16 valve 179ft/lb. From 3500 to 8300 I have over 85% of maximum torque on the 16 valve, on the 8 valve torque hits 85% of maximum at 4400 and drops below again at around 7200. Thats why I changed to 16 valve.. Here is a real example from a big rolling road day at Walkers workshop on Sunday 15th, two engines, one an 8 Valve 'Kent' Crossflow, 1780cc, fully worked big valve head, 296 degree cam 40 Webers and 4->1 exhaust, the other a 16V Rover K series 1788cc, standard head, standard plenum, 268 degree cams, 4-2-1 exhaust. Both engines made around 146BHP (xflow 145, K series 147) The following figures are torque in ft/lbs

RPM 8v 16v 1500 45 56 2000 68 91 2500 101 130 3000 112 133 3500 112 129 4000 111 132 4500 126 140 5000 129 136 5500 130 134 6000 126 126 6500 112 118 7000 99 108

Speaks for itself... at 1500 RPM the 16v has 24% more torque, at 2500 the 16v has 29% more torque, at 4000 18% more. These are real life engines, no theory here, in order to match the 16 valves output the 8 valve has to use a lot more cam and a big valve head fully reworked. This has worsened its low down torque. The output from the 8 valve is considered very good for a road engine too. A naturally aspirated 1788 K series 16 valve engine fully reworked (by me) was on the dyno today at Walkers Workshop and made 251BHP and 163ft/lb of torque (90ft/lb per litre). See it in CCC magazine next month, show me an 8 valve aspirated 1800cc engine with those sort of power and torque figures and I'll show you my testicles on a silver salver. Dave" [/quote]cliff notes!dohc makes more peak and broader power with less mods, lower cam profiles, and more reliability. this is proof, no speculation or theory. the dohc is a better platform all around.

food for thought..

[U12 2NR]

I think this is just stating the blatant obvious.

[blue_hauder]

Yea it might be obvious, but the KA24E is a 12 valve and this talks about 8 valve and 16 valve

[TomsMR2]

its still relative. alot of people were saying its not worth it to switch to dohc, and to stick with sohc.. i think it might be worth relooking into it. alot of the 8v stuff applies to 12v.

[U12 2NR]

when it comes to KA's it's another story. SOHC Stanzas have a quarter mile time of 16.5, and DOHC Altimas have a quarter mile time of 16.4. The information posted above may be relevant for that particular engine, and the DOHC may very well be easier to pull horses from, but which one is worth paying attention to doesn't really matter. The KA is not an engine to be all motor with, if you want power, you have to go with forced induction or nitrous. Sure some people are capable of low 15 second times, even high 14 second all motor KA times, but lets face reality, that's not enough to compete with the faster cars which are 13 seconds or better. When you're going any of those routes, you need to properly build the KA. A well built KA, SOHC OR DOHC are both capable of very good power, regardless of which one has the edge over the other.

[McAdam]

I'll throw down my 2 cents here. he talks about cylinder filling, right? well since the KA SOHC has 2 intake valves, the cylinder filling is just as good as the DOHC, theoretically.. but it suffers on the exhaust side. but then again everyone knows that exhaust is not nearly as important as intake. Plus, the question begs to be asked, why does NISMO only make parts for the SOHC, why do all the big HP race teams use the SOHC? oh well.

yes, 2 valves per cylinder sucks. it really sucks when its not even crossflow. but I love my L series motors anyway! I'mma gonna fix that one of these days!

McAdam

[TomsMR2]

hes talking about specific displacement FULLY raced prepped motors. so actual brands dont matter, and are irrelevant.

nismo makes dohc parts too.. nissan motorsports makes primarily sohc parts, because thats where their research went.. into sohcs.

[jam149]

I think the DOHC motor may be able to make more HP - but not cheaper. Like someone said, the SOHC has a bit more development behind it (it's used in the GT3 cars). Pricing out the cost to build one up seems pretty good (mostly from the cost of redoing the valvetrain) compared to the DOHC version.

[Dattebayo]

Yes, 2 cams are better than one! All of you suckers who think sohc's are better SHOULD wise up. The power fall off is the primary reason of course. But really some sohc nuts i meet say the timing chain is their other reason for choosing the lower class (?)... i cant stand them and i really think there should be a seperate forum subject just for all the sohc goons... But hey ill throw you a bone, at least their pistons are good for power on a dohc.

[U12 2NR]

yeah..that was real constructive. thanks

[jrc90240sx]

I like both engines. I belive the SOHC to be cheaper to a point, but after that point the money difrence becomes mute. say you compaire my engine build from one engine to the other.

my SOHC cost me about 4kthe DOHC would have been about 4.6-5k with the added price of the exta cam, shims, timing chain parts, and extra head work.

after that the cost is mute, turbo cost would faver the DOHC sense there has been more market for that engine, witch alows for cheaper and more avalible parts. so in the end i belive the price would be within $500 of each other, witch when going for 350+ hp isnt that much money.

[singlecamhonduhkilla]

SOOO... THE VAST MAJORITY HERE VOTES FOR SOHC BEING BETTER??JOE

[U12 2NR]

no

[C-Kwik]

I suggest you guys read this. Particularly the part about the lift.

http://www.nissanperformancemag.com/june03/nerds/

[jam149]

Related to cams, I think that with rocker arms, the SOHC motor can run a more agressive cams. With the shim on bucket design on the DOHC cams, I think the cam profile cannot ramp up too quickly without causing too much friction against the shim, and possibly binding.

Now which is better - who knows! There has definitly been more deveopment into the SOHC in past years. And I've heard the GT3 guys telling of 230+ N/A HP out of the SOHC motors. Not bad.

I don't know of any numbers for "big" n/a HP in the DOHC.

joe

[TomsMR2]

^ you can run obsurdly high lift on short or long duration with shim/bucket setups... ive seen 10.5mm lift on 302 degree cams on the bucket/shim dohcs. setup properly, anything can run obsurdly large cams.

psst. 230 hp na for 2.4L isnt fantastic for a race motor. f1 1.6L toy motors put out 240hp.

[C-Kwik]

Shim/Bucket lifters are light. They don't require as stiff a spring. Therefore the friction should be less than that of a rocker arm. At all times, there will only be one point of contact(tangent) between the cam and the lifter. This goes for any valvetrain. There is no more friction in one set-up than another valve spring rate aside. The exception to this is roller rockers but these tend to be used as a way to remedy friction problems(particularly on motors that use pushrods).

As far as GT3 motors, get one and try to drive around on the street. Let alone getting it to last for any significant length of time. They are built as pure race motors with no thoughts to streetability. High idle. Poor low-end power. Loose tolerances particularly when cold.

[F4ucc]

F1; 1.5 L motor with boost puts out 1500 HPS in late 80, I believe you're refering to Fomula Junior 1.6 L motor puts out about 240 hps in NA form.

Cheers

[jam149]

This thread is supposed to point out that the DOHC is soooo much better than the SOHC. I'm just saying, it has it's advantages, but in the case of the KA24E vs the KA24DE, I don't think it's WAY better, and in some cases it may actually have an advantage (from a cost standpoint).

Quote »get one and try to drive around on the street[/quote]I never said it'd be drivable. I don't think a DOHC motor running similar HP numbers would be much better for the street either.

I don't know of anybody running 230+ RWHP DOHC's (although I'd like to!). I've seen buildups for 210 crank HP, but nothing over that.

joe

[jam149]

In relation to the cams, I didn't say you can't run very agressive cams with the shim/buckets. I just stated that you cannot have a crazy ramp-up angle on the shim. Reference paragraphs 5,6,7:

<http://www.twelve100.com/faq%2...y.htm> joe

[7thGear]

i'm just quickly going to throw down my 2 cents because i am on break and if i repeat what someone else has said donw towrry about it

as said, 8 vs 16 is one story, but the KA e has 12 valves, 2 of wich are identical to the DOHC intake , and the exhaust is actualy a bit bigger than the dohc single valve, so they dont suffer THAT much compared to dohc, if the exhaust valve on the SOHC was the same size as the intake valve, then yes DOHC would clearly be the obviouse choice, but since its 4mm wider in diamater, id say the diffrences are minsclue.

alright out.

[SingleCamSam]

But you forget that the 2 exhaust valves on the dohc flow much more air than the single larger sohc valve. They also maintain better flow velocity at all rpms.

[Dattebayo]

sam's right. And i'd like to add that i had a dohc n/a motor with all the trimmings including pdm's cams and nismo's SOHC high compression 90mm pistons . The pistons work in both engines, but because of the way the circlip hooks on the comp. is ALOT higher in dohc. I'm sure my CR was close to 12 to 1 and i'm also sure that it was putting down 210 rwhp if not more. And im not even rich. (but YES i was running 104 octane ALL the time...)

To sum up, i think that the DOHC is definately more of a challenge to outfit for n/a, but the results are well worth it. As for better? Go drive the two and compare. You'll know im right.

[SingleCamSam]

Quote »Yes, 2 cams are better than one! All of you suckers who think sohc's are better SHOULD wise up. The power fall off is the primary reason of course. But really some sohc nuts i meet say the timing chain is their other reason for choosing the lower class (?)... i cant stand them and i really think there should be a seperate forum subject just for all the sohc goons... But hey ill throw you a bone, at least their pistons are good for power on a dohc[/quote]

:rolleyes

[Dattebayo]

oh sure roll your eyes. Have you ever heard that question, "how do i get more power out of my sohc?" Im sure you know the answer. Go get a dohc, sucker.

But wait a minute, if you do, you cant be SingleCamSam anymore. Oh well.

[7thGear]

if only you can graft a variavle valve timing "set up" on to the KA, either one of those, man...

are u peeps sure v-tec heads dont fit on to ka blocks? what if i use an insane ammount if duct tape? come on!!!:D

[Dattebayo]

It was said in a previous post that there is variable cam timing on one of Nissan's models. You could maybe work that out somehow with a little fab work over the timing chain cover... Or you could put the back sprocket and shifter from a bike on there haha

[7thGear]

i was thinking something crude'er

have a pull/push lever inside the car to physicaly punch the new camshaft in and out of position and write "NOS" under it, hahaha,

[Dattebayo]

that is so awesome. i gotta do that. Oh yeah and put honda stickers all over the engine.

[7thGear]

just cuz it has variable valve timing doesnt mean its a honda