View Full Version : SOHC vs. DOHC (yes, again)...
08-08-2007, 09:50 AM
Does anyone here have any experience in the differences in a ported SOHC vs. a ported DOHC 2.0/2.4 head?
I never really considered the SOHC until I looked at the SOHC valvetrain for the first time a few days ago. For a race-only application (high rpm, solid adjustable lifters, hight lift cam, big valves, etc.), I think the valvetrain is potentially better. The rocker/shaft design is (IMHO) more robust at high RPM than the DOHC design. I think the DOHC design is likey to toss rockers (just like our 8V setup) if anything resembling valve float is achieved. Plus, I think it wouldn't be too terribly difficult to make adjustable (possibly even high strength billet) rockers for the SOHC setup. I realize there are off-the-shelf adjusters for the DOHC, but there is nothing available to replace the rockers. Jesel makes a very nice setup for the OHC Ford V8's. It would be nice if they had that setup for the DOHC Neon head. But, the cost is way high (~$100/valve for Ford V8's).
Anyway, what about the flow? I know the DOHC flows better out of the box than the SOHC (only marginally on the intake, but much beter on the exhaust). But, can the SOHC be ported to the point where there is really no difference? Or is there some limitation on the SOHC head that keeps it from being the way to go?
Keep in mind that this is going on a 2.4-based (155 cuin) NA engine that I intend to rev to ~7500 rpm for drag racing only...
08-08-2007, 10:00 AM
Just from a visual, the DOHC exhaust ports are much larger than the SOHC ones. The intake ports are similar in size, but the exhaust ports on the stock SOHC heads is about the size of a quarter.
I've never tried to port any of mine, but if you wanted a spare SOHC head to cut up or play with I've got one with bent valves sitting on a motor in my barn.
The SOHC Magnum heads are supposed to be much improved from the other SOHC heads. They are not as easy to find since they were only on the later neon R/T's and ACR's, but that would be best way to get the sohc valvetrain and a better flowing head.
08-08-2007, 11:08 AM
Yeah, but how big can the SOHC exhaust ports be cut? I'll see if I can find stock port flow info on the later model R/T head...
08-08-2007, 06:03 PM
I building a hybrid with a 2.2 and SOHC neon head.Its just a stock head for now,Im gona use it to experiment with some things.
08-08-2007, 07:24 PM
I seem to remember Andre saying that stock SOHC ports are really bad, if ported, they can be made to flow but I believe the DOHC are still better of course but the SOHC can flow more than a 8 valve head. I would get Andre to answer here, :thumb:
BTW, had an SOHC apart last week and yeah, the ports look small and look like they flow like crap.
08-08-2007, 08:13 PM
Steve Menegon did some experimenting years ago with the SOHC head.
The standard 2.0 SOHC head flows worse than a stock 2.2 8V. It can be improved upon, but it will always be an obstacle.
However, if you use a MAGNUM SOHC head found on 01-03 Neon R/T's and ACR's there is Much more potential. The exhaust ports on these heads are MUCH better than standard SOHC better. It's debatable wether it will ever be as good as the DOHC head. There is a reason why all the big boys race the DOHC heads.
I agree with you that the valvetrain is a much beefier design! Fortunately, all standard SOHC stuff interchanges with MAGNUM stuff.
08-08-2007, 10:52 PM
I have a Magnum sohc head that came off a 2001 RT. I had this head for quite a while now, still sitting in my friend's shop, The exhaust ports on the head sit much higher than on the regular head, giving it a much better radius. The valve rockers are TOUGH! The only reason I got this head, (for free) was because I have a friend who is a mechanic at Chrysler, and told me they had the complete engine, but it was towed behind a motorhome in 1st gear at 100kph down the freeway before the owner realized something was wrong. If I wanted the head, I had to take the whole engine. The #1 piston let go, was only a small piece of it left in the water jacket, along with a piece of the connecting rod. One combustion chamber had damage, but has since had some aluminum welding done to it. There were multiple bent valves, but the rocker arms were unscathed. The cam, which is the best of the sohc cams, also looks very good, apparently the car only had 10,000 kms on it. The cast oil pan had 2 huge holes, with the crank having a bare journal from cyl #1. The head is at my friend's, who's been drag racing since the 70s, because he was gonna port it, but hasn't got too far on it, too many projects.
Anyways, all this jabber, the rockers are tough...
Oh ya, I also have a set of new Crane valve springs for this head which have never been mounted.:D
Rockers survived, engine didn't.
08-09-2007, 06:46 AM
so is there any actual documented problems with the dohc valvetrain breaking or is this just a paranoia/excuse to use crappier head thread?
Seems to me that DCR has taken that valvetrain well over 10k
08-09-2007, 07:42 AM
I what way is the SOHC "crappier"? From what I understand, the Magnum flows nearly as well as the "old" DOHC. If it can be ported to flow what's required to make X hp, and the rockers are a more robust design, then I'd say it's the better choice.
Actually, stock vs. stock, the DOHC is clearly better. But, I'm not talking stock here. My only concern with the DOHC is the rocker arraingment. It's not paranoia to think the rockers can be spit out. It has happened, just like it has with our 8V engines. And, there's no easy way to get around that issue.
The SOHC, on the other hand, uses an overhead rocker on a shaft, much like the T3 (and nearly every Mopar V8 up to ~1990). The stock parts aren't anything special with the built-in hydraulic lash adjuster. But, I think it would be pretty simple to have billet roller rockers made.
If Jesel starts making their roller rockers for the DOHC head, then that would seal it for me. Here's a link to the Ford followers - Jesel Online (http://www.jeselonline.com/v2/index.php?categoryid=43).
I've seen another design that doesn't use the ball post at all, but I can't remember who makes it. I'll try and dig that up.
EDIT: Here it is, these look more robust, but way too expensive... SSS Rockers (http://www.secondstreetspeed.com/articles/modular%20rock%20&%20roll/modular_roll.htm)
08-09-2007, 08:39 AM
If you upgrade to 2001-up rockers and lifters on a DOHC head, you will never have a problem. Earlier lifters were the problem.
08-09-2007, 09:21 AM
I'm going to go with solid lash adjusters, and probably the 2.7 followers on my 420a head. I was really just wondering if anyone had tried to do anything with the SOHC heads.
08-09-2007, 12:30 PM
2 valve set = $1750.00
4 valve set = $3500.00
Followers, Lifters, & Adjusters.
But they did pick up 40ft/lbs and looks like around 60 hp, :thumb:
09-17-2007, 07:50 PM
Im still in the proses of building a SOHC 2.2 with a VNT turbo from a jeep liberty diesel,Im doing it to experiment with the Idea and see what kind of power can be goten outof it and keep the efficency up there a ways.Its gona be a fun project.
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