Originally Posted by Sick95SOHC

This one is for all my fellow SOHC comrades in arms. For years, hell, more than a decade, we’ve endured the lashing tongues of DOHC haters telling us we were idiots for picking the side we did in the HP struggle. We suffered fallen heroes like JeffB#2 and maybe Len before I got here but he’s president of the haters now so I don’t know, but the battle waged on. My friends, a revolution is at hand. It’s taken a few years of trial and error research but I think I have finally unlocked the key to power in the SOHC head.

Looking at the intake port shape/size of the DOHC head, Honda B and K series heads, and so many others that had a proven record of making serious power, I could see that the general shape across the board was the same. What was glaringly obvious and different to everything else was the SIZE of the SOHC intake port. As for our exhaust ports and the engineers responsible for that design, insert choice 4 letter words here.

So even if I could get the intake ports to the size of the DOHC head, I thought that whatever power I gained in the top end would come at such a severe penalty in the low and midrange that it wasn’t even worth trying. I had to know if there was any way I could get back some of this midrange power I anticipated losing. There wasn’t much I could do on the exhaust side since header design was and for the most part still is a very debatable and inexact science on these motors, something suited for someone with an engine dyno that could make quick and easy changes to primary length, collectors, megaphones, reverse cones blah blah blah. I decided to focus on the intake manifold. I read everywhere, long runners are good for low end and short runners are good for the top. But what is too long and what is too short. There’s a popular formula out there, it uses estimations of numbers like “Estimated Valve Closed Duration” and “Pressure Wave Speed” and “Reflective Value”. In my opinion these are all crazy guesstimations. Is that valve closed duration calculated at the cam lobe or the valve. Most likely at the valve, but nobody could make that clear, because the two numbers can differ by more than 30 degrees. So maybe I could have figured that part out, but then you “choose” which reflective value you want to use based on the pressure wave speed. Well what’s your pressure wave speed. How about pick a number between 400 and 1250 ft/sec. AYFKM? I had to take a more practical approach to get my answer so I did this. http://forums.neons.org/viewtopic.php?f=8&t=294784

That’s all I needed to know, my midrange wouldn’t be gone forever. So in anticipation, I built Morpheus.

http://forums.neons.org/viewtopic.php?f=8&t=349003

The call went out to crower, this manifold just looked like it meant business. I wanted a huge cam for it, something bigger than anything out there for the SOHC head.

With the manifold taken care of I was ready to tackle the head. The call from crower came in, after reviewing my specs they decided they were going to be able to make that cam for me after all. It was on. This head was gonna have to flow like Victoria Falls. Since I used the stock DOHC intake manifold gasket as a template on the manifold I obviously had to do the same on the head. Thing is, on the head, the stock SOHC intake port is about 37mm wide. It’s 46mm wide on the DOHC. I had a long way to go. I had made the ports on Morpheus 46mm wide at the narrowest point. Knowing I couldn’t get the ports on the manifold to line up exactly with the head if I ported them to the same size I had to open up the ports on the head a little more to make sure I didn’t have all that rushing air in the manifold coming up against a wall when it hit a step because the ports were mismatched. Practicing on a spare head I was able to open up the ports on the head to 48mm. Don’t ask me how close that comes to the water jacket because I didn’t try going any more than that, that was gonna be more than enough width so that’s where I stopped. This port was huge, bigger than what I thought was even possible, bigger than a stock DOHC port. This was beyond any race porting I had ever seen. This was superporting.

I had been driving around with an untouched head on the car for months. I wanted to see what the porting would do without any exhaust port modifying so since it’s easy enough to port the intake side with the head on the car I opened up the ports right there. I was thinking of opening up the ports by 4 or 5mm at a time then driving it for a week so before more porting, but the head I used for the runner length tuning was at about 42mm or so and that worked well, so I just decided to open it up to the full 48mm.

With Morpheus bolted up I got on the road with my laptop for some tuning. As I expected, I wasn’t gonna get good drivability without some seriously patient tuning, but with all that taken care of I had no complaint of midrange power loss. As happens on any manifold with a huge throttle body, going WOT with ITB’s below 3000rpm or so got me nowhere in a rush. Once at 4000rpm it was a different story. I had all the power I wanted, more so than with any setup I had ever built. Not being a big fan of the butt dyno I looked at how the tune on my VE table had changed over the other ITB manifold (Mufasa) I had. Morpheus was commanding more fuel below 5500rpm, and about the same up to about 6500. This wasn’t working out so bad. The setup would be my daily driver for the next months while I superported another head, but this time reworking the exhaust ports too.

I don’t have any examples to compare the stock SOHC exhaust port to. There’s nothing out there quite as bad, it’s just such an incredibly poor design a monkey could draft up a superior design with chalk on a driveway. When I look at those ports I have to consciously control my gag reflex, like when someone hands you a beer in the middle of a bad hangover. Who’s the design manager that saw those humps and signed off on them sending this head into super mass production. “You’ll lose massive amounts of torque if you remove it” say the masses. I wasn’t buying it for a second. The fact that it’s been reduced to half its size on the more powerful magnum head was more than just a hint that they were rectifying a major design flaw. The size of the port, the shape, the volume, it’s all off. So I’ve changed it all. I spend more time modifying 1 exhaust port than I do all intake ports. In this port I believe is where all the magic happens.

Once I got this fully superported head done and strapped it on the car it was a night and day difference. There was no loss of midrange power and on the top end I found myself having trouble controlling my Air/Fuel ratio above 7300rpm. Datalogging would show that the stock injectors were approaching 100% duty cycle. This would be my new daily driver for the next 4 months until Morpheus’ throttle shaft snapped. In the mean time, impressed with the results, I decided to go for broke and superported Mufasa, the other ITB manifold. So the runners were much shorter, I figured I ‘d just build another manifold if it didn’t work. Best decision I ever made. With Mufasa on the head, the air/fuel ratio was now completely uncontrollable beyond 7000rpm. If it’s even possible, datalogs showed the injectors going up to 117% duty cycle. I’d be holding steady at about 12.7:1 AFR then within a second be at 16:1. Not something I expected with the crane #14. With completely maxed out injectors, in my mind I wasn’t gonna wait to get on the dyno to convince myself I did something right.
Damas y caballeros, I present to you the superported SOHC cylinder head.


This is with a stock DOHC intake gasket on a port from each head for the sake of comparison



The port itself




Intake manifold side with the same gasket


Problem with the manifold’s runners is that they are only 45-46mm wide on the outside where they meet the flange, so my porting it out to 46mm meant that I cut all the way through every runner






The new and improved








Surprised I even had this picture. I’m not as well versed on combustion chamber theory as I would like to be so I left the CC’s mostly untouched, save for minor exhaust valve unshrouding and a light polish.




After sweeping the floor around the desk I ported on





The before and after. In blue is the best I dynoed with the setup that did the runner length tuning and in red is after superporting. Crane #14, Mufasa, Fast Fabs header. Same compression ratio (~10.5:1), same cam and ignition timing.




These are my best numbers with the two cams. Two heads, both superported. One head shaved .070” to give me a 38cc combustion chamber, 12.5:1 compression ratio just like that.
Blue: Mufasa, Crane #14, 10.5:1
Red: Mufasa, Crane #5, 12.5:1


Yeah Boy!


So there you have it. As of writing this I still don’t have that crazy crower cam running right but I figure I’ve finally got the flow to take on cams bigger than the crane #5. What I’m most excited about though is thinking that we can finally have serious discussions about 2.4 SOHC’s. Don’t get me wrong, revving up to 9000 rpm knowing and feeling you’re still making power up there is exhilarating beyond words for me, but the extra 50ft/lb+ of torque offered by a stout 2.4 setup makes it seem almost pointless to go crazy on a 2.0 since it can be done for pretty much the same money. Plus you get all that power some 800 rpm sooner. It just makes sense.

But that’s in the future, for now you gotta check out what these heads did with other stuff on the dyno. This is the Intake Manifold Shootout, 6 superported manifolds and a gasket matched stock manifold.
DOHC What!!

http://forums.neons.org/viewtopic.php?f=8&t=349006