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07-21-2003
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Rare Opel hi-po cylinder head comparison
Just thought some of you might like to see a unique comparison of two Opel cylinder heads. On the right is a fully ported 2.2 Opel head. To the left is a very rare Group 2 racing head, in completely stock 'as cast' form. I have not yet tried to optimize the Group 2 head, due to its' rarity, but once I make some resin castings of the ports which I can modify for flowbench use, I'll be tricking the head out. Look carefully at it, I only know of three of them in the USA!
I'm going to be writing an in-depth article for the Opel Motorsport Club's newsletter, comparing the various factory CIH Opel heads, from 1.5 to 2.4 litres. So over the next few weeks, I'll be compiling all the data I have on stock airflow specs, combustion chamber volumes, and photos of all the various heads, plus the performance potential of each head.
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My Flickr photos. 'Bei dem Kerl ist Genie und Wahnsinn auch nah beieinander. Alles würde ich dem nicht nachmachen, aber er bringt einen auf neue Ideen/Sichtweisen' ...that's the nicest thing anyone has said about me all year  Jan. 3, 1984 - Jan. 3, 2009, that's 25 years of this damn Opelitis! C.R.L. 9/22/69 - 12/8/99 J.M.L. 3/3/43 - 6/15/04 Last edited by RallyBob; 07-22-2003 at 05:23 PM. |
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07-21-2003
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Here's the combustion chamber of the modified 2.2 head. It has been slightly unshrouded for improved airflow, and has been machined to fit 1.94" intake and 1.625" exhaust valves. Stock valves on the 2.2 are 1.77" intake and 1.57" exhaust. Airflow has been improved 21% (intake port) over that of a stock 2.2 head. Intake port airflow is a whopping 66% more than a stock 1.9 head's intake port.
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07-21-2003
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This is the stock combustion chamber of the Group 2 head. Those of you who are familiar with a 340 Chrysler engine will note that the chamber is very similar to that engine's, commonly called a 'semi-hemi' chamber.
To homologate this head for use on a 2.0 litre engine, the head was factory machined for OEM Opel 2.0 valves. Note the large 'edge' at the bowl/seat area to accomodate the small valves. For racing use, larger valves are used and the edge is machined away, improving airflow dramatically. |
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07-21-2003
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Bob |
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07-22-2003
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Define 'later large valve head'....?
If you mean a 2.2 or 2.4 head, yes they are both newer, and have larger valves. I have one of the 2.2 heads depicted in my photos above, albeit modified. The intake ports are approximately 5/8" higher than a 1.9's, therefore intake manifolds cannot be swapped. If you compare the photo to that of a 1.9 head, you can clearly see the ports are higher. Bob |
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07-22-2003
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my definition is a 2.0 to 2.4 ltr head
but anyway thanks bob what i was going to say to try and do to make some more power opel did at the factory so it is irrelevant also for my own knowledge should i buy a 2.0 head or can i use my 1.9 head for my turbocharged engine plans? which would be better
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-JOSH- |
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07-22-2003
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Bob |
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07-22-2003
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So yes, you can modify a 1.9 intake to fit, but it requires redrilling the dowel holes in the proper location and size, and welding flanges at the bottom of the intake to support it and allow the bolts to hold the flange correctly to the head. Not a big deal, I've modified them for years. But it's not a direct bolt-up. Bob |
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07-22-2003
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well i was making an observation
i plan on using duel side draft weber intake manifolds and jenvey low profile throttle bodies so i would probably use a 2.0 head because the manifolds are easier to come by
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-JOSH- |
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07-22-2003
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i meant 2.2 head on the last post
hey bob on a side note who makes high quality engine bearing for opels of all the components those are what im lacking in info
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-JOSH- |
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07-23-2003
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Bob could you put smaller valves in a 2.2 Head?
reason i ask is the 510 can use any head that will bolt up in GP class maybe we could ask for the same thing in FP or GT4 since the heads are no longer made Davegt27 |
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07-23-2003
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 In a nutshell, I will also use AE bearings (also from England). Glyco is another brand (German) which is very good, but they're often VERY expensive, 3-4 times the cost sometimes. Bob |
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07-23-2003
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But I digress. You could put a little bit smaller valve into the 2.2 head, say 1.70" intakes and 1.50" exhausts, if you put seats into the head. But then you'd have a lip at the port/seat interface and would kill airflow. And the 2.2 head is crappy on the exhaust side as it is (only 77 cfm, a 1.9 head would smoke it with the same sized valves). I think a 2.2 head on a GT4 engine would work well if we could use 45 mm throttle bodies. Don't think the rule makers would like it one bit however, we already have the biggest engine. They'd want to stick us in GT3, or add weight. I think more could be had by developing cams specific to the Opel head. But that entails a ton of computer simulation and real world dyno testing with lots of cams ($$$$$). I know from the testing I did it gets real expensive REAL fast. If my friend didn't own a dyno, I'd have been doomed. Just the box of jets and the cam swaps for a weekend of testing cost me $2000. Bob |
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07-23-2003
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I'll go out on a limb here and hopefully not hang myself... As you cannot use roller cams in GT4 your stuck with 'standard' cams. Your limitation here is acceleration of the valvetrain(lifters, rockers, valves and retainers) right? Is there not room to take lightening of the valvetrain to the next level to allow more aggressive ramps? With Ferreas new gun drilled valves, some custom(hollow) lifters and removal of some of the weight from Bobs roller rockers, I'd think there to be room to remove considerable weight. While Bobs rockers are a pretty good design and admitedly most of the weight is near the fulcrum(lower polar moment of inertia) I can still see room for improvement. FEA is also now within reach of racers with even a modest budget. Just don't go crazy, only spring for it where it's going to count.....Bob and Bob, how far have you all gone to remove weight(beyond the norm)? Also, Bob L, you had mentioned in the past an idea of using a larger diameter lifter to help allow faster ramps on the cams? It's not immediately obvious to me how this helps. Care to share? -Travis |
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07-23-2003
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Travis, I'm talking about custom designed patterns specifically for the flow characteristics and valvetrain design. So yes, this would include lightening components and matching spring rates to cam profiles.
But as you know, this kind of development gets expensive fast. I can't see myself dumping 10 G's into cam and valvetrain development at this point of my life. I have no aspirations of winning any National championships (I'm in it for the fun of it), and I'm not in the business of selling parts anymore. Therefore, the payback to me would be non-existent. I don't mind experimenting, but pushing the R & D threshhold usually requires finding the limits...and breaking parts. Too much money for me! Profiles shapes are critical. I've seen large differences in power from one brand of cam to another, even with similar 'numbers' such as lift, duration @ .050", and advertised duration. It has to do with the opening and closing ramps and critical lift area 'under the curve'. A larger lifter diameter will allow for more aggressive ramps without the lifter edge 'digging' into the side of the cam lobe. Fords use a larger lifter diameter, and at one time had a significant advantage over Chevys in NASCAR. So NASCAR allowed Chevy to use the larger lifters, which they all do now. Chevy also uses big block Chevy cam bearings, which are bigger than the small block's. A bigger bearing allows bigger cam lobes, again, easier on the valvetrain, therefore more aggressive lobes can be used. Based on this, you could use a billet steel Opel cam, enlarge the head for bigger cam bearings (even needle roller bearings), and bore/hone the head for bigger lifters. You could also use the ceramic-metallic lifters some are using now....a few Opel owners have even had custom ones made. They are so hard, they don't wear at all....you can swap them from lobe to lobe, and run ridiculous spring pressures. They're also $600 a set. Now you'd have a mega-buck cam/lifter setup but no development time. More $$$$$. Bob |
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07-23-2003
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first off i have been pondering the possibility of using a modified head for a different engine which might have a similar bore and bore spacing an aluminum head would be a must as well as a crossflow ohc design
the is a guy Pete Aardema that has been doing swaps like this for years he just had a short article written about him in hot rod mag i am thinking a head for a dohc caddy north star engine might be close which would be sweet but i dont have or have yet to find engine blueprints for the cih engines so if you could help me find some bob please let me know
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-JOSH- |
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07-23-2003
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07-23-2003
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Bob |
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07-24-2003
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I did the vast majority of the valve train work during the development of our F-Production head. Now it is only a matter of merging that to bigger valves... "only merging" is a relative term. many $$$$, a lot of time, and several "booms" went into developing the F-Production engine and cam package. Keep in mind, truly competitive National F-Production cars are faster than GT-4s
So, having learned from F-Production, I built my first "new" GT-4 head this spring. It was really fast... set a lap record... but the springs were a "tad" too soft for the bigger valves. The computer simulation said it was good, but in practice... when the springs softened after one race Mr. Valve(s) met Mr. Piston(s). For cam development, it is exactly as Rally Bob says. Flow head --> model head dynamic flow and velocity characteristics --> 100's of simulation and "monte carlo" runs ---> Grind new masters, grind new cams, test it out and see what happens. Change cam ---> change valve springs and find out on the track if Mr. Valve stays away from Mr. Piston. Engine goes BOOM and you start over. This is how it went on the F-Production engine... but now it pulls most GT-4 engines... with stock size valves and 40mm (32mm Venturi) carbs. Engine development is not for the timid nor light of wallet. |
