Opel hi-po cylinder head comparison

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.

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.

For clarity:

A 1.9 head, showing the lower intake port locations compared to a 2.2 or 2.4 head.

davegt27 said:

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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Well, it's currently not legal to use the 2.2 head in any SCCA racing, as the head never came on any US vehicles. I still think the head is not the problem, but rather the induction restrictions. A big-port head won't help if we have to use smaller valves and small carbs and venturis.

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

RallyBob said:

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 ($$$$$).

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By developing cams are you refering to simulation to help select between off the shelf lobes or custom masters?

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

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