Side By Side Cylinder Head Comparisons/ RallyBob's Performance Suggestions

[Gary]

Here is a side-by-side comparison of the Opel 1.9 and 1.5 combustion chambers.

[RallyBob]

Hmmm, maybe once I've got the digital camera thing figured out, there's a possibility of creating a "library" of sorts to identify the various heads. Unfortunately, most of the ones I have are already modified, so this defeats the intent of identifying cyl head types easily. But with all the various Opel owners out there, we could perhaps photograph and label the vast selection of heads. 1.5, 1.6, 1.6s, 1.7, 1.9, 1.9h, 2.0, 2.0E, 2.2, 2.4, 2.0 group 1, 2.0 group 2, etc.

Speaking of cyl heads, is there much difference between the 70 and 73 head design, other than solid/hydraulic lifters? I have a spare 73 and I've not taken both motors apart to see where they changed the design to drop compression, combustion chamber or piston design.

[Gary]

There are several differences. The biggest one being the '73 head has 2 extra bolts that go into the timing cover. There may also be a difference in the number of cam bearings (3 vs 4) and the valve seats.

[RallyBob]

There are a few differences worth noting.

*The 1973 head will have 2 extra bolt holes at the very front (as Gary mentioned). These bolts are not extra head bolts, but rather they're intended to reduce oil leaks at the timing cover (the timing cover is also redesigned). They're socket cap-screw bolts, 8mm x 1.25 pitch.
*In conjunction with the added bolts, the head utilizes a longer camshaft thrust button (plastic bolt at the nose of the cam).
*Cylinder head is a slightly thinner casting, ports have less "meat" for material removal, if desired.
*1973 head has 4 cam bearings and hydraulic camshaft. Hydraulic cams have slightly higher valve lift than solid cams, but less duration.
*1973 head is cast from a different iron alloy than the earlier heads. The exhaust seats are induction hardened (flame hardened). They are very brittle as a result, and the later heads are VERY prone to cracking.
*Combustion chamber volume is the same as the early head, the compression difference is a result of a piston change. Early pistons are flat-top with two valve reliefs, the later pistons have a larger dished area to reduce total chamber volume, and therefore compression.

Thanks for all the info guys, I'll probably stick with my original head and just have hard seats put in. I'm about to order some 11:1 forged pistons and soon a cam. Any suggestions on other upgrades or where to get some parts? If there is no other source I'll probably get the cam from OGTS, along with lifters, but the cost is pretty substantial there. I'll do my own head work... clean up the combustion chambers and ports, have a header ordered already, just waiting for it to show, and once I get the gaskets I'll port my intake manifold (spare) to match them. Have a Weber carb with the mini k&n filter already as well. I plan to have the flywheel lightened up a few lbs and drilled for an s-10 clutch.

Are there any differences in the blocks between the 70 and 73? If there is any advantage to one I'd definitely like to know before I start in on one and figure out it was not the better choice.

[RallyBob]

A suggestion....you should be cautious about running that kind of compression unless you have a really aggressive camshaft to go with it. I'd say in the neighborhood of 240 to 250 degrees @ .050". Otherwise detonation will rear its ugly head in a big way. You'll also need to re-curve the distributor...no more than 36 degrees total, and no vacuum advance. Probably 15 to 20 degrees of initial (idle) timing depending on cam choice, the bigger the cam the more initial timing you'll need.
Personally, I'd rather run 9:0 compression and go for better airflow from the head...in the form of bigger valves and professional porting, you'll make far more power than you will with stock valves and high compression. Also beware of what you do to the head if you port it yourself, and refrain from porting the exhaust ports (at all). They flow VERY well, and Opels make more power from increases in intake airflow.
I'm not speaking as a backyard mechanic, I have done professional headwork on Opel heads for 15 years, and have the flowbench and dyno results to back me up. Just don't want to see you spend your money in the wrong places! :)

I can get the valves enlarged at the shop I take everything to, I was thinking of it, but wanted to look at the combustion chambers to see if and how much it would be advantageous to go out, a friend of my dad's put larger valves in one of his heads and actually dropped his flow on the bench because the valve was too close to the side of the chamber. He had to grind away a bowl next to it until it had enough clearance to flow well and try to match the shape on the rest of the chambers.

The cam I was planning on buying is the 300 degree cam, I think that is seat to seat rather than 050, but I'm not sure.

Any thoughts on which block to use? 70 or 73... I'd rather keep my 70 block as a spare in case I throw a rod I don't ruin my numbers matching block.

I'll polish the exhaust, and port the intake, do you know about how much material is safe? I have access to a flow bench to check my progress, but I don't want to risk punching a hole through the runner.

[RallyBob]

Shrouding is definitely an issue with the 1.9 Opel head. You need to unshroud the inlet valve area if the valves are enlarged. Exhaust is not as sensitive to this.

Either block is fine to use, but the later block *might* have the weaker cast steel rods. They're slightly larger, and heavier, but far weaker. The 1970 block would have forged rods. With new rod bolts, they're good for 8000+rpms.

Regarding the porting work. I can't get into too much detail without pictures, but essentially you can polish the exhaust ports, and trim the exhaust guides about 3/16 shorter, and blend the bowls. Leave it at that, it will outflow a small-block Chevy already. The intake side is trickier, and easy to make flow WORSE than stock if you're careless. The safest way is to blend the bowl areas, keeping a venturi shape, don't let it intersect the valve seat area at a 90 degree angle. You can also grind most of the intake valve guide down in the port. A safe way to visualize this is imagine carving it down until the guide area looks just like the hood bubble on a GT....with a hole in it. Also, keep away from the divider area between the intake ports...no reason to remove any material here, it will divert the airflow incorrectly into the combustion chamber. Leave the intake port floor alone as well. Remove about .100 from the roof, and about .075 from the *outer* wall of the intake ports (opposite the divider area). This is by no means an extreme example of porting, but it is a safe bet. The ports vary in thickness over the years, but the thinnest I've seen them is .220, the thickest .260 (I've cut a lot of heads in half for inspection)

With this type of intake port work, and a 1.72 intake valve, you should see an improvement of around 26% in terms of airflow, and a better intake-to-exhaust proportion. The improved proportion will lower exhaust temps, reduce the chance of detonation, and require a leaner air/fuel mixture, besides making more power.

So you would recommend a 172 intake, how bout exhaust, 1.50? or is that too much?
What readily available valves do you use? Or are they a custom valve? If I can use like a SBC or similar valve that would be great.
I'm trying to learn as much about these motors as I can, the Internet sources I've looked at don't really go as in depth as I want to get.

Thanks

Dan

[RallyBob]

Well, yes and no. I feel a 1.72 valve is a safer bet. I personally prefer to use a 1.84 or 1.85 valve. The problem is, the larger the intake valve on a 1.9 head, the more know-how you need in order to make it work well. If the combustion chamber is unshrouded, as mentioned previously, the 1.84 valve flows better. But, an oddity with the 1.9 head is that it flows worse at higher valve lift. It doesn't just max-out at a particular flow number, it gets worse, and the resulting turbulence will KILL power. A 1.72 valve hits peak flow at about .475 lift. A 1.84 valve hits peak at .440 to .450 lift. Any higher lift and you go slower...I **** you not. I mean, you have to take into account valve lash and all that, but you get the idea.

There are ways to eliminate the turbulence and get higher flow at high lift, but it took me about 3 years on a flowbench to figure it out. And the porting is critical, it is all too easy to mess it up. Besides, unless you're running twin 48 Weber sidedrafts, you'd never notice the difference. A stock intake and 32/36 Weber will limit you to 140-145 hp no matter what cam and head you use.

If you are keeping the lift moderate, go for the 1.84 intake valves and 1.5 exhaust valves. Use standard length small block Chevy valves. Pontiac 400 valve springs (1.440 dia.) and Chevy chromoly or titanium retainers, with + .080 to + .100 installed height.

Do you have any spare ported heads you are willing to part with, or would you be willing to do the work? If so what would you want to do this? You know a lot about the workings of the opel heads and are the most qualified I know of, nobody in town wants to work on it.

[RallyBob]

I don't have any spares I'm willing to part with, pretty much everything I have has been assigned a purpose. Although I DO admit I have more cylinder heads than I have cars, I just have different engines for different race classes and applications.

I actually just officially closed my Opel business two weeks ago, but haven't done the head work for about three years for customers. I closed my fabrication/race shop about that time, and ran the parts company for a few more years, but my real job and my desire to play with race cars for myself again made me decide to close everything up for good.

I only have three customers now who I will do engine and suspension work for, and only because I engineered their cars to begin with, and I feel I owe it to them to keep them running. They are also long-time friends. That, plus it doesn't hurt that they pay me very well, which was never an issue when I was in business for myself! But I can certainly offer advice if you need it.

[RallyBob]

Dan, I finally got my digital camera figured out, and took a picture of a 1.9 head with 1.85/1.50 Chevy valves in it. As you can see, without unshrouding the chamber (yet), the intake valve gets VERY close the the edge of the chamber, which hurts airflow drastically.

Bob

Those things are huge. I'd like to see how far out you go with your shrouding. I've still not pulled apart my good 1.9 l, have the 73 engine all torn down though. some strange things built into these motors.

[RallyBob]

I'm going to port the head one night this week...I'll take photo documentation as I go. So if you have any specific questions, maybe I can post a photo that answers your questions.


Bob

A question about the old and new heads:
The early heads seem to have 3 mounting screws for the thermostat housing, whereas the later heads have 2. Did this change happen at the same time as the 10/12 bolt change? Can early thermostat housings be put on later heads and visa versa?
Thomas

Well, yes and no . . . respectively. On the later heads, the right front corner is where one of the "extra" two head bolts drop down to thread into the timing cover, exactly where on the older heads the third (furthest front) thermostat housing bolt hole is located. In other words, Opel had to "lose" the front thermostat bolt to add the extra head bolts at the front. Hence the two-bolt housing. Have never seen anyone use a early thermostat housing on a later head, or vice-versa, and probably for good reason . . . Mark

Bob,
-What length Chevy valves do you use, and do you have any problems with adjusting valve lash?
-Does a 1.5 head respond better or worse to the larger valves than a 1.9?
-Do I need to install hardened valve seats when I modify the heads for larger valves?
-I always thought the 75 head with hardened seats, better cooling passages, and stainless valves was one of the best cheap heads, but it it really any better?
Do you have any similar tricks for a 1.1 litre head?
Thanks
Stephen

[RallyBob]

Bob, What length Chevy valves do you use, and do you have any problems with adjusting valve lash?

*****Standard length. Because of the variable rocker arm geometry of the Opel (sliding tip), a longer valve will reduce valve lift, so in this case going to a longer valve will reduce performance and cause erratic wear. Valve lash is adjusted the same, no problems.

-Does a 1.5 head respond better or worse to the larger valves than a 1.9?

*****The ports are virtually identical, but the 1.5 has smaller valves than the 1.9. So proportionately, the 1.5 should improve more. However, nothing is ever that easy I'm afraid. The 1.5 head will require more unshrouding when larger valves are used due to the smaller chambers. Ultimately, the 1.5 head will not flow as much air as the 1.9 head because of this fact, all other factors being equal.

-Do I need to install hardened valve seats when I modify the heads for larger valves?

*****I highly recommend this for the exhaust seats.

-I always thought the 75 head with hardened seats, better cooling passages, and stainless valves was one of the best cheap heads, but it it really any better?

*****The 1975 head has flame-hardened seats. They are not press-in inserts. Because of this, and the material used for the head casting, this head is horrible, they crack VERY badly. The coolant passages are no better in this head, and the valve sizes are the same size and material, although there is some dispute about the larger intake valves (1.65) being installed on some 1975 heads. I've never seen any, but others have. It was probably a mid-year change if this is the case.

Do you have any similar tricks for a 1.1 litre head? Thanks Stephen

*****I did some light research on the 1.1, but never pursued it. Not enough interest to warrant a full-blown performance evaluation IMO. And the stock 3-bearing crank is really the limiting factor anyway for power. But, I did discover that you could use valves from the European 1.6 litre OHC engine in the 1.1 head. They're larger in diameter, but the stem diameter and length is the same as the 1.1 head.

With a stock cam, how would street drivability be with such a large valve change on the 1.1?

[RallyBob]

Large valves alone usually don't affect drive-ability. In fact every head I've done with large valves, regardless of make, has improved drive-ability/torque. The porting work that accompanies the larger valves is usually to blame when drive-ability suffers. Keep the ports moderate in size, or increase compression at the same time to improve vacuum/draw into the system, and you will lose nothing. Modest increase in other areas (exhaust diameter, intake manifold porting), will typically enhance overall drive-ability.

But changing one area of the engine only, and making too radical a change, will almost always make the engine *unhappy* is some respect. Many people do this, then blame the modification. Too big a cam in a stock engine, too big an exhaust on a stock engine, too much compression. Engines like to be modified with symmetry in mind. Make smaller changes to multiple areas to retain balance, and the engine will respond accordingly.