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I've read different things about porting and some said to not match the sizes of the openings like you would on a typical V8.
Gasket matching on an Opel is not a good idea, and will be detrimental to performance. The gaskets are much larger than the port sizes, and even on a full race head the gasket sizes are far larger than the ports need to be.

I would definitely enlarge the header flange entries, but of course you need to be careful not to break thru the tubing where it meets the flange, or make it overly thin there. Re-welding *might* be necessary.
 

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Detonation

I would look to individual cylinder tempetures (coolant flow or air pockets) also individual Air fuel and ignition, is that cylinder slightly advanced or slightly leaner than the rest?
Lastly this points to a coincidence that leads to whether or not that fancy corresponding bump in the combustion chamber is really doing anything. Perhaps it is providing a sharp angle of metal to act as a glow plug and preigniting the mixture!

I really doubt that the weld in the exhaust header was the root cause!:no:
 

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Looks like that cylinder ran lean, for whatever reason. I'd double check the carb connections/gaskets/fuel passages/venturis, etc.

Running twin DCOE's help narrow the problem easier than a single downdraft, since you have one barrel feeding each cylinder. You don't have the normal fuel distribution issues you get with a stock intake.
 

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Discussion Starter · #125 ·
I've been taking notes on this and I'll try to deal with all of this this time around.

I never heard detonation. While a Bonneville run is just a straight line it keeps you busy monitoring the gauges and paying attention to every noise. In three runs I never heard any pinging or knocking. The plug looks like a classic pre-detonation failure.

The dual Webers are great but like Bob said, A/F is not averaged across all cylinders so one cylinder can get severely shorted on fuel.

Then there is the possibility of vacuum leaks. I did check for this when I installed them and everything seemed fine, but that doesn't mean they can't turn up later.

I've been wondering if I shouldn't check the cam timing for all 4 cylinders, on the off chance that the timing for #4 is different.

I'll be checking the combustion ratio for all four cylinders this time.

Also, this -- 4-Channel EGT Digital Pyrometer Gauge + Probe Kit - Gas Race Series EP

It should be helpful during tuning and driving.

The head will get a good cleaning and I'll smooth out any rough spots in there. I've never done it, but I think the valves will need to be lapped again.

The block will get a proper cleaning this time, too. This is LeMons, but it's so much work and missing a race really sucks, so a little extra money will need to be spent.

Costs will include a gasket set, head gasket, and shop costs for tanking the parts. I can borrow tools to hone the cylinders. So far, not bad, but we mustn't forget pistons. OGTS has 2.0 L flat tops. I've never purchased pistons before so I need to read up a bit on this. Like, will they work with our connecting rods. Do I need to check their weights? And so on.

One thing my Honda has that I wish I could fab up for the Opel are oil squirters. Splashing a little oil on the bottom of the pistons sounds like a great way to get a little more cooling where it needs to be.

Thanks all for the comments.
 

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I never heard detonation.
I'm not saying you had any detonation, but chances are if you did, you wouldn't hear it anyway at a venue like Bonneville.

OGTS has 2.0 L flat tops. I've never purchased pistons before so I need to read up a bit on this. Like, will they work with our connecting rods. Do I need to check their weights?
They won't work. One, they're cast instead of forged and are much weaker. Two, they are a true 95 mm (3.74"), while the Americanized 2.0 litres are all 3.75" (95.25 mm). And then the pin end of the rods has already been bored oversize to either .912" (Ford) or to .927" (Chevy) diameters, and won't work with the Opel .906" pin diameter.

One thing my Honda has that I wish I could fab up for the Opel are oil squirters. Splashing a little oil on the bottom of the pistons sounds like a great way to get a little more cooling where it needs
You know those holes in the sides of the Opel rods? Those spray the piston undersides.
 

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Discussion Starter · #127 ·
They won't work. One, they're cast instead of forged and are much weaker. Two, they are a true 95 mm (3.74"), while the Americanized 2.0 litres are all 3.75" (95.25 mm). And then the pin end of the rods has already been bored oversize to either .912" (Ford) or to .927" (Chevy) diameters, and won't work with the Opel .906" pin diameter.
Well, dang.

I'll make some measurements when I get them out.

I recall you saying that you sold these pistons to Ford Cook. Can you recommend a source for replacements, or do I need to cast and forge my own? ;)

Failing that, we'll go back to using one of out 1.9L motors.
 

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Well, dang.

I'll make some measurements when I get them out.

I recall you saying that you sold these pistons to Ford Cook. Can you recommend a source for replacements, or do I need to cast and forge my own? ;)

Failing that, we'll go back to using one of out 1.9L motors.
They're made by Venolia. You can buy more. I only would need to know the pin diameter that's in there, and I could look up the job number, and you can order them yourself.
 
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