They are to provide superior sealing. Yes to helping aluminum heads and intakes seal. The silicone beads help seal. Any of the thicker composite intake gaskets can be a tight fit if heads are milled or intakes are slightly warped as many aftermarket ones are. The crossover is usually blocked as most aftermarket performance heads don't have a crossover. Yes, it will eventually burn through, unless it has a steel core, which most don't have.
If you get on the Edelbrock website and you look at your intake manifold and look at the installation instructions, they'll tell you what Fel-Pro gasket to use as an alternative from there gasket set to be used for your Edelbrock branded intake manifold.
For example my intake manifold is in Edelbrock Performer EPS...
The instructions say if I don't use the Edelbrock intake manifold gaskets, the FEL-PRO alternatives are #1256 and #1205... However it states that 1205 is only used if you have an aluminum set of heads...so I bought the 1256...
My only issue with these is that they have the restrictive block plates for the exhaust port cross member, rather than full blocked...
My issue with that is I have a non-emissions engine and from what I read and hear online, the use of the exhaust port cross member ports is basically for emissions use only and I could be losing performance power and gas mileage versus blocking them off completely.
Here is a 1205...
You mentioned that with the 1205 not having a steel core would eventually burn through if I blocked the exhaust ports with just them...which is guaranteed to happen in my opinion.
One thing about the FEL-PRO PrintOSeal gaskets, is that they usually have two types, the original type like what you see with the 1256 and 1205 pictured, and they have a steel core version in the same version as the original PrintOSeal but only with a steel core center sandwiched between two gaskets... And they have the same part numbers as the originals but they have an "S3" at the end of the original part number, and they're 0.05" thicker ...
Here is the 1205S3 steel core gasket set...
I wanted to test that, he said he used it and they're holding up for him but he's not saying how long he's been using them I wanted to try these so bad but I'm in no financial position to be playing with money right now, so I went ahead and bought what would recommended in the instructions for my intake... You think if I call FEL-PRO, that they'll recommend that ? lol...
But if my engine is not emission setup, what are my cons for using the ones that I bought with the restrictive plates vs full blocked plates on my exhaust heat crossover ports ?
BONUS QUESTION: With a non emissions setup, should I even be running a PVC ? Probably so since it's a daily driver huh ?