Is it normal for the upper intake (plastic) to swell when I rev engine to approx. 3000 rpms.

 

no it's not supposed to "swell". I don't even know how it could swell.

Please explain what it is doing in more detail and I'll try to help you more.

 

I replaced the lower intake manifold do to some sludge on my radiator cap. I found a leak in front where the silicone seal's between the manifold and top of block. I installed a new upper manifold as well (plastic), replaced the spider injectors and pump, she has never run this good in a long while. I can now run 87 octane fuel and have no pinging. It has 220k on it. Last time I could run that fuel is when it had 90k on it. Thats when i had my 100k tune up done alittle earlier by dealer, ever since then I always had to run 91 octane in it to prevent pinging. After my repairs i did my testing, service engine light went out, no leaks, when i was reving engine to approx. 3000 rpms i would watch where the injector connection is and it swell in size, rise up approx. 1/8''. Still running strong. Just concerned, you think it would contrac and not expand?

 

I would think there would be a vacuum in the manifold. Are you sure it's not the whole engine moving on the motor mounts? Still not sure how the intake would "swell".