The High Heat product failed exactly where I want it to fail, in the middle of the epoxy.  It also handled 60 lbs. (231 psi) but only for 14 minutes.  Note that you can’t see any part of the nuts, you can only see epoxy.  The bond was stronger than the epoxy material.

Based on the results of my tests, I decided to use the JB Wed High Heat product for my intake port modifications.  Not only does it appear to have better adhesion, the fact that it’s a putty rather than a paste makes it much easier to apply and form into the shape you want inside the port.  It’s in my head right now, and it’s runnin good.  I have 94 miles on the epoxy mod and all seems well.  I pulled the carb and manifold off to get a look at how the epoxy is holding up.  Here’s how it looked after 94 miles.

I know that 94 miles isn't much of a test but I figured it was prudent to make sure it wasn't falling apart before something ugly happened.  It looks good to me.

Aside from some discoloration, it looks solid.  I will probably do another inspection around 500 miles.  I’ll let you know the results.

For now, filling in the Dipsy-Doodle (DD) in the exhaust port will be on hold.  Flow tests showed decent improvements when the DD was filled in, but If I can’t come up with a suitable filler, I will never find out how well it works in the real world.

I have looked at some literature on a couple of possibilities.  Blue Magic 8024 Thermo Steel is billed as “suitable for aluminum application”.  There’s another product, Pyro Putty 2400.  Do any of you have any experience with either of these products?

Manley used to sell a product called 40180 Miracle Epoxy.  It was intended for exhaust ports.  I called Manley to inquire about it and the rep said they discontinued it.  I imagine because it can’t hack the heat.  I can find some venders that say they have the 40180, but when I try to order I always get “out-of-stock”.  Any of you have any experience with this Manley product?

If any of you have experience (good or bad) with filling in exhaust ports with some sort of ceramic paste or possibly even epoxy, please let us all know the specifics.

I hope some of you find this information useful.  My stage II head with epoxy modified intake port feels really good.  I am hoping to get it on a dyno soon, then I will have some hard data.

Knowledge is power.

Mike

Stirring creates tiny bubbles
Maybe spreading it thin on your mixing pallet and let it exhale, stick your palm sander in a vise and hold your pallet on it, shake the crap outta the epoxy, and of course, using anything from bondo to JB Weld, the first swipe has to wet the surface by pressing the adhesive tight into the surface.
A vacuum would be a great idea.
I've used compressors from dead refrigerators, and they are good enough to pull the A.C. system down on the car.
I've used a retired breathing treatment nebulizer to bleed brakes,
Be creative,,
I tapped into the vacuum on the bike to suck a storage bag down to make some clothes smaller to fit in my saddlebags..

Armen, thanks for the info regarding the Bultaco epoxy job.  It's always reassuring to get input based on personal experience.  Sounds like your Taco was major fast and the JB Weld held up good.  

Versy & JOG, the epoxy product did not have a porosity issue.  It's a two-part epoxy and it had ample strength and adhesion.  I used it in the intake port and it is holding up well.  The product with low strength and major pososity is a water base paste.  It's strange stuff.  I'm thinkin if I subjected it to a vacuum it might not cure.  I guess it's possible that if I pulled enough vacuum it would cause the water to flash off.  Not sure how it would set up like that.

The interesting thing about the gas holes and porosity is that it didn't seem to develop those issues until I cooked it.  When I initially applied the Extreme Heat paste and let it cure for several days, I blended it into the substrate with a die grinder and porting roll.  Although it exhibited a sand-like porosity (sort of like sandstone), it didn't have craters and gas holes.  The big craters and gas holes don't seem to show up until I cook it.