It will definitely change the torque value, though by how much I an't say.  Most factory fasteners torque values are stated using 30 weight oil on the threads. 

I would go to studs and nuts if you're having an issue.  You can use Nylock nuts if the issue persists. 

I wouldn't use anti seize on intake bolts, light engine oil or thread sealer depending on engine and where the bolts thread into. When I would install intakes I would torque them in sequence in incrementing torque values until you reached the final value you want. For example if the final torque is 45 ft/lbs, I would do one round at 15/20 then 35 then 45 and recheck them all atleast twice more at 45. By the time you get through a whole sequence the ones you started on will be loose due to the gasket compressing. That's why I do them multiple times.

I use ARP stainless bolts with antiseize on intakes bolted to aluminum heads. I have not experienced loosening.  I always torque the head bolts at least three times at the final value.
Seems the thing to do is retorque them if they loosen.

rpm wrote:

Thanks Steve, at least I know I'm not doing it wrong. Suppose I should've check them during the Bash trip knowing they had loosened after the first 500 miles. I did make a mental note, but I lost the note. I had so many things on my mind thrashing and driving during its maiden voyage, the intake bolts kinda slipped my mind.

Thanks again everyone.

Coulda been worser, Bob.  I know a guy that had his upper control arms try to fall off.  FWIW, I have AFR heads with the stock intake and have had to re-tighten the manifold bolts twice now after a proper three-round torque sequence.  Nature of the beast, I think.

BB

BB

Gotta agree on lock washers.  Totally bogus.  Fastener stretch is what keeps a fastener torqued, not a spring under the bolt head.  On a nut and bolt connection if you're that worried about it loosening spend the extra couple cents and buy Nylock nuts or all metal locknuts for high heat applications where there's concern about the Nylon softening or melting out. 

Finally, when in doubt there's always safety wire.  Race cars use it, they got it from the aviation industry.  On the AT6 I restored with my neighbor all critical fasteners were safety wired.  The stuff to do it used to be kind of spendy, but its come down in price a lot in recent years.  All you need is a jig to drill bolt heads/nuts, safety wire pliers, and a spool of stainless safety wire.  Then you just spend a little time thinking about where the wire goes so it doesn't allow them to loosen.  It can't be that hard; I was doing it when I was 12. 

I've used "locking" header bolts before and this is what I found: don't install the locks at first.  Run the engine and heat cycle everything, retorque them, THEN install the locks.  I can't say on this specific design, but on the Stage 8 header bolts they absolutely do work, if you follow the aforementioned. 

Bob, I was a great Christmas and New Year. Hope the same for you as well. I didn’t realize lock washers were taboo. I will have to look into that.
 
Two things caught my attention in the post.

rpm wrote:

Before I change bolts or go to studs I'm going to put some witness marks on the bolt heads and intake and keep any eye on them.

At each re-torque, there was at least 1/8th of a turn of rotation.

 
Are you sure there is a problem here?? From the comment on witness marks, I assume the bolts have never been loose enough to be turned with your fingers.  Is the movement during re-torques the main proof of loosening?? At 20 ft lb, you’re not talking about a lot of force.
 
What’s the chance the bolt is moving in reaction to the sensitivity or lack thereof for a small torque value compared to the overall range of the torque wrench? Not sure that make sense or not, it’s hard to type what I’m thinking!!