Chevy Impala SS Forum banner

1 - 8 of 8 Posts

·
Registered
Joined
·
1,557 Posts
Discussion Starter · #1 ·
i know a lot of people say go grade 8 but whats the thread and length size?
 

·
Registered
Joined
·
581 Posts
3/8"x16 thread pitch and 1.5" long for the bolts used with spacers(rear 2 and forward 2 on each side) and 3/8"x16 1 3/16 long (though a 1 1/4" long bolt should be fine) for the other 2 on each side, though one of them is a stud on the passenger side for the alternator bracket. Look at ARP's header bolts they are either ARP's stainless steel(which is as strong or stronger than grade 8) or their own ARP steel alloy which is much stronger than grade 8 as well. Because you are going to use them with manifolds look at their 5 pack of bolts as they are available with a larger flange surface than header bolts do, if you go with ARP's bolts. If you go with hardware store grade 8 bolts then get the black oxide grade 8 flange bolts. The spacers are reusable so you can just put them back on instead of buying new ones, and maybe wire wheel them to take surface rust off, but that's up to you as they will just rust up again. Took that information off of the Caprice parts manual. - Peter
 

·
Registered
Joined
·
8,571 Posts
A pic to go with Peter's description.
 

Attachments

·
Registered
Joined
·
581 Posts
Though I am a bit curious, why exactly are the spacers needed? I say this as headers do not require them. I have always known they have been there, just never knew what exactly they are for. - Peter
 

·
Super Moderator
Joined
·
8,898 Posts
They allow for thermal expansion of the outer ends of the manifold. They also allow those outer bolts to be longer and it helps spread out the stress along the longer bolt shank as well.

These threads are also good reads:
thread 1
thread 2
thread 3
 

·
Registered
Joined
·
8,571 Posts
Joel,

Yep, as Yogi said, It's Deja' Vu -- all over again. ;)
 

·
Registered
Joined
·
100 Posts
So, do we have to use those exact spacers or just something like washers to space out the bolts?

Also, why is cutting the crossbars significant? I'm guessing it helps reduce warpage that breaks bolts?

Is this what is everyone doing? Cutting on the red lines?



*EDIT*
Nevermind, found my answer explained very clearly:

- Take your chances w/ removing the spacers and cut the bottommost brace on the factory manifold. Although initially intended to lend structural support to the manifold, it's been demonstrated that the brace also impairs the ability of the manifold to expand and contract front to rear causing subsequent manifold warpage, cracking or breaking of bolts. Even if using the factory spacers, cutting the brace has shown no deleterious effects and could be argued to be preventative insurance.
 
1 - 8 of 8 Posts
Top