head gasket bore size

[1974dodgecharger]

So my edelbrock head gaskets bore size is 4.505'' with .038'' thickness and I bought some cometics and the bore size is bigger at 4.560 and I wanted a thicker gasket to decrease the ratio a tad so they are .051''.

Will that bore size increase on the gasket be an issue?  My piston bore is 4.280, but heck the edelbrock gasket is bigger than piston bore already 

[b5blue]

I "think" all head gaskets are made to allow for overbore.

[Challenger340]

The larger gasket bore sizes are not an issue on the smaller Bore engines as long as patent sealing surfaces are present, at least not that I've heard about ?

Cometic recommend sub 50Ra finish numbers on both Block & Heads for use of their Gaskets, although many report just slapping them on old surfaces with no problems(unknown for how long though ?)

FelPro "composition" style gaskets are far more forgiving of surface imperfections and poorer surface finishes for sealing applied on 40 year old Blocks, especially after cleaning during R & R.
The std Fel-pro #1009 measures .039" thickness compressed and on a 4.460" Bore for 9.9 CC's
with,
the Big Bore Fel-pro #1105 measures .051" thickness compressed, and on a 4.590" Bore for 13.7 CC's

My point being;
IMO, far too much emphasis has been placed on "MLS" gaskets as the best Head gasket choice when mating Aluminum Heads on a "cast"  Block to account for the difference in expansion rates.
In my experience, just putting the cart ahead of the donkey... especially since the same Gasket Rec takes NO ACCOUNT of the MLS Head gaskets requirement for finer Ra and surface finishes(all manufacturers), usually NOT present in R & R jobs or older builds.

Again IMO,
If you are going to squirt a ton of Nitrous or Boost through an AL Head/Cast Block combo ?... by all means spend for the Cometics, and get your Block & Heads surfaced accordingly for best results to sealing.
However,
if this is an R & R job on old or used AL Head & cast Block surfaces, NO Nitrous or Boost running N/A ? My best choice is the composition style Fel-Pro's, and I have NEVER heard of a problem in 30 years.

[1974dodgecharger]

good info Challenger340.....

as you know I will run boost through it I decided on these cometic pairs because I found a cheap set at 130 bucks vs 190 bucks person had a old set sealed in package he never used since 2012 build he tried.

if the block is in the car still can it be, 'surfaced' and smooth out with fine sandpaper?

If I cant resurface the block should I use some, 'sealant' even though cometics say its not needed?

[Challenger340]

Nope, don't try sand paper on a Block still in the car, you will probably do more harm than good !
and,
Nope again on the sealant, as the Cometics already have a coating designed to seal/bond under heat to the mating surface, hence why they want the fine Ra finish for best adhesion/grab.

MLS work like this.... 3 layers, consisting of 2 "thin" outer layers over the 1 center "thick" spacer. The idea being each outer layer "bonds" to the respective Head or Block... allowing each to expand at different rates under heat, ie: the Aluminum Head and the Cast iron Block, which each allowed to then slide slightly against the center spacer.
Again, a better system for extremely long term use where literally millions of thermal cycles in Block/Heads of dissimilar expansion rates are expected, and why manufacturers switched to using them originally on Cast Block 4 bangers with Aluminum Heads with emissions mandates to push peak ignition temps above 2400* F to combat Oxides of Nitrogen(brown smog), with BIG disparities in expansion because of those temps.

Lots of people report using the Cometics/MLS on old surfaces with no problems....
That said,
I don't do it..... and we recommend just the composition FelPro 1009 or 1105 when mating a "used" surface on either the Block or Head(especially 40 year old stock surface Blocks) as far more forgiving, even with a shot of steroids.

[1974dodgecharger]

ahhhh....man alright Challenger340....no turning back now guess I will try to clean the block surface and heads as much as possible and work the cometics then.....don't want to put them to waste.