Originally Posted by 71fj40guy
So I am pulling my heads to send them out for a 3 angle valve job and I need recomendations on what is the best, longest lasting head gasket I should get. This is a stock 290hp gm performance crate motor with cast iron heads, a 4.00 inch bore and 0.028 inch compressed thickness.
I've been reading that I should look at MLS style gaskets.
Do I need to stick with a 4.00 inch bore gasket or can I get one thats a little larger so my choice of brand/style is better (if I can go a little larger then how much is too much)?
X2 for both F-BIRD'88's and cdminter59's comments.
The 290 horse crate engine has a serious miss-match between the camshaft and the heads. A lot of cam duration with a late closing intake valve against low (really low) compression ratio. These leaves a lot of power and a lot of fuel economy on the table.
A set of L31 Vortec heads makes this a 330 horse motor with no other changes. Certainly milling the heads you have say .030 inch and using a Fel Pro rubber coated .015 shim gasket part number Q1094 will help some by bringing the CR up. This doesn't bring the better combustion chamber, spark plug location and porting of the L31 so it isn't going to gain anywhere as much with just increasing compression with the heads you have, but it will be noticeable.
This engine doesn't need fancy head gaskets like MLS or copper. These are things for very high compresion ratios and/or the use of aluminum heads where the gasket needs to deal with being sandwiched between metals of quite different thermal expansion ratios.
The stock bore gasket like the mentioned FelPro use a 4.1 inch bore, this is plenty. You're walking a line where you don't want the compressed gasket hanging an edge into the chamber, nor do you want a large space that increases chamber size thus reducing compression ratio and traps a lot burnt gases that contaminate the fresh charge with unburnable fumes.
The rubber coated shim will work just fine as long as the mating block and head decks are flat, clean and undamaged, and you take care to chase the female head bolt threads in the block and clean the bolts themselves. Assembly requires a sealant that prevents coolant from getting into the threads, it will corrode them and leak coolant along the bolt shanks into what ever cavity the bolt passes. The bolts also require a lubricant on the threads and under their heads to get proper torque readings which are essential to getting even clamping forces on the head that don't cause it to warp resulting in the head gasket leaking. The answer here to both needs is found at the home improvement center as plumber's pipe thread sealant with Teflon. This stuff doped on the bolt threads and I like to paste it into the female threads of the block so the entering bolt pushes the sealant/lubricant ahead of it such that the bottom of the bolt is sealed against the coolant even getting a little way up the threads. The Teflon sealant also has about the same lubricity as engine oil that is specified for torque values of the factory head bolts (aftermarket bolts like ARP use a different alloy in the bolts that require a proprietary sealant and lubricant thus they use torque values differnt from the OEM bolts) DO NOT CONFUSE THIS. Factory OEM or OEM replacement bolts get Teflon Plumbers Sealant, speciality bolts like ARP get that manufacture's recommended most likely propietary sealant/lubricant. Getting this wrong most certainly will result in at least leakage and at most damaged to even destoryed castings.
You don't need to worry about plumber's Teflon thread sealant being pushed into the cooling jackets, unlike other curing compounds this stuff will remain soft and the action of the water pump will beat it into a fine suspension with the coolant so it will not plug cooling passages, unlike RTV.