I used the stock replacement fel-pro pan style...1 piece design. It still had plenty of room for me to port the intake runners on the intake and gained a bunch of power. Its much better to go with the stock replacement, small runner, and then match it up to the biggest side...intake manifold or cylinder head...if its protruding into the runner, then you can trim it to perfect size with an exacto knife. Its better than the air stream hitting a sudden expansion...(even if its only 1/16" thick) and then going into a tumble. That hurts flow almost as bad as a protruding gasket. Its a good idea to pop the intake off and replace the intake gasket..get rid of that crap stamped steel **** if you have it and use something that can actually seal under boost, on an engine with less than perfect blueprinting (all the angles have to be dead nuts perfect for it to seal, and if you have to use sealant around the ports for it to seal, then its not right and the sealant will just blow out under pressure or vacuum.) Then you can be totally sure you have no vacuum leaks or incorrectly diagnosed blown head gasket issues....like when a coolant passage leaks to the lifter valley or vice versa, or the EGR pockets (6 of them) are leaking oil into the exhaust ports and you're blowing smoke or consuming oil...with this engine, bad intake sealing can cause a slew of problems and mis-diagnosis. Plus when the intake is off you can also look around at the head gasket edge and see if they've blown out into the lifter valley, and you can see if the backs of the intake valves are covered with carbon. .100 thick of carbon is like chopping .100 lift off your cam...it kills performance. With all new hoses and sensors and everything set right, it still didnt seem right or idle right. After I pulled the intake and replaced the gaskets with a fel-pro pan style gasket and ported the intake while I was at it, the improvement in power and driveability was amazing. So many people ignore the intake manifold which is too bad. They think the lumpety lump idle is from the cam when its from vacuum leaks that cant be found and therefore, dont exist...until you change the gasket and realize how messed up it was. I gained 3 inches of vacuum at idle and dropped 2 psi, which is alot of air, and I only went 2" into the runners and took them out to the gasket line. Plus the coolant consumption and steam coming out of the exhaust was gone...everyone said I had a blown head gasket. Nope. Plus a friend was consuming oil on his new motor and everyone was saying turbo or bad head gasket. I suggested that since he used the steel shim intake gasket, that oil from the galley was leaking into the EGR pockets and into the exhaust stream. Didnt seem likely, but the swap to a fel-pro fixed that. A layer of rubber isnt going to seal against 25psi ontop of all that area. If it needs silicone, its not right!
