Originally Posted by F-BIRD'88
Build for 91 octane reliably you want a true 9.5:1 or alittle less. Use GM 350 5.7" connecting rods. use ARP rod bolts. A few of the rod bolt heads will contact the cam lobes. You have to grind the rod bolt head edge to allow .030" clearance minimum on a few of the rod bolts when using GM 5.7" rods with a 400 crank. The machine shop can take are of this for you or you can do it yourself. Requires mocking up the block, crank, rods, pistons and camshaft. I usually borrow a big race roller cam (260+ dur@.050) to do the rod bolt clearancing so that any street sized cam that the motor will see in the future, will fit with out rod bolt head interferience.
Use Keith Black Hyper KB -168+.030 22cc D dished pistons. You must set the top ring end gap large. .032" is not too large for this type piston.
it is just right for this hyper piston and mild N20.
With a non decked 400 block and felpro .039" 400 gasket your cr will be 9..30:1... with a cleanup cut on the block (.005") your cr will be 9.4:1. I would not go higher.
The above mentioned Comp XE274H10 will work well with a Performer RPM manifold.
The heads must be drilled for the extra 400 steam holes.
The Stock GM 400 cast crank is plenty strong.
The bottom end assembley must be rebalanced.
Are your TFS heads the 23deg heads or the "Twisted Wedge Heads"?
I would be very careful with timing using that cam with this build. The Comp XE series is designed to build a cylinder pressure and Comp is revising their recommendations for them because of that (they work almost too well). Also, the KB pistons require less total timing (around 30 degrees). I would recommend a cam with a little more duration at .050" lift and decking the block to optimise quench. This build will probably end up costing more than you think (they always do).