Sal, I think Ford took care of the humps…

Here's a couple thoughts:

1.) I've never seen a ridge at the top of a cylinder in an EFI engine.  Just because you can see cross hatch doesn't mean the bores are fine.  I've never seen an EFI engine where I couldn't still see cross hatch, even engines that had zero compression in a cylinder due to bad rings.  There seems a real tendency to try and skirt taking a block to the machine shop.  Honestly, worst case you need a new set of pistons.  Having a block bored and honed around here costs about $200-$350.  Ring seal is the single most important thing in an engine.  Any engine with significant mileage on it is going to have bores that are no longer round or straight regardless what the surface of them looks like.  The block moves around from thermocycling.  This is just what happens to cast iron.  I knew guys years ago who used to put the blocks of their future race engines in a tow rig for 100k miles before building the block into a race engine.  The block took a set being used like that and then was stable for the machining, creating a much better ring seal.  I'm a big fan of doing something right, and doing it once.  Fresh bores are a known quantity.  Used ones are not.  Just my $0.02.

2.) Ditto the heads.  A lot of GT40 and GT40P heads are cracked.  You won't be able to see the cracks with the naked eye most of the time.  Take the heads to the machine shop and get them Magnafluxed.  If they are crack free do the minor port work 6Sally6 suggests (do not touch the port floors in those heads, and don't try to change the shape of the ports, just blend and smooth), install new seals and springs to match the cam.

3.) Roller rockers are definitely worth power, as you are removing the second greatest friction point in the engine after the rings.  Now, you are talking like 10HP, not 100HP.  You are tied to pedestal rockers without a lot of expensive machine work (not worth it IMO).  Stay with a stock 1.6:1 ratio.  If you want a bit more cam, just get a bigger cam instead of changing rocker ratios. 
 

Last edited by TKOPerformance (4/12/2022 4:33 AM)

One more thing on the heads: in the ports the two areas where you should spend most of the time are the throat (just behind the valve head) and the short side radius.  Just blend the throat into the back of the valve seat.  Often there is a step there that creates a big disruption to smooth flow.  The short side radius is typically the roughest section of casting in the port, so again, just make it smooth.  The GT40 and GT40Ps don't respond well to hogging out the ports.  Where the shine is low lift flow.  If you start trying to make the ports bigger you will ruin the low lift flow. 

Last edited by TKOPerformance (4/12/2022 4:39 AM)