Originally Posted by Burns331
What years of intech heads will work/be most benificial.
Are the manifolds on the 4v heads the same as the stock PI heads?
What pistons should i look at?
How far can the mod block be bored? .060?
Any other suggestions?
The heads should be from 99-04. Ford *May* have used the generic "03 C-head" found in the cobra/mach1/aviator/maurauder in the 03-04 navi.
Earlier heads are referred to as big port navis in the mustang world.
The "03" c-head is a better NA head.
Dohc headers/exhaust manifolds are different from 2v headers.
Dohc intake manifolds are also different. You'll also need a navigator timing cover. The COP's will have to be changed and/or the polarity has to be reversed or something to that effect. Check for Mustang GT writeups swaping to 4v's for those aspects of the swap.
10:1 CR will cost you, as you'll need a custom piston. A flattop 4.6 piston in a 5.4 will give you 9.6:1. A custom piston will be ~$800 more.
.030 over is usually considered the limit. Every now and then someone does one .040 or .060 over. Personally I would go .020 over. Early 5.4 iron blocks had some issues with having "voids" around the bores leading to failures in hi-po applications. The newer NVH block may have taken care of that, but I can't say.
IMO the Navi intake is junk, it's fine for what it is, but trying to make a hi-po engine out of it is a waste. I'd look for a Boss intake from Oz (ebay), it's for a dohc 5.4 but uses the smaller ports of the generic c-head.
Boss intake, c-heads, FGT cams with forged internals and you're looking at around ~ 330rwhp 370rw tq through a mustang manual tranny. Less with a heavier auto truck tranny/and 4wd. That combo would be you're best bang for the buck. You could improve on the numbers a bit with porting etc, or going with Cobra R stuff but that's going to double or triple the price tag.