GT-40 HP gains

pythontaco said:

Probably like 20-30 go. I've heard of as much as 50 though. Things is you need more than just heads new upper lower intake maf and tb.

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I am not completely familiar with the minor differences in the sn95 5.0's, but I wanted to clarify a few things;

The heads will work with your stock intake manifold, "if" you plan on retaining your stock intake manifold.

the Explorer, Cobra, and GT40 intake manifolds will not have the "elbow" the sn95's have on the upper intake manifold (which places the TB further out). However, I know a few aftermarket vendors offer just the elbow so you can use pretty much any EFI intake manifold on your combo.

The Explorer intake manifold has a 65mm TB, you might need to go with an aftermarket TB to work with the throttle cable linages on your sn95, but if you want to go with a bigger TB, the opening in the upper intake manifold will need to be ported to accept it (for instance a 70mm).

To really get the full benefit of the GT40 or GT40P's, I would suggest getting them ported from a reputable vendor. You'll also need to upgrade the springs (as most will point out). At that point, the loaded set of heads, after porting and machine work/assembly, will push the "budget minded" idea of this swap.

You'll also want to port the lower intake manifold (regardless of retaining your stock manifold or going GT40).

A cam is the "heart" of the package, get a decent grind, not something mild.

I have a stock AOD trans notch, with f303 cam, full valvetrain, ported GT40's and ported Explorer manifold, along with shorties, and a 70mm TB, 76mm MAF. I have retained the STOCK cat's along with the full belt driven components and stock airbox. So this is a true H/C/I swap going from stock to GT40, I hear stock 5.0's put down about 170rwhp (with the AOD), I saw 221rwhp (in 106 degree AZ heat, and 4,500ft DA). So that's a true 30-50rwhp gain.

Manual trans mustangs, with off-road pipes, AC delete, air pump delete, electric fans, will put down 270-290rwhp. (with similar cam)