As I posted in another thread, I installed EFI exhaust manifolds on my 67 F100. I put a Walker Y-pipe on it and will run a single 2.5" exhaust on a Smithy glasspack. I could tell by the seat of my pants that I have more power, but how much? I installed the Edelbrock 1v intake which Edelbrock had claimed to increase torque by 10-15# and 8-20 hp gains. From the factory, my engine was suppose to be rated around 170 hp and 260 ft lbs of torque. It has been rebuilt prior to me buying it. Oh ya, it has a rebuilt Autolite 1100/1101 single barrel carb and a Duraspark II with HEI module.

I'm just looking for an estimate on the Torque and HP gains made by going to the EFI Exhaust manifolds with a single 2.5" glasspack and no Cat. Regardless, it sure feels fun!

 

First thing to consider is that those HP ratings are prior to '71 when they changed from gross to net horsepower ratings. You're probably more so looking at about 120hp and 260 tq. stock. (Ratings on the carb'd 300 engine throughout most its run).

The EFI engine is rated at 145hp and 265tq.

Considering that you now have the same exhaust as that engine (maybe even a bit more free flowing), I would imagine it's somewhere between the two ratings. You're obviously not going to have the efficiency and power of computer controlled fuel injection, but that exhaust setup makes a huge difference. I remember when I first put them on mine and still had the 1bbl. It felt like a new truck. Actual numbers are hard to say without putting it on a dyno.