Exhaust I.D. for Max Torq. on 134 F-head

Good morning fella's! I built the header on my 134 f-head. I then ran 2 inch tube with .120 wall from the header to a Thrush muffler (Not The Cherry BomB)... My exhaust pipe Inner Dia. is 1.75 inches. I pulled a intake off of a 1996 ford ranger and fabbed it to the carb. Now she can breath well, it really helped me and it revs faster. On the flip side, I think I lost some low end torque due to lack of back pressure.

My question to you all is:

What Inner Diameter of the exhaust pipe would restrict the flow enough to get me the back pressure I need to gain back that torque? I plan on machining a ring and tack welding it in the exhaust, I think this should work?

There has to be a couple 134 motor gear heads on here...

Thanks for any help fella's!
Pottsy

 

Supertrapp!! this is a motorcycle muffler from the early 80's but they have since designed larger ones for automotive use, they are expensive but are very very good at tuning your engines powerband for a specific purpose.

 

longer collector smaller pipe