86 brat with a fresh 32/36 Weber (manual choke). Exhaust modifications?

[Zosojojo]

    1st: So, my Subaru brethren, I have installed a new 32/36 Weber (with intake conversion plate) on my 86 brat (ea81, hydraulic lifters, a reputable smog tech told me it is a federal emission, high altitude model). On the Weber, there are two inlets, one for fuel and the other (I assume) for vacuum advance. This second inlet/outlet is located near the bottom of the carburetor. I directed a vacuum line from the distributor to that second inlet, bypassing one of the many thermovaccum valves. It runs great, but I would like confirmation on if that is the correct setup. I have also modified the throttle pedal so that it has the travel distance to activate the secondary.

   

    2nd; My main concern; Judging by the sound it made at full throttle, I have a suspicion that the stock exhaust limits the additional air/fuel mixture created by the new setup. I believe that the stock exhaust was causing too much back pressure. I felt a great power gain until about 5/8 throttle (after I knew the secondary kicked in); after that, there was no difference. Also the sound was congested. I felt like I was driving a Honda with one of those bad exhausts. In my panic, I put a lot of effort into straight pipping the system. I realize that, the way I put it together, the system produces no back pressure. This is what I have done; I rented a tail pipe cutter from a locate parts store, and cut the "y" pipped catalytic converter to maintain the header connection and 90 degree angle. I then used various adapters and exhaust clamps to fasten two cherry bombs to those headers. From each head there is about a foot of 1,7/8" pipe then two feet of cheap cherry bomb As it is, it is a duel cherry bombs pointed at the ground. The exhaust output is located in the middle of the vehicle. I am a back alley mechanic with no professional training. I realize that the series of metal pipes under an automobile is designed and mass produced for a reason. I want to understand this system to maximize the investment of the Weber. I am willing to make a custom exhaust that produces maximum efficiency at about 2800-3500 rpm (modern day highway speed in 4th gear). I want a system that has power if I need it (/WANT IT =P) but also economy. What this post boils down to is this; Would a modified exhaust give me this desired outcome or would the stock exhaust (catalytic converter 'n' all) achieve this performance? 

 

As always, Thank you for your attention, I wish to hear from you soon!

Edited May 24, 2017 by Zosojojo

[DaveT]

Going by what I've read on here, from members with more experience tweaking engines than I, you could get a small gain by building an exhaust with pipe a size or 2 bigger than stock, keeping more or less to the factory plumbing arrangement.

 

The major limiting factor on the EA81 and 82 engines is the porting in the heads and the valves. And if you try to modify that stuff, it's big money and or time and little gain.

 

A noticeable gain can be had by fitting the spfi system from an ea82 onto an ea81. I don't recall how that compared to a weber though.