sidepipes killing power

[dav65mus]

Hi guys, I would think I could get an informative answer here about the sidepipes on my classic roadsters austin healey sebring. I know these must have been custom built for the car since I have never seen another one with these... they are a 1 5/8" tri -y design that slip fits to a glasspacked sidepipe. The problem is the glasspack inside the sidepipes is only 1 3/4" i.d. !!
The car was originally built in 1986 and has a stock hydraulic flat tappet stock iron headed late 70's 302 in it. The only mod is a low rise edelbrock performer 289 intake and holley universal 600 vac. sec carb. It is a 4 speed car and has a 3.0 trac loc 8 inch rearend in it. Since the car is all mustang II based it is the mustang II 4 speed trans (RAD trans ?)

I would like to put a fresh motor in the car and go 331 or 347 but I am afraid I may be my wasting money with the 1 3/4" i.d. sidepipes. From googling about sidepipes I found a site that showed max h.p. for different size pipes and with dual 1 3/4" max power supported was about 210 h.p. which is probably about what my stock motor makes now. The motor runs fine, burns a nice tan color on all 8 plugs.... it is just not making much power to make the car really fun.

I have thought of several other options such as going to a t5z and 3.80 gears to make this motor feel peppier or just adding some afr 165 or tfs 170 heads to the shortblock along with linkbar lifters and a small hyd roller cam, but I have had a nice 331 in a 65 mustang and I know how much tq. that 1/4" extra stroke makes!

I love the sidepipe look and sound (makes my healey kind of like a poor man's cobra) so removing them is not an option. I would appreciate any suggestions or comments on what you might do. Thanks in advance.

Dave