glad you asked as I was going to be posting some updates soon because...back, seats, back, alright!
more on the back seat later (i haven't had on in there for a long time)
the exhaust thingy (i was reading your exhaust modification RJB510 with excitement then disappointment at the outcome, oh well bigger muffler?) the exhaust thingy didn't really work as i planned. i had it right in front of the rear muffler. maybe not ideal. and i switched the vacuum on and off with an old lego pneumatics switch i had from an 80's set as i drove along.
low response driveability didn't really improve from seat of the pants feel unless i really dialed in a lot of closure on the butterfly but then it would open very quick under only slightly more engine load which wasn't ideal in mimicking a smaller exhaust. also when it was very closed like that the engine felt very restricted and it just felt bad for the engine even if i was just poodling along.
although on freeway driving the droning lessend quite a bit even if the butterfly was only set at a half closed position.
I could maybe have tinkered with it to delay the opening event or have the thing open another pipe to the muffler or something but didn't get inspired with the initial results to warrant more cutting welding and laying under my car getting a stiff neck. so off it came.
but i did at least finish off a fine 2 1/4" straight through system in mild steel this time not SS which i don't like the sound of. very happy with the home built exhaust and i do think its allowed some more HP through compared to the silly little 2" center pipe and then 2/14 press bent mangled looking thing i had before.
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will post up a few more updates soon.
sorry for all the lower case i's in the post.