Currently have: -K&N air filter 14” x 2” maybe a bit more if measured base to cover. -Holley Street Avenger Carb 770 CFM -Edelbrock Performer Buick 455 Intake -‘70 455 Block .030 Over -‘71 Heads Hardened Valve Seats -TA 290-94H Cam -TA Stage 1 Shorty Headers 1-7/8” x 3” -2-1/2” H-pipe -2-1/2” MagnaFlows -2-1/2” Tailpipes I was thinking of getting a taller air filter or the flow through the top lid type to let more air in. Also, a full 3” exhaust system - shorties to tailpipes.
Loose the K&N air filter and run a quality paper element air filter. The K&N filters are full of holes that let dirt in. Take yours off and hold it up to the sun while looking thru the pleats. Now do the same to a Quality paper element.
I can tell when I swap the stock air cleaner with a 3" tall filter for an open 4" filter. Worth a whirl. You might have to try a few to find one that works with your carb and hood. Check out a drop-base filter housing and go up from that.
If the Street Avenger is a vacuum secondary, I'd change it for a Q-Jet set up for your combo, or a mechanical (double pumper) secondary Holley. The vacuum secondary Holleys open the secondaries WAAAAAAAY to slow
You would find more power by running 3" tube to your H pipe , the outlet side is fine with 2.5" . If you do that mod and have the money , a X pipe in and of itself with a 455 cid motor is worth 5 more hp up at 5000 rpm. A V8 motor built like yours is rather insensitive to primary header length even to the tune of a 6" difference in tube lenght, but not so to collect lenght and area!
My research showed that a 3" muffler flows the same as 2.5 pipe. Not a lot of gain to be had for the amount of money for new exhaust.
http://www.v8buick.com/index.php?threads/stock-air-cleaner-better-flowing-air-filter.318530/ Hey, at least it gets your attention! Also, some good data there on air flow.
https://www.ecklerscorvette.com/corvette-air-cleaner-base-1965-1972.html Might look into something like this. Not sure it will fit your holley but it can make room for a taller filter element.
the old " put a double pumper on it" most vac secondary carbs are smarter than your right foot, "open to slow?" the motor knows what it needs, and the secondary's open AS NEEDED. if you open all 4 barrels at low rpm, the velocity slows, and atomization decreases, and HP decreases! yea, the noise is louder, (if thats what you want) race cars ( where the throttle is open wide ALL THE TIME, do benefit from mech secondary's. but your street car doesn't. years back a guy named Waddell Wilson did some extensive testing on our dyno, same motor, just changing carbs, was vac vs mech secondary's, mid range torque was noticeably more with vac, as carb opening was optimum . max hp was identical as all carbs flowed the same, at WOT. does he need more cfm on his motor, depends on how much time is spent at wide open throttle. and is he seeking the max hp, ( at max rpm)
Thanks for all the info everyone. Me coming from Fox body Mustangs, I know alota folks, including myself were running 1-3/4" long tubes to 3" collectors, 3" mid-pipe, and 3" mufflers. This was only with naturally aspirated small block 347" HCI'd strokers. My car made 410 RWHP and I know another that did 466 RWHP running 10's. That's why I was thinking to myself, hmmm this is a 455" BB, shouldn't this exhaust be bigger??
While I do agree a 770 avenger wouldn't be my first choice of carb, I don't think your handicapping yourself much. Remember, these big block Buicks got their reputation with the hearty low end torque they make, so your not gonna spin them as high as a small block brand x engine. Also the science of back pressure plays into that.
