Matt is right, long stacks = lower RPM power, and short stacks = higher RPM power.
So if your cam/ motor combo is higher power at high RPM you'll run better with short stacks.
It's no secret that SBC's will make more power the higher you rev it, but in order to run higher RPM's you need a better lower-end and better valve train. So your questions should be what RPM should I shift at and what RPM thru the lights.
Now my guess is you don't have a 10,000 RPM Chevy, because if the tubing you just bought is 2.5" ID, then your Hilborns are no bigger the 2.5" . Most of the 10,000 RPM Jr fuel engines are using 2 7/8" injectors unless they are racing the 14° heads and are JrFuel"A" class that the rules allow 3 1/8" injectors, where a couple of teams are running 10,500 to 11,000.
My JrFuel "B" SBC 9700 to 9800 RPM is running as short a stack as we can get to fit on the injectors.
One of the JrFuel "C" teams running at around 9,000 RPM is running 4" or 5" stacks, on 2 3/4" Hilborn's. You could call Don Enriquez at Hilborn, that's what he runs.
So you need to find-out what RPM your engine is making the best power, and set-up your stacks, torque converter,shift points, and rear gears/ tires size to LET your engine run in the best RPM range. You'll have to dyno your engine if you can't find out what you need from your cam guy or engine builder.
A tuning tip about stacks is if it turns out you want 8" stacks, and you are racing a track that has a crappy start line, put your short stacks on because they will kill some of your torque/ bottom end power so you can get off the line.
Here is a picture of my 2 7/8" Hilborns, but now I run angled Kinslers with sort stacks, I can post pictures of them too, but I figure you'd like to see my Hilborn's.
Good Luck with your combo
Jon
