I think one thing that people are over looking are the LSx cars. Most of these cars are closing in on the 240 duration numbers and are still in the 10s! Now, I know that the intake on the LSx cars are a much better design compared to the 5.0 guys, but those are some large duration numbers for a 15" runner.

 

I read 13"?? (haven't seen anything official) with a good deal of runner taper... that makes for a shorter effective runner length. Either way, the LS1 isn't needing alot of rpm to make good numbers with the smaller cams... it has a great cylinder head. There are 230-ish cammed cars running in the 10's without much trouble.
I don't feel that 240 is as much duration as some would like to think. I'm running a mid 240 duration cam in my 383. Idles well enough and I've turned a couple of high 9-second passes. Runners are about 4" long although I was told, "6 inches with a gradual taper would be ideal". The 4" LT4 runners (spacer underneath) have almost no taper to speak of but they seem to be working ok for me.

-Mindgame

 

A friend's FoxBody is a 351W that runs 126mph with a Performer RPM intake, 248/252 @.050 , roughly .590 lift @3350 pounds. The car isn't loud inside, the AC blows ice cold at idle, and the factory vacuum brakes work perfect with no canister. The heads only flowed 255cfm, the compression is a tad over 11:1 and it runs on 93 unleaded.

Kinda sounds mismatched, but the thing hauls with a best of 10.9 on a 1.6x 60' and he can drive it anywhere with the TKO 5speed with OD and 4.11 rear gears.

The RPM intake had some of the divider removed for future N20 use, but it picked up 2mph over a Victor Jr.

Another buddy picked up 2 tenths and 2mph from the Victor Jr. to the Performer RPM in the low 11's with his 420ci SBC powered Vega.

Just my useless $.02

 

I'm saying 11.5-12" on a LS1 but the cross sectional is BIG. Then again so is the head.

Yeah a 220-230 cam in a LS1 stock bottom end is pretty dam good if you don't want to turn RPM with it. Which on a stock bottom keeping it below 6,800 is a great idea.

A LS1 almost always has very aggressive camshafts in terms of ramp and .200 duration vs. .050 duration. They also have a pretty light valve and a big base circle and cam journal.

The problem that I see with LS1's is the DCR vs. P to V clearance. You can't mill the heads, or put too much valve in them, or run too much cam so you are pretty dam stuck with a stock bottom if you don't want to flycut the bastards. Then again a built bottom with some compression and cam can REALLY sing with the heads and runner length of a LS1.

Hot Rod has a nice test of the LS1 vs. the GMPP LS1 single plane, and you can see how extra runner length makes hp, even though it flows like dump.

Bret