Alright here we go again: My 360 is alot of off teh back shelf used parts but it started out with a used Performer when I built it. It was there on hand and the price was right. After running like this a year of so I came across a used LD4B and made a swap. can't remember off hand the numbers but it was almost unbeleivable to me for such a simple thing. Used this 3 or 4 years and then tried a friends LD340. There was a slight increase but not near what there was going from the Performer to the LD4B OR what you would expect from such a port difference in sizing. Like I said there was some what of an increase but it was minimal.
The LD4B plenum height, and size and the runner size is all very close to the LD340 till the ports get down to where they meet the heads. The runners are also reversed.