I don't think it's as simple as "larger scoop=better performance". For one, there's the argument about larger scoop blocking airflow to the radiator. But also, the size and the shape of the RPi scoop are already optimal, based on testing by RPi. Bigger scoops, or scoops of different shapes will certainly create worse airflows, resulting in losses of power.

 

Some time have too much air going in is not a good thing.

 

+1000 The problem is that the engine produces peak HP when AFR (Air/Fuel Ratio) is optimized. I think RPI has done enough research into the design of the scoops that bigger scoops won't do much good at all without increasing the fuel going into the engine as well. Which there is VERY limited amount of tuning possible in any car makers OEM fuel system. You'd need to find things like bigger injectors and a higher capacity fuel pump - which are better suited to turbo or supercharged applications to produce any decent amount of power, then you'd get into the problem of compression. Forced induction engines require lower compression to operate effectively.
Example: the stock M5 has a compression ratio of 12:1 - way too high for super gains from FI. To see real performance gains from FI you'd need to lower that to 9:1 or 8.5:1.

 

Thanks for entertaining the thoughts guys. It may not be a simple case of enlarging surface of the scoop for more gains. I do agree there is a law of diminishing returns.

 

I have 2004 545i and bought Dinan CAI back in 2006 and just installed 2 RPI scoops (same kit they sell for M5's) due to the Dinan CAI has the extra scoop so there are 2. When I got the CAI installed I noticed a louder bark from the exhaust when accelerating, really kool, but I cannot say any noticeable acceleration gains. I do not have a chip. So now with the 2 RPI scoops, I want to say you can feel a slight push at about 70MPH at full throttle, but so slight, I would hesitate to say if worth the $200 bucks to install the RPI scoops, plus the $1,100 I spent in 2006 for the Dinan CAI??? But they make sense I know they are there to maximize performance. What is anyone's take on my further investing into a Dinan Chip or other?
I plan to invest in a quad exhaust as I just installed a M5 bumper and looks rather stupid to have just to have the driver side exhaust sticking out. So a free flowing exhaust + a chip, maybe then there will be a more noticeable jump in acceleration or is a chip worth it? But for now I need to pay about 2,000 bucks to have an Indy do a Valve Cover and Timing Cover gasket job + install new water pump at the same time. Now at 72K miles I need new Control and Trailing arms as the ball joints make a loud crack sound when I brake, and probably new shocks, and the fuel pump and filter is due to go out soon as is the Cylinder valley cooling pipe, spark plugs, and my rear tires (20's) are nearly bald due to the BMW negative camber ? So the exhaust will have to wait a while. If you see a blue 545I with one exhaust sticking out with a M5 bumper driving around Orange County, CA wave! also I started a charity fund for all my needed maintenance & repair costs ( so far I estimate $28,000 in maint + repairs since 2006 starting at 22K miles, and does not include the 2K I need to spend right away for the valve cover job) PM me if you like to help out! BMW die "Utlimate Bankrotteur-Maschine"

 

My old friend and I drove each others car when we meet up and go for a drink, mainly b/c I wanted to feel KW v3 on his 535xi.

He has RPi scoop, Dinan stage II software, Dinan muffler, AR downpipes.

Mine is same year 2008 535i, RPi scoop and exhausts, GIAC flashed, 20" heavy 3 pc wheels. Hands down mine blows his away from every speed range.

Dinan power is very conservative. Dont waste your $$$

 

yes Dinan is more on the conservative side when it comes to performance as well as higher side when it comes to price, but some feel the dinan warranty bridges the gap between Dinan's performance and price when compared to other tuner companies...