I should preface this by saying that I'm not trying to reinvent the wheel. We are all aware that the stock intake system is actually designed very and it is hard to improve upon. There have been members that have gone into the 10 sec 1/4 mile range on the stock intake setup. However, being that type of person who's never happy, I can't help by try and take a stab at creating something different. As long as I don't lose any power, I'd be happy with just a better induction noise at the end of the day for not more than a couple days of work.

The current modifications on the vehicle are 77mm pulley, 82mm throttle body, ecu/tcu tune, belt wrap kit, 550cc injectors, cooling mods, headers, and full 3" exhaust.

My plan is to mount the engine air filters in front of the radiator and behind the grille. I've personally used this type of system on a G37 and GT-R in the past with good results. In general with this type of setup, you gain more engine/induction noise and a bump in top end power as compared to a ram air or or short ram style of intake which nets more down low.

Looking at the stock oval radiator openings, you can see that about 60% of the surface area is blocked by the hood latch buckets along with the what I assume are splash shields in front of them (see pictures). Also, on the driver's side, there are two hoses that literally sit right in front of the oval opening blocking even more of the surface area. I have measured the stock piping dimensions and these are my findings (give or take a couple tenths). The oval radiator opening measure 3.3", inlet on the bottom of the air box is 2.7", and the outlet on the top of air box is 2.5". I assume that the stock intake system is designed to neck down in size from large to small in order to create a faster velocity of air moving through the system when used as ram air?

I can easily run 3" pipe from the air filter all the way to the throttle body. If I hypothetically carve out some more room, I may be able to run 3.5" from the air filters to the throttle body. Inside of the engine bay is easy to fit a bigger pipe but snaking it around the headlights is definitely tricky. I couldn't find any magic formula or table stating that 3" piping is good for X amount of horsepower/cfm as I'm sure that there are too many variables to do that.

K&N told me that the stock panel filter in a K&N replacement flows about 400 CFM for a total of 800 CFM. I gave them the engine size, approximate horsepower, and a few other details and was told I should shoot for a total of around 1,200 CFM (pair) when picking new filters. The filters that I chose to use are stated to flow a max of 820 CFM per filter. These will fit easily while giving me plenty of headroom.

The couple questions that I have are in regard to the pipe diameter and bend radius.

Would 3" piping be sufficient for this intake or would I be better off trying to use the 3.5" size from start to finish? Would it be better to have more velocity (smaller pipe) or more overall volume (larger pipe)?

The bends that go along the left/right of the radiator have to be 90 degree radius. These pipes are 24" overall length and have more of a sweeping or long radius instead of being short/tight. I will then have to use a 70 degree bend coming off the left/right y-pipe. Everywhere else is pretty smooth/straight. I understand that bends in an intake system aren't desired but there's not much that can be done about this. Since these bends aren't super abrupt/short, should I be worried about reducing velocity here?

I encourage constructive criticism and am primarily looking to learn more about intake system design whilst encouraging conversation. Let me know what you think!





pictured with 3" pipe


driver's side opening


passenger side opening

 

Nice plan. I wish I still had the picture I took of my stock airbox inlet area. Part of the filter element actually physically blocks the incoming air just pass the plastic tubes. It's very obvious and to me this is one area the OEM exhaust could have been improved. I wanted to keep engine bay looking close to OEM so I went with the Renntech Carbon fiber air box. The design solves the slight blockage of the OEM box. I also retro fitted Carbonio intake tubes designed for the CL55. I have used K&N filters for all my cars since the 70's and suffered no ill effects. Tear down of engines I have rebuilt showed no negative perceived effects from using K&N filters. Just make sure clean and maintain them regularly. Too much filter oil or letting them dry out are surely not a good thing. I have many more mods to my M113 but, just wanted to add my 2 cents about filtration of the OEM system. Good luck on your project!

 

to remove the cooler and tubes on the driver side you just got to rearrange it. move the HE to the front and the a/c condenser behind the radiator. you can reroute or remount the cooler so the lines are out the way. you can also cut off the covers that block the passage to the intake. I bought some carbon fiber beast tubes off an e55/cls55 wasnt going to mod it but didnt fit to well on the SL55. i might have to go your route CL55 tubes or just plain 45 degree CF tubes. lmk how it works out for you!