Thanks for your suggestions/tips.
I take your word regarding benefits/restrictions from bi pipes and put them on my list.
Darin intake: I did it, but did NOT log an performance difference. Could be that the rest of my current setup is hitting the limits (assuming that even on my custom stage 2 tune, the ECU throttles back to 'safe' limits if for example fuel injectors are maxed out, IAT getting to high, or similar). IIRC, there is also a very detailed post out there measuring the impact of the Darin mod with really detailed data logs during various driving conditions. He did not find any improvements that are not falling within the measuring tolerance/variations.
Also IMO, any cone MUST hold up to a physics/math check: surface area bigger than stock.
And certainly cannot be a 'HOT AIR INTAKE' (as seen on lots of kids' cars, trading a functional true cold air stock intake for a HOT air intake (that admittedly may be a nice noise maker). Consequently, it need to suck in cold air from the front (or other places). Carbonio does it right, or cone in stock box (plus Darin?) (only if larger surface area can be fit in).
MAF limit: larger MAF housings are installed not because they are a flow bottleneck, but rather that the sensor measures air speed, and is calibrated to provide a max output signal (5V I think?) when the max speed it is designed for has been reached. Modified engines need to flow more air. Increasing the MAF area (and corresponding change of the tables so the ECU gets the correct flow reading) reduces the air speed in the same ratio as the area increases, thus also increasing the upper limit (example: 72 mm ID to 85mm diameter = 1.18 diameter increase = 1.39 area increase. Stock MAF measuring limit (say 280 g/sec - I am at 260 g/sec) x 1.39 = new measuring limit of 389 g/sec. The limit is signal limit, not necessarily a flow restriction.
Intercooler: any increase in volume in the 'pressurized' part of the intake will also result in an increase it lag (more air volume means more time to compress). So 'bigger is better' deserves an asterix, or at least be aware of the downside. I have looked at 800HP twin turbo 300ZX with huge turbos (and similarly upgraded Supra) and was amazed by the (relatively) small diameter piping they run. I put 2.5" piping on my 1.8T (and regret getting the 2.75 thick intercooler (cause lots of install headaches and was clearly NOT needed for my relative mild power goal of 300 hp). Next 1.8T will get 2.25 piping (2.5 max) and 2.5 thick intercooler.
In a similar fashion on the exhaust side: I found that back pressure is NOT only your enemy, it is also your friend (if you are looking for reduced turbo lag, spool up. At least for low/mid range torque/power. High rpm peak HP applications are a different story, I am sure.
Surprised that no one is hitting on the throttle body diameter? In my naturally aspirated (Corvette) times, this was one of the first things to do. Not an issue on our turbo engines?
Originally Posted by Trigger Happy