Question on stock z4 2.5 gains

[cabear]

just a curious question, is there a specific reason the exhaust is a dual pipe set up? i guess i don't understand the logic behind it as most inline 6's use a y-pipe configuration to a single inlet muffler, whereas bmw's use a smaller diameter dual set up which seems a bit inefficient, at least when it comes to conventional ideas. using my knowledge from other inlines 6's (turbo supras, NA is300, etc) the y-pipe into a 2.5-2.75 inch exhaust yields good results and would save some weight as well.

Also a properly made header would benefit the new exhaust design even more, as the stock header is something that could be bottlenecking us m54 users as the stock headers don't flow all that well due to their small ports and pinched off design. this bottleneck would also explain the lack of gains made from intake additions, as you can't have much more going in if it can't go out.

any thoughts? i've been racking my brain trying to come up with mods to do yet everyone seems to be doing the same thing with the same results. there still isn't some sort of tuning ability for the DIY'er other then a reflash, which isn't going to give you the custom tune you need to take advantage of the mods you have. is there anything like the hks, greddy or apex'i piggyback fuel computers to tune bmw's with? (using a wideband of course)

anyone have any ideas there? i'm currently thinking of modding the exhaust with a y-pipe, single pipe design more akin to what the japanese tuners use. i refuse to believe that BMW engines can't make the NA power their japanese rivals can. i firmly believe that a lot of their designs come from not wanting to step on the upper model's power (2.5's can't be as fast as 3.0's and the 3.0 can't be in the same level as the M version)

[cabear]

also in case anyone wonders why i bring this up, i used to own a gs400 and for the most part all users said that lexus tuned it so well that there were no gains to be had. that went on for the longest time until someone actually went in and looked for the bottleneck, which were the stock headers. a fellow went and designed a better flowing header that when coupled with a good exhaust and freer intake, led to gains that weren't seen before the header's introduction. it wasn't so much that lexus made the ultimate machine as lexus tuned the car's exhaust to be quiet at the cost of performance.

There's always room to be made and i really want to see what i can uncork out of this 2.5. any help would be appreciated.

[goldguilexx]

i think its not so much that there is no room for improvemnt on the Z's but that its all done to the point where any gains are so minimal that ist not cost effective. Like the header deal, 4 to 5 hundred bucks (ebay headers) and maybe 5 to 7 extra hp mayyyyyyybe! intake (AFE) i probably lost HP (but according to them gains of 5) but it does sound cool! Exaust is mostly a sound preference for most people wanting it louder or deeper type of deal. HP gains?? nah, maybe 1? and not to mention theres hardly any room for better pipes down there. Most all bends that the car has are bent there to avoid another component. Any straighter pipes would involve moding the car to big extents. and RPI scoop gives you better MPG +2 or 3 depending on how you drive.

[cabear]

well after doing soem more research i found that even with a smoother, larger intake, better headers and a well thought out exhaust system i'm still gonna be hindered by the lack of tuning options. I gotta look more into that. I read one tuner used an apexi safc to help tune but i have to see what the results were in that.

[jra]

search e46fanatics.com, esp for technik gen III headers and ess/active autowerke software.