detach8
Well-Known Member
Re: BMW Performance Intake & Exhaust for E90 320i?
I cannot be sure but it is especially true when moving at speed above 40kph when engine drops to 5th or 6th gear the rattles will reccur at around 1,500 rpm if i put some load on it, e.g. uphill climb.
i would theorize that at those speeds there is actually quite a bit of air being "scooped" into the engine and that makes it run slightly lean. i would believe the engine is already quite lean to reduce the emissions. if i am going to get it tuned, it will run even more lean.
with the scoops -- at 1,500 rpm the engine is very hesitant to rev, which is another sign of lean mix. but if i go over 3,500rpm it takes off like a rocket.
now it seems that BMW wants the engine to pull the air by itself and not have the air forced into the engine. racing and street driving is quite different. if i'm racing and constantly have the engine revved above 3,000 rpms then having air forced make a little bit of sense, but imagine the engine at idle and you are blasting it with air, all the ECM is going to do is either 1) feed more fuel to compensate for the extra air which would cause a rise in rpm or 2) close the throttle (valves in our case of valvetronic), both with a negative effect on linearity of the rev range and likely make it harder for the engine to properly rev-match during gear shifting.
without the scoop the effect is more linear, i.e. no sudden rocket at 3,500rpm but also no hesitant revving near 1,500 rpm.
it is true that after removing the scoops i find the gear shifts a little quicker also.
i mean, i understand the theory of it. i used to drive the nissan latio which had air intakes at the crack of the bonnet opening. air goes right into that crack. but that engine does not have valvetronic and i think does not even have VVL -- only VVT. it spends a lot of time revving since it's such a damn small engine in the first place.
anyway... it's ok -- it's just a piece of metal. i would rather spend that money on something that makes a bit more sense, e.g. better sparks or air filter. cheers~
I cannot be sure but it is especially true when moving at speed above 40kph when engine drops to 5th or 6th gear the rattles will reccur at around 1,500 rpm if i put some load on it, e.g. uphill climb.
i would theorize that at those speeds there is actually quite a bit of air being "scooped" into the engine and that makes it run slightly lean. i would believe the engine is already quite lean to reduce the emissions. if i am going to get it tuned, it will run even more lean.
with the scoops -- at 1,500 rpm the engine is very hesitant to rev, which is another sign of lean mix. but if i go over 3,500rpm it takes off like a rocket.
now it seems that BMW wants the engine to pull the air by itself and not have the air forced into the engine. racing and street driving is quite different. if i'm racing and constantly have the engine revved above 3,000 rpms then having air forced make a little bit of sense, but imagine the engine at idle and you are blasting it with air, all the ECM is going to do is either 1) feed more fuel to compensate for the extra air which would cause a rise in rpm or 2) close the throttle (valves in our case of valvetronic), both with a negative effect on linearity of the rev range and likely make it harder for the engine to properly rev-match during gear shifting.
without the scoop the effect is more linear, i.e. no sudden rocket at 3,500rpm but also no hesitant revving near 1,500 rpm.
it is true that after removing the scoops i find the gear shifts a little quicker also.
i mean, i understand the theory of it. i used to drive the nissan latio which had air intakes at the crack of the bonnet opening. air goes right into that crack. but that engine does not have valvetronic and i think does not even have VVL -- only VVT. it spends a lot of time revving since it's such a damn small engine in the first place.
anyway... it's ok -- it's just a piece of metal. i would rather spend that money on something that makes a bit more sense, e.g. better sparks or air filter. cheers~
Last edited by a moderator:
