# 82 733i - Many many many questions...



## NewBmw733IDigIt (Feb 25, 2009)

Hey Everyone. I hope we are all having a great memorial day weekend!!!

I have two simple questions this time around..

1. I had a bit of a fire with My cat's on My 82 733i..So I decided at this point I have to just cut the out and replace them at another time when I can spend 935.00 on the assembly. SO I removed the cat's from the down pipe to the muffler in the back of the car where it splits into two pieces. I had a pipe made by an incredible exhaust person..The cost was 58.00..AT this time it was a way better price then 935....Now I heard so many conflicting statements about if I remove the cats it will run better if I remove the cats it will run worse..I was not sure...I put the pipe on....The car runs even better...It was fast before..Now it is really really fast..It has a very low rumble to it as well..But it runs great...Can anyone here tell me why...I hear so much crap...I would appreciate any information for everyone on the site..

2. Some people are telling me I should drill huge holes in my air box..That I should modify it..I figure BMW knows what they are doing why would I want to destroy what bmw created. I know their engineers are much more aware of airflow then I am..I know I had to eliminate the cats for finacial reasons. Not for performance reasons. I would rather not just randomly drill holes in my air box and guess if it works or not...

Please any answers good or bad would help..I am an extremly objective person I can take good and bad answers and make a choice..

Thanks to everyone for your help..

HAVE A GREAT, SAFE, MEMORIAL DAY WEEKEND!!!


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## drivinfaster (Nov 24, 2007)

welcome to the fest. :thumbup:

as to the performance issues, i would say the increase of power is related to no longer having restricted cats. if you were to have aftermarket performance cats, or even oe replacements (more $$), then you should not feel any decrease in performance with the cats being reinstalled. 

the 'cats vs no cats' performance issue is moot when it comes to daily drivers, though, but do not attempt to try to convince the knuckle dragging, pushrod loving engine junkies that advocate this proceedure as such. the explanation would only make their heads hurt. 

as for holes in the airbox, i say ditto. putting holes in the airbox will just suck up hot air and water that comes up. don't do it. you could try a cone style airfilter, but that would also most likely suck up more hot air from the engine compartment unless you made a modification to the current airbox to shield it somehow.

if you want more power, upgrade via proven methods. exactly what these would be for your vehicle i am not sure. the technology has progressed such that there are probably more viable options now than when this vehicle was new. that's what the search function is for. also, whatever works for the 3.5 should also work for the 3.3, i believe, so you may wish to see what the 633csi guys are doing for better performance.

good luck.


df


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## NewBmw733IDigIt (Feb 25, 2009)

*DF...Thank you*

You made me feel a bit better about doing what I did..

I was not going to drill into that air box....

Hot air is bad for intake? Why is that? Air molecules?


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## drivinfaster (Nov 24, 2007)

the hotter the air, the less dense it is, the less oxygen it will contain per cubic foot. you do not want hot (as in engine bay temps) air coming into the engine. 

in the old days of carburators, a thermactor system would allow for heated air drawn up by tubes that looked like mini dryer vents over the exhaust manifolds before it passed through the venturi where it would mix with the atomized fuel. this warmed air would help vaporize the fuel drawn through the venturi and circulate through the intake to the combustion chamber. once warm, this system would close off allowing the cooler, denser air to enter the cylinders as the engine temperature itself would help volitize the fuel for better combustion.

we don't need 'warmed' air with port fuel injection, though. 


df


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