After market Air filters, and Decat

[ro284]

I have never quite understood this in all that i have read on here. it Generally appears that you can do any two mods to a standard RX7, before you need an ECU, one mod being Aftermarket Air Filters, and the other to remove the cat, but fitting Aftermarket filters implies that Mazda designed the standard air box to be restrictive!And new filters are only more efficient at letting more air in, but this can only be the same volume of air! or is it? although insurance companies seem to figure this is a performance mod! it is also an efficiency mod! So is the decat one mod? and if you do the two do you risk blowing the motor? or make it last longer with no restrictive cat in the way of releasing more heat out of the engine? in other words which mod makes the engine run lean? any advice much appreciated,
Cheers Bob
Cheers Bob

[ReX 7]

The CAT is a restriction to the flow in the exhaust and the aftermarket filters do let more air get through to the turbos than the std airbox. If you start doing anymore mods then that and you can run the risk of running lean due to maxxing out your injectors.

[rx7veilside]

air filters are vastly overrated..u can get more air but it is normally warmer due loosing the ability to supply a cold feed most people do it to a)get induction roar and whhoossh sound on lift off/and then flow a bit more air.i would challenge anyone to say they get any kind of noticable perfrmance increase.i have done this on nearly every perf car i have ever had and it really is normalyy a few bhp

[probedb]

Well Mazda design to a budget not just for best performance. I\'m sure I\'ve seen a modified stock airbox which gives better air flow for the FD but can\'t remember who made it?

I think the effect seems to depend on the car, better with an air feed and ram-air if possible. For some engines (Mazda KL-DEs for example) it takes a lot to get any decent horsepower from them so every little helps

Removing the cat is another matter  :evillaugh

[Ricco_04]

A lot of manufacturer\'s design products that all work together so they can then tune them specificially.  If they where to design products to the max then you would have an origional car with a 4" exhaust, heat shield\'ed twin mushroom cones etc.  All gives you more power but will also use more fuel.  Even on a car that does as little as the rex there has to be some sort of economy - hence the restrictive parts.

Also with a lot of tuning goodies they push the power band higher up the rev range...

I could of course be talking bolox!  :rollin

[Mave]

Both cats and intakes are restrictive to the engine, and reduce the engine effiency. If you got rid of the filter and exhaust pressure losses, you would expect the engine to give more power for your fuel.  :burnout

However, everything is a trade off..... on most cars, big exhausts = more noise, so the manufacturer aims for a market / legislative noise level. With intakes, aftermarket filters tend not to filter so well (I guess I might get shot down in flames there...) and with the Rex in particular you\'ve got the added problem of needing to avoid heat soak back into the intake system. :eek