Have the Injen CAI (still trying to find MAFci for it, anyone have a lead?) and looking to make the next logical performance adder. I was thinking either the optimized throttle body or a cat back exhaust.

-side not: I am one of the lucky ones that didn't get the CEL from the Injen intake!

Am I correct in thinking that increasing the flow of intake without increasing the flow of exhaust is not the most beneficial way of increasing power?

I have heard of someone cutting the exhaust right behind the flanges (behind mufflers) and they got a pretty good sound, but does that increase flow at all?

Sorry I know this goes in a couple different directions and asks a few questions but thanks in advance to everyone!

 

I can get you info on the 3.0 litre, but you didn't tell us anything about your vehicle.
Year, make, model, engine size?

"modifying the catback or mufflers may provide little or no gain, because all of the restriction is further upstream. (especially on 3.0 ltr)
If anything, some of the catbacks are actually reducing overall power, because they're slowing down what little exhaust velocity there is, by the time it gets done going through the twists and honeycombs of doom."
FOR MORE: Exhaust Technology (Sizing/Velocity) by Crossbow

 

Sorry I am used to posting in the 3.0 specific forum on mazda6club. I have an 04 Mazda 6s 3.0 v6. Love the car but tough to find performance adders.

 

The Mazda 6's exhaust changed after 2005 for the worst. Yours being a 2004, cat-back should be Ok, may gain up to 5HP. Headers are good but are tricky and not for emission legality.
There is no Tuner that reprograms ECU for V6, however, piggyback tuners like CPE Mafci or the one Great NY sells are about it. Check EBAY for used ones from CPE. I hope you have changed your plugs by now, and possibly ign coils.
Optimized throttle body will help about 3-5 HP. Steeda throttle body spacer should help a bit as well, by leaning out your rich air/fuel abit. Make sure you don't go leaner than 13:1 on over 5000 rpm. Max power is between 12.5 and 13. I cut the thickness on my Steeda Spacer down to 1/2 thickness for better driveability at bottom end----good compromise---still gained upper end. Check on DYNO after driving it for 1 week. Also if you do Steeda spacer you must do the following: EGR Modification/Optimization: - Mazda 6 Forums : Mazda 6 Forum / Mazda Atenza Forum

STEEDA LINK: http://www.steeda.ca/ford-fusion-par...-Body-Spacers/ Canadian
P/N 555-3132 Mazda is same as Ford Fusion

OR GO BIG: https://www.mazdaforum.com/forum/nit...3-0-ltr-28429/

 

Thanks for the tips! That spacer might be a worthy investment , I think for now I might do a couple DIY's and see where that gets me. I'm gonna start with the EGR mod and the coolant bypass. Also I found a really good write-up optimizing my TB so I think I'm going to attempt that one as well since I'll have it off. Does anyone have any cautions about those 3 before I attempt them? They all seem pretty straight forward.

Here's the link to that write-up: Optimizing the Mazda6 Throttle Body How-to

Thanks!

 

Before doing any mods please disconnect the negative terminal of the battery, followed by a quick brake pedal application. After mods are done, hook it back up and let it idle for 10 minutes before driving. Re-learning will begin and it will re-learn for 50-100 miles (don't have to drive it all at once----don't floor it for a few miles anyway!)
Don't do Coolant By-pass if you have snow---Texas then by all means!
While you're at it clean your MAF, throttle body and EGR. There may be a vac hose connected under the plenum as well.
Change your PCV valve while you are there.
Throttle Body: To make sure everything lines up good i just had my shop use old screws and did not countersink or knife edge. Use loctite when putting screws back in. When drilling for countersinking your butterfly may not line up properly and you may not find same thread. Also knifing butterfly may cause idle issues if sanding edges down too much.
Get new gasket for throttle body and new intake plenum seals. I believe you have to remove plenum to do EGR mod (easier to pull out with plenum gone).
GASKET: Mahle W0133-1807640 Throttle Body Gasket | Auto Parts Warehouse
Plenum Seals: OES Genuine W0133-1639826 Intake Plenum Gasket | Auto Parts Warehouse
For more on intake plenum see pics: Mazda Forum - Mazda Enthusiast Forums - UseYourNoggin's Album: Intake Plenum & PCV Valve. 2006 Mazda 6 V6 3.0 ltr.

Good Video: