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Is this recommended for a mild NA car with I/H/TB and flashpro tuning? I keep reading conflicting reviews and opinions on these forums - Some say 3" is too much unless you go cams and such, others say 3" is best for even basic K motors while some others say something like the Invidia Q300 70mm is more than plenty.
Hi blacksheep, the k20 VTEC engines are extremely efficient engines with high flowing cylinder head and unusually large OEM camshafts. If you are planning to upgrade the I/H/TB (especially a 3" header) then its a very good idea to use a true 3" exhaust. Our 3" is designed to be high flowing, not restrictive, but also not loud or obnoxious - ideal for a street driven Si. There are many happy q300 customers also, but ours is a little different and offers some benefits (like vband) and many prefer the Full-Race exhaust note. lastly, if you ever went turbo or SC in the future this is already the ideal exhaust to have in place.

What's the difference between the 2.5 and 3" adapter for the full race catback? I have stock cat and header
for stock cat and stock header you need the 2.5" adapter
if you have an aftermarket header/cat/test pipe with 3" diameter, then you would want to use the 3" adapter

Will the 2.5 adapter work if I decide to get a header in the future and does it draw less power then the 3"? Would the 3" not fit with stock parts?
yes the 2.5" adapter will work with any aftermarket 2.5" header

the 3" adaptor can fit with stock parts, but it requires smaller nuts/bolts to align. not ideal, but if you are planning to get a race header in the near future it may be worthwhile
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