Yeah under the axle will work but you'll end up hitting the pipes with the axle at full extension. dumping before the axle means you get one less resonator.

the 3" n/a exhaust I would still consider "experimental" as many of the old skoolers don't accept or haven't adopted it into the fold yet. If you're down to try it - go for it. I will be doing it when it comes time for exhaust, for now i'm making do with what I have - RB collected header into a blown resonator, stock mid pipe, blown RB power pulse muffler. Sounds rather tinny, but at least its not open header. More important fish to fry for me right now, as this exhaust technically gets the job done.

a 2.5" system will work plenty fine. I've even heard a lot of peeps preferring 2.25" on stock porting. If you're set on the pre-axle dump, i dont think i'd go 3" - as J9 mentioned it will be that much louder, plus that much less room for 1 more resonator.

 

alright so you guys think doing a longer collector to a muffler (dynatech split-flow) to a universal rb muffler to a dump out the side before the rear tire would be efficient enough?

EDIT: and how would you do under axle? anyone have a picture i can see of theirs? personally i dont want my system getting ripped out of my car when i hit a speed bump or a pot hole or going into a driveway....

 

I've thought about using a 2 into 1 muffler for this, but be careful. Some of them split in an odd fashion or loop back into a center baffle. I'd be curious to hear from someone who's actually tried it and can speak from experience. Could be a practical way of solving 2 issues at once

 

ummm starfox07 post a video with a very similar setup like same stuff but his goes out the back

 

this is what the split flow is

 

this is the one id get if i was going with 3"

 

Mine is the collected street header, so the gasses have already merged before they hit the split flow. I bought it mainly because it appeared to be one of the more tough small mufflers you could buy.

 

so i have happened to notice that in an FC, the stock exhaust manifold will dyno approximately the same as a header, its within the margin of error for different wear/mileage, etc.

when i pulled my S5 apart, i measured everything, Mazda uses 50mm ID pipe, and this seems totally fine. the restriction in the stock system is the baffled muffler, and the cat(s).

going a little bigger on the pipe is probably good, but a 2.5" .065 wall tube, which is common, is 60mm ID, which is probably perfect.

combine with a muffler that flows more and the collector back part is 90% there.

going from 2.5 to 3" gets louder, or at least lets more low frequency sound out, so it gets hard to muffle. power gains on a stock or street port are probably going to be small and way up top too.

its easy to over think the exhaust.

 

Did you see Hyper4mance2k (or whatever his name was) dyno sheets for his 3" flared exhaust? I think he had 15-20hp more over the RB system. I think he was running a header similar in design to the Defined header

 

He was also spinning 9,000rpm

 

ok i kinda wana go louder lol but thats just me but we will see i got to measure everything out and you know that takes time when your car is in a gravel driveway with flat tires hahahaha

 

yep! i've seen the car in person actually.

i think from an armchair tuning perspective he changed a lot more than the diameter of the exhaust.

the header he used has much better bends out of the engine, which is i think overlooked and kind of important.

the tuned length is different

and the mufflers were different too.

 

i see hmmm im thinkin go with the cheaper rout and do the 2.5" all the way back with a longer collector and both the mufflers then out the side i hope if it all measures out i gota fit a cat/test pipe in too inspection sucks and when i get to vegas smog is guna suck worse but thats what moneys for right?