My 3" custom exhaust with spring loaded flapper valve
#1
My 3" custom exhaust with spring loaded flapper valve
3" miata exhausts tend to be too loud for my taste despite the use of a large Magnaflow, and for the longest time I was thinking of a butterfly restrictor after the final muffler.
Turns out, Dynomax now make a muffler with a built in spring-loaded flap, the Dynomax VT series:
http://www.dynomax.com/mufflers.php?muffler=vt
Neat idea, though annoyingly the flapper isn't sold separately.
Here's a vid where you can hear it open up. Fast forward to 0:34:
Turns out, Dynomax now make a muffler with a built in spring-loaded flap, the Dynomax VT series:
http://www.dynomax.com/mufflers.php?muffler=vt
Neat idea, though annoyingly the flapper isn't sold separately.
Here's a vid where you can hear it open up. Fast forward to 0:34:
#2
Because I wanted a bigger muffler, I decided to cut the valve out of a VT muffler and install it just before my tailpipe, and use a bigass Magnaflow.
My old 2.5" system had a 5x8x22" Magnaflow, a 16x4" resonator, and a metal cat that interchanged with a louvered resonator.
My new 3" system has a 5x11x22" Magnaflow, a 14x4" resonator, and an FM "hybrid" cat which is 3" behind the cat and 2.5" in front.
Result: At light throttle and cruise the exhaust is slightly louder than my 2.5" system using the resonator instead of the cat. When I get on it, it's very noticeably louder. I also tested the system idling and revving without the flapper valve in place. It was MUCH louder at lower RPMs (<3000).
Peak backpressure, at 15 psi boost, 7000 RPM, measured at top of downpipe:
Old system: 10 psi (270 whp)
New system: 5 psi
My old 2.5" system had a 5x8x22" Magnaflow, a 16x4" resonator, and a metal cat that interchanged with a louvered resonator.
My new 3" system has a 5x11x22" Magnaflow, a 14x4" resonator, and an FM "hybrid" cat which is 3" behind the cat and 2.5" in front.
Result: At light throttle and cruise the exhaust is slightly louder than my 2.5" system using the resonator instead of the cat. When I get on it, it's very noticeably louder. I also tested the system idling and revving without the flapper valve in place. It was MUCH louder at lower RPMs (<3000).
Peak backpressure, at 15 psi boost, 7000 RPM, measured at top of downpipe:
Old system: 10 psi (270 whp)
New system: 5 psi
Last edited by JasonC SBB; 12-30-2011 at 12:45 AM.
#8
The DSM guys have been using these for a while. Be aware that either the springs lose tension over time/ use/ heat, or the little wove steel wire cushion on the flapper tends to wear out/ disappear, and the flapper starts to rattle/ clunk at idle some times. The Mitsu guys claim a 6 month max lifespan before the rattle begins.
I don't know if you'll have as much trouble with it, as 1.) you're not moving nearly the air that a GT35R EVO moves, and 2.) you're a probably not putting the thermal stress on it that the DSM guys are.
I don't know if you'll have as much trouble with it, as 1.) you're not moving nearly the air that a GT35R EVO moves, and 2.) you're a probably not putting the thermal stress on it that the DSM guys are.
#15
I've been planning on swapping out my rearmost 5x8x14 3" magnaflow on my suby wagon with one of these dynomax VTs. Wagon is a little drone-y on the highway. I haven't due to the supposed blow out of the little pad and/or worn out spring after a little while, and my brackets are welded to the muffla.
Anyway. I hope it works out for you, keep us updated.
Anyway. I hope it works out for you, keep us updated.
Last edited by TurboTim; 12-30-2011 at 07:15 PM.
#18
Not sure why ours is different, turbo size (doubt it) or muffler design? Mine is offset but I can still roll a golf ball through it.
Anybody know if there is any semi accurate decibel reading apps for iphone or android? Now I'm curious.
#19
I've been planning on swapping out my rearmost 5x8x14 3" magnaflow on my suby wagon with one of these dynomax VTs. Wagon is a little drone-y on the highway. I haven't due to the supposed blow out of the little pad and/or worn out spring after a little while, and my brackets are welded to the muffla.
Anyway. I hope it works out for you, keep us updated.
Anyway. I hope it works out for you, keep us updated.