I've owned my Mazda RX-8 for over eight years and gone from show car to race car. During this time, I've been seeking ways to extract power from the car in naturally aspirated ways [keep the turbos with the RX-7s]. I have experimented with nearly a dozen exhaust combinations seeking the best balance of noise v performance.
Before talking about the modification, let's address the differences in open v restricted exhaust systems:
Open Exhaust systems
-- They allow maximum flow at high RPMs / MPH
-- Conversely the lack of back pressure in the exhaust system at low RPMs/ MPH creates torque loss
-- Loud and raspy
Restricted Exhaust systems
-- Have a limited maximum flow, thus capping max torque
-- Excellent back pressure, creating low-end torque for low RPMs/ MPH.
-- Quiet until you're going wide open throttle
So what does this all mean?
How does one gain the maximum exhaust flow with on-demand performance and [audible] discreteness?
A 3rd exhaust exit controlled via vacuum pump -- That's how!
The vacuum butterfly valve welded to the [now uncapped] middle end piece of the factory cat-back:
The vacuum pump tucked into the open truck space:
How does this exactly work?
The MAF [mass air flow sensor] is tapped to send signal to a relay when I am going WOT [wide open throttle].
I have a toggle switch in the cabin on a factory panel with open space
-- I power the air pump, which then allows this system to function
With the signal being sent, the relay allows the vacuum to reach the butterfly valve on the exhaust
What is gained?
Increased acceleration above 6,000 RPMs [This engine safely revs to 8,500 into the low 9,000 RPMs]
Less engine lag when shifting at WOT
-- Without this, the back pressure is caught within the system and creates a bogging-effect
Exhaust system flow optimized
-- The factory cat-back's construction has a perforated pipe that ends in a capped section, which forces the air out to the sides of the pipe, to an exhaust tip
-- That section, if uncapped allows for a straight-through un-muffled exhaust system
Large fireballs out of the center of the car
Again, this is a prototype; I do not have video yet as there is an exhaust leak at the header where there is a V-band that is giving me a hard time. From my road tests, the car pushes through the RPMs now where it used to slow down after 5,000 RPMs.
This content has yet to be published on my blog: Franeke ; so consider this Steemit-only content :P!
