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post #1 of (permalink) Old 12-08-2016, 13:05 Thread Starter
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Join Date: Dec 2012
Car: MG TF
Posts: 55
Standard backbox with valve - mod project

Background: I have a Toyosports, nice sound but awful quality. First the hanger failed and sliced open the back-box (soldered it shut and reinforced the hanger), recently it developed a rattle. Cut it open and found that one of the channel separators failed:

I soldered everything back, altered the separators to allow for less restricted airflow and reinforced them. Also, removed 60% of the wool. Will put it back this weekend to see how it sound. I'm expecting it to be quite loud and rewarding

However, I'm no more into extreme sounds, but I like the idea to have the car sound sporty, but silent while cruising. I have the original exhaust with noise control valve (it's a TF135) and am considering to alter it to make it louder but still controllable.

What I would like to do is to remove the separators (a-la-Toyo) and part of the wool just for the right tailpipe, the one with the valve on. The left one air path would be mostly left untouched.

Then I'll wire a 3-ways switch to the cabin to control the valve:
A - Automatic (controlled by the ECU i.e. valve opens at around 3k rpm)
C - Comfort (valve always closed)
S - Sport (valve always open

I'm pretty sure the Comfort mode will not substantially alter the engine breathing because I'm now using a 115 exhaust with small tailpipes and car behavior is not affected. And the car is designed to run with a single tailpipe up to 3k revs, Comfort mode will be for highway cruising at just about that rev.

The real question is: how would the sound be in Sport mode with a almost completely free tailpipe and a more restricted one? And how quite will the Comfort one be?

I now there's only one way to find out, but maybe if somebody already tried to modify the standard backbox I might have a hint

Would it work? Or should I just stick with the standard backbox and just wire the switch?
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