After installing some LG headers last year, I was still a little disappointed with my exhaust sound with the z06 axle-back. I didn't really want to get a new axle-back as I'm cheap and liked how quiet the z06 exhaust was for long highway trips.

So, I figured cutouts were the way to go. I found this video and decided to duplicate it because I didn't want to fuss with trying to weld the titanium Z06 axle-back.


Boy was this a bad idea. I had seen a few people say cutouts before the rear subframe could damage the rear leaf spring. They were definitely right.



This was after using it sporadically for ~3months and a single session at Putnam.









So, not only did the QTP cutout itself fail in less then 6 months, I had a broken spring.

So, I wanted to see what was actually going on. I went and ordered this:
https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1

Probes:


What I found with my original setup (I wish I had pics/vid of the thermocouple) was that no matter what I did on the street (within reason) I couldn't get a higher reading than 120*F. It usually hung out between 80-100*F with an ambient of 80*F.

The moment I opened the cutouts at a cruise, the temps increased from 80*F to 130*F. Now this really isn't too shocking but what I though was interesting to find was, even doing a 50-70mph pull in 5th, the temps skyrocketed to over 300*F! I cold only imagine higher RPM and longer duration would make it higher. I honestly would have though at speed the heat would be able to dissipate enough to not heat the spring that much. During this testing I had suspicion of a bad cutout but never went to confirm, so I don't know if both banks were heating the spring or just one.

In my eyes there are 3 solutions to this:

• Move the cutouts to before the muffler, require welding titanium
• Get coilovers.
• Make a heatshield.

Making a heatshield is probably the cheapest option.

Things are on hold until I get one of the cutouts fixed, but I started by buying full downturns instead of the 45* ones from QTP:



This seemed to help keep it below 200*F with similar ambient temps but I know now I only have one functioning cutout. I plan to add an aluminum sheet between the exit of the exhaust and the rear spring.

 

Your cutouts appear to be much closer to the spring that the video you patterned off of.
And, I would absolutely have the most radius on them as possible, with the full turndowns. Keep us posted.

 

I couldn't tuck them any further back or else the motor for the cutout would've fit between the exhaust and transmission.

 

A rather expensive experience you had there. Good luck getting it all sorted out.

 

Any thoughts about that everything else back there is being subjected to the same heat? Tranny (have you monitored this?), wiring, under carriage, fuel tanks, etc... not something I would do TBH.

 

No sign of damage elsewhere. Like I said, had I a normal stainless axleback, I'd have moved them further back.

 

Not surprising considering how they discharge onto the spring. I had a similar setup for years with no problems but I designed my system so that it dumped more downward and avoided exhausting onto the composite spring.. I have since removed and sold the cutouts and switched to coilovers but the composite spring I removed from the car was in excellent condition.

 

My solution (build in progress) is different.

1) Stock mufflers, titanium.
2) Start with the bypass mod.
3) Stick an electronic valve into the bypass pipe. (Or, more accurately, build the bypass pipe around the valve.)
4) Figure out fitment and mounting.

In this way, you never actually dump exhaust underneath the car; it always dumps out the back - but with the flick of a button, you get the noise and breathing from a largely un-muffler-restricted path.

The thing I'm currently stuck on though is figuring out who welds titanium where I live... and precise dimensions and gaskets and whatnot to do it right. I'm kind of lazy because my exhaust is great except for the drone, and I'm used to the drone, so I kind of don't care for my own sake.

 

That's the problem I had. The few people I know that could weld didn't want to touch titanium.

 

This is my cutout bypass

 

I'd love to have done that, but again, titanium. I also don't want to spend ~$1k on an axle back just to start chopping it up. Also, I wouldn't go with electric again. Vacuum actuated is much better.

 

You get what you pay for.... DMH FTW
My set up...

 

Thanks for sharing hopefully others will see this and understand with you have to be very carfull with this type of mod.

 

I have wanted to do this mod but was unaware of the risks of not having it mounted in the correct location and have the pipes pointed away from key components. If others have additional pictures of their setup along with what types of cutouts they used I would love to read about your setup. Thanks for sharing.

 

This was setup on my 99 coupe. Had LG headers and was cammed. Put the DMH electric cutouts on the 90 degree bend just before it entered the mufflers. Never any issues and sounded great. I didn't want any issues with heat under the car or drone so that is why I put them where they were. No issues, and if I ever do cut outs again, they will go in the same place

 

Did the tips that point down from the cutouts come included with the DMH cutouts or did you have to have the exhaust shop fab them up?

 

^^^ included from DMH.

 

Strangeloves, fantastic setup. This is precisely what I'm planning on. That doesn't look like the stock titanium axleback though, is it?

 

No it's a Corsa Tigershark that came with the car when I bought it.

When open it sounds exactly the same as the Corsa but 10 db louder
Running it out the tailpipes is a little quieter than under the axles but smoother with no vibration in the cabin.

 

What cutouts and model did you select? I looked my GHL exhaust and saw I could run a comparable setup and have the cutouts bypass the mufflers and go right to the tips. I think this is the cleanest way to go, plus no worries regarding heat damage.

Your setup looks really good BTW.