ZR-1 Exhaust Cutout Project

[Tony Davila]

This month’s project involves installing custom cutouts on a stock ZR-1 exhaust system. The original system I had was a 3” B&B exhaust system w/ X-pipe. Every time I would drive up to BG I had to wear earplugs because of the drone and it was driving me crazy. I needed a solution in order to enjoy both the sound of the exhaust and lack thereof.


I started looking on the web and eBay and found some 3” vacuum actuator cutouts. I picked up two for $220. I then came up with a game plan on how I was going to get this to work. After trial and error I found that it was a pain trying to get the vacuum actuators to work. The vacuum actuators that came with the system required at least 10 inches of vacuum to close the system. So just going up a small hill would have opened up the system early at part throttle and this isn’t what I wanted. My goal was to run it in the open mode at all times but have the option to close them for long trips for peace of mind and a quite cabin. Lucky for me Daniel McGuffee gave me his old exhaust system to play with.


eBay item Vacuum Actuated Cutouts

I have seen other systems and didn’t want electric cutouts just due to cost and potential for failure. I am also a do it yourself kind of guy. My plan was to install them so that it was not visibly noticeable, the stock mufflers size aided in keeping them hidden. Some of you may ask why use the factory mufflers with their tiny opening and restrictive nature. Answer: The factory mufflers are built with a design called Helmholtz resonance. [The theory of Helmholtz resonators is used in motorcycle and car exhausts to alter the sound of the exhaust note and for differences in power delivery by adding chambers to the exhaust. Exhaust resonators are also used to reduce potentially loud and obnoxious engine noise where the dimensions are calculated so that the waves reflected by the resonator help cancel out certain frequencies of sound in the exhaust.] The factory mufflers are best at reducing sound and resonance and almost every one of you guys probably still have them.

Original Helmholtz design factory muffler.

So come along on my journey and see what I did. I have tested the system and it works bad azz. No resonance in the cabin with the system closed running through the mufflers and it sounds stock. With the system open it sounds like an open header car, loud. I may need to put some bullet mufflers after the X-pipe to quite it down a bit. I’ll be up at BG next month so if your there you will be able to hear it.

First I modified exhaust system by installing a $30 eBay X-pipe then installed a coupler on the passengers side to get rid of the slip fit. I also install my own design high frequency (sort of) muffler. This design is to kill the high pitch a strait pipe makes. It works pretty well, it doesn't sound like a Corsa at wide open.

Custom built high freq killer.


Modified exhaust cutout

I had to place them at an angle that would keep them hidden, still function without interfering with suspension items and not burn anything. R&D came next to make it functional.

More to come.