Exhaust cutout

Hi folks! Hey, did any of you ever have any experience with an exhaust cutout? The thing that you use to bypass the CAT and regular exhaust. I’m doing an exhaust for the DelSol my Son and I are building and I was considering it. The front of the exhaust will be a header, flex pipe then the cutout, thn back through the normal CAT and muffler. Any thoughts? Rocketman

Why do you want to install an exhaust cutout?

Do you plan on racing the vehicle at the track?


Why? All they do is make a racket and mess up the ECU.

And totally illegal.


Only knew guys with cutouts in the olden days so they could be loud when they wanted, and quiet if they were in a residential neighborhood, or passing a police car. No clue how o2 sensors will react, or emissions test, but what the heck you can always disconnect if there are issues. Flex pipe would be a second choice for me.

Might be a fun experiment to try. Does it just allow a different path in parallel w/the old path, or is there some kind of door which prevents exhaust going down the old path, and so all of it has to go to the cutout path? How would you the driver do the switchover? From inside the cab, or do you have to open the hood? It would be interesting to know how this affects the intake manifold vacuum reading.

There’s some kind of door. Typically it’ll be solenoid operated, but manual works too.
But you 'd better check your state regulations. They may be illegal.

There are also pipes with a “dump” upstream from the exhaust system that have bolt on caps. Remove the caps and the exhaust takes the easy path right out the dumps. Again, these are not legal in all states.

I’d suggest sticking with a conventional Del Sol exhaust system. Any modifications carry operational risks, and unless you’re son is willing to take them…

I remember seeing exhaust cutouts listed in the J.C. Whitney catalog back in the 1950s and early 1960s. There was a mechanical cable that had a control handle under the dashboard to open and close the exhaust cut out…
I am currently trying to figure out if such a cutout could be installed in a Nissan Leaf (electric car) to make it sound more powerful. I assume.it would be spliced into the negative cable leading back to the battery.

lol …

@Triedaq Just stick a playing card in the Leaf’s wheel spokes :slight_smile:

Besides, a Del Sol is a Civic. A civic with an open pipe sounds like a gas-powered string trimmer.

As a kid. I remember the rumble of the old flathead Ford V8 with unmuffled exhausts. The unmuffled exhausts of engines that were not V8s didn’t sound the same. The old Flxible buses used Buick straight 8 engines with an unmuffled exhaust. They were noisy, but lacked the pizzas of a V8 with an open exhaust. I don’t think anything but a V8 sounds good with an open exhaust

I can understand the need to make an engine sound more powerful. I bought a Black and Decker battery powered lawn mower. I mounted a model airplane motor on the handle so that my neighbors know that I am mowing grass.
Back in 1954, Buick advertised that the new Buicks came equipped with a zero back pressure muffler. I would bet that in 50_years time, the exhaust system on the DelSol is designed so that an open exhaust won’t aid the performance. There used to be the concern with an open exhaust that when the engine is,shut down the cooler air coming back up the pipe could warp the exhaust valves.

My assumption is this cutout would be for use on a street car. If it was a race car then there would be no need for a cut out at all as the exhaust would be opened up no matter what.

Any benefit to this would be at wide open throttle and that would open up can of worms along with sounding like a run amok chainsaw.

Some may remember guys putting expansion chambers on older 2-stroke motorcycles and what those sounded like at 7K RPM. Glass cracking horrid…

@Triedaq,thats why they made reverse flow mufflers(you have to cap the exhaust on a turbo diesel tractor when you transport in open air,to keep from spinning the oiless turbo) the reverse flow muffler stopped the convection thay could pull cold air past the hot valves.

I had a friend with a 56 Ford with 2- 4 barrel carbs and manifold from a 57 T-bird . He put on an exhaust cut out, it made the car louder,and SLOWER.

@missleman If the Del Sol is a pre-96 model then it won’t have downstream (after the cat) O2 sensor. Just the upstream, which would probably be before the flexpipe, in that case it wouldn’t affect the ECU at all as the cut out would be after the last sensor in the exhaust.

I had a similar setup with my old Bronco, custom made dual exhaust, no cats, no mufflers, and since the 02 sensors were in the headers (had to weld a bung in them) there was no effect on the ECU as there was no 02 sensor after where the cat would normally be, as far the ECU knew, everything was completely normal. If you have an OBD-II car, with downstream 02 sensor(s), then there are things call MIL eliminators to “fool” the ECU into thinking everything is hunky-dory. I have them on my Mustang. It should be mentioned that if you live in an area that does emissions testing, then you’re basically boned if you run MIL eliminators and no cats.

I went to a minor league baseball game over the weekend, and during a break in play they brought this special-purpose truck to the field. As far as I could tell, the purpose was the players could through baseballs at it and try to break the headlights to win a prize. But the truck was interesting. It had a dual exhaust system, no tailpipes or mufflers so a lot of noise, and each pipe on either side direct from the engine was huge and pointed straight up, and flames of fire was coming out of both of them. It was pretty impressive.

I doubt it would pass emissions.