So whats the deal with the exhaust cut outs? they caught my attention and seem interesting but what exactly is the purpose? from going to street to strip? or just to be loud as he|| for the fun of it? will it affect header/exhaust performance? thanks guys.

 

im not gonna lie i got my cut out just to **** off the *****s who think louder is faster. i felt a good loss of low end tq with my l98 but it also seemed to pull a bit harder once i got above 3k. performance wise you are better off with a 3 inch exhaust or even true duels if you are making the power.

 

For a carbed car, theoretically, the cutout should produce (or rather free up) power.

the exhaust exits sooner, and has less obstacles, and less backpressure to fight before exiting. Even if its a 3" full exhaust, it is still less work for the exhaust to exit sooner.

In any case, when i upgraded my exhaust from factory, to a 3" y-pipe, and a high flow cat, the car felt VERY VERY light, with lots of torque. It felt like it weighed half as much, because of the power freed up.

This exhaust also has a cutout, and at the track, when the cutout is open, it seems to have a tad amount of improvement, but i dunno if you can justify it with a cutout. Definately sounds loud though.

However, i think i picked the wrong cutout to be able to maximize the scavanging effect.

 

A properly located cutout will allow the headers to do their job to the fullest. It has to do with exhaust pulse scavenging and raising the engines volumetric effeciency. The real benefit is felt when the air/fuel ratio is adjusted to take advantage of the deeper breathing. One tune for the track and open headers. Another for when the exhaust is buttoned back up.

 

So where is the proper location for cutouts ?

 

After Y pipe before Cat...

the electric ones are nice... you can partially open by tapping the switch... until it opens fully...

Raf

 

The proper placement for the cutout will depend on the RPM range and peak
HP you are tuning for. Valve timing is also considered among other things.

The opening of the cut-out to the atmosphere determines the tuned length
of the secondary exhaust pipe.

If you don't have the software, or formula to figure it out, the next best thing
is to place the cut-out before any major restriction (IE: catalytic converter).

You will however feel a drop in low end performance because of the change
in tuned length. A shorter secondary pipe caters to higher RPM use. This is
best utilized in high RPM racing.

 

Just keep in mind, its illegal to bypass a cat. But if you dont care about that, it should be placed just after the headers (as close as possible), before any major bends, but also in such a place where the exhaust can exit PAST the car.

I put mine IN PLACE of the catalytic converter.

 

Is that your recommendation for best power, or ease of installation?

 

I see what you mean, now, i have my headers connecting to a Y pipe to a single cat to the pipe that goes to the muff. so that means i would only need one correct? or two? one for each end of the headers? i know they are illegal but its not like id be riding around all day everyday like that..screw that. where can you get the electric one from? in year one, they have the ones where you can dis-connect the flanges im guessing just by hand.

 

I have a Race Ready E-cutout where the plate goes in my Borla.

 

Here some times from the track before the head swap, with my cutout open and closed. The car:

86 IROC-Z
305 LB9 TPI
700R4
-Flowmaster muffler only, replaced cat with 3in cutout.
-K&N's, MSD Cap, Rotor, Spark Plug wires(the basic tuneup stuff).
-Everything else was basically stock, including the exhaust manifolds.

These are 1/8th mile track times.
9.87@ 70.09 MPH w/2.16 60ft: Cutout Open

9.90@ 68.50 MPH w/2.12 60ft: Cutout Closed

On the 9.90 pass everything was better time wise, until the 330-594ft mark.

 

Very interesting question, would i benefit from putting a cut-out on my car. I have a 3 inch single catback. I don't want to tune it just for the cut-out, would i benefit from this.

 

For power.

Dont take this as gospel, as i dont fully understand the scavenging effect. Its dependant on many things, like engine displacement, stroke, firing order, and type/length of exhaust.

But i would imagine, if the exhaust exits sooner, its better, would be the same effect (or close to) as open headers, which is what you are trying to accomplish.




If you have a y-pipe, just get a single cutout. I have shorty headers, and similarly shaped stock y-pipe (only larger), and i struggled to see how i could put two cutouts in there and make them fit.

If you have longtubes, or if your y-pipe goes around your tranny, thats different.

 

I'm no expert, but I believe with supporting mods(headers,cat-back,etc..) you'd probably see some gains up top.