Just curious, I had cutouts put on when the exhaust was done up for the ls1 swap because the car has a 2.25" dual system and I wanted to be sure the exhaust wasn't holding me back...but it actually seems to run better with them capped. Could it just be feeling increased torque? Or could the cutouts actually be cause changes in the pcm what would cause a power loss?

I do know for some reason only 1 o2 sensor hasn't been tuned out, and with the cutouts open my mpg goes to absolute ****. Seems to run fine but almost like it kinda "bogs" a little in mid range rpm versus having them closed.

The cutouts are between 1.5' and 2' behind the collectors of the longtubes btw.

 

That actually sounds about normal for an open cutout. There always is a little bit more torque with it capped.

 

sounds exactly like what I just went through. my car got tuned with a VERY MILD pinhole exhaust leak downstream of the O2s and caused it to be tuned incorrectly. This resulted in shitty gas milage and complete loss of power in the bottom end. This is because every pulse of the exhaust actually sucks air in that pinhole causing the O2s to read clean air, resulting in false lean condtion. This, in turn, caused the pcm to richen up the A/F and make it act like a turd. Got it sealed up and retuned. BAM, the car with open exhaust runs now with more power than it does closed like it should. Sealed exhaust is key for a tune. After the tune, open her up like she should be!
~Austin

 

My LS7 with ATS 1 7/8 headers dropped about 17hp with my DMH low-profiles open. Sure did sound cool tho.

 

show off.

im getting my car dynoed tomorrow and im curious about this too. i notice a lot better low end throttle response when i cap off my cutout.

 

that sucks. sounds like the tip of the ice berg if you ask me.
maybe you should let me take that car off your hands...




give me the car!

 

You can have the same problem by putting the cut out to close to the O2's. I found out the hard way after killing a few plugs.

 

sorry, sorry, sorry. I get a little excited.
I did gain a few ft/lbs with them open, but the BEST thing is its great for cookin' fart can rice.

 

wonder if that might be where some more of my power is hiding...on the dyno I had them open and it took me a good several tries backing onto the stupid rollers (i suck at backing into small spaces)

I'm just searching everywhere I can because the car only put down 325hp/340tq (granted I was only getting 92% throttle at the time) so I've kinda been scratching my head but I keep noticing it feels slower with the exhaust open

if that turns out to be the case then so much for trying to bypass my small exhaust haha

 

I lose 15rwhp and 14 rwtq with my cutout closed....

 

I gain more power everywhere with my cutout open. It's hard to compare them on the dyno. My a/f with the cutout open was 13.2 up top, capped the cutout and it went up to 13.7 but still didn't make more power than with the cutout open. Plus, I like it loud.

 

Depends on the tune. Do some WOT tuning with it open and you'll probably make more with it open. Tune it closed you will be better off closed.

 

I've run my car at the track many times with the cut-out open on some runs, and closed on others. I could not tell any difference in times or mph with it opened or closed. I don't think it sounds any better with it open except at idle it sounds good. Cars with cutouts don't sound good at WOT imo. Duals with bullets sound much better.

 

I have true duals without cutouts. I wish I had dual electric cutouts tho. I would sacrifice 10 hp for how loud cutouts are. My exhaust is pretty loud so I'm leaving it alone.

Weird tho, I would think with the cutout open you would gain hp.

 

You're right about the sound.If you are not making big power and you have a free flowing exhaust you won't see a big difference with the cut outs open or closed.

 

I always thougth mine felt stronger (SOTP) with it closed. I did however notice a significant time improvement with it open. It felt like I just lost the low end grunt with it open. Either way the time slips show me to be wrong.

 

same, mine feels like it losses a little grunt down low open but gains a lot up top...

open ex: just normal driving say rolling at 25 and punch feels stronger capped, but if i hammer it on the highway at 60 or 70 much quicker open!

 

I feel a definite off-idle loss of torque with mine open.

Ran by best 60' with it capped.

 

2mph at the track was gained by having it open over a stock catback

 

You'll get better TQ in the bottom end of the powerband with it closed, however, the engine will be able to breathe better on the top end with it open. Basically you will feel a better take off with it closed, but with it open you'll gain a couple horses when you're near or at WOT