Well, luckly enough on Saturday, poor turn out at the track, so open time trials, so deicide to do some cutout runs, with some tuning along the way.

best I could muster was 14.9 with cutouts open.
Closed them back up, and what do you know 4/10's just disappear like nothing.

But sounds so damn mean with them open, but can't figure out why they run slower??? 60' are the same. Guess I have to wait on a WB to see what going on.

O2s were about 920's open or not, if I pull fuel, knock appears open or not

any ideas??

CT

 

How far down the line are the cut outs?

 

Thats alot from cut outs... you may need to put them farther back how is the rest of your exhaust made? wheres the cutout? what size pipe are you running?

 

In my past experience cut outs work well, but you need to retune for them because normally the exhaust travels through your cats then mufflers not mention 6' of tubing so with the cutouts your going to run rich which needs to be adjusted to optimize power.

 

If the exhaust system is too much better at getting air out than the intake system is at getting air in, cylinder pressure will be lost. This balance is different for every RPM, probably1 most was lost at lower rpms with your truck.

 

exhaust system: no cats , 2.75" factory pipe off each header. cutouts are place where the last cat was, about 4" behind the cab on a my reg cab truck. then which is y-ed into a 4"inch short pipe into flowmaster "race series" muffer 4" in 4" out followed by 4" diesel pipe over the axle exiting at a 5 inch diesel tip. ( dad had a duramax exhaust system that he did not like, and was free)

I think James B. is on the right path. Same thing happen when I had cats cut off, took me while to work around the power loss through tuning. Just did not realize it thanks James B.

Cause if I pull fuel from pe table knock appears, I am think that my fueling is close.

thanks for the ideas, thinking I need to swing the balance of airflow back the other way. heads!

 

I lost 2 tenths with my cut-outs open.

 

Oops was still on Mj's sn I lost two tenths with them open.

 

Dang, I picked up 1 tenth with them open on mine. But my cutouts are way down the line and I still have my cats.

 

I had a similar experience with another vehicle. From what I understand, with the cutouts open, you've lost backpressure which is necessary to keep your cylinder pressures up. As soon as you open the exhaust, the backpressure drops and so does your cylinder pressure - and torque with it. In my case, my ET's went up, but my MPH increased - which indicated that I was making more peak HP, but at the cost of midrange torque. Unless you've make cam and tuning changes, you probably will be better off running through your mufflers...