I am guessing your thinking on the tune to fatten it up a tad with open exh. As for me I just run capped up all the time and leave everything the same at the track as how I drive on the street. I run a full exh system but I use a TTI mandrel bent X-pipe 3" system and the Ultra-Flow mufflers so I dont know if I would pick up much uncapped anyway. Ron

My old DartSport had a 3.5" X-pipe and 3.5" Magnaflow race mufflers. It was fairly quiet, people used to tell me they couldn't hear me pull into the staging lanes. The car would go 9.90 with the exhaust system and 9.90 with it removed from the car, didn't slow it down one bit, if it weren't for the 75 pounds it added, it would be a hair quicker through the exhaust.
If you're running small pipes and restrictive mufflers it's gonna slow down through the exhaust.


As far as the cutouts go, the very best way to mount them is to have the exhaust go 'straight' out the open cutouts, and have the street exhaust system branch off that, if that makes sense, I'll attach a photo.
I don't have room on my Duster to do it that way so my cutouts will be a couple feet after the collectors and the open cutouts will brach out the side. It will still sound good though and will let the pressure out.

Mine will be more like this....

Thx for the input

I asked about tuning because I found my mph dropped a little with open cut outs - I kind of assumed it was either a loss of back pressure or leaning out.

If improvement can be seen by using cut outs with a fatter tune....Ill give it another try.

My exhaust might be a little restrictive...my mufflers aren't.

I have found that MOST cases with open headers to exhaust
will need a different tune.. open will tend to be lean.. anything
you can do to help reduce back pressure will help... adjust the
tune for max MPH

back pressure is no friend to horse-power

I would think in many (if not, most) cases Capped Cut-outs themselves would ADD some backpressure to the system when they are closed for normal street operation . You are somewhat dead-heading a pressure wave back into the main flow stream. That why I think if you bridge an H pipe across them (instead of caps) you're adding system volume and reducing some Db levels at the same time.