67mustang302

4Stroke Performance Tuning by A Graham Bell has a LOT of information from bottom end, to carb to efi to exhaust. Starts with the basics and goes through the advanced principles of some stuff

Soaring

Yes, you will gain some horsepower. I had a 1951 Ford flat head V8 back in the late 50's and took it to the track. I had welded a pipe coming off the exhaust pipe right in front of the muffler and ran it to the side in front of the back tires. I had a plate covering the end, and on race day at the track I would simply take that plate off and shut off the entrance to the muffler with another plate inside the pipe with a round metal that had a handle sticking up on top of the pipe. Everybody who raced back in those days had cut outs to gain more horsepower. You couldn't hear yourself think on the track.

dozierstang

Yep, I did a long investigation on opening up my exhaust before I actually did the work. Everything I found came back to gaining HP and losing torque. There is a line however where you will gain HP and torque but only up to a certain point, then you start losing the torque. It is the sound that you have to deal with then....as Soaring said, so loud you can't hear yourself think.

67mustang302

If you have a properly selcted/tuned exhaust system for your application and good mufflers you shouldn't even need cut outs. If I put cut outs on my car I'd just lose power everywhere, even high rpm. A good exhaust system uses the outflow of exhaust gas to generate a pressure drop in the system to help draw the exhaust gasses out of the cylinder/primaries. Putting cutouts on aPROPERLY tuned exhaust system will negate that pressure drop by causing a sudden drop in flow which prevents the high velocity drawing effect from occuring, and alsogenerate improper power pulsing. The 3 things a good exhaust system needs is enough flow to not be a restriction, proper power pulsing and enough VELOCITY to draw the exhaust out. The number 1 mistake people make is causing something in the exhaust system to be too big, which though it will POTENTIALLY alow for more flow, actually generates less flow, because there's not enough velocity in the system to move the exhaust gasses out effectively. Cutouts on a restrictive exhaust system will make you more power, but that's because you have the wrong exhaust system, cutouts on a proper exhaust system will throw the tuning off and cause you to lose power pretty much everywhere(except in some cases at very high rpms). An engine is an air pump, air in, air out, they both need to be efficient. Having cutouts, or too big a primary tube or too big an exhaust pipe, is just like too big a manifold or too big of a carburetor, it reduces velocity and efficency, and therefor power. [sm=rant.gif]

Soaring

"Properly" tuned exhaust systems is the operative word. I dare say that 2% of you guys have your exhaust "properly" tuned. But, I do agree that a properly tuned system is better than open headers, but open headers are better than 98% of the exhaust systems represented here for a gain in horsepower. Loss of torque? Yep.

blee69mustang

do any of you guys have it and just use it when your at car shows? thats what i was planning on doing, just open them up when i go to a car show. but keep them closed when i'm driving long distances.