exhaust question
 

The other day i took off my exhaust system and just keep my headers.. Love the sound it makes.. turns everyones head. anyway. i know that with that i have a big power loss.. from what i understand thats because of no back pressure.. but wouldnt back pressure help? no resistance on the valves trying to close? then would changing from a 2 1/2 exhaust with dual flows to a 3in headder and 4 foot long 3" pipes and turn downs make me lose power too?

Running open headers will also turn the heads of police officers so get ready to start getting tickets. No matter what size the exhaust it will give you some back pressure, so I am not sure what you are after. Do yourself and the people that live around you a favor, install some kind of exhaust.

This backpressur issue always starts a huge debate and I have never seen a totally satisfactory answer but will be glad to give you my understanding of the problem.
It is a complex problem because we expect our engines to work over a wide range of rpm's and temperatures, both of which dramatically impact the exhaust. For best power, minimum backpressure is best, but at the same time, exhaust flow velocity shoud be maximim. Now, these are two things that can't exist together and therefore a balance has to be reached. Generally, more power can be found by opening up the exhaust but often at the expense of low end torque. This is becuse opening up the exhaust will lower the exhaust gas velocity which is vitally important in helping the exhaust gas to be removed from the cylinder, and to help with the intake charge comming in as well depending on your cam overlap.
Think of it as water flow in a hose. If you have a garden hose flowing 5 gallons a minute you have good pressure, but it is hard to get more water out. If you swithch to a 5 ft culvert, the 5 gallons a minute is just a dribble, no pressure, but also no velocity.
Your exhaust system needs to be balanced to your driving. If you don't rev the engine, or have small displacement, smaller exhaust is better. If you have a big block at the drag strip and live in the 6000 rpm range you want big open exhaust. Most hot rodders find power gains by going to slightly bigger exhaust, which will help support more power (bigger cam, more air, more gas, etc.)
If you have lost all your low end torque you probably need the put the exhaust pipes back on to get your exhaust flow back up. But I'll bet it sings at high rpms.
Related, have you changed your timing? When I had open headers (installed, drove to muffler shop) my timing was way off and didn't have a bit of power.

Thunderbolt is right on. Back pressure "per se" never increases anything except loss. An exhaust velocitity in the headers in the right amount will help in removing exhaust from the chambers and cramming more charge into the chambers, but only at a certain RPM range. Scavenging is the name of the game here.

Balancing the headers with the torque range of the engine is absolutely necessary for good performance.

Rev