question about backpressure and sidepipes...

[D347643]

i finished installing my sidepipes today and despite 90% of stangers flaming them and glasspacks but i think it sounds pretty badass. they are 3 inch all along the outside but right when it curves (behind the front tire) it goes to 2 1/8 at the tip for like 2 inches (how the pipes came) but then its 2 1/2" all the way to the headers from there.

my question is.... it almost feels like my car is a little slower now and could that be due the the bottle neck when it is 2 1/8 for 2 inches? i would have made it bigger than that but the pipes are chrome and if I cut the chrome i heard that it will start peeling off. i figure that backpressure is good, to a point, but you need a decent freeflowing exhaust also

thanks,

Drew

 

[88stangmangt]

it feels a bit slower because you killed most of your backpressure i once wanted to run side pipes but decided not to due to the lack of back pressure.

P.s. those 3" pipes arnts helping either.

 

[D347643]

yeah i know about the 3 inch pipes and them not helping haha. is the exhaust size/backpressure directly affected by hp? i had planned to run an s trim or turbo with the 351 im about to drop in, would that be good for 3 inch piping?

Drew

p.s. if i recall, having no backpressure is nothing a turbo couldnt fix

 

[88stangmangt]

ya but............. you never stated that above a 351 would do fine with 3" but mufflers are needed to keep up the back pressure.

 

[mattfleming]

real common misconception.. backpressure is BAD. exhaust velocity is GOOD. Exhaust is tuned on motor output. a car with a low cam, torquey manifolds, small tube headers, etc. are best suited with a smaller pipe. This lets the exhaust have good scavenging in those RPMS. thast why a stock system makes good torque in most scenarios with smaller pipes. When people go to headers, they complain of loss in low end. However, this increses the efficiency in the upper RPMS.. which is why with breathing modifications you get more power up top.
If you were to match your 3 inch pipes with a victor manifold, a x cam, etc the car wuold absolutely fly (assuming you had the headers to match) and pull higher RPMS.. where it is pushing more air and scavenging would be present in those RPMs
If you dont have a lot done to a motor.. smaller pipe is best.. if you have things that increase airflow, its better to go up in size. a majorly upgraded motor will require that big pipe.
backpressure is bad. plain and simple. it causes a pumping loss. instead of scavenging and pulling gasses out, it takes power from firing cylinders to push the gas out of the pipe. However, this smaller pipe will probably make more low end torque.. so it will feel faster to an extent from throttle response. however quarter mile times will prove you wrong. Hope i cleared this up. DONT go sticking a potato in your exhaust for some pressure
straight through mufflers are great.. straight through mufflers with 3 1/2 inch openings arent that great. all about balance.