Backpressure
Originally Posted by ls1_chevelle
So why run a X-pipe? lol
-Matt
-Matt
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No back pressure makes for great top end HP. However longer thinner tubing makes better low end torque and lowers the tq. curve by keeping exhaust velocity up, which aids exhaust scavanging. Its not actually the backpressure that aids in low end, its the smaller longer tubing, and sadly backpressure is a side effect. The key is to find a happy medium.
their is no need for any back pressure and agree with artic white. i have the biggest i can get and fit 4" lookes like my diesal truck. have no issues just compliments on the sound......
Launching!
Joined: Dec 2001
Posts: 222
Likes: 0
From: DFW, TX
Originally Posted by Orange99Z
An X-pipe scavenges the exhaust from the opposite cylinder bank. Wouldn't that create less back pressure? The engine doesn't have to work as hard to push the exhaust out if it's being pulled.
Originally Posted by GuitsBoy
No back pressure makes for great top end HP. However longer thinner tubing makes better low end torque and lowers the tq. curve by keeping exhaust velocity up, which aids exhaust scavanging. Its not actually the backpressure that aids in low end, its the smaller longer tubing, and sadly backpressure is a side effect. The key is to find a happy medium.
try this answer on for size....
you dont need any back pressure if your cam timing is perfect. but cam timing can be 'perfect' only at a certain rpm range and it's a narrow one at that. the example was the true racers run open headers. yeah, thats true, but they also run their engines within a 1500 rpm window or less.
the average racer/street car sees a 4000 rpm window and in some cases is restricted to emissions or sound regulations...not to mention the lifespan of the engine internals. you cant have a perfect setup all the time but that seems to be what everyone wants....or tries to do...an it usually leads to a lot of headaches and mismatched setups.
your best bet is to get exhaust that you think sounds nice, flows a little better, and fits good.
/bow...leaving stage.
you dont need any back pressure if your cam timing is perfect. but cam timing can be 'perfect' only at a certain rpm range and it's a narrow one at that. the example was the true racers run open headers. yeah, thats true, but they also run their engines within a 1500 rpm window or less.
the average racer/street car sees a 4000 rpm window and in some cases is restricted to emissions or sound regulations...not to mention the lifespan of the engine internals. you cant have a perfect setup all the time but that seems to be what everyone wants....or tries to do...an it usually leads to a lot of headaches and mismatched setups.
your best bet is to get exhaust that you think sounds nice, flows a little better, and fits good.
/bow...leaving stage.
TECH Senior Member
Joined: Apr 2002
Posts: 6,080
Likes: 17
From: So.Cal.
I think you don't need or want back pressure;
back pressure is just a by-product of [lack of] tube diameter and [excessive] tube length;
if you could produce 'negative' back pressure, you would suck out the combustion chambers and improve cylinder fill.
back pressure is just a by-product of [lack of] tube diameter and [excessive] tube length;
if you could produce 'negative' back pressure, you would suck out the combustion chambers and improve cylinder fill.
TECH Fanatic
Joined: May 2004
Posts: 1,030
Likes: 0
From: Wichita KS
yeah, its a game of velocity. Higher velocity is the idea, but with only a certaing amount of gas being expelled under force, velocity becomes inversely related to the size of the tubing. BUT after a certain point the smaller point does not allow for enough gas to escape when the engine is pumping the most exhaust gases out. Therefore there is a happy medium. Also things like high velocity merge collectors and x pipes can help increase velocity without decreasing overall flow capacity.
Its all about velocity.
Its all about velocity.
Thread Starter
Staging Lane
Joined: Feb 2006
Posts: 58
Likes: 0
From: Simpsonville, SC
I am running open headers on my car now...been that way for about a year. I have a TSP X-pipe but it slowed me down and now I want to put some type of muffler on my car b/c it finally getting annoying...I was thinking bout 3 1/2 bullets..
When I had the heads and cam put on my car I was running QTP's, off road y-pipe and an SLP loudmouth catback (basically straight pipes out to the rear of the car). The car was way too loud and it seemed like it wasn't making torque. I got rid of the Loudmouth and put on a Magnaflow muffler and the car was night and day. So I think that back presure is important if you are running a full exhaust. It might be different if you're dumping out of the headers but it does make a difference on a full exhaust.
