blackfbird98

trying to explain the whole backpressure myth to my buddies, hoping to get some REAL information as to whether backpressure really matters on our v8's. both of my buddies drive ls2 gto's and seem to think that without backpressure they will blow their motors. (i am running pacesetter lt's no cats no mufflers tht dump before the axle on my 2000 z28) pretty much im looking for an explanation for backpressure about our ls cars and when it really comes into play.

CamaroZ28_LS1

iTrader: (5)

Well a car needs some back pressure and exhaust scavenging to help with torque as far as I know... It won't blow an engine up with out any back pressure. Running long tube's greatly reduces back pressure and increases exhaust flow, the tubes are tuned for scavenging to produce torque still. But you do lose some low end torque with header but gain top end hp and torque. I have had headers to a straight through 3" header back exhaust with no muffler and my engine was fine. Now if you were to run open heads, the heat would destroy the heads.

Turbo cars need back pressure in the exhaust to create higher exhaust pressure to spool the turbo. It depends on what and how you use your exhaust for your set up. just a common idea.

RPM WS6

iTrader: (3)

Back pressure does not make power, but scavenging does.

As far as "blowing up the motor", if they actually think that a lack of mufflers or cats will cause this, then they should really spend some time researching the basics of engine operation and modification before doing anything with their cars. I think they may be the victims of some seriously bad information.

blackfbird98

great info i appreciate it guys, if you find anything else interesting please by all means post it up cause i will be showing them this they are very stubborn and i want them to have the right idea and not go into modding blind

SexyTransAm

iTrader: (6)

lol u need new friends

Element

iTrader: (5)

Backpressure reduces exhaust velocity, which is the exact opposite of what turbo guys want. The "turbo cars need backpressure" is something I see fairly often, but if you think about it, you want the highest pressure differential possible between the manifold outlet/turbo inlet, and the turbo outlet, which means absolutely no backpressure on the turbo outlet side. Pressure on the turbo inlet side is a function of the flow characteristics of the turbo and the engine it's attached to, and doesn't factor into the "exhaust backpressure is a good thing" argument.

Backpressure is never a good thing, on any engine setup. A combustion engine is nothing but a big air pump; anything that hinders it from pushing air out the exhaust side (like backpressure) will have a negative effect on the amount of power it can make. Scavenging is the opposite of backpressure - creating a vacuum in the primary that helps suck exhaust out of the cylinder when the exhaust valve opens, rather than putting a positive pressure on the primary side of the exhaust valve, which slows the removal of exhaust gases from the cylinder.

09camaro383

iTrader: (2)

Nascar's and Drag cars only have headers with minimal turns and sometimes their engines blowup but not because they don't have enough back pressure but because all the power they are producing and always finds a weak spot

jimmyblue

iTrader: (11)

Volumetric effciency has as a fundamental term, the
input-output pressure difference.

Backpressure while the exhaust valve is open, and the
piston is still on the power stroke, would aid torque.
But this is not how things are supposed to be, ideally.
Cam phasing might give you some EVO time before you
bottom. But the same backpressure opposes the piston
for the remainder of the exhaust stroke, for net loss.

blackfbird98

lol i know, they were gettin on my nerves pretty bad they insist that you NEED backpressure and that it will hurt the car to not have it.

zachrywd_01TA

Z28_LT1

iTrader: (2)

+1 on that.