How much back pressure?
 

with a LM2 do you lose back pressure like in the LM? And does an x pipe eliminate your problem of back pressure or just improve it?

thanks

any aftermarket exhaust that flows better than stock makes you lose back pressure...you really lose it when you get highflow or remove your cats.

x pipe will make yer exhaust sound rasssssssssssssspy

i know that and that doesnt bother me. My question is i was told by a shop that for a v6 x pipe is the way to go b/c you will lose to much back pressure with a h pipe (which i dont know to believe or not)

Fuck that california shop..the pressure should be the same in both an H and X unless the diameter of one is larger.



H pipe, ched.

Ideally, to make the most power, you want 0 back pressure but realistically, you need. However, the amount you want is very small so what they are saying that it will decrease back pressure too much makes no sense. Plus, x-pipes reduce back pressure better than h-pipes which is part of the reason why they make more power over h-pipes.

You can loose power by having too much of an open exhaust. Whether or not this will ocurr with an LMI on a V-6, I have no idea and I am not sure if any really knows. If I were you, I would call SLP.

You do not need a crossover pipe on the 3.8 as its an even firing motor. Meaning it fires two pistons at the same time so a crosspver would do nothing for it.

so its the actual xpipe that gives the exhaust the raspy sound? I didnt know that. On the Hpipe is the lateral pipe that connects the 2 pipes from the headers hollow(gases flow into it) or is it just a connection piece?

Yes, the H-pipe is tubing so gasses flow into it. Hence why it's a type of balance pipe.

you want 0 backpressure, but it's pretty unrealistic and anything that isn't high reving, high compression and or blown with a lot of boost. If I had a nickel for every post saying you loose torque or hp when you loose back pressure I could buy a large island. Back pressure is very often confused with velocity. What happens in an open or over sized exhasut is, you lose velocity, thus creating pooling of spent gasses in the combusition chamber which causes you loss of power. a slight amout of back pressure on a stock engine may maintain some velocity, so indirectly it can be traced back to back pressure, but it really is loss fo velocity that causes loss of power.


the easyest way to visualize this is a city that is on a large lake or ocean. At the shore you may have a 2-3 mph breeze - open pipes with nothing to maintain velocity. Go a few blocks in where there are tall building and streets running perpindicular to the shore and you'll notice the breeze is a lot stronger becasue the same volume of air at teh shore that was floating about all happy and loose is now being psuched into little alleys' - exhasut manifolds and by being pushed into the smaller space tall the air particles are fighting for their place and get some speed going. go tot he other end of the street that dumps inot a field and you'll notice the same happy light breeze you did at the shore.

or on a golf cousre that is wide open on the front 9 you'll say, wow, what a nice day, no breeze syunny warm... he bck 9 that may be carved amongts the trees, you'll be like hey, it sure got windy all of a sudden... same effect.

So, if we use your logic, then it would be smarter to get a smaller pipe so the velocity would be faster.

I think the whole point is to have the right balance. If you have the right amount of velocity, you will have the correct amount of back pressure. If you have too much velocity, then you will also have too much back pressure. If you have too big of a pipe and too slow velocity, then you will have no back pressure. So, if you could actually measure the back-pressure, you would probably be able to say if you have enough, too much, or not enough velocity.

The fact remains, if you make your exhaust too large, you will loose power. If you make your exhaust too small, you will loose power.

No, you need a correctly sized system like you pointed out. I was using extremes as an example becasue soo many people dont' get it. kind of like trigonometry.

holy crap lot of info i have to catch up on and read this all

they say they have no clue about the v6 and have never worked on them.
but they recommended the power flo.

OMG!!! a logical and informative (and correct) post about back pressure...BRAVO!!! :worship2:

Well, that was a nice try. At least they were honest.

haha well Ive heard some clips on youtube with sixers and powerflo was loud but not demonic. But thats fine i think ill will test out the p flo

evil... that was a great detail but I think you forgot to mention what all that wind in the park is for so I'll pick it up:

the simple act of creating a little restriction and thus trading volume for velocity has effects at the front and rear of the gas pulse and creates a sympathetic pull in the rest of the system. By increasing the velocity to the point of diminishing returns you create the right conditions for the front of an exhaust pulse to pick up speed and that causes it to literally drag the tail end of the pulse from the cylinder with more force than otherwise possible (this allows your NA cams with big overlap to work best at filling the cylinder). It also causes a pressure differential at the open faces of each of the other exhaust primary pipes upstream from it and allows that famous scavenging effect to take hold.

Basically, gas in a tube acts like a string. If you pull the front of it hard enough the rest will follow. If you use open flowing mufflers then the gasses will be able to escape faster and at higher overall volume which is good for power but the rest of the system needs to match or things get random.

Fact is fact though that the highest output cars in the world use just open headers. Those cars also use power adders which changes some factors. Any car using blower or turbo grind cams would do just as well to open the snot out of your system from headers back since boost oriented cams have low to no overlap and scavenging them doesn't really work well like it does on NA cars.

For cheddar... I don't like LM's on 6ers. Sounds chitty to me. I do really like magnaflow but they don't sound particularly muscular on 6's... just better than LM. Flowmaster sound ricey to me on 6's.

I an going with the power flo mufflers