onebadyfz450

After my last track attendance, people were saying that my car doesnt have enough backpressure.

Its a 95 5.0
Stock Manifolds
Upr Non catted X-pipe
Magnaflo 2 1/2 Tails
Slp tips

so no cats, no muffs. is this bad, if i need to switch to muffs, what type....
the Slp kit, has those resinators, do i need something like that or muffs,
thanks[/align]

1990lxhatch

Backpressure is generally a bad thing. Mufflers are actually good for a straight through exhaust system because they create just enough backpressure (about 1psi)to help scavenge spent exhaust gasses from the cylinder. This is a similar principle to long intake runners and how they help fill cylinders with air using the momentum of the moving air.

You don't NEED them. Four stroke engines can run just fine with absolutely no backpressure. But to get an idea of how backpressure affects a fours stroke - pull your headers and run open ports sometime. Runs great up high - runs rough down low. Then run open headers -runs nearly the same as it will with a full exhaust system

dudeboy

Backpressure is the wrong term...
'pipe length tuning' would be more appropriate...

Backpressure means there is a restriction, which is bad.

Tuning the length of the primaries can help with scavenging.
But,
Unless you are going to experiment with a variety of primary lengths, don't worry about it...
Just run what you have.


The guys telling you to increase the backpressure... Did they drive Hondas???

onebadyfz450

no everyone that was giving me ideas drive mustangs.
ok my car runs a 14.9 which is ****ty, so thats what they came up with, they said, having no muffs gives me no backpressure, so thats causing my car to run like crap.

67mustang302

Backpressure = bad. Most people confuse backpressure with exhaust pulse wave tuning. A shock wave moving through a gasseous medium is TOTALLY different than the movement of the same medium, which would create pressure. Ideally you want 0 backpressure with ideal pulse wave tuning to assist in scavenging, but like was said, unless you're going to dyno tune a whole series of different primary lengths/diameters, don't worry. And you have stock manifolds, so if anything you have backpressure that's restricting power somewhat(possibly).

WhiteWindsor

For your car, 14.9 is about right. What are your friends running in their mustangs that they seem to think yours is so slow?

cleanfitty

I believe that on a stock engine you should have something to create some backpressure to give the exhuast some turbulance and help scavenge gasses. (if you get me a bean burrito I can scavenge some gasses pretty well [:@])

If your engine is all race, than the lessrestriction thebetter.

dudeboy

[&:]Guess that's why everyone waits until the rest of the motor is HEAVILY modified to upgrade the exhaust [&:]


It ain't about backpressure

cleanfitty

I said "some backpressure" in other words "some restriction"

I don't give a rats **** if you call it 'pipe length tuning'

Upgrading exhaust on a stock motor yeilds some very small results and most people upgrade their exhaust for primairly fora louder more aggressiveexhaust note(and looks).

This is why every exhaust manufacturer suggests that going too big will actually hurt performance.

This is why no one runs a dual 3" exhaust system (unless you have a massive build).

This is why you don't get headers with real huge primaries (unless you have a massive build).

This is why almost everyone who runs dumps says they felt a loss in torque when they took the tails off, and most people who add tailpipes feel an increase.

From what I have read, the original poster has a stock engine, hence my responce.

67mustang302

Backpressure is undesirable, period. Pressure wave tuning is TOTALLY different than backpressure. And pressure wave tuning is NOT about running the largest exhaust possible, it's about running the exhaust system size that yields the best power(which is usually much smaller than most people think). Basically backpressure is resistance to flow, and exhaust needs to flow to be exhausted(that IS why it's called exhaust after all). Pressure wave tuning is about having the proper pipe length and diameter so as to generate pressure pulse waves in the primaries that travel back up the primary and generate a vacuum effect as they rebound off the exhaust valve/port, and thus give better scavenging. Ideally you want good wave tuning with no backpressure. Backpressure means that not all of the exhaust is getting out of the cylinder, since there's a resistance to flow.