Interesting Exhaust Info....

[VMax2007]

I am not an exhaust expert and I did not write this, but I found it very interesting and I did learn something, so I thought I'd share it with you guys (and gals).....

 

This is an exhausting topic.....

Just covering some of the basics of exhaust sytems:

To start we all know that increasing pipe size increases power ... to a point. If your car has single exhaust it is well worth investing in dual exhuast, even a poor system can increase mileage by 20% or more.

With a few exceptions, small blocks like 2" up tp 2-1/4" depending on cubic inches and the level of mods done to the engine.

Big blocks generally like 2.5". What is overlooked is how much 1/4" increases the area of the pipe.

 

2" is 3.14 square inches

2 1/4 is 3.98 " "

2 1/2 is 4.91 " "

3" is is 7.07 " "

 

You can see going from 2.5" to 3" increases the pipe size by over 40%. This is very important as will be discuss later.

 

Most are familiar with the H pipe this ties a dual exhaust together & was used from the factory on most High Perf Big Block applications. What this does is at higher rpm you will make excessive pressure in the exhaust in pulses as the firing cylinders push the burnt gases out & this allows the pressure to cross over to the other pipe instead of creating a blockage that can be felt at the cylinder head & allowing the exhaust to be more efficient. These will increase power & mileage even on the small 273 /318 CI engines.

The newest idea is the X pipe, this crosses the left exhaust into the right tailpipe & right into left. These have been proven to be more effecient than the H pipe & still allow the balancing effect of the H pipe. They also make the exhaust quieter but remove the distinctive right & left sound, The 2 tailpipes sound the same with a drone instead of firing left & right. I have made my own X pipes & find they fit far better then off the shelf X pipes.

When installing an X or H pipe be careful with the placement. It is better to have it behind the tranny to allow removal when neccesary.

There are 2 ways of bending pipe. Most places have a bender but it crushes the pipe as it is bent & forms ribs into the pipe as it is bent, All factory systems were bent this way, but both crushing & having ribs in the pipe restricts flow. The other way to bend pipe is mandrel bending where a plug is used inside the pipe as it is bent to keep the pipe the exact size & perfectly round, these will make more power. TTI ( Tube Technologies Inc) has an awesome product. They are mandrel bent & fit perfectly.

Stock manifolds are basically restrictive & are designed for production ease over power, except in some cases of the early max wedge cars where elaborate manifolds were cast. Some other manifolds are far better than others & most can be ported to help power & still retain the stock looks.

For more power you need headers. These are difficult to install can make spark plug changes tough & often leak if they are poorly made. The advantage though is first smooth mandrel bent tubing & scavenging. Scavenging is the effect of the hot exhaust exiting in a hurry & by using a long primary tube the pulse of hot gas will leave a vacuum behind it. This pulse vacuum will pull the next pulse of exhaust into the header, this effect is not a minor one. This will also pull intake air into the cylinder & can increase cylinder filling to above 110% at higher RPM. Most manifolds & shorty headers cannot do this as the individual runners inside the manifolds are too short to be effective. Again TTI has an awesome product for quality, fit, & spark plug changes.

Backpressure, this term is misunderstood. Back pressure is real & affects the exhaust. A poor flowing muffler will create a plug in the exhaust & that is backpressure as the engine has to work to push exhaust through the muffler. Most mufflers do not work the way you would think looking at them. Often the mufflers you can see right through are extremely

restrictive, while others with odd deflector plates inside kill off the pulses in the system & increase flow. It is worth buying good mufflers. Some will actually help scavenging even with manifolds as the whole exhaust system will help pull exhaust away from the heads.

The other use for backpressure is "you need backpressure to make power". This is not true. What is needed is velocity. This is where we get back to pipe size. Often a smaller system will make more power than a larger system as the exhaust leaving is kept at very high velocity in the smaller pipe. This is what creates the very important scavenging. If the pipe

size is increased the flow slows down & power is lost whether in the primary tube of a header, or the exhaust system behind the header or manifold. As seen above, increasing a pipe by 40% will make a HUGE difference in velocity & scavenging.

With most cars being operated 90% of the time in the under 4000 rpm range it is better to err on the side of smaller

 

 

instead of bigger. Whew! I'm exhausted.....

[MaxLTZ]

Interesting indeed; nice post.

 

I'm actually cutting in a Super 44 in to my stock VMax exhaust tomorrow. I plan on keeping the headers, cats, and associated pipe stock. That would be the 3" pipe from the headers to the muffler, however I am changing the 2.5" bit from the back of the muffler to 3". I doubt that will have much if any effect on the overall exhaust flow.

[Bobslob]

Interesting indeed; nice post.

 

I'm actually cutting in a Super 44 in to my stock VMax exhaust tomorrow. I plan on keeping the headers, cats, and associated pipe stock. That would be the 3" pipe from the headers to the muffler, however I am changing the 2.5" bit from the back of the muffler to 3". I doubt that will have much if any effect on the overall exhaust flow.

 

Your truck came with headers! man think of all the other guys that got ripped off.

j/k I think you mean exhaust manifold.

sorry just had to be a smart a$$.

[BigJayDogg3]

Umm . . . speaking hypothetically, and asking the question for people who don't know, not me cuz I already know . . . what is the difference between exhaust manifolds and headers?

[Mark_in_Tulsa]

I think this was written up for old school muscle car motors.

 

The LS motors have a pretty large amount of valve over lap in them. At least the 4.8, 5.3, and the 6.0 do. So you do need the right amount of back pressure or you will lose low end TQ. Which is where we spend most of our time driving in our brick shaped trucks. So losing back pressure to an extent will hurt our mpg, due to loss of TQ.

 

But if your racing, and have the right cam...etc then yeah you need a higher flowing exhaust.

[BigJayDogg3]

Couldn't you also get a freer flowing exhaust if you had forced induction?

[MaxLTZ]

Interesting indeed; nice post.

 

I'm actually cutting in a Super 44 in to my stock VMax exhaust tomorrow. I plan on keeping the headers, cats, and associated pipe stock. That would be the 3" pipe from the headers to the muffler, however I am changing the 2.5" bit from the back of the muffler to 3". I doubt that will have much if any effect on the overall exhaust flow.

 

Your truck came with headers! man think of all the other guys that got ripped off.

j/k I think you mean exhaust manifold.

sorry just had to be a smart a$$.

 

 

Oh yeah, man. Its a new option. High-flow headers!

 

You know what I meant damnit!