Let me start off by saying I am by no means a genius when it comes to how power is obtained through mods, I read the forum and go off of what is said in threads. I do some homework but I have to admit I am lazy. I have been told by different people which size to go with for my exhaust (true dual) and have gotten conflicting sizes. If I have asked you about this, this does not mean I dont believe what you told me so please dont take it that way.

I am going to keep the cats, put on JBA shorties into 12" Magna Flows, but I dont know which size pipe to go with 2.25", 2.5" or 3". I have an 08 Q/C, 1500, 5.7 Hemi, 4X4. Thanks for your help as this will make my decision final.


Adam

 

considering 3" is stock you wouldnt want to go any smaller

 

Hes going to true duals, so 3" would be hurting not helping if he stuck with that.

I voted 2.25" for true duals from the header back.

 

This really isn't the sort of thing you put up for a vote and then go with the public concensus. How many guys on here have really fast trucks? Maybe 5? I don't get my diet advice from fat people, weight training advice from skinny guys, and I don't get my performance advice from a forum full of mostly slow trucks.

NO OFFENSE INTENDED!

I spend a lot of time on a performance oriented site and there is no question that 2.25" is the way to go for true duals. The fastest trucks in the country are running 2.25". Not one guy has shown any sort of respectable time with a larger setup on true duals.

 

Thanks guys, no offense taken frog this is what I need. A no **** answer for this. You are probably right this isnt a poll-able question. I just want to make sure that I make the right decision, because I will have to live with it. And since I really have no idea what to do I take what is said on this forum and run with it.

 

Dumb question: why does a 2.25" run better with the true duals? Since the oem is 3" why is it better to go smaller?

 

OEM has one pipe, a true dual has two. So the back pressure in a 3" single pipe is going to be greater than that of 3" dual pipes. To make up for this, you go with two 2.5" pipes so the pressure is closer to that of a single 3" pipe.

Say you have a soda with one normal size straw. If you add another normal size straw you be able to get more than whats needed. So you put two smaller straws to get the same amount as one normal straw lol

It's pretty much self explanatory

 

Excellent explanation! I understand completely. Thanks for putting it in terms that a less than mechanical person such as myself can understand.

 

Two 2.25 in exhaust pipes = 4.5 in total flow potential, as opposed to the 3 inch with restrictive bends. Plenty of flow to support most engines, even heavily modded engines. Make sure you replace the restrictive "Y" pipe while you are at it. Crawl under your truck and look at it, EWWWW! it necks down to about 2 inches of area where the pipes come togeather.

http://moesperformance.com/index.php...roducts_id=157

 

Funny, I just responded to a very similar post on another forum. It had the same erroneous misconception it.

Think back to basic geometry. Remember, the area of a circle is Πr².

The area of a 2.25" pipe is 3.14 * 1.125 *1.125= 3.97. *2 pipes= 7.95 square inches.

The area of a 4.5" pipe is 3.14 * 2.25 * 2.25= 15.9 square inches. Not even close. Two 2.25" pipes are NOT the same as a single 4.5" pipe.

Comparing a si/so to a si/do.

The area of a 3" pipe is 3.14 * 1.5 * 1.5= 7.06 square inches.

So at first glance, the the 2 pipes at 2.25" are better. A closer look reveals the increased drag from the extra sidewall of the pipes. This negates the small increase in area.

A 3" single exhaust provides similar flow characteristics to a 2.25" dual exhaust. No one would ever dream of going to a single exhaust larger than 3", therefore, the only logical conclusion is that a properly flowing dual exhaust will built with 2.25" pipe.

As I said previously, there are a lot of FAST trucks out there running 2.25" duals. I reccomend you give a call to magnaflow or flowmaster and get their profesional opinion. You will waste a LOT of money by going with too big of a diameter. And your truck will be slower as a result.