Dodge Charger Forum banner

1 - 10 of 10 Posts

·
Registered
Joined
·
1,672 Posts
Discussion Starter #1
Anyone running 3 inch exhaust piping on their 5.7? Can anyone tell me the pros & cons of running a 3 inch exhaust?
 

·
Registered
Joined
·
230 Posts
i know you can use kooks long tube headers, on your rt, that's meant for a rt and connect srt's aftermarket catbacks to it. a bigger exhaust wont help you until you install heads and cam and/or force induction. that's a 2.75 inch diameter exhaust, i'm not familiar with anyone using 3 inch diameter exhaust on a 5.7 car.
 

·
Registered
Joined
·
864 Posts
Yeah. 3.0" is a real bad idea on a 5.7 unless you are CRAZY modded. There is a reason why the stock system is 2.25" (I believe anyway). That is Velocity!! In an exhaust you want to get the exhaust gasses out ASAP. The exhaust moves out quicker when its hot and naturally moves slower when its cooler. So if you have 3" pipes sure it can in theory breath better based on exhaust pipe volume but what happens is it cools down sooner and looses its velocity sooner because you have more volume to move out of the pipes. I am not an expert or may be slightly off on a point or two but you have to find the sweet spot of velocity and pipe diameters. Most after market systems are 2.5" for this very reason. They would make them 2.75 or 3.0 if there were gains to be made.
 

·
Registered
Joined
·
244 Posts
The reason the stock system is 2.5" is because 3" pipe is bigger thus hard to fit, generally louder and generally more expensive and 3" isn't needed under 450HP (give or take). So if your engine is say 400hp, then there is little to be gained with a bigger setup because the 2.5 isn't restrictive _at the power level_, not accounting for the muffler, which can vary wildly with design.

If your theory held up, then why do drag cars run open headers? Less restriction you have the better...
 

·
Registered
Joined
·
864 Posts
If your theory held up, then why do drag cars run open headers? Less restriction you have the better...
They run open headers because they can expell the gasses quicker. Pipes to big slow the velocity so it takes longer for the gases to be pushed out. Street legal cars cant have side exhaust or open headers so you need to design one that will run the length of the car and get the gasses out ASAP.
 

·
Registered
Joined
·
244 Posts
That holds true for the header pipes, but not the exhaust after the collector. The exhaust is being pushed out, not sucked like say the intake tract of a manifold, where bigger isn't always better, due to velocity.

There isn't anything magical about a race car that makes them expel gasses quicker. If a racer could build an exhaust setup that increased the velocity like you mention, they would. everyone single one of them would. It is a restriction, so they don't.

At a point, size will be a point of diminishing returns. Sure you could put on a 3" dual exhaust on your stock SXT, but it isn't going to help because the engine won't make enough power to utilize it anything over 2" or so. In other words, it is no longer a restriction. It won't really hurt it either.

You want the gasses out ASAP? build an exhaust that has NO restrictions, and will fit. Header pipe size and length is a different story.
 

·
Registered
Joined
·
22 Posts
From my understanding, if you go too big on the exhaust, rather than the exhaust moving fairly uniformly at an even pressure through the pipes, it causes turbulent and erratic flow along with increased backpressure. So the only way you would benefit from 3" pipes is if you bore/stroked the engine or otherwise increased the amount of exhaust it expels by forced induction/camming.
 
1 - 10 of 10 Posts
Top