Performance 340 2-1/2 vs 3 exhaust systems ?

[Moparfiend]

So was wondering for my application what is a better performing tube size for exhaust 2-1/2 or 3?

I don’t have any cam specifications buts its very aggressive. Holley 650 double pumper on a high rise M1 with a spacer. Stock steel J heads. Unknown compression maybe 10:1 given the aggressive can profile.

I understand that the scavenging effects maybe better using the smaller diameter tubes with a small block. But have no way to determine this.

 

[moparnation74]

Tti headers and 2 1/2 system from them......

 

[Darter6]

My 2 cents. Unless you have a big inch,big horsepower engine, 3''is of no benefit. It may kill low end torque. I run 2 1/2'' on my 472.

 

[R413]

You haven’t told us enough information to make a good decision.
What is the use of this car?
What is the max RPM?
What is the cam size?
What is the REAL compression ratio?
These all will tell how much air will move through it.

What you have told us with the 650 carb and stock J heads this has no need for 3” pipes.

 

[slepr1]

I watched a youtube video (Nicks Garage) on this because I was thinking of doing 3" exhaust. They did a dyno test on the difference. I can't remember the exact numbers but the outcome was to stay with 2.5", which I did for a 485hp 440ci.

 

[Moparfiend]

You haven’t told us enough information to make a good decision.
What is the use of this car?
What is the max RPM?
What is the cam size?
What is the REAL compression ratio?
These all will tell how much air will move through it.

What you have told us with the 650 carb and stock J heads this has no need for 3” pipes.

Unfortunately to give you this information I would have to tear down the engine. I received the engine with no build sheet or information. The car is a driver with performance set up.

 

[Moparfiend]

Yeah I was figuring just a small block the 2-1/2 would have better scavenging and better pulse draw which equates to better efficiency. Seems like so far everyone who has made an opinion agrees even if they don’t explain why.

 

[Darter6]

Chrysler engineers (Not that I'm bias ) were pretty smart guys. Most cars had tail pipes smaller than the rest of the system. Starting large and decreasing toward the back bumper. Had something to do with the gasses cooling causing a scavenging effect.
Or something like that.