What's the best exhaust diameter?

[Hussam]

Hello everyone,



I've just swapped a new engine, it's code is 131C4,


It is originally for FIAT 131 racing, producing about 115 HP.



NOW, I am making a custom exhaust piping to increase power gain. I am thinking of 2.5 inches pipe diameter.

What do you think the diameter should be to help increase power gain??

 

[varesecrazy]

Hello everyone,



I've just swapped a new engine, it's code is 131C4,


It is originally for FIAT 131

What do you think the diameter should be to help increase power gain??

POWER .. at what RPM

1500RPM - TINY

5000RPM.. MASSIVE

 

[Hussam]

POWER .. at what RPM

1500RPM - TINY

5000RPM.. MASSIVE

Well, That's a good point. Thanks for referring to it, I don't know how I didn't pay attention to that.
Actually I'm planning on using the car on a daily basis, so I'd like to maximize the gain at low to mid range RPMs with reasonable output on 5000 RPM in case of serious action pumps in! What do you recommend, knowing that I'll try doing the following:
1- 1- Using 202 St. St pipes
2- 2- Try making mandrel bends
3- 3- Try to avoid bending as much as I can
4- 4- Use only one resonator/muffler in the end of the pipe after the (S) bend above the rear differential assembly


5- To conclude, I want to maximize power output at lower and mid range RPMs while somehow not consuming much fuel.


Please take into account that the engine is still stock with no modifications at all. I'm planing afterwards to tune it a bit by bit but I'm running on low budget